Original Russian Text © 2019 A.A. Medvedev, N.O. Telnova, A.V. Kudikov, published in Forest Science Issues Vol. 2, No. 3, pp. 1-12

           A.A. Medvedev, N.O. Telnova*, A.V. Kudikov

Institute of Geography of the RAS

Staromonetny per., 29, Moscow, 119017, Russia

*E-mail: natalia.telnova@gmail.com

Received 01 July 2019

This paper presents the results of long-term remote monitoring of tree overgrowth on abandoned agricultural lands. This monitoring is based on multi-temporal satellite images with ultra-high spatial resolution and highly-detailed optical survey from Unmanned Air Vehicles (UAVs). Successful use of photogrammetric dense point clouds was demonstrated for three-dimensional reconstruction of tree canopy structure on abandoned agricultural lands by using the tree canopy height digital model. Spatial data were obtained on tree expansion on the fallow in 2005–2018, current tree canopy heights and its vertical growth, stem density, and canopy closure. The study revealed distinct spatio-temporal heterogeneity of tree overgrowth on the fallow. In the first years after land abandonment the most rapid regeneration and dispersal of trees occurred from the forests resulting in very dense but low tree cover adjacent to the forest. Later, tree overgrowth occurred in isolated hotspots and was characterized by very intensive vertical growth of the tree canopy.

Key words: Central Non-Chernozem region, fallows, post-agrogenic succession, UAVs, digital canopy height models.

Taking agricultural land out of cultivation and turning it into fallows with subsequent overgrowth of natural vegetation is a significant type of change in land cover and land use patterns in many countries worldwide. During the 20th century, about 70 million hectares of agricultural land were taken out of cultivation in Russia alone, about 2/3 of which – during the crisis of the late 1980s–1990s (Lyuri et al., 2010). Since the 2000s, the opposite trend has been observed in Eastern European countries, i. e. active taking previously abandoned arable lands up for cultivation, whereas the driving forces of this process show significant differences (Estel et al., 2015). These processes have also been observed in many regions of the European Russia, where large agricultural holdings play the main role in taking arable land abandoned in the 1990s–2000s up for cultivation (de Beurs et al., 2017). However, in the majority of the Central Non-Chernozem region, fallow agricultural land still occupies a significant area, and the removal of new land from cultivation is compensated by the expansion of arable land only at some local points. Macro-regional spatial patterns of the ratio between abandoned and currently used agricultural land in the Central Non-Chernozem region are clearly observed using multi-temporal data of medium-resolution remote sensing. The contour map shown in Fig. 1 is based on data from Lesiv et al., 2018, and reflects the spatial patterns of changes in the structure of arable land in parts of the Central Non-Chernozem region.

Figure 1. Distribution of arable and abandoned lands in parts of the Central Non-Chernozem region. Compiled according to data provided by (Lesiv et al., 2018)

The largest overgrowth of tree and shrub vegetation during the 2000s is observed in the northern part of the region within the landscape zone of mixed coniferous and broad-leaved forests in Smolensk, Tver, Kostroma, Yaroslavl, and Ivanovo regions (Fig. 1). The process of overgrowth is almost non-existent in the southernmost parts of the region within the forest-steppe zone (southern parts of Orel, Tula, and Ryazan regions). At the same time, a number of areas of the central Non-Chernozem region (Moscow, Kaluga, Tula, and Orel region) show more contrasting distribution pattern of the share of overgrown agricultural land, which is mainly confined to the territories located within the landscape zone of broad-leaved forests. Over the past 15 years, there have been diverse changes in the structure of land use, represented by both the overgrowth of tree and shrub vegetation on old fallows, and their re-plowing.

Numerous recent studies of remote indication and monitoring of non-cultivated agricultural land employ time series of remote sensing data (RSD) of low and medium resolution and are focused on analyzing patterns of spatio-temporal differentiation of changes in the structure of agricultural land use, determining the time of removing the land out of cultivation and the nature of overgrowth on fallow lands at the macro-regional and regional levels (Alcantara et al., 2013; Estel et al., 2017; Koroleva et al., 2018; Lesiv et al., 2018).

The objective of this study is to assess the speed of tree and shrub vegetation expansion on fallows within the landscape zone of broad-leaved forests and to reveal spatial heterogeneity of this process at the local level based on the integrated use of multi-temporal ultra-high-resolution remote sensing data from space and unmanned aerial vehicles (UAVs).

MATERIALS AND METHODS

We selected a plot of arable land in Dubensky rayon of Tula region, which was taken out of cultivation in the early 2000s as an object for studying the spatio-temporal features of post-agrogenic succession using multi-temporal data of ultra-high-resolution remote sensing (Fig. 2). The non-cultivated land is located on a levelled watershed surface and gentle slopes near the water dividing line, with small massifs of polydominant broad-leaved forests adjacent to it from the north and south. The plot area is about 1.5 ha. In the absence of anthropogenic disturbances, grazing and mowing in particular, since the termination of plowing, a herb-type birch forest has grown on the fallow. These communities are indicative of the intermediate stage of post-agrogenic succession typical for the zone of broad-leaved forests (Lyuri et al., 2010). The tree cover is dominated by the warty birch (Betula pendula) and downy birch (B. pubescens), which have formed a dense closed stand with sparse and depleted ground cover on most of the fallow.

Figure 2. Layout of the studied object (A), oblique image from an UAV (B), and orthophotomosaic from UAV imagery (C)

We selected all multi-temporal satellite images of very high and ultra-high resolution relevant for the study area available in the archives: OrbView-3, Geoeye-1, Quickbird, and WorldView-2, which formed an intermittent time series for 2004–2015 (Table 1). To fill the chronological gaps in the overgrowth on fallows, from 2013 to 2018 an annual multi-season survey was conducted by various unmanned aerial vehicles (UAVs) at the altitude of 100 m.

Table 1. Main characteristics of archival satellite images

To extract the quantitative parameters of the tree-shrub vegetation growing on the fallow and their annual changes during 2013–2018, three-dimensional models obtained from the UAV survey data were used, i. e. photogrammetric dense point clouds sufficient to extract the quantitative parameters of tree vegetation in small areas, comparable in accuracy with the materials of airborne laser scanning (Dandois, Ellis, 2013). After removing the noise and classifying a single dense point cloud with the allocation of the «ground level» class, ultra-highly-detailed digital surface and terrain models are built on their basis. The arithmetical difference between the surface and terrain digital models can be interpreted as a digital model of tree canopy heights used to quantify and 3D model the structural parameters of tree and shrub vegetation and their changes over time (Lisein et al., 2013). To address the issue of tree canopy delineation in a dense closed stand, where the data from a summer UAV survey did not make it possible to obtain a sufficient number of points describing the ground level, we additionally used the materials of aerial surveys conducted during the dormancy of tree vegetation in late autumn and winter. That way we built a highly-detailed digital terrain model of the study area and multi-temporal digital models of the tree canopy heights with a spatial resolution of 6 cm and a vertical accuracy up to 5 cm (Table 2).

Table 2. Main characteristics of UAV aerial surveys and derived materials

The number of trees and shrubs and their dispersal within the fallow was determined separately for each time slice provided by single satellite images based on photointerpretation. For UAV data, in addition to photointerpretation of trees by multi-season orthophotomosaics, automatic delineation of tree and shrub crown peaks was performed using a digital model of tree canopy heights by the surface local maxima method (Mongus, Žalik, 2015). Crown coverage required to determine the projective canopy coverage (crown closure) was calculated using an object-oriented segmentation algorithm for the tree canopy height model using the watershed-based method (Ke, Quackenbush, 2011). The accuracy of automatic detection of crown peaks was assessed based on the results of synchronous time recording of individual tree statistics and photointerpretation of individual trees, and, depending on the density of the tree canopy, amounted to 70–90 %.

As a result of visual and automated interpretation of highly-detailed RSD, spatial distributions of the following main structural parameters of the tree vegetation growing on the fallow were obtained for different time slices: stand density, tree canopy height, and crown closure. The use of multi-temporal materials from UAV surveys provided spatially-distributed data on the vertical growth of the tree canopy on the non-cultivated land.

RESULTS AND DISCUSSION

The analysis of a complex time series of RSD from space and unmanned aerial vehicles allowed us to reconstruct in detail the chronology of overgrowth of tree and shrub vegetation on the fallow and to identify individual stages of this process. The main indicator of spatio-temporal heterogeneity of post-agrogenic succession over the period of remote monitoring is the change of the density of trees and shrubs on the fallow land.

With the available intermittent time series of satellite images, we can date the time of land removal out of cultivation as 2005 at the earliest. Initially, the recovery of tree vegetation occurred from the forest edge, where several large clusters with a very high density of birch undergrowth had been already formed by 2007. In general, since 2004, there have been two periods of the most active expansion of tree and shrub vegetation on the fallow, i. e. 2007–2009 and 2013–2017. The latter period is characterized by the more active renewal of tree vegetation in the central part of the fallow, remoted from the adjacent woodlands, as well as along the western and eastern parts of the site sharing borders with the road and meadows in use (Fig. 3).

Visualization of the spatial distribution of the identified structural parameters of the stand growing on the non-cultivated land revealed several patterns of post-agrogenic regeneration of tree vegetation, depending on their location in relation to the neighbouring forests (Fig. 4).

Figure 3. Change of overgrowth of tree vegetation on the fallow. Compiled on the basis of the results of satellite imagery and UAV material photointerpretation

Figure 4. The height of the tree canopy formed on the fallow by 2018. Created on the basis of materials of a multi-seasonal UAV survey

In the first years after the cessation of agricultural use (2004–2009), the fallow parts adjacent to woodland showed very quick and intensive regeneration of tree vegetation, but as of 2018 the formed canopy was very low in height (3–4 m), with the maximum stem density throughout the entire fallow (up to 7 trunks per m²) and crown closure, the cessation or substantial slowing of vertical growth during 2013–2017. In the central part of the fallow, the regeneration of tree vegetation began only 8–10 years after the termination of plowing, and most likely had a focal character. In 2015–2017, there was a sharp increase in the vertical growth of stands up to 30 cm over the period (Fig. 5), with maximum heights of the formed tree canopy throughout the entire fallow (6–7 m), lower density of individual trunks and lower crown closure (Fig. 6).

Figure 5. Vertical growth of the tree canopy on the fallow in 2015–2017. Based on the materials of a multi-temporal UAV images

Figure 6. Density of the tree stand formed on the fallow since the termination of its agricultural use, 2005–2017. Based on the materials of multi-temporal UAV surveys

Remarkably, clear boundaries of the fallow were preserved for the entire period of monitoring, created in the west by a local road, and by a meadow plot, used for pasture, in the east, which prevents tree vegetation from growing here. The peripheral areas of the fallow adjacent to these borders have lower tree stand density and crown closure.

CONCLUSION

Combining ultra-high-resolution satellite images with the materials of multi-temporal optical ultra-highly-detailed UAV survey allowed us to assess the structural parameters the changes over time of the tree and shrub vegetation forming on the fallow, to identify and map the spatial differentiation of the speed and pattern of post-agrogenic succession on the fallow land unused since 2005. Feasibility of data obtained by multi-temporal optical aerial ultra-low-altitude UAV survey was shown for the delineation and quantitative morphometrical analysis of digital models of tree canopy heights. We found that, in general, since the removal of the land from agriculture, during 2005–2018, a closed monodominant tree cover formed almost throughout the entire fallow. At the same time, post-agrogenic renewal of tree vegetation was characterized by significant spatial heterogeneity, which was clearly seen at the local level, and it proceeded with different speed and intensity of overgrowing.

ACKNOWLEDGEMENTS

The research is carried out as part of the state assignment of the Institute of Geography of the Russian Academy of Sciences «Geoinformation and cartographic analysis and remote monitoring of the interaction between nature and society» No. АААА-А19-119022190168-8.

REFERENCES

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Koroleva N.V., Tihonova E.V., Ershov D.V., Saltykov A.N., Gavriljuk N.A., Pugachevskij A.V., Ocenka masshtabov zarastanija nelesnyh zemel’ v nacional’nom parke «Smolenskoe Poozer’e» za 25 let po sputnikovym dannym Landsat (Scales of overgrowth on non-forested lands of Smolenskoe Poozer’e national park: an assessment for the 25 years on remote sensing Landsat data) // Lesovedenie, 2018. No. 2. pp. 83-96.

Lesiv M., Schepaschenko D., Moltchanova E., Bun R., Dürauer M., Prishchepov A., Schierhorn F., Estel S., Kuemmerle T., Alcantara C., Concepcion P.C. et al., Spatial distribution of arable and abandoned land across former Soviet Union countries, Scientific Data, 2018, No. 5. URL: https://doi.org/10.1038/sdata.2018.56.

Lisein J., Pierrot—Deseilligny M., Bonne, S., Lejeune, P.A., Photogrammetric workflow for the creation of a forest canopy height model from Small Unmanned Aerial System Imagery // Forests, 2013, Vol. 4, No. 4, pp. 922-944.

Lyuri D.I., Gorjachkin S.V., Karavaeva N.A., Denisenko E.A., Nefedova T.A., Dinamika sel’skohozjajstvennyh zemel’ Rossii v HH veke i postagrogennoe vosstanovlenie rastitel’nosti i pochv (Dynamics of Agricultural lands of Russia in XX century and Postagrogenic Restoration of vegetation and soils) M.: GEOS, 2010, 426 p.

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Reviewer: PhD in biology, research officer M.A. Medvedeva

Original Russian Text © 2019 O.V. Ryzhkov, G.A. Ryzhkova, published in Forest Science Issues Vol. 2, No. 3, pp. 1-50

O.V. Ryzhkov*, G.A. Ryzhkova

V.V. Alekhin Central Chernozem State Nature Biosphere Reserve

Russia, 305528, Kursk oblast, Kursk district, Zapovedny settlement

*E-mail: ryzhkov_oleg@mail.ru

Received 15 June 2019

Methods of cartographic studies of the wood vegetation of the reserve, including those using modern GIS technologies and satellite positioning devices, are presented. Dynamics of the spatial structure and composition of oak forests over the past 50 years is analyzed. Results of the study of the main tree species of the reserve using GPS (GLONASS) survey and GIS are shown. Patterns and special features of the tree and shrub distribution in the open spaces (fallows, virgin steppes, and pastures) are presented.

Key words: forest-steppe, nature reserves, oak forests, mapping, GPS, GLONASS, satellite positioning devices, geographic information systems (GIS).

The forests of the Central Chernozem Reserve (CCR) are located in the south-western part of the Central Russian Upland within the central strip of the forest-steppe zone (Kursk oblast). Ravine and watershed oak forests, mostly coppice ones, are predominant here.

It is a common fact that various types of digital cartographic materials presented in a certain system of coordinates or projection form the basis of geographic information systems (GIS). During the pre-GIS times (1950s to 1990s), there were only hard copies of the maps of the reserve.

Mapping of the vegetation cover, including woody vegetation, has been used to study the natural complexes of CCR since the middle of the past century. A significant part of cartographic materials of that period was represented by geobotanical and forest management maps. The results of cartographic studies of that time are covered in a series of publications (Kartometricheskie issledovanija…, 1975; Kashkarova, Rubajlo, Utehin, 1973; Neshataev, 1970, 1983, 1996; Neshataev, Novikova, Uhacheva, 1982; Petrova, 1990; Ryzhkov, Sobakinskih, 2006; Utehin, 1967, etc.). Cartographic work mainly involved continuous planimetric eye survey, creating a stationing grid on the ground and writing down the results on paper. Plant associations or their complexes and types, i.e. polygons in the modern sense of GIS, were used as mapping units. Large territorial units of the CCR (sites and ecosites) usually were the objects of research.

The geographical location of the Central Chernozem Reserve, which lies in the central forest-steppe zone, determines the direct contact between forest and steppe vegetation, so many researchers have been paying great attention to the relationship between them. A separate cycle of mapping on the reserve territory included studying the distribution of tree and shrub species in strictly protected areas (both virgin and former fallow lands). The most studied fallow in this respect is Dalneye Pole fallow of Kazatsky site of CCR, a part of which (29.6 ha) was mapped three times: in 1970, 1980, and 1999–2000. The survey of 1970 and 1980, resulted in preparation of location maps of the bases of tree trunks and contours of shrub thickets (Krasnitskij, 1973; Krasnitskij, Soshnin, 1984), and the mapping of 1999–2000 resulted in a detailed map of projective covers of trees and shrubs (both single and thickets-forming). Dynamics of the distribution of woody vegetation on Dalneye Pole fallow was analyzed in a series of papers (Ryzhkov, Ryzhkova, 2000a,b,c; Ryzhkova, Ryzhkov, 2001). It is exactly the mapping of tree and shrub distribution across the steppe that underlies the testing of modern survey methods, which is the subject of this article.

Forest management works were carried out 5 times (in 1953, 1968, 1979, 1990 and 2000) within the territory of the reserve. Afforestation plans were made in hard copies, and it was only in 2000 that both hard copies and electronic versions were created (maps were digitized at the federal state institution Voronezhlesproject, initially in WinGIS software with subsequent conversion to MapInfo in Cartesian coordinates).

Multi-temporal series of geobotanical and forest management maps objectively reflect the general trends in vegetation dynamics. However, taking a plant association or a forest type as a mapping unit suggests significant errors in the accuracy of rendering their contours, which is also due to subjective factors. In our opinion, the most detailed and complete reflection of the dynamics of woody vegetation is provided by regular cartographic works performed at stationary research sites, or SRSs (permanent test plots (PTPs), profiles, transects, registration sites, individual restricted access facilities, etc.). In this case, real individual trees and shrubs or their biogroups (thickets) are taken as mapping units. SRSs mapping of vegetation, in contrast to more generalized geobotanical mapping, is of paramount importance, since in this case, due to the high accuracy of the grid (5 × 5 m or 10 × 10 m) and terrain association, a detailed and objective survey of the vegetation cover is provided, and, accordingly, high-quality maps of various thematic areas are obtained. Obviously, no linking natural objects and geographical coordinates, which are used in modern GIS, were not even in question during the pre-GIS period.

The cartographic materials compiled from surveys on stationary sites are the most accurate and objective in terms of reflecting the statics and dynamics of vegetation cover, forming the basis for a comprehensive study, analysis and modelling of the development of natural ecosystems. Stationary cartographic works are even more important when repeated, which makes it possible to track local and global dynamic trends of the vegetation (Ryzhkov, 2006b). The method of stationary studies of woody vegetation in nature reserves has been published before (Ryzhkov, 1996b).

Stationary methods of studying the vegetation cover of the reserve have been being practiced on its territory since the end of the World War II. N. A. Prozorovsky laid the first two permanent test plots for the study of forest vegetation of the CCR in the forest ecosites Dubroshina and Solovyatnik on Streletsky site in 1945 (Letopis’ prirody…, 1949). G. M. Zozulin mapped these PTPs repeatedly in 1950 and analyzed the dynamics of changes in their vegetation over a five-year period (Zozulin, Kusmarceva, 1951). The results of one of the first cartographic studies are also provided in the scientific report of the reserve for 1949–1950 (Letopis’ prirody…, 1951), which contains diagrams of distribution of tree and shrub vegetation in logs compiled by G. M. Zozulin. Special symbols designating the bases of tree trunks and clusters of shrubs were approximately applied on the diagrams according to relief features. These images are a prototype of modern mapping materials based on GPS (GLONASS) survey of woody vegetation. In the following years, cartographic research on the SRSs of the reserve was conducted by G. M. Zozulin (1952), S. S. Levickij (1958, 1961), F. I. Hakimzyanova (1968), A. M. Krasnitskij (1963), and others. The full review of these works was given by (Ryzhkov, 2006b).

A number of forest PTPs was laid in 1963 by A. M. Krasnitskij and in 1968 and 1979 during subsequent forest management measures, in the oak forests of the CCR, where forest-taxation studies are carried out from time to time, in particular complete enumerations and mapping of stands, undergrowth, understorey and grass cover. These PTPs now form the basis of the GIS forest unit of the CCR.

Modern methods of the vegetation mapping have been implemented in the reserve. These methods make use of new satellite positioning devices, unmanned aerial vehicles (UAVs), and desktop and mobile geo-information systems.

The objective of this paper is to give a review of cartographic research results in the CCR and demonstrate the advantages of using modern GIS software and hardware to study forest-steppe ecosystems.

The tasks of this paper are: to show the dynamics of forest vegetation based on the materials of periodic mapping at the PTPs, to assess the state of stands of the main species, and to present the findings of studying tree and shrub distribution in the steppe.

Several methodological approaches are distinguished, depending on the types of source data intended for GIS. Next, the methods and results of mapping woody vegetation at SRSs will be discussed.

MATERIALS AND METHODS

1. Transferring data to GIS by scanning hard copies of cartographic bases with or without subsequent vectorization of its objects.

The eye survey of tree and shrub vegetation on forest PTPs was preceded by creation of a stationing grid of 5 × 5 m on the ground. Layout plans of trunk bases and projections of tree crowns by species and tiers (also showing standing dead trees and windthrow) were drawn at a scale of 1:100 on grid paper in the field for each test plot. It is the horizontal structure of forest communities on 14 SRSs, namely, the projective cover of stands, undergrowth and understorey based on mapping data from 1991–1993 and 2002 (Ryzhkov, Ryzhkova, 2006a) which was studied in greatest detail. This method was fully polished when mapping complex watershed oak forests and waterlogged birch forests of the Zorinsky site of the CCR (Zolotuhin, Ryzhkov, Filatova, 2001; Ryzhkov, Ryzhkova, 2001).

In 2002–2006, those paper plans were scanned and their fragments were stitched into single bitmaps. Next, it would technically make sense to register the resulting rasters directly in the GIS and vectorization directly in association with terrain. However, no desktop GIS version was available in the reserve during mapping and creating the electronic map archive. Therefore, digitization was made in AutoCAD. The objects were vectorized manually («on the screen») in Cartesian coordinates. As a result, layers that reflect the location of trunk bases and projections of tree crowns of each tree species were obtained, which allowed us to estimate their quantitative proportions by automatically calculating the area (previously, the areas of crown projections had to be measured on a paper base with a planimeter, which led to overestimation of the values by about 4% (Ryzhkov, 2006c)). Guidelines were developed for rasters digitizing in AutoCAD and subsequent usage of the resulting vector objects in GIS (Ryzhkov, 2000; Ryzhkov, Vlasov, 2000; Ryzhkov, 2001a; Ryzhkov, 2006a).

As the licensed version of the MapInfo Professional GIS appeared in the reserve, it became necessary to link the AutoCAD-vector layers of crown projections of the stands to the bases of tree trunks, as well as the projective coverings of undergrowth and understorey of forest PTPs. The standard MapInfo tool allows registration of vector layers only by three reference points, which is clearly not enough for accurate transformation. Therefore, we used the loose MiTransformer module, which, based on affine or projective transformations, allows registering vector objects of several tables at once using an unlimited number of reference points which provides high quality of terrain association.

To automatically create a vector layer of basal areas of tree trunks at forest PTPs, the function of creation circle with the given centre and given diameter in the MapCAD module was used, and the values of the latter were taken from the numeric field of the table (database) (Ryzhkov, 2013). Trunk centres were marked on top of the bitmap by manual application of a symbol inside each circle.

Transformation of vector objects in GIS from a LAYOUT projection (Cartesian coordinates) to one of GIS map projections may be followed by emersion of artefacts, i.e. foreign details or noise of the resulting objects (e.g., distortion of border smoothness) that are absent in the original objects. Basal areas are easily adjusted by constructing centroids to generate circles with given diameters. Correct transformation of the borders of crown projection polygons requires preliminary generalization (thinning) of their nodes using appropriate GIS software (MapInfo or ArcGIS).

The following approach, which is currently used, is better in terms of methods and time. The raster of each forest PTP is registered in the MapInfo Professional GIS (current license Advanced v.16.0.4) using four boundary points, the coordinates of which are determined by static survey in the leafless period using modern GNSS equipment (Trimble GeoExplorer 6000 GeoXH CE receiver) with 0.2–0.3 m accuracy (achieved with long-term recording of coordinates in RTK mode with a fixed device). Further, in the GIS environment, the objects were vectorized manually on the screen with terrain association in the universal transverse Mercator projection (zone 37, Northern hemisphere (WGS 84) [EPSG:32637]) and subsequent analytical calculations are carried out (Ryzhkov, Ryzhkova, 2019b). The mapping materials of the stands of the watershed oak forest of the “Poyma Psla” site of the CCR were processed this way (Ryzhkov, Ryzhkova, 2019a).

The described method based on digitization of paper diagrams allows using map materials obtained in a conditional (usually Cartesian) coordinate system in GIS. The next two methods are based on data from field surveys of objects with satellite positioning devices of different classes, which makes possible their export to GIS based on the obtained geographical coordinates.

2. Total survey using personal navigation devices and GIS.

GPS (and/or GLONASS) survey, which is performed by satellite positioning devices, is one of the ways of quick collection of data for GIS. These devices can record geographical coordinates of waypoints and tracks and store them in non-volatile memory. It was the use of GPS receivers that, starting in 2000, initiated the creation of geospatial databases in the CCR. The reserve staff is currently using over 10 portable Garmin GPS navigators (GPSMAP 76CSx, GPSMAP 78S, OREGON 550, GPSMAP 64ST, etc.) as well as smartphones and tablets, including protected ones, with the location detection function. The above-named mobile equipment makes it possible to navigate through bitmaps.

The resulting point and line objects were exported to GIS using specialized software. The finishing processing (boundary smoothing, converting polylines to polygons, etc.) was made with geoinformation systems. The main disadvantages of this method are its inability to save the necessary attributes with graphics, and low accuracy of recording coordinates (3–5 m and more). Certain guidelines have been prepared for collecting GPS data (Ryzhkov, Ryzhkova, 2006b, Ryzhkov, 2014b) and their processing in the MapInfo GIS environment, in particular creating smoothed polygons (Ryzhkov et al., 2013; Ryzhkov, 2014a), sharing GPS (GLONASS) devices and GIS during mapping of natural objects in real time (Ryzhkov, 2010, 2011), and a review of methods for geoinformation mapping of natural objects and their application in protected areas has been published (Ryzhkov, 2008, 2009b).

3. Total survey using high-precision GNSS equipment, UAVs, mobile and desktop GIS.

Starting from 2016, detailed cartographic studies have been carried out at the CCR including application of modern hardware and software, i.e. high-precision GNSS equipment, UAVs, mobile and desktop GIS. This equipment was tested when mapping the distribution of trees and shrubs on the Second unmowed section of the Streletskaya steppe which is the largest and most representative part of the Streletsky site (with an area of 101.6 ha). This object has been completely protected since 1935. No total ground mapping was arranged here previously.

The work involved the Trimble GeoExplorer 6000 GeoXH CE two-frequency satellite receiver and two UAVs – DJI Inspire-1 Pro of the cartography laboratory of the Institute of Geography of the RAS and DJI Inspire-1 of the Central Chernozem Reserve. Mapping was carried out in real time (RTK) mode with continuous reception of corrections via 3G-modem from the Regional centre for navigation services for Kursk oblast (planimetric accuracy of recording the objects’ coordinates under open sky was 2–3 cm). The high-resolution pictures, obtained from drones, were used to create orthophotomaps of the terrain and refine controversial contours in hardly accessible areas of steppe shrub thickets.

Data was processed, analysed, and visualized in MapInfo Professional v.15.2.4 64bit GIS environment, raster was converted in Global Mapper v.13.0, and data management was made in Trimble GPS PathFinder Office v.5.81. Mobile application: TerraSync Centimeter Edition v.5.41 based on Windows Mobile v.6.5.

High accuracy of location detection by the Trimble GeoExplorer 6000 GeoXH CE allowed using a virtual stationing grid for mapping instead of a real one, the creation of which required considerable effort during conventional mapping of vegetation cover in previous periods. Such a two-layer virtual stationing grid with a square size of 100 × 100 m (1 ha) was formed in the GIS environment MapInfo Professional v.15.2.4 64bit with the Create Grid tool (hectare squares were further divided into smaller squares of 10 × 10 m (1 are) in order to minimize skips of young individuals when mapping). The main and additional stationing grids with unique numbering of squares were uploaded into the device in SHP format for subsequent staking-out.

With the mobile GIS TerraSync of the Trimble GeoExplorer 6000 GeoXH CE receiver, it is possible to use background raster maps (satellite images, forest management diagrams, etc.) in GeoTIFF format as support mats. Raster and vector images were uploaded to the receiver via the GPS PathFinder Office v.5.81 Data Transfer module. TRIMBLE has also developed a stand-alone Data Transfer program for the same operation.

A unique feature of the GPS PathFinder Office desktop software is the ability to develop a mobile GIS structure as a field data collection form with a specific list of fields, which was used during the woody vegetation survey.

Two types of data were saved during mapping: point (trunk bases) and polygonal (crown projections) ones. At the same time attribute information based on these data was collected.

Field work included mapping of woody vegetation with a complete enumeration of trees and shrubs (all specimens starting from the immature age state were taken into account, and juvenile plants found were also recorded). Trimble GeoExplorer 6000 GeoXH determined geographical coordinates and altitude of the trunk bases of single trees and shrubs above sea level, in order to consistently form an array of waypoints suitable for building point-based thematic maps in GIS. Isolated contours (thickets) of vegetation were mapped by traversing their perimeter with the above device. At the same time, polygon nodes were entered into the receiver’s memory every second. The device was configured to record only high-quality objects, the planimetric coordinate error of which did not exceed the set value (in most cases, it is usually 2–3 cm when the sky is open and 50–100 cm under tree crowns and in dense thickets of shrubs).

Simultaneously with the mapping, detailed attribute information was collected for each object. For a complete enumeration in the field, the following information was entered in a special form: site, ecosite, author(s), date, time, polygon or point number, species, origin, trunk perimeter or diameter at breast height (cm), trunk height (m), age, condition, diseases, life form, fructification, notes for entering additional information and photos (only selected objects were photographed).

Parallel to ground mapping of woody vegetation, aerial photography of the section was carried out with DJI Inspire-1 drones. The resulting pictures were combined into single images that were used to create orthophotomaps of the unmowed area. Some photographs, including images of tree and shrub crowns in hardly accessible areas (impassable thorny thickets), were recorded separately in GIS and used as an underlay for manual digitizing of the crown contours on the screen.

The point layer of distribution of single trees and shrubs and the polygonal layer of projective covers of tree and shrub vegetation of the Second unmowed section of the “Streletskaya steppe”, obtained in the mobile GIS TerraSync Centimeter Edition v.5.41, together with all attributes were exported via MIF exchange files to the MapInfo GIS. They were used to create 1:5000 and 1:400 thematic maps (on 134 pages). A detailed method of GIS mapping of woody vegetation using modern hardware and software was published by (Ryzhkov et al., 2017).

Let us mention, that the direct application of high-precision geodetic devices for mapping woody vegetation under the forest canopy lacks efficiency since there are significant obstacles for satellite signals. Even when receiving differential corrections in RTK mode, the accuracy of determining coordinates in this case usually does not exceed 1.0 m, which is clearly not enough for correct coordinate recording. In addition, stable mobile or radio connection is required. Therefore, conventional mapping involving the creation of a stationing grid on the ground or geodetic devices of another class, e.g. total stations which use the line-and-angle resection is preferred in highly closed stands. The staff of the reserve has certain experience in operating such equipment.

RESULTS AND DISCUSSION

We used the methods described above to study both individual components of forest-steppe ecosystems and general trends in their dynamics. It makes sense to show the patterns of weather changes in the studied area prior to making results review. The CCR has its own weather station «Streletskaya Steppe», which has been taking continuous observations 8 times per day since 1947. Analysis of the dynamics of the main weather parameters has shown that over the recent 20 years, annual air temperatures has been exceeding the average long-term values (Fig. 1), whereas the amount of precipitation has been equal to or lower than the average values (Fig. 2). In general, over the entire observation period, the average annual air temperature increased by almost 1°C (from 5.0° (1956) to 5.9° (2019)). Thus, according to long-term observations, the weather in the reserve area has become hotter and drier. However, the last decade is characterized by significant weather extremes including abnormally high amounts of precipitation in certain months (Table, Fig. 3).

Figure 1. Long-term dynamics of average annual air temperature

Figure 2. Long-term dynamics of annual precipitation

Table. Extreme values of air temperature and precipitation in the last decade (2010–2019) in the CCR area during the observation period since 1947.

Figure 3. Abnormal climate indexes of recent years
(according to the «Streletskaya Steppe» weather station)

General weather characteristics and features in the area of the reserve were published by (Nepochatyh, Ryzhkov, 2016). Long-term series of observations of the climate and biota of the reserve allowed identifying the main climate-influenced trends in changes in biotic components of biogeocenoses over the past 100 years (up to 1999) (Ryzhkov et al., 2001; Ryzhkov et al., 2018). As mentioned above, the early 21st century is characterized by significant climate changes, the impact of which on the CCR flora and fauna was analyzed in 2000 – 2013, and the results of the research were published in 2017 (Ryzhkov et al., 2017a,b). These weather trends and anomalies have certainly affected the structure and dynamics of the forest vegetation of the CCR, which is reflected by the results of the research. We present the main findings including those obtained with the help of analytical GIS tools and based, in particular, on the construction of digital terrain models (DTMs) and generation of DTMs-based derived vector coverage to study the spatial distribution of trees of individual species by altitude, slopes and direction of slopes.

Dynamics of the spatial structure of oak trees (projective cover of stands,

undergrowth and understorey) on forest PTPs based on mapping data of different years

The results of research in this area were being reported in the public literature in 1995-2019 (Ryzhkova, Ryzhkov, 1995; Ryzhkov, 1996; Ryzhkov, Ryzhkova, 1999; Ryzhkov, Ryzhkova, 2001, Ryzhkov, Ryzhkova, 2006a).

1. In the 1960s, the oak stands of the CCR, having the common oak (Quercus robur L.) as the edificator species, were far more differentiated by tiers. Their overall projective cover was maximal and relatively uniform. The associated species were insignificant in the horizontal structure of communities (Fig. 4).

Figure 4. Dynamics of the structure and species composition of the forest stand from 1968 to 1991. (Streletsky site of the CCR, Babka ecosite, forest PTP No. 12)

Note. Figure legend:

2. As a result of the massive drying of oak forests in the forest-steppe in the 1970s, there was a significant thinning of stands in the CCR, mainly due to the death of undersized and stunted oak trees. Vertical stratification of communities became simpler, which was manifested in the dominance of the first tree tier (Fig. 4). Large gaps were formed in the forest canopy. The total projective cover of stands decreased (Fig. 5).

3. Due to changes in the light regime, the resulting gaps became quickly colonized by broad-leaved oak associates (especially Norway maple) and wild fruit species, which had significantly expanded the species composition of stands by 1990s (Fig. 5, 6) (Ryzhkov, 1997). A chronological gap is observed in the populations of the common oak: exclusively mature generative trees continued to dominate, whereas, with rare exception, there were no individuals of pregenerative fractions.

4. Oak forests have powerful undergrowth which was formed by bird cherry (Prunus padus L.) (Ryzhkova, Ryzhkov, 2003; Ryzhkova, Ryzhkov, 2004) and (or) common hazel (Corylus avellana (L.) H. Karst.) which created additional obstacles to the successful regeneration of the oak. At the same time, bird cherry inhabits mainly simple-structured coppice oak forests with common oak dominating the tree tier: cherry creates dense undergrowth, in which it accounts for more than 90% of the projective cover (Fig. 7). Moreover, within the reserve this species can participate in the third and even second tiers of the stand. The formation of cherry-oak forests is observed in some forest ecosites which is a unique forest type for the forest-steppe. Hazel, on the contrary, is usually confined to complex multi-species broad-leaved forests. As populations of this species mature, small isolated contours merge into large continuous loci with very high projective cover (Fig. 8). Over time, hazel actively settled in the forests of Kazatsky and Streletsky sites of the CCR including in watershed areas where it was previously either absent or exterminated (Fig. 9). According to the findings of three-time large-scale geobotanical mapping made by Yu.N. Neshataev (1968, 1979, 1993), the area of distribution of Corylus avellana increased from 55.4 to 97.0 ha (Ryzhkov, 2001b) in Kazatsky forest.

Figure 5. Dynamics of the structure and species composition of the forest stand from 1968 to 1993.
(Kazatsky siteof the CCR, Kazatsky forest ecosite, forest PTP No. 6)
Note. For figure legends, see the note to Fig. 4.

Figure 6. Dynamics of the structure and species composition of the forest stand from 1968 to 1993.
(Streletsky site of the CCR, Dedov-Vesely ecosite, forest PTP No. 19)
Note. For figure legends, see the note to Fig. 4.

Figure 7. Projective cover of bird cherry
(Streletsky site of the CCR, Petrin Les ecosite, forest PTP No. 9, 1992)

Figure 8. Dynamics of the horizontal structure of the common hazel population
(Kazatsky site of the CCR, Kazatsky forest ecosite, forest PTP No. 4)

From 2008 to 2014, we were performing complete mapping of the common hazel population of Streletsky site of the CCR using Garmin personal navigators. The resulting waypoints of location of the bushes’ bases were processed with GIS analytical tools. For example, derived maps created on the basis of Streletsky site DTM were used for automatic sorting of hazel detection locations by altitude, slope ranges, and slope directions using MapInfo Professional geographic operators and SQL queries (Ryzhkov, Ryzhkova, 2010a; Ryzhkova, Ryzhkov, 2011; Ryzhkov, Ryzhkova, 2014b). A similar GPS survey was made on the same area for small-leaved linden (Ryzhkov, Ryzhkova, 2010b).

Figure 9. Resettlement of the common hazel from Temnaya hollow to the watershed
in Dubroshina ecosite of the Streletsky site of the CCR (based on mapping materials from 1994 and 2008)

Figure 10. Local drying of an oak in Temnaya hollow
(Dubroshina ecosite, Streletsky site of the CCR)

5. Currently, natural thinning of parent stands of oak of vegetative origin and strengthening of phytocenotic positions of other broad-leaved species continues. The last local foci of reserve oak forests drying were recorded in 1999–2000 and were associated with late spring frosts, the consequences of which were aggravated by summer droughts (Fig. 10).

In 1999–2000, about 20 oak trees per 1 ha were lost in the reserve’s oak forests. The rate of thinning of oak stands was low during the subsequent period from 2001 to 2018. On average, 1 to 8 trees per 1 ha died every year (Fig. 11).

Figure 11. Long-term dynamics of current common oak mortality in the CCR
(according to the data on 13 forest PTP)

The dynamics of the number of dry trees changed dramatically against the background of ongoing active fall of old standing dead oak trees and rare appearance of fresh standing dead wood. From 1970 to 2000 the process was undulating, with slight changes in the number of standing dead wood ranging from 150 to 250 trees/ha, but starting from 2001, there was a pronounced trend of a constant annual decrease in this figure (Ryzhkov O. et al., 2013). By 2018, the amount of standing dead oak trees has decreased to 73 trees/ha – the all-time low, which is explained, on the one hand, by the absence of current foci of oak dying-off, and on the other hand, by active turning of standing dead wood into windthrow. Windthrow (partly windsnap) of dead trees contributes to the progressive accumulation of dead wood, which in 2018 amounted to 542 trees/ha, whereas the stock was over 84 m³/ha.

Thus, the following features are typical for the process of oak mortality in the forests of the CCR in the last decade:

– stable annual decrease in the number and stock of standing dead trees and the same stable increase in these indicators for windthrow;

– low rates of thinning of oak stands.

The data on the trees of common oak that have changed their life state are regularly updated in the GIS on the PTP maps.

During World War II, the majority of the reserve’s oak stands were cut down, with the exception of a small number of so-called «standards», which had been 40–45 years old by that time. In 2008–2010, we carried out GIS mapping of such old-aged oak trees that were found in Streletsky site (Fig. 12).

Figure 12. Scheme of distribution of old-aged common oak trees
in Dubroshina and Solovyatnik ecosites of Streletsky site of the CCR (2010)

6. Shade broad-leaved forests are starting to form within the modern boundaries of the forest-covered area of the CCR. This is evidenced by the dynamics of the species composition of the young generation in oak forests surveyed during repeated mapping on individual forest PTPs, these forests represented mainly by broad-leaved oak associates (Ryzhkov, Ryzhkova, 2004). Rejuvenation of forest-forming species populations is observed only in those habitats where illumination is not a limiting factor of the environment (clearings, ecotones with steppe, etc.).

We have carried out cartographic studies of common oak populations in the areas of contact between oak forests and open spaces (former fallows and virgin unmowed steppes). An important result of this work is the assessment of the current status and population structure of the major forest-forming species of the forest-steppe zone. The largest and most representative unmowed section of Streletskaya steppe, which was surveyed in detail in 2016, turned out to be a suitable area for self-reproduction of seed oak forests in the reserve. Coppice oak stands in the CCR gradually die off and do not produce viable offspring under their canopy. The success of oak regeneration in the ecotone zone of the unmowed section is objectively confirmed by mapping materials. Its population enjoys a full-fledged structure with a clear predominance of young trees (Fig. 13). We are currently witnessing the initial stage of formation of highly productive seed oak stands that will replace the coppice stands (Ryzhkov O. et al., 2017b,c). This conclusion is valid only for the areas with light mode of open places in natural areas of contact between forest and steppe.

Figure 13. Natural seed regeneration of common oak in the ecotones between
forest and virgin unmowed steppe (2016). Note. The image shows virginal oak plants on the Second unmowed section of Streletskaya steppe.

7. Abnormal weather conditions in 2009–2012, in particular heat and drought, led to the drying of upper soil horizons in the forests, which in turn caused a massive dying off of aspen trees, especially on Streletsky and Kazatsky sites of the CCR (Fig. 14). The woody vegetation of the «Osinovy Kust» forest PTP located on the Streletsky site in Petrin Les ecosite (Krasnitskij, 1983) was studied to the greatest extent. Aspen (Populus tremula L.) had been the dominant species of the stand here for a long time. The detailed cartographic studies that were performed at this site in 1975 and 2004, showed a significant increase in the projective cover of the aspen stand (Ryzhkova, Ryzhkov, 2006). However, the above-mentioned weather anomalies drew aspen population to the stage of regression. In this case, mostly mature generative trees that made up the population nucleus of this species died (Fig. 15). The information about dying off of aspen stands and its dynamics has been published by (Ryzhkova et al., 2012; Ryzhkov D. et al., 2015; Ryzhkova et al., 2018).

Figure 14. Disintegration of aspen stands on Kazatsky and Streletsky sites of the CCR

The process of disintegration of aspen stands is clearly demonstrated by the bar chart of long-term dynamics of the relative participation of aspen in the total woody litter, which decreased from 95.1% in 1970 to 2.4% in 2017 (Fig. 16).

8. In contrast to aspen, silver birch (Betula pendula Roth) has demonstrated an expansion of its growing area as evidenced by modern cartographic studies. This species was previously extremely rare in the CCR. Only 10 specimens under 4 m high were found in all the oak forests of Streletsky site, 6 trees in Solovyatnik, 1 tree in Petrin Les, and 3 trees in Dubroshina. (Alehin, 1940). New information appeared later about the distribution of birch: 99 trees in Solovyatnik, 7 trees in Dubroshina (Levickij, 1957).

In 1994, we performed complete enumeration and eye mapping of the location of birch trees in Dubroshina, Solovyatnik and Dedov-Vesely ecosites and published the resulting data on changes of the range of this species and its occurrence in the forests of Streletsky site of CCR (Ryzhkov, 1997). Sections of the northern slope of Petrin Log with the sparse tree tier and the presence of clearings turned out to be the most optimal ecotopes for birch settlement (Ryzhkov, 2001b).

.

Figure 15. Dynamics of aspen projective covers based on mapping materials of different years (Streletsky site, «Osinovy Kust» PTP). Note: in 2017, projections of aspen crowns were rendered visually without detailed field mapping.

Figure 16. Dynamics of the relative participation of aspen fractions in the woody litter
at «Osinovy Kust» forest PTP

Figure 17. Scheme of distribution of the silver birch across Streletsky site
of the Central Chernozem Reserve based on mapping data of 2008–2011

In 2008-2011 total ground GIS-mapping of silver birch population was made based on GIS-survey within Streletsky site, and accurate maps of silver birch distribution were created (Fig. 17). There were 1,514 trees of this species mapped in total, and the majority of them were highly viable (Ryzhkov, Ryzhkova, 2014c).

Thus, despite suboptimal light conditions of the modern forest communities of the reserve, Streletsky site still has the ecotopes that are suitable for the settlement and spread of silver birch, which is confirmed by the results of our research.

To improve visualization of birch settlement process, the method of draping the DTM with various raster images was applied (Ryzhkov, 2013).

During the field GPS-survey, collecting of attribute information was accompanied by taking pictures of each birch tree with subsequent linking of the images to the corresponding record in the geodatabase in GIS environment (Fig. 18).

Figure 18. Visualization of an image of a silver birch tree
from a GIS attribute table entry

9. Geoinformation mapping methods were also used to study populations of rare tree species inhabiting the reserve, in particular of the dwarf almond (Amygdalus nana L.). We have collected the most complete geospatial information concerning dwarf almond not only in the reserve but in Kursk oblast as a whole. The population of this species was mapped in detail in Khvoshchevoy Log of the Streletsky site of CCR in 2009, at Gorodnoye ecosite, Barkalovka site, and at Pokosnevo and Bukreevo ecosites, Bukreevy Barmy site in 2011, and at Kazatsky site in 2012–2013 where Barybin Log was found to have region’s largest habitat of the species (Ryzhkov, Ryzhkova, 2012b). The method of total planimetric survey using satellite positioning devices was applied.

According to the mapping materials of 2012–2013, the total projective cover of dwarf almond on Kazatsky site of the CCR was 12.9 ha (Fig. 19). A DTM of the site territory was constructed. It served as the basis for generating polynomial covers of the main morphometric parameters of the terrain and enabled analyzing the spatial structure of the dwarf almond population depending on these parameters (Ryzhkov, Ryzhkova, 2014a,b).

Figure 19. Scheme of projective covers of dwarf almond on Kazatsky site of the CCR, 2013

10. As noted, the Central Chernozem Reserve is located in the border area between forest and steppe, therefore the forest-steppe relationship has always been of great priority. Studying the distribution of tree and shrub vegetation both in former fallows and virgin steppes has its advantages over the study of typical forest ecosystems in terms of GIS, since in open spaces it is possible to use both personal navigators and high-precision GNSS equipment. The following were the most significant thematic cartographic works performed in the CCR using satellite positioning devices:

2007. Mapping of the distribution of woody vegetation on the fallows of Bukreevy Barmy site of the CCR.

The site is located in the central part of the Central Russian Upland, in the upper reaches of the Oskol river basin. The research was carried out on the largest fallow with an area of 20 ha. At the time of mapping, it was 29 years old. We recorded the coordinates of the plant trunk bases with a personal navigator Garmin GPSMap 78s. 38 species of trees and shrubs were identified in 2007. The data was processed with GIS analytical tools. Having a significant array of GPS points that have three-dimensional coordinates and are more or less evenly distributed over the territory of the fallow, we were able to build maps of projective covers of tree and shrub species in the MapInfo environment. Vertical Mapper module was used for this purpose to generate heights-based raster network files or GRD files. The network of heights of specimens of woody species of Bukreevy Barmy site of the CCR, helped to create vector maps of projective covers of trees and shrubs with certain heights and calculate their areas. We believe that the possibility to obtain vector projective covers of tree and shrub vegetation from a GRD file is extremely important. This method can be considered as an alternative to time-consuming manual planimetric plotting of crowns on paper in the field (Ryzhkov, 2013).

2004, 2011. Mapping of the distribution of tree and shrub species in the pasture of Streletsky site of the CCR.

Dynamic maps of single-growing trees and shrubs were made in the above years on the test plots of 15.5 (2004) and 5.0 (2011) ha on the basis of GPS-surveys. Personal satellite navigators Garmin GPS 12CX (2004) and Garmin GPSMap 78s (2011) were used for mapping. MapInfo Professional 10.5.2 rus GIS helped to analyze the appearance and death of different types of trees and shrubs on the pasture test plot (5 ha) for the period from 2004 to 2011. It was found that the rate of repopulation of the groups of trees on pasture is about 18 trees per year per 5 ha, whereas the rate of elimination is about 5 trees per year (Ryzhkov, Ryzhkova, 2012a).

2016. Mapping of the distribution of woody vegetation on the Second unmowed section of Streletskaya steppe.

The satellite receiver of geodesic class Trimble GeoExplorer 6000 GeoXH CE and the DJI Inspire-1 UAV were used for the survey.

56 growing species of woody plants, including 23 species of trees and 33 species of shrubs were found in the area under survey (Ryzhkov et al., 2017). A total of 7,251 individual plants and 1,787 thickets were taken into account. The total projective cover of tree and shrub vegetation made up 14.3 ha (or 14.1% of the area of the Second unmowed section), of which single plants accounted for 3.0 ha and thickets – for 11.3 ha (Ryzhkov O. et al., 2017a,b). This value of the total projective cover is the highest among all previously mapped unmowed sections of the reserve. 1.6% of this value accounts for the forest, which in 80 years after the foundation of the unmowed section (from 1935 to 2016) has occupied 1.67 ha of it (Ryzhkov, Ryzhkova, 2018).

The Central Chernozem Reserve is actively developing cooperation, including international cooperation (Ryzhkov, Tregubov, 2006), in terms of mastering and sharing experience in the use of GPS and GIS technologies in protected areas (Solncev et al., 2006). Appropriate guidelines and practical training courses have been developed for the employees of nature reserves and national parks (Ryzhkov, 2007; Ryzhkov, 2009a).

CONCLUSION

Modern GIS technologies, especially those based on data collection using high-precision satellite positioning devices, quickly provide reliable information about natural objects and enable regular monitoring of their condition. Such monitoring provides the most valuable information by total mapping of woody vegetation of the CCR on permanent test plots, as well as by studying populations of individual species on protected areas. The accumulated long-term series of observations in conjunction with cartographic materials formed the basis for short-term forecasts of the development of forest ecosystems in the CCR (Ryzhkov, 2002). The main conclusions from the completed studies for the period from 1989 to 2019 are as follows:

1. Zonal forest forming species, i.e. the common oak, is gradually losing its role of the dominating species. Coppice oak stands of the 5th-6th generation cannot form viable undergrowth under the forest canopy and will be replaced unidirectionally by associate species. However, in ecotone zones between forest and steppe, where light is not a limiting factor of the environment, full-fledged populations of common oak develop with a significant proportion of plants of pregenerative stage. Thus, instead of coppice mother stands, in the long term seed oak forests, that will be geographically linked to the current forest edge, may develop.

2. Aspen stands of the CCR proved to be extremely sensitive to climatic anomalies and are currently at the disintegration stage. In some areas, the population is rejuvenated: rootshoots appeared after the death of generative trees, but it remains to be seen whether they will last for long. In most cases, former aspen forests are replaced with other types of forest with new wood edificators represented by shade-resistant species (most likely Norway maple).

3. Birch stands turned out to be more resistant to adverse environmental factors. Active spread of the silver birch is seen on the Streletsky site of the CCR, mainly along the slopes of the northern direction.

4. Powerful undergrowth of cherry and hazel has formed in oak forests, which also creates additional shade under the forest canopy. These species have almost completely displaced light-demanding shrubs (blackthorn, common buckthorn, rose hips, etc.) from oak forests. The area of hazel growth has a tendency to increase and spread from logs to watersheds; new centres of its settlement are found.

5. In the forest-steppe confrontation, the former is stronger now. In the natural course of processes, the CCR is experiencing afforestation of open areas (steppes, restored on former fallows; virgin meadow steppes in non-mowed mode; pastures, etc.).

The scope of potential application of geospatial information in forest science will undoubtedly be growing, as modern GIS technologies have already become an integral tool for understanding the nature of the forest.

ACKNOWLEDGEMENTS

In 2016, cartographic studies were carried out with the financial support of the project of UNDP/GEF/Ministry of natural resources of Russia No. 00072294 «Improving the protected areas management system and mechanisms in the steppe biome of Russia».

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Neshataev Ju.N., Novikova L.A., Uhacheva V.N., Osnovnye tendencii izmenenija rastitel’nosti Kazackogo uchastka Central’no-Chernozemnogo zapovednika (po itogam geobotanicheskogo kartirovanija 1968 i 1979 gg.) (The main trends in the vegetation of the Cossack site of the Central black earth reserve (according to the results of geobotanical mapping in 1968 and 1979)), Nauchnoe nasledie V.V. Alehina i razvitie ego idej v zapovednom dele, Kursk, 1982, pp. 49-52.

Petrova I.F., Tendencii izmenenija lugovostepnoj rastitel’nosti Central’noj lesostepi (Tendencies of change of meadow-steppe vegetation of the Central forest-steppe), Moscow, 1990, 206 p.

Ryzhkov D.O., Ryzhkova G.A., Ryzhkov O.V., Raspad osinovyh nasazhdenij Central’no-Chernozemnogo zapovednika (The Decay of aspen plantations of the Central black earth reserve), In: Biologicheskoe raznoobrazie kak osnova sushhestvovanija i funkcionirovanija estestvennyh i iskusstvennyh jekosistem: Mater. Vserosp. molodjozh. nauch. konf. (All-Russian. youth. scientific conf.) 8-10 June 2015, Voronezh: Istoki, 2015, pp. 267-271.

Ryzhkov O.V., Sostojanie i razvitie dubrav Central’noj lesostepi (na primere zapovednikov Central’no-Chernozemnogo i «Les na Vorskle») (Condition and development of oak forests of the Central forest-steppe (on the example of reserves of the Central Chernozem and «Forest on Vorskla»)), Avtoreferat dissertacii na soiskanie uchenoj stepeni kandidata biologicheskih nauk, Krasnodar, 1996a, 22 p.

Ryzhkov O.V., Stacionarnye issledovanija drevesnoj rastitel’nosti v zapovednikah (Stationary studies of woody vegetation in nature reserves), In: Pochvennyj i bioticheskij monitoring zapovednyh jekosistem: Metodicheskoe posobie (Pochvennyj i bioticheskij monitoring zapovednyh jekosistem: Metodicheskoe posobie), Moscow: KMK Scientific Press Ltd., 1996b, pp. 51-60.

Ryzhkov O.V., Dinamika sostava lesov Central’no-Chernozemnogo zapovednika (Forest composition Dynamics of the Central Chernozem reserve), In: Mnogoletnjaja dinamika prirodnyh processov i biologicheskoe raznoobrazie zapovednyh jekosistem Central’nogo Chernozem’ja i Altaja, Trudy Central’no-Chernozemnogo gosudarstvennogo zapovednika, Issue 15, M: KMK Scientific Press Ltd., 1997, pp. 73-86.

Ryzhkov O.V., Metodologija ispol’zovanija vektornyh kart rastitel’nosti v lesovedenii i vizualizacii graficheskoj informacii (Methodology of use of vector maps of vegetation in forest science and visualization of graphic information), In: Botanicheskie, pochvennye i landshaftnye issledovanija v zapovednikah Central’nogo Chernozem’ja: Tr. Associacii OOPT Central’nogo Chernozem’ja Rossii, Issue 1. Tula, 2000, p. 120-130.

Ryzhkov O.V., Ispol’zovanie Autocad 2000 dlja sozdanija vektornyh kart lesnyh fitocenozov (Using Autocad 2000 to create vector maps of forest phytocenoses), In: Rastitel’nyj pokrov Central’no-Chernozemnogo zapovednika: Tr. Centr.-Chernozemn. gop. zapovednika, Issue 18, Tula, 2001a, pp. 82-93.

Ryzhkov O.V., Sostojanie i razvitie dubrav Central’noj lesostepi (na primere zapovednikov Central’no-Chernozemnogo i «Les na Vorskle») (Condition and development of oak forests in the Central forest-steppe zone (by the example of nature reserves in the Central Chernozem and «Forest on the Vorskla»)), Tula, 2001b, 182 p.

Ryzhkov O.V., Lesnye jekosistemy Central’no-Chernozemnogo zapovednika: proshloe, nastojashhee, budushhee (Forest ecosystems of the Central Chernozem reserve: past, present, future), In: Izuchenie i ohrana prirody lesostepi (Study and conservation of forest-steppe): Scientific-Practical Conf., Dedicated. 120th Anniversary of the Birth of V.V. Alekhina), Tula, 17 January 2002, Tula, 2002, pp. 11-14.

Ryzhkov O.V., Metodicheskie aspekty primenenija GPS i GIS dlja izuchenija osobo ohranjaemyh prirodnyh territorij (Methodological aspects of the use of GPS and GIS for the study of specially protected natural areas), In: Ispol’zovanie GPS- i GIS-tehnologij dlja izuchenija osobo ohranjaemyh prirodnyh territorij (na primere landshaftnoj struktury Voronezhskogo gosudarstvennogo biosfernogo zapovednika) (The use of GPS — and GIS technologies for the study of specially protected natural areas (for example, the landscape structure of the Voronezh State Biosphere Reserve), Pod redakciej: V.N. Solnceva, O.V. Tregubova, O.V. Ryzhkova, B.A. Alekseeva, S. Kola, P. Uorda, Tula, 2006a, pp. 14-115.

Ryzhkov O.V., Obzor stacionarnyh kartograficheskih issledovanij rastitel’nosti Central’no-Chernozjomnogo zapovednika (Overview of the stationary mapping studies of the vegetation of the Central black earth reserve), In: Kartograficheskie issledovanija v Central’no-Chernozemnom zapovednike: Tr. Centr.-Chernozemn. gos. zapovednika, Issue 19, Kursk, 2006b, pp. 35-39.

Ryzhkov O.V., Ruchnoj i jelektronnyj metody opredelenija ploshhadej proektivnyh pokrytij drevostoev (obzor, preimushhestva i nedostatki, sravnenie) (Manual and electronic methods of determining the areas of projective cover of stands (review, advantages and disadvantages, comparison)), In: Kartograficheskie issledovanija v Central’no-Chernozemnom zapovednike: Tr. Centr.-Chernozemn. gop. zapovednika, Issue 19, Kursk, 2006с, pp. 138-140.

Ryzhkov O.V., Metodicheskoe posobie k seminaru «Geoinformacionnye sistemy i osobo ohranjaemye prirodnye territorii» (16-21 aprelja 2007, Elizovo) (Handbook for the seminar «Geoinformation systems and specially protected natural areas» (April 16-21, 2007, Elizovo), Tula: Grif i K, 2007, 240 p.

Ryzhkov O.V., Primenenie metodov nazemnogo sputnikovogo pozicionirovanija i GIS dlja izuchenija redkih vidov bioty na osobo ohranjaemyh prirodnyh territorijah Kurskoj oblasti (Application of methods of terrestrial satellite positioning and GIS for the study of rare species of biota in specially protected natural areas of Kursk region), In: Principy i sposoby sohranenija bioraznoobrazija (Principles and Methods of Biodiversity Conservation III): All-Russian. scientific conf. Joshkar-Ola; Pushhino, 27 January – 1 February 2008, Joshkar-Ola; Pushhino, 2008, pp. 581583.

Ryzhkov O.V., Kurs prakticheskih uprazhnenij k seminaru «Geoinformacionnye sistemy na osobo ohranjaemyh prirodnyh territorijah na primere nacional’nogo parka «Kurshskaja kosa» (9-15 nojabrja 2009 g., pop. Rybachij) (Course of practical exercises for the seminar «Geoinformation systems in specially protected natural areas on the example of the national Park «Kurshskaja kosa» (9-15 November 2009, Rybachy village)), Kaliningradskij regional’nyj fond sohranenija i razvitija nacional’nogo parka «Kurshskaja kosa», Proekt «Shkola sodruzhestva», Rybachij, 2009a, 195 p.

Ryzhkov O.V., Metody geoinformacionnogo kartografirovanija prirodnyh ob»ektov (Methods of geoinformation mapping of natural objects), In: Geoinformacionnoe kartografirovanie v regionah Rossii (Geoinformation Mapping in the Regions of Russia): mater All-Russiann scientific-practical conf.), Voronezh, 2-4 December 2009, Voronezh: Izd-vo «Istoki», 2009b, pp. 184-187.

Ryzhkov O.V., Ispol’zovanie novyh sredstv integracii GPS i GIS v srede Mapinfo professional 10.5 (modul’ Geographic tracker 4.0) pri provedenii geograficheskih issledovanij (The Use of new means of integration of GPS and GIS in the environment Mapinfo professional 10.5 (module Geographic tracker 4.0) in the conduct of geographical research), In: Geoinformacionnoe kartografirovanie v regionah Rossii (Geoinformation Mapping in the Regions of Russia): mater. II (correspondence) All-Russian scientific-practical. conf., Voronezh, 15 November 2010, Voronezhskij gosudarstvennyj universitet, Voronezh: Izd-vo «Nauchnaja kniga», 2010, pp. 63-68.

Ryzhkov O.V., Sovmestnoe ispol’zovanie GPS (GLONASS)-priborov i GIS pri kartografirovanii prirodnyh ob̕ektov v real’nom vremeni (Joint use of GPS (GLONASS)-devices and GIS in mapping natural objects in real time), In: Geoinformacionnoe kartografirovanie v regionah Rossii (Geoinformation Mapping in the Regions of Russia): mater. III (correspondence) All-Russian scientific-practical. conf., Voronezh, 15-18 September 2011), Voronezhskij gosudarstvennyj universitet. Voronezh: Izd-vo «Nauchnaja kniga», 2011, pp. 111-116.

Ryzhkov O.V., Razvitie geoinformacionnoj sistemy Central’no-Chernozemnogo zapovednika (Development of geoinformation system of the Central Chernozem reserve), In: InterKarto/InterGIS-19: Ustojchivoe razvitie territorij: teorija GIS i prakticheskij opyt. (Intercarto / InterGIS-19: Sustainable Development of Territories: GIS Theory and Practical Experience): Materials of the international conference, Kursk, Bogota (Kolumbija), 2-7 February 2013, Kursk, 2013, pp. 220-239.

Ryzhkov O.V., Metodika sozdanija sglazhennyh poligonov v srede MAPINFO PROFESSIONAL v.12.0 po dannym priborov sputnikovogo pozicionirovanija (Methodology of creation of anti-aliased polygons in the environment of MAPINFO PROFESSIONAL v.12.0 according to the satellite positioning devices), In: Sovremennye tehnologii v dejatel’nosti OOPT (Modern Technologies in Activity of the OOPT): Mater international scientific-practical conf. (selected) 12-16 May 2014, Kurortnyj poselok Naroch’, Belarus’, 2014a, pp. 94-107.

Ryzhkov O.V., Priemy povyshenija tochnosti opredelenija koordinat i zapisi trekov personal’nymi GPS-navigatorami GARMIN pri s»emke prirodnyh ob»ektov (Methods of improving the accuracy of positioning and recording tracks personal GPS-navigators GARMIN when shooting natural objects), In: Sovremennye tehnologii v dejatel’nosti OOPT (Modern Technologies in Activity of the OOPT): Mater international scientific-practical conf. (selected) 12-16 May 2014, Kurortnyj poselok Naroch’, Belarus’, 2014b, pp. 86-93.

Ryzhkov O.V., Formirovanie sglazhennyh poligonov v srede Mapinfo Proffessional v.12.0 po dannym priborov sputnikovogo pozicionirovanija (Formation of smoothed polygons in Mapinfo Proffessional v environment.12.0 according to satellite positioning devices), In: Sovremennye tehnologii v dejatel’nosti OOPT (Modern Technologies in Activity of the OOPT): Mater international scientific-practical conf. (selected) 12-16 May 2014, Kurortnyj poselok Naroch’, Belarus’, 2014c, pp. 133-134.

Ryzhkov O.V., Puzachenko A.Ju., Vlasov A.A., Zolotuhin N.I., Korol’kov A.K., Filatova T.D., Stoletnjaja dinamika klimata i bioty Central’noj lesostepi (na primere Central’no-Chernozemnogo zapovednika i prilegajushhih territorij (Centenary dynamics of climate and biota of the Central forest-steppe (on the example of the Central Chernozem reserve and adjacent territories), In: Vlijanie izmenenija klimata na jekosistemy: Serija publikacij Departamenta prirodoohrannoj politiki i jekspertizy Vsemirnogo fonda dikoj prirody, Ohranjaemye prirodnye territorii Rossii. Analiz mnogoletnih nabljudenij, Issue 4, Moscow: Russkij universitet, 2001, pp. 69-81.

Ryzhkov O.V., Ryzhkova G.A., Izuchenie gorizontal’noj struktury lesnyh soobshhestv na osnove vektornyh (cifrovyh) kart (Study of the horizontal structure of forest communities on the basis of vector (digital) maps), In: Rol’ zapovednikov Kavkaza v sohranenii bioraznoobrazija prirodnyh jekosistem (The Role of the Caucasus Reserves in Preserving the Biodiversity of Natural Ecosystems) Yubil. conf., dedicated. 75th anniversary of the Caucasian GOP. natural biosphere. Reserve: Abstracts of reports, Sochi, 1999, pp. 60-63.

Ryzhkov O.V., Ryzhkova G.A., Analiz dinamiki rasprostranenija derev’ev i kustarnikov na zalezhi Kazackogo uchastka Central’no-Chernozemnogo zapovednika po materialam kartirovanija 1970, 1980 i 1999 godov (Analysis of the dynamics of the spread of trees and shrubs on the deposits of the Cossack site of the Central Chernozem reserve on the materials of mapping 1970, 1980 and 1999), In: Botanicheskie, pochvennye i landshaftnye issledovanija v zapovednikah Central’nogo Chernozem’ja: Tr. Associacii OOPT Central’nogo Chernozem’ja Rossii, Issue 1, Tula, 2000a, p. 136146.

Ryzhkov O.V., Ryzhkova G.A., Dinamika vnedrenija drevesno-kustarnikovyh vidov rastenij na nekosimoj zalezhi Kazackogo uchastka Central’no-Chernozemnogo zapovednika za 58 let (Dynamics of introduction of tree-shrub species of plants on the certain Deposit of the Cossack site of the Central Chernozem reserve for 58 years), In: Chtenija pamjati prof. V.V. Stanchinskogo (Readings Memory Prof. V.V. Stanchinsky), Issue 3, Smolensk: Izd-vo Smolenskogo gospeduniversiteta, 2000b, pp. 364-368.

Ryzhkov O.V., Ryzhkova G.A., Izmenenie chislennosti i proektivnogo pokrytija drevesno-kustarnikovyh vidov na nekosimoj zalezhi Kazackogo uchastka Central’no-Chernozemnogo zapovednika po materialam kartirovanija 1970, 1980 i 1999 godov (Changes in the number and projective cover of tree-shrub species on the certain deposits of the Cossack site of the Central Chernozem reserve based on the mapping materials of 1970, 1980 and 1999), In: Stepi severnoj Evrazii: strategija sohranenija prirodnogo raznoobrazija i stepnogo prirodopol’zovanija v XXI veke (The Steppes of Northern Eurasia: a Strategy for the Conservation of Natural Diversity and Steppe Environmental Management in the XXI Century): Mater. international symposium, Orenburg, 2000с., pp. 339-341.

Ryzhkov O.V., Ryzhkova G.A., Lesa Zorinskogo uchastka Central’no-Chernozemnogo zapovednika (Forests of the Zorinsky site of the Central Chernozem reserve), In: Prirodnye uslovija i biologicheskoe raznoobrazie Zorinskogo zapovednogo uchastka v Kurskoj oblasti: Tr. Centr.-Chernozemn. gop. zapovednika, Issue 17, Tula, 2001, pp. 140-186.

Ryzhkov O.V., Ryzhkova G.A., Vozrastnaja struktura i zhiznennoe sostojanie popolnenija drevostoev v dubravah Central’no-Chernozemnogo zapovednika (uchastki Barkalovka i Bukreevy Barmy) za period 1991-2003 gg. (Age structure and life as the replenishment of trees in the oak forests of the Central Chernozem reserve (areas Barkalova and Bukreeva the Barm) for the period 1991-2003 period), In: Aktual’nye problemy upravlenija zapovednikami v Evropejskoj chasti Rossii (Actual Problems of Management of Reserves in the European part of Russia): Materials anniversary scientific-practical. conf., dedicated 10th anniversary of the state. natural Reserve «Voroninsky», village Inzhavino, Tambov region, 21-24 September, 2004., Voronezh: Voronezhskij gosudarstvennyj universitet, 2004, pp. 138-141.

Ryzhkov O.V., Ryzhkova G.A., Analiz mnogoletnej dinamiki gorizontal’noj struktury dubrav Central’no-Chernozemnogo zapovednika na osnove stacionarnyh issledovanij (Analysis of long-term dynamics of the horizontal structure of oak forests of the Central Chernozem reserve on the basis of stationary studies), In: Kartograficheskie issledovanija v Central’no-Chernozemnom zapovednike: Tr. Centr.-Chernozemn. gop. zapovednika, Issue 19, Kursk, 2006a, pp. 52-64.

Ryzhkov O.V., Ryzhkova G.A., Ispol’zovanie navigacionnyh priborov dlja fiksacii mestonahozhdenij i predstavlenija kart arealov vidov iz Krasnoj knigi Kurskoj oblasti (The Use of navigation devices for fixing the locations and presentation of maps of species ranges from the red book of the Kursk region), In: Issledovanija po Krasnoj knige Kurskoj oblasti (Studies in the Red Book of the Kursk Region): Mat-ly scientific-practical. conf. Kursk region, Kursk district, village Zapovednyj, March 2006, Kursk, 2006b, pp. 9-12.

Ryzhkov O.V., Ryzhkova G.A., Izuchenie dinamiki rasprostranenija leshhiny obyknovennoj na Streleckom uchastke Central’no-Chernozemnogo zapovednika s ispol’zovaniem metodov GPS i GIS (Study of the dynamics of the distribution of common hazel on the Streletsky site of the Central black earth reserve using GPS and GIS methods), In: Geoinformacionnoe kartografirovanie v geografii i geojekologii: sbornik statej, Voronezhskij gosudarstvennyj universitet, Voronezh: Izdvo «Istoki», 2010a, pp. 67-86.

Ryzhkov O.V., Ryzhkova G.A., Rasprostranenie Tilia cordata v lesnyh urochishhah Streleckogo uchastka CChZ (Distribution of Tilia cordata in the forest tracts of the Streletsky district of the Central black earth reserve), In: Problemy monitoringa prirodnyh processov na osobo ohranjaemyh prirodnyh territorijah (Problems of Monitoring Natural Processes in Specially Protected Natural Territories): mater international Scientific Practical konf., dedicate. 75th anniversary of the Khopzhor State nature reserve, village Varvarino, Voronezh region, 20-23 September, 2010), Voronezh: VGPU, 2010b, pp. 377-379.

Ryzhkov O.V., Ryzhkova G.A., Ispol’zovanie GIS-kartografirovanija dlja izuchenija dinamiki rastitel’nogo pokrova pastbishha Central’no-Chernozemnogo zapovednika i proektirovanija zapovedno-rezhimnyh meroprijatij (Use of GIS mapping to study the dynamics of vegetation cover of the pasture of the Central Chernozem reserve and the design of conservation measures), In: Mater. mezhdunar. nauch.-prakt. konf., posvjashh. 130-letiju so dnja rozhdenija professora V.V. Alehina (Mater International Scientific-Practical Conf., Dedicated the 130th Anniversary of the Birth of Professor V.V. Alekhina), Kursk, village Zapovednyj, 15-18 January 2012), Kursk, 2012a, pp. 168187.

Ryzhkov O.V., Ryzhkova G.A., GPS-kartografirovanie populjacij mindalja nizkogo na uchastkah Central’no-Chernozemnogo zapovednika Barkalovka i Bukreevy Barmy v 2011 godu (GPS mapping populations of almonds low on the territories of Central-Chernozem reserve Barkalova and Bukreeva the Barm in 2011), In: Geoinformacionnoe kartografirovanie v regionah Rossii (Geoinformation Mapping in the Regions of Russia): mater IV (absentee) Vserop. scientific-practical conf., Voronezh, 15 November, 2012, Voronezh: Izd-vo «Nauchnaja kniga», 2012b, pp. 105-110.

Ryzhkov O.V., Ryzhkova G.A., Ispol’zovanie cifrovoj modeli rel’efa dlja izuchenija prostranstvennoj struktury populjacii mindalja nizkogo v Central’no-Chernozemnom zapovednike (The Use of digital elevation model to study the spatial structure of the low almond population in the Central black earth reserve), In: Aktual’nye problemy jekologii Rossii i stran blizhnego zarubezh’ja (Actual Problems of Ecology of Russia and Neighboring Countries): mater All-Russian scientific conf. from Intern. participation (Kursk, 12 November, 2013), Kursk, 2014a, pp. 80-83.

Ryzhkov O.V., Ryzhkova G.A., Ispol’zovanie cifrovyh modelej rel’efa dlja analiza geoprostranstvennyh dannyh Central’no-Chernozemnogo zapovednika (The Use of digital elevation models for the analysis of geospatial data of the Central Chernozem reserve), In: Sovremennye tehnologii v dejatel’nosti OOPT (Modern Technologies in the Activities of Protected Areas), Mater international scientific-practical conf. (selected), 12-16 May 2014, The resort village Naroch, Belarus’, 2014b, pp. 108-144.

Ryzhkov O.V., Ryzhkova G.A., Primenenie metodov GIS-kartografirovanija dlja izuchenija dinamiki rasprostranenija berezy povisloj (Betula pendula Roth) na Streleckom uchastke Central’no-Chernozemnogo zapovednika v 2008-2011 godah (Application of GIS mapping methods to study the dynamics of the spread of birch (Betula pendula Roth) on the Streletsky site of the Central Chernozem reserve in 2008-2011), In: Flora i rastitel’nost’ Central’nogo Chernozem’ja – 2014 (Flora and Vegetation of the Central Black Earth Region — 2014): Mater interregion. scientific conf. (Kursk, 5 April, 2014), Kursk, 2014с. pp. 148-153.

Ryzhkov O.V., Ryzhkova G.A., Les i step’ v Central’no-Chernozemnom zapovednike: metody i rezul’taty kartografirovanija rastitel’nosti (1999–2016 gg.) (Forest and steppe in the Central Chernozem reserve: methods and results of vegetation mapping (1999-2016)), In: Sbornik tezisov Vserossijskoj nauchnoj konferencii «Nacional’naja kartograficheskaja konferencija – 2018» (Book of abstracts of the All-Russian Scientific Conference «National Cartographic Conference – 2018»), M., Rossijskaja gosudarstvennaja biblioteka, 16–19 October 2018, M.: Geograficheskij fakul’tet MGU, 2018, pp. 237-238, DOI: 10.15356/ncc2018; http://ncconf.ru/.

Ryzhkov O.V., Ryzhkova G.A., Dinamika sostojanija drevostoev pojmennyh dubrav uchastka Pojma Psla Central’no-Chernozemnogo zapovednika (Dynamics of forest stands of floodplain oak forests of the floodplain area of the Central Chernozem reserve), In: Flora i rastitel’nost’ central’nogo Chernozem’ja – 2019 (Flora and Vegetation of the Central Chernozem Region — 2019): Mater. Interregion. scientific konf., dedicate. 50-year-old organization of participants in the Central Chernozem Reserve Barkalovka and Bukreeviy Barma, Zapovedny village, 13 April, 2019, Kursk: Mechta, 2019a, pp. 140-146.

Ryzhkov O.V., Ryzhkova G.A., Rezul’taty izuchenija lesnyh jekosistem Central’no-Chernozemnogo zapovednika na osnove GIS-tehnologij (Results of the study of forest ecosystems of the Central Chernozem reserve on the basis of GIS technologies), In: Ajerokosmicheskie metody i geoinformacionnye tehnologii v lesovedenii, lesnom hozjajstve i jekologii (Aerospace methods and geo-information technologies in forest science, forestry and ecology), Moscow, 22-24 April, 2019, Moscow: CFEP RAN, 2019b, pp. 157-159.

Ryzhkov O.V., Ryzhkova G.A., Nepochatyh L.V., Mnogoletnjaja dinamika otpada stvolov duba chereshchatogo v lesah Central’no-Chernozemnogo zapovednika (Long-term dynamics of mortality of the trunks of oak-trees in the forests of the Central Chernozem reserve), In: Flora i rastitel’nost’ Central’nogo Chernozem’ja – 2013 (Flora and Vegetation of the Central Chernozem Region – 2013): Mater interregion. scientific conf., Kursk, 6 April, 2013, Kursk, 2013, pp. 132-138.

Ryzhkov O.V., Ryzhkova G.A., Ryzhkov D.O., Obzor novyh vozmozhnostej versii 11.5 GIS MapInfo Professional dlja sozdanija kart proektivnyh pokrytij rastitel’nosti na osnove splajnov (Review of new features of version 11.5 of GIS MapInfo Professional for creating maps of projective vegetation coatings based on splines), In: Flora i rastitel’nost’ Central’nogo Chernozem’ja – 2013 (Flora and Vegetation of the Central Chernozem Region – 2013): Mater interregion. scientific conf., Kursk, 6 April, 2013, Kursk, 2013, pp. 138-140.

Ryzhkov O.V., Ryzhkova G.A., Ryzhkov D.O., Metodika GIS-kartografirovanija drevesnoj rastitel’nosti s ispol’zovaniem sovremennyh apparatnyh i programmnyh sredstv (Methods of GIS mapping of woody vegetation using modern hardware and software), In: Sovremennye tehnologii v dejatel’nosti osobo ohranjaemyh prirodnyh territorij: geoinformacionnye sistemy, distancionnoe zondirovanie zemli: sbornik nauchnyh statej – Minsk, 2017a, pp. 63-72.

Ryzhkov O.V., Ryzhkova G.A., Ryzhkov D.O., Proektivnye pokrytija drevesno-kustarnikovoj rastitel’nosti Vtorogo nekosimogo uchastka Streleckoj stepi Central’no-Chernozemnogo zapovednika po materialam kartografirovanija 2016 goda (Projective covers of tree-shrub vegetation of the Second non-existent section of the Streletskaya steppe of the Central Chernozem reserve based on the mapping materials of 2016), Vestnik TvGU, Serija «Biologija i jekologija», 2017b, No 3, pp. 91-99.

Ryzhkov O.V., Ryzhkova G.A., Ryzhkov D.O., Rezul’taty kartirovanija populjacii duba chereshchatogo na Vtorom nekosimom uchastke Streleckoj stepi Central’no-Chernozemnogo zapovednika v 2016 godu (Results of mapping the population of English oak on the Second non-irrigated area of the Streletskaya steppe of the Central Chernozem reserve in 2016), In: Flora i rastitel’nost’ Central’nogo Chernozem’ja – 2017 (Flora and Vegetation of the Central Black Earth Region – 2017): mater interregion. scientific conf., Kursk, 8 April 2017, Kursk: Mechta, 2017с, pp. 126-131.

Ryzhkov O.V., Ryzhkova G.A., Zolotuhin N.I., Zolotuhina I.B., Filatova T.D., Mnogoletnie rjady dannyh Central’no-Chernozemnogo zapovednika i vozmozhnosti ih migracii v GIS (Long-Term data series of the Central Chernozem reserve and the possibility of their migration to GIS), In: Sovremennye tehnologii v dejatel’nosti osobo ohranjaemyh prirodnyh territorij: geoinformacionnye sistemy, distancionnoe zondirovanie Zemli: sbornik nauchnyh statej, Minsk, 2018, pp. 64-69.

Ryzhkov O.V., Sobakinskih V.D., Obzor geobotanicheskogo i lesnogo kartografirovanija uchastkov i urochishh Central’no-Chernozjomnogo zapovednika (Review of geobotanical and forest mapping of sites and tracts of the Central Chernozem reserve), In: Kartograficheskie issledovanija v Central’no-Chernozemnom zapovednike: Tr. Centr.-Chernozemn. gop. zapovednika, Issue 19, Kursk, 2006, pp. 6-34.

Ryzhkov O.V., Tregubov O.V., Razvitie rossijsko-amerikanskogo sotrudnichestva po ispol’zovaniju GPS- i GIS- tehnologij na osobo ohranjaemyh prirodnyh territorijah (Development of Russian-American cooperation on the use of GPS and GIS technologies in specially protected natural areas), In: Ispol’zovanie GPS — i GIS-tehnologij dlja izuchenija osobo ohranjaemyh prirodnyh territorij (na primere landshaftnoj struktury Voronezhskogo gosudarstvennogo biosfernogo zapovednika) (The use of GPS — and GIS technologies for the study of specially protected natural areas (on the main landscape structure of the Voronezh State Biosphere Reserve), Pod redakciej: V.N. Solnceva, O.V. Tregubova, O.V. Ryzhkova, B.A. Alekseeva, S. Kola, P. Uorda, Tula, 2006, pp. 197-208.

Ryzhkov O.V., Vlasov A.A., Metod sozdanija vektornyh kart lesnyh fitocenozov dlja ispol’zovanija v sistemah GIS (Method of creating vector maps of forest phytocenoses for use in GIS systems), In: GIS v nauchnyh issledovanijah zapovednikov Sibiri (GIS in the Research of Reserves in Siberia): Tez. report conf., dedicated. 75th anniversary of the gop. natural Reserve «Stolby», Krasnojarsk, 2000, pp. 14-15.

Ryzhkov O.V., Vlasov A.A., Ryzhkova G.A., Filatova T.D., Zolotuhin N.I., Zolotuhina I.B., Nepochatyh L.V., Vlasova O.P., Vlasov E.A., Mnogoletnjaja dinamika klimata i bioty Streleckogo uchastka Central’no-Chernozjomnogo zapovednika (Long-Term dynamics of climate and biota of the Streletsky site of the Central Chernozem reserve), In: Voprosy geografii, Sb. 143, Geograficheskie osnovy zapovednogo dela (k 100-letiju zapovednoj sistemy Rossii), Redkol.: V.M. Kotljakov, A.A. Chibiljov, A.A. Tishkov, Moscow: Izd. dom «Kodeks», 2017a, pp. 267-285.

Ryzhkov O.V., Vlasov A.A., Ryzhkova G.A., Filatova T.D., Zolotuhin N.I., Zolotuhina I.B., Nepochatyh L.V., Vlasova O.P., Vlasov E.A., Monitoring klimata i bioty Streleckogo uchastka Central’no-Chernozemnogo zapovednika (The monitoring of the climate and biota of the Streletsky site of the Central Chernozem nature reserve), In: Tr. Mordovskogo gop. prirod. zapovednika im. P.G. Smidovicha, E.V. Vargot (otv. red.), A.B. Ruchin, A.A. Hapugin, Saransk – Pushta, 2017b, Issue 18, pp. 17-32.

Ryzhkov O.V., Zolotuhin N.I., Ryzhkova G.A., Vidovoj sostav dendroflory Vtorogo nekosimogo uchastka Streleckoj stepi Central’no-Chernozemnogo zapovednika (po materialam kartirovanija 2016 goda) (Species composition of the dendroflora of the Second non-irrigated area of the Streletskaya steppe of the Central Chernozem reserve (based on the mapping of 2016)), In: Vseros. nauch. konf. «Nauchnye issledovanija na zapovednyh territorijah» (All-Russia. Scientific Conf. «Scientific Research in Protected Areas«): book of abstracts, Simferopol’: IT «ARIAL», 2017, pp. 43.

Ryzhkova G.A., Ryzhkov O.V., Nekotorye rezul’taty issledovanija gorizontal’noj struktury zapovednyh dubrav (Some results of the study of the horizontal structure of protected oak forests), In: Materialy Rossijsko-Ukrainskoj nauchnoj konferencii, posvjashhjonnoj 60-letiju Central’no-Chernozemnogo zapovednika (Materials of the Russian-Ukrainian scientific conference dedicated to the 60th anniversary of the Central Black Earth Reserve), Moscow: KMK Scientific Press Ltd., 1995, pp. 125-127.

Ryzhkova G.A., Ryzhkov O.V., Rasprostranenie drevesno-kustarnikovyh vidov na nekosimyh zalezhah Kazackogo uchastka Central’no-Chernozemnogo zapovednika (Distribution of tree-shrub species on certain deposits of the Cossack site of the Central Chernozem reserve), In: Rastitel’nyj pokrov Central’no-Chernozemnogo zapovednika: Tr. Centr.-Chernozemn. gos. zapovednika, Tula: Grif i K°, 2001 (na oblozhke 2002), Issue 18, pp. 94-224.

Ryzhkova G.A., Ryzhkov O.V., Rasprostranenie cheremuhi obyknovennoj v lesnyh jekosistemah Central’no-Chernozemnogo zapovednika na osnove analiza mnogoletnih nabljudenij za opadom (Distribution of common bird cherry in forest ecosystems of the Central Chernozem reserve based on the analysis of long-term observations of the fall), In: Flora i rastitel’nost’ Central’nogo Chernozem’ja – 2003 (Flora and Vegetation of the Central Black Soil Region – 2003): mat-ly science. conf., Kursk, 2003, pp. 28-31.

Ryzhkova G.A., Ryzhkov O.V., Dinamika listovogo opada v dubravah Central’no-Chernozemnogo zapovednika (Dynamics of leaf litter in the oak forests of the Central Chernozem reserve), Lesovedenie, No 5, 2004, pp. 20-27.

Ryzhkova G.A., Ryzhkov O.V., Dinamika rastitel’nosti lesnoj postojannoj probnoj ploshhadi «Osinovyj kust» po materialam kartirovanij raznyh let (Dynamics of vegetation of the forest permanent trial area «Aspen Bush» on the materials of mapping of different years), In: Kartograficheskie issledovanija v Central’no-Chernozemnom zapovednike: Tr. Centr.-Chernozemn. gop. zapovednika, Issue 19, Kursk. 2006, pp. 103-110.

Ryzhkova G.A., Ryzhkov O.V., Izuchenie dinamiki rasprostranenija leshhiny obyknovennoj na Streleckom uchastke Central’no-Chernozemnogo zapovednika s ispol’zovaniem metodov GPS i GIS (dopolnenie) (Study of the dynamics of the distribution of common hazel on the Streletsky site of the Central black earth reserve using GPS and GIS methods (Supplement), In: Geoinformacionnoe kartografirovanie v regionah Rossii (Geoinformation Mapping in the Regions of Russia) mater. III All-Russian scientific-practical conf., Voronezh, 15-18 September 2011, Voronezhskij gosudarstvennyj universitet. Voronezh: Izd-vo «Nauchnaja kniga», 2011. pp. 117-120.

Ryzhkova G.A., Ryzhkov O.V., Nepochatyh L.V., Usyhanie osinovyh nasazhdenij Central’no-Chernozemnogo zapovednika (Desiccation of aspen plantations of the Central Chernozem reserve), In: Flora i rastitel’nost’ Central’nogo Chernozem’ja – 2012 (Flora and Vegetation of the Central Chernozem Region – 2012): Mater. nauch. konf., Kursk, 6 April 2012, Kursk: Kurskij gos. un-t, 2012, pp. 138-142.

Ryzhkova G.A., Ryzhkov O.V., Ryzhkov D.O., Raspad osinovyh nasazhdenij Central’no-Chernozemnogo zapovednika (2008-2017 gody) (Decay of aspen plantations in the Central Chernozem reserve (2008-2017), In: Flora i rastitel’nost’ Central’nogo Chernozem’ja – 2018 (Flora and Vegetation of the Central Chernozem Region – 2018): Mater. nauch. konf., Kursk, 21 April 2018, Kursk: Mechta, 2018, pp. 105-111.

Solncev V.N., Ryzhkov O.V., Tregubov O.V., Alekseev B.A., Kaluckova N.N., Anciferova A.A., Ispol’zovanie GPS- i GIS-tehnologij dlja izuchenija osobo ohranjaemyh prirodnyh territorij (na primere landshaftnoj struktury Voronezhskogo gosudarstvennogo prirodnogo biosfernogo zapovednika) (The use of GPS and GIS technologies for the study of specially protected natural areas (on the example of the landscape structure of the Voronezh state natural biosphere reserve)). Tula: Grif i K, 2006, 216 p.

Utehin V.D., Rastitel’nost’ Central’no-Chernozemnogo zapovednika i ee produktivnost’ (Vegetation of the Central Chernozem reserve and its productivity), Biogeografija, fenologija, 1967, Issue 1, pp. 18-21.

Zolotuhin N.I., Ryzhkov O.V., Filatova T.D., Istorija organizacii, nauchnye issledovanija i obshhie svedenija o Zorinskom uchastke Central’no-Chernozemnogo zapovednika (the History of the organization, scientific research and General information about the Zorinsky area of the Central black earth reserve), In: Prirodnye uslovija i biologicheskoe raznoobrazie Zorinskogo zapovednogo uchastka v Kurskoj oblasti: Tr. Centr.-Chernozemn. gos. zapovednika, Issue 17, Tula, 2001, pp. 7-30.

Zozulin G.M., Kusmarceva N.M., Izmenenie granic drevesno-kustarnikovoj i travjanistoj rastitel’nosti na opytnyh uchastkah Central’no-Chernozemnogo zapovednika za 5 let (Changing the boundaries of tree-shrub and herbaceous vegetation in the experimental areas of the Central Chernozem reserve for 5 years), Botan. zhurn., 1951, Vol. 36, No 3, pp. 240-248.

Reviewer: PhD in technology, researcher Podolskaya E.S.

Original Russian Text © 2019 A.D. Nikitina, S.V. Knyazeva, E.A. Gavrilyuk, E.V. Tikhonova, S.P. Eydlina, N.V. Koroleva, published in Forest Science Issues Vol. 2, No. 3, pp. 1-21

                    A.D. Nikitina*, S.V. Knyazeva, E.A. Gavrilyuk,
E.V. Tikhonova, S.P. Eydlina, N.V. Koroleva

Center for Forest Ecology and Productivity of the RAS

Profsoyuznaya st. 84/32 bldg. 14, Moscow, 117997, Russia

*E-mail: nikitina.al.dm@gmail.com

Received 24 June 2019

This article presents the results of assessing the quantitative changes in vegetation cover areas of the Curonian Spit national park (NP) using materials from high spatial resolution multi-temporal multispectral imaging from ALOS and Sentinel-2 satellites. Automated classification algorithms Random Forest and Maximum Likelihood Estimation were tested. Based on the obtained data of automated interpretation of satellite images, ecosystem monitoring indicators of the national park (forest cover percent, share of coniferous trees in stands, share of waving (open) sands and sands covered with vegetation (fixed sands) were calculated, and dynamic maps of these indicators as well as a map of multi-temporal state of vegetation were compiled. Cartographic assessment reflects the main trends in the dynamics of the Curonian Spit NP vegetation structure over the ten-year period from 2007 to 2017: an increased percent of forest cover, increased share of vegetation-fixed sands on the side the Curonian Lagoon as a result of forest protection measures; decreased forest cover percent and increased share of waving sands on the side of the sea coast as a result of foredune destruction under the influence of wind, wave and recreational loads.

Key words: vegetation cover, forest stands, high spatial resolution satellite data, classification of satellite images, automated interpretation, classification algorithms, recognition accuracy, indicators of environmental monitoring, dynamics maps

Figure 1. Results of the Curonian Spit vegetation classification after combining classes for ALOS and Sentinel images; classes: 1 – water bodies, 2 – sand dunes, beach,
3 – meadow vegetation, 4 –psammophilic vegetation, 5 – pine forests,
6 – black alder forests, 7 – birch forests

A territorial observation unit, i.e. a forestry compartment was identified to calculate the quantitative values of the indicators. ArcGIS software package and spatial analysis (vector overlay, calculation of area characteristics) and geoinformation mapping methods were used to calculate the dynamics indicators and to compile maps. Calculation of the difference between the values of each indicator in 2017 and 2007 formed the basis for dynamics mapping. The indicators assessed were the forest cover percent, share of coniferous trees, shares of waving (open) sands and sands covered with vegetation (fixed sands).

A map of the multi-temporal state of vegetation was compiled based on the results of automated interpretation of satellite images for the Curonian Spit NP. The map reflects changes in the boundaries (contours) of plant communities and displays the combined borders of classes in 2007 and 2017 using the qualitative background technique (types of plant communities and natural objects in 2007 are filled with colour, and those in 2017 are shaded with colour).

RESULTS AND DISCUSSION

Class structure of plant communities for forestries of the Curonian Spit NP in 2007 and 2017 was analysed based on the results of classification of multi-temporal satellite images. In all cases, the share of forest stands exceeds 68%, with a maximum percentage of 72.2% in 2017. In general, the species structure is characterized by the predominance of pine forests (over 40%). Their share has slightly increased by 2017 (from 42 to 44% in Zolotye Dyuny forestry and from 43 to 48% in Zelenogradskoye forestry). The share of birch forests ranges from 13 to 19% with the decrease by 2017. Black alder forests account for the smallest share in the forest cover structure. Thus, the overall structure of the forest cover of the NP territory only slightly changed over the 10-year period from 2007 to 2017. When analyzing the dynamics indicators calculated for the Zelenogradskoye and Zolotye Dyuny forestries, we can conclude that there were no significant changes in the territory of the forestries as a whole during the period from 2007 to 2017 (Fig. 2).

The change in forest cover percent does not exceed 3%, and the change in waving sands is not more than 1%.

A

B

Figure 2. Indicators of vegetation cover dynamics of the Curonian Spit NP for the forestries:
A) Zelenogradskoye; B) Zolotye Dyuny: 1 – forest cover percent; 2 – share of coniferous trees;
3 – share of waving sands; 4 — share of fixed sands

Figure 3. Changes in the forest cover percent of the Curonian Spit National park
in the period 2007-2017

Figure 4. Fragment of the map of the multi-temporal state of vegetation on the territory of the 13th quarter of Zolotye Dyuny forestry. Classes: 1 – sand dunes, beach, 2 – meadow vegetation, 3 – psammophilic vegetation, 4 – pine forests, 5 – black alder forests, 6 – birch forests

Figure 5. Dynamics of the waving sands of the Curonian Spit National park
in the period 2007-2017.

Figure 6. Fragment of a map of the multi-temporal state of vegetation on the territory of the 12th and 13th compartments of Zelenogradskoye forest district. Classes: 1 – sand dunes, beach, 2 – meadow vegetation, 3 – psammophilic vegetation, 4 – pine forests, 5 – black alder forests, 6 – birch forests

CONCLUSION

Reviewer: PhD in geography, associate professor Malysheva N.V.

Original Russian Text © 2019 A.O. Kharitonova, A.S. Plotnikova, D.V. Ershov, published in Forest Science Issues Vol. 2, No. 3, pp. 1-17

A.O. Kharitonova*, A.S. Plotnikova, D.V. Ershov

Center for Forest Ecology and Productivity of the RAS

Profsoyuznaya st. 84/32 bldg. 14, Moscow, 117997, Russia

*E-mail: Kharitonova@ifi.rssi.ru

Received 30 June 2019

Recurring fires have a significant impact on the dynamics and functioning of forest ecosystems. The fire regime determines conditions of occurrence, spread and long-term consequences of forest fires. A significant change in the fire regime in the natural complex may indicate at possible loss risks of the key components of the ecosystem. This study presents current and historical fire regimes mapping results for the Pechora natural reserve and its surroundings — Kurinsky and Yakshinsky forest districts. The input dataset consists of fire historical fires records for the area taken from several sources: historical fires dataset of the Pechora natural reserve covering period from the second half of the XIX century till nowadays, which was received from both satellite images interpretation and reserve’s records archive analysis; hot spots detected by airborne-based and ground-based means covering period from 1987 to 2011 and the dendrochronological reconstruction of fires in the pine forests of the reserve’s surroundings for a 600-year period. We applied a methodology of mapping forest ecosystems fire regimes at local level for mapping both current and historical fire regimes. The methodology is based on the LANDFIRE classification, which accounts for fires frequency and fires severity. Results analysis of historical fire regimes indicate the dominance of “less than 200 years” fire return rate, associated with low-to-moderate fire severity for the most of the area. As an exception, the mountainous part of the Pechora natural reserve is characterized by a long period of fire return rate. The analysis of current fire regimes has revealed long periods of fire recurrence in both the reserve area and the forest districts area. We also showed a human impact on the increase in fire frequency. An assessment of the deviation of current fire regimes from their historical values showed that current fire regimes are within their normal historical range in most of the study area.

Key words: fire regime, the Pechora-Ilych Nature reserve, LANDFIRE, FRCC, GIS analysis

Figure 1. Relief of the study area according to the ASTER GDEM V2

Figure 2. Vegetation of the Pechora-Ilych Nature reserve and its surroundings

Figure 3. Fire history data and boundaries of spatial units for mapping fire regimes in the study area

A	B

Figure 4. Fire regimes of the Pechora-Ilych reserve and surrounding areas:

A) historical, B) current

Figure 5. Deviation of current fire regimes from the historical ones (in terms of fire frequency)

Reviewer: PhD in technology, research officer F.V. Stytsenko

Original Russian Text © 2019 E.I. Belova, D.V. Ershov, published in Forest Science Issues Vol. 2, No. 4, pp. 1-20

E.I. Belova*, D.V. Ershov

Center for Forest Ecology and Productivity of the RAS

Profsoyuznaya st. 84/32 bldg. 14, Moscow, 117997, Russia

E-mail: belova@ifi.rssi.ru

Received 23 September 2019

This paper considers remote sensing estimation of forest renewal in Suzemskoye forestry, Bryansk oblast. The objective was to study the possibility of assessing forest renewal on clear fellings through planting forest crops using the time series of vegetation indexes (NDVI and SWVI). The time series consists of cloud-free summer composite images based on Landsat data from 2002–2015. We used 2003 forest management plans and taxational descriptions of Kholmchenskoye forestry division which is part of Suzemskoye forestry as reference data. As a result, a linear relationship was obtained between the values of vegetation indexes, their time dynamics, and forest taxational characteristics (forest type, species composition, and age group). This enabled 80.1%-accurate detection of the forests regeneration if Steklyanskoye, Krasnoslobodskoye and Kokorevskoye forestry divisions, which are part of Suzemskoye forestry of Bryansk oblast. These forests were renewed after clear fellings. The results of this study can be used in practical forest management where the issue of monitoring reforestation and afforestation activities is highly relevant.

Key words: reforestation, time series, vegetation indexes, NDVI, SWVI

Modern forest management practices are based on the principles of sustainable forest management, which presuppose the availability of up-to-date operational knowledge about the forest condition. The forest management materials are the main source of data on forests. In the European part of the Russian Federation, forest management works are carried out every 10–15

years (Order of the Ministry of natural resources…, 2018). However, in the case of intensive forest management where the main anthropogenic load on forests as a natural resource is felling for harvesting wood, this interval of updating forest taxation materials may be too long.

In accordance with the Forest Code of the Russian Federation, such felling is allowed only with subsequent reforestation of these areas (Forest Code…, 2006). Forest renewal shall be effected by way of natural, artificial and combined forest recreation (Forest code…, 2006). According to the Rules of reforestation, the forest plots subjected to artificial or combined reforestation are usually considered forested land when forest plants reach the parameters of the dominant forest species in terms of age, number of trees, and height. For example, for the common pine, the age is 9 years (Order of the Ministry of Natural Resources…, 2016). In case of 15-years-long intervals of forest management fieldwork the data lose their relevance. Therefore, monitoring reforestation activities, both natural and through forest crops planting, as well as updating forest taxation materials and forest maps require an independent way of assessing the state of stands on clear fellings between forest management works.

Such a method can use remote data that are publicly available, e.g. Landsat data (NASA, USA) etc.

Currently, there is a huge number of studies looking into vegetation dynamics based on satellite data. Some major projects are Global Forest Change (GFC) (Hansen 2013) and The Global Land Analysis and Discovery (GLAD) (Potapov 2015). These projects use data from Landsat satellites with a medium spatial resolution equaling to 30 m to analyze the changes in vegetation cover. There is also a huge time-series data archive (for over 30 years).

These projects resulted in creating satellite thematic products that reflect forest area growth and reduction. Assessment accuracy of the above characteristics was 87% for reduction and 76% for growth of forest cover according to GFC, and over 90% according to GLAD products.

At the same time, these products also have a number of disadvantages:

1. GFC project has only the data on total increment as of 2012;

2. GLAD project has been implemented in Eastern Europe;

3. they are not related to the Russian forest management.

The first research attempts in this area were carried out by the authors of this article in 2014 for the forests of Krasnoyarsk krai (Belova et al., 2015). This article continues the research on the possibility of detecting the overgrowth of the felling areas by young trees in Krasnoyarsk krai. The main objective of this paper is to study the possibility of remote assessment of forest renewal in clear fellings through planting forest crops and creating an automated method based on the knowledge obtained. The results of the work are useful for the entire forestry practice in terms of improving the methods of state monitoring of forest reproduction.

MATERIALS AND METHODS

Region of study

The territory of Suzemskoye forestry located in the south-west of Bryansk region was selected as a test plot. This is the area of coniferous-deciduous (mixed) forests of the European part of the Russian Federation. As in the entire European part of Russia, forestry activity in the Suzemskyoe forestry is intensive. Reforestation is carried out mainly through planting forest crops. According to the data provided by the Russian Statistics Agency as of 2012, reforestation amounted to 3.453 ha, of which 3.138 ha were artificially restored. Pine and spruce are the species mostly planted in the fellings. Natural restoration of vegetation happens rarely here in contrast to the forests of the Western and Eastern Siberia. Pine, spruce, birch and oak, less often – black alder and aspen are the main forest-forming species of the test plot.

Kholmchenskoye forestry division, which is part of Suzemskoye forestry, was chosen for the study.

Baseline data

Ground reference data were used for the study, i.e. forest management plans and taxational descriptions of the selected district as of 2003.

Below are the main taxation characteristics that we used in our work: plot area, species composition, forest age and type.

Time series of summer cloud-free composite satellite images were used as remote data. Composite images were constructed based on Landsat-5/7/8 data for 2002–2015 (Belova et al., 2011). The time series is not continuous. No summer composite images for 2003, 2004, and 2012 were built due to the lack of the required amount of satellite data (images). Each composite image consists of three spectral bands, i.e. red (630–690 nm), near-infrared (770–900 nm), and mid-infrared (1.550–1.750 nm), spatial resolution is 30 m.

Methods

Using composite images for each year from the time series, we calculated the vegetation indexes NDVI (Normalized Difference Vegetation Index) and SWVI (Shortwave Vegetation Index) (1, 2):

NDVI = (NIR−RED)/(NIR+RED), (1)

SWVI=(NIR-SWIR)/(NIR+SWIR), (2)

where RED is the red spectral band (630–690 nm);

NIR is the near-infrared spectral band (770–990 nm); and

SWIR is the mid-infrared spectral channel (1.550–1.750 nm).

According to the forest management plan and taxational descriptions, plots with the following land categories were selected for the territory of Kholmchenskoye forestry division: closed forest crops of different age and composition; crops at the recovery stage (not yet closed at the time of taxation) of different composition and age, as well as felling sites of different time ranges. The plots with closed forest crops were divided into 3 classes according to the composition: spruce, pine, and deciduous trees. The class of deciduous trees included the plots with oak, aspen or birch.

For further work, the plots were filtered by area. The minimum area was assumed to be 1 ha, which corresponds to a 9-pixel image fragment. 800 plots were selected in total. The boundaries of the areas were vectorized. To exclude the influence of bordering pixels, the spectral brightness of which is formed not only from the brightness of the vegetation inside the plot, but also from the brightness of vegetation on its border, each plot was provided with a buffer zone inside, as large as one pixel (Fig. 1). All pixels of each plot, except for the buffer zone, were considered as a single spatial study object.

Figure 1. Example of a plot with a buffer zone inside

For each plot, average values of vegetation indexes for each year were calculated for each plot (3):

𝑀_𝑥=(Σ₁ⁿx_i)/n, (3), (3)

where x stands for the vegetation index value of the i pixel inside the plot;

n is the number of pixels in the plot; and

i is the pixel number in the plot.

Next, the accumulated average values of vegetation indexes for each year were determined for each plot (4). These values were placed in a two-dimensional SWVI–NDVI space to obtain a set of accumulated curves that characterize the state of vegetation in each plot.

V_годi=Σⁱ₂₀₀₂(M_x)_i, i=2002, 2005, 2006…2015, (4)

where i is the year;

– average vegetation index value in the plot for the i-year.

For example, for 2007, the accumulated average values of vegetation indexes for the plot are as follows:

Figure 2 shows accumulated curves for nine plots.

Figure 2. Accumulated average values of vegetation indexes for each year in the SWVI–NDVI two-dimensional space

RESULTS AND DISCUSSION

The relation of the accumulated values of vegetation indexes of forest crops in fellings is linear (Fig. 2), and the state of the vegetation on a plot can be characterized by the slope angle of the linear function: . The greater the angle of slope, the higher the probability that woody vegetation is either absent in the selection, or isn’t closed.

The restored links made it possible to calculate the threshold values of the slope angle for closed forest crops (without breaking down by breed composition). To do this, the following equation was solved:

Y = A × X + B, где B = 0, (7)

As a result:

A = 1.829, R² = 0.976

CKO = 0.126,

As is seen from the graph (Fig. 3), most points belonging to the accumulated curves of the plots with closed forest crops lie within the interval . Thus, this interval which is the reference sector allows repeated determination of the state of vegetation on fellings where reforestation was carried out at any time using current data from the Landsat satellite.

Y = A × X, (8)

Y = (A + 2CKO) × X, (9)

Y = (A — 2CKO) × X, (10)

Figure 3. A set of accumulated curves (indicated by points) for all the plots of the test area

Studies have also shown that the slope angle of the linear function depends neither on the species composition of the stands, nor on the age of stands, nor the forest type (Fig. 4). The values of the linear regression coefficient A for different tree species are close, therefore the proposed method cannot be used to determine the species and the age of the restored forest crop.

Figure 4. Set of accumulated curves (shown by points): a) closed pine crops by age groups; b) closed deciduous crops by age groups; c) closed spruce crops by age groups

Validation of the results obtained

Test plots of Steklyanskoye, Krasnoslobodskoye and Kokorevskoye forestry divisions (which are included into Suzemskoye forestry) were selected for the assessment of the method using the A coefficient threshold values that were based on the analysis of the vegetation indexes of plots of Kholmchenskoye forestry division.

Based on the forest taxation data of year 2003, 549 plots were selected, each being over 1 ha in size with closed crops of different age and composition, as well as with non-closed crops of different age and composition, which resulted from felling of different time ranges. Like in Kholmchenskoye forestry division, each plot here contained a buffer zone, excluded from the subsequent analysis, in order to eliminate the influence of the brightness of the plot’s border pixels.

Summer cloud-free composite images for years 2002–2015 were built for the territory of the forestry subdivisions. NDVI and SWVI vegetation indexes (1, 2) were calculated for the same period.

Using the formula (3), annual average values of vegetation indexes were calculated for each of the 549 plots. Then, accumulated curves were constructed for each plot using the formula (4).

Due to the absence of summer composite images in 2003 and 2004, the plots classification was carried out using satellite images made in 2005, as the closest year to the date of forest management materials. Based on the obtained threshold values of the linear regression coefficient of Kholmchenskoye forestry division, we classified 549 plots into the following classes: 1) closed crops of different species composition and age; 2) non-closed crops and fellings.

We compared the results of the classification with the taxational descriptions of these forestry divisions. The comparison results are shown in Table 1.

Table 1. Verification of classification results

Error analysis has shown that classification accuracy of the reforestation state depends on the plot area (Fig. 5), as the maximum number of errors occurred on the plots with an area under 2 ha. This is probably due to the spatial resolution of the Landsat satellite (30 meters or 0.09 ha), which generates images of plots, smaller than 2 ha with many mixed pixels at the forest – non-forest border. Using Sentinel-2 satellite images (10–20 m) might probably reduce the magnitude of error for reforestation sites, smaller than 2 ha.

Comparison of the obtained results with previous studies

The authors of the article carried out similar studies on the territory of Usolskoye and Chunskoye forestries of Krasnoyarsk krai (Belova et al., 2015), where natural forest restoration prevails in contrast to Suzemskoye forestry of Bryansk oblast. According to the data of the Federal State Agency for 2012, artificial restoration in Krasnoyarsk krai was observed on 7.217 ha, whereas natural restoration was observed on 49.832 ha.

Figure 5. Distribution of classification errors by plot areas

As the graph (Fig. 6) shows, the range of values of the linear regression coefficient A for the reforestation sites in Krasnoyarsk krai is wider than for the test plots of Bryansk oblast. This may be due either to different forest growing conditions, or to differing species composition in these forests. Therefore, the linear regression coefficient A is variable and depends on the forest’s geographical location, the type of forest conditions, the species composition of stands, etc.

Also, our research in Krasnoyarsk krai has shown when validating the results that the main sources of classification errors were the plots subjected to reforestation activities. Most likely, this is due to the fact that the region is dominated by natural vegetation restoration on fellings, that is why forest crops containing plots were excluded from the sample when solving the linear regression equation.

Figure 6. Accumulated curves for the forest that restored naturally in Krasnoyarsk krai

Thus, for each type of landscape or forest area, it is necessary to determine the reference values of the linear regression coefficient A using the taxation materials for the time series of satellite images. The adjusted regression model can then be repeatedly used to detect closed crops in the fellings when monitoring forest vegetation.

CONCLUSIONS

In the course of this research, forest management materials and a time series of Landsat cloud-free composite satellite images were studied and analyzed. The relationship was obtained between the dynamics of vegetation index values and the state of vegetation in clear fellings in the European part of Russia. This relationship characterizes the overgrowth of clear fellings during artificial reforestation.

The main conclusions drawn from this study:

1) this algorithm for analyzing the restoration dynamics of woody vegetation makes it possible to record the transition of the felling area from an unforested area to a forested one, both in case of natural and artificial restoration.

2) the obtained reference values of the coefficient of the linear regression model may be repeatedly used during detecting the closure of forest crops in certain forest growing conditions.

3) plots under 2 ha in size require other classification methods or satellite data with higher spatial resolution, since there’re over 70% of classification errors in case of Landsat model application.

4) this algorithm is not sensitive to the species and age composition of the stands. Using this method, it is possible to record the transition of the felling area from an unforested area to a forested area without the possibility of assessing the species-age structure of the stand.

ACKNOWLEDGEMENTS

The research was financed from a grant of the Russian Science Foundation (project No. 19-77-30015). The preparation and analysis of the thematic satellite images were carried out as part of research of the Center for Forest Ecology and Productivity of the RAS A18-118052590019-7).

REFERENCES

Belova E.I., Ershov D.V., Opyt ocenki estestvennogo lesovosstanovlenija na sploshnyh vyrubkah po vremennym rjadam LANDSAT (Assessing reforestation on clear cuts based on Landsat time series), Lesovedenie, 2015, Vol. 5, pp. 339-345.

Belova E.I., Ershov D.V., Predvaritel’naja obrabotka vremennyh serij izobrazhenij Landsat-TM/ETM+ pri sozdanii bezoblachnyh kompozitnyh izobrazhenij mestnosti (Preprocessing Landsat TM/ETM+ data sets for creating cloud-free composite imagery), Sovremennye problemy distancionnogo zondirovanija Zemli iz kosmosa, 2011, Vol. 8, No. 1, pp. 73-82.

http://www.consultant.ru/document/cons_doc_LAW_296757/77e0bc4c1b732cffc4ef23c2113effb964769f33/ (2019, 28 August)

http://www.consultant.ru/document/cons_doc_LAW_64299/710f2a2a776bb8cff9e204556177d7cb26f79dee/ (2019, 28 August)

http://www.consultant.ru/document/cons_doc_LAW_207285/4f0faeaf51f7cf71d1e928c355da9b3db3d3545d/ (2019, 28 August)

http://www.gks.ru/wps/wcm/connect/rosstat_main/rosstat/ru/statistics/environment/# (2019, 28 August)

Hansen M.C., Potapov P.V., Moore R., Turubanova S.A., Tyukavina A., Thau D., Stehman S.V., Goetz S.J., Loveland T R., Kommareddy A., Egorov A., Chini L., Justice C.O., Townshend J.R.G., High Resolution Global Maps of 21st Century Forest Cover Change, Science, 2013, Vol. 342, pp. 850-853.

Potapov P.V., Turubanova S.A., Tyukavina A., Krylov A.M., McCarty J L., Radeloff V. C., Hansen M.C, Eastern Europe’s forest cover dynamics from 1985 to 2012 quantified from the full Landsat archive, Remote Sensing of Environment, 2015, Vol. 159, pp. 28-43.

Reviewer: PhD in biology Medvedeva M.A.

Original Russian Text © 2019 N.V. Baranovskiy, A.V. Zakharevich, published in Forest Science Issues Vol. 2, No. 1, pp. 1-15

N.V. Baranovskiy^*, A.V. Zakharevich

Tomsk Polytechnic University

Lenin Av., 30, Tomsk, 634050, Russian Federation

^*E-mail: firedanger@yandex.ru

Received 11 March 2019

Experemental modeling of spruce needles ignition

Forest fires occur as a result of natural and man-made causes. It is known that particles heated to high temperatures are a common source of high temperature. The purpose of the work is the physical simulation of the ignition of typical forest fuel (spruce needles) by a carbonaceous particle heated to high temperatures and the identification of the typical ignition conditions of forest fuel. Every year, field observations and collection of forest fuel samples for experimental studies are carried out in the Timiryazevskiy forestry of ​​the Tomsk Region. Typical forest fuel (spruce needles) is considered. The sources of heating during the ignition of forest fuel were simulated by the particles made of graphite in the shape of a parallelepiped with characteristic dimensions in three coordinate directions (14 mm, 8 mm, 8 mm). The weight of such a graphite particle was 1.3 g. Experiments were performed in the range of changes in the initial temperatures T₀ from 1113 K to 1273 K. Numerical analysis shows that at a low sedimentation height, the particle retains its heat content to the maximum and cools down only in the near-surface layers. Initially, the mechanism of ignition as a result of the action of a burning graphite particle was investigated. The physical mechanism of the ignition of the forest fuel layer is established when a carbonaceous particle heated to high temperatures falls out in a flameless mode. A series of experiments were carried out and the dependence of the ignition delay on the initial temperature of the particle was obtained. The analysis showed that the dependence of the ignition delay on the initial temperature of a particle can be approximated to a first approximation by a straight line. The obtained results can be used for the development and verification of mathematical models to simulate the ignition of forest fuel by the particle heated to high temperatures.

Key words: forest fuel, mechanism, experimental modeling, ignition delay, particle, spruce

Forest fires occur due to natural and man-made causes (Hu and Zhou, 2014). The main natural cause is the impact of a cloud-to-ground lightning discharge, which results in the fragmentation of wood (Baranovskiy et al., 2017). As a result, wood particles heated to high temperatures are formed. Such particles can fall onto a layer of forest fuel and cause it to ignite (Suzuki and Manzello, 2019). As a result, a surface forest fire occurs (Grishin, 1997). Another scenario corresponds to anthropogenic impacts when there are still fires left in the forested area (Yanko, 2005). When wood cracks in a fire, its small particles can move to a layer of forest fuel near the fire and cause ignition. As a result, the occurrence of a surface forest fire is possible. It should also be noted that the formation of such particles is possible directly during active forest fires (Manzello et al., 2006). Subsequently, such particles, as a result of vertical and horizontal transport, can leave the forest fire zone and are transported to a distance of several hundred meters (Terebnev et al., 2007). Then, such particles settle on a layer of forest fuel and cause a new fire. This is exactly how spotted forest fires occur (Grishin, 1981).

To develop next-generation systems for forecasting forest fire danger, it is necessary to take into account the physicochemical processes that occur when the layer of forest fuel is ignited. To identify the physical mechanism and carry out subsequent verification of such models, it is necessary to conduct experiments for the physical modeling of the ignition of typical forest fuel by a particle heated to high temperatures, which is a widespread source of high temperature.

The aim of the research is the physical modeling of the ignition of typical forest fuel (spruce needles) by a carbonaceous particle heated to high temperatures and the identification of the ignition conditions for the typical forest fuel.

STUDY AREA

The ecological system of forests of the Russian Federation occupies 1.2 billion hectares of territory and contains about 25% of the forest resources of the entire planet. Russian forests are not only an economic but also an important environmental resource, since the Russian Federation provides the annual carbon storage of 29 billion tons. The global processes of regulating the state of the environment, biodiversity, climate, and river flows are significantly affected by Russian forests (Kuznetsov et al., 2005).

The Tomsk Region, especially its northern part, is a fairly typical forest-covered territory of the boreal zone. Through this example, a fairly general description of the conditions for the occurrence of fires is possible. The region has large forest resources. The land-forest fund occupies 90.5% of its entire territory. An area of ​​17 million hectares is covered with tree species, including 9.9 million hectares of coniferous trees (Panevin, 2006). The main relief types within the Tomsk Region are the watershed plains and river valleys along with the hollows of the ancient runoff (Evseeva and Zemtsov, 1990). Dividing plains are represented by positive and negative morphostructures.

Forests of the region are located in the river basin. The Ob River is situated on an exceptionally flat territory with excess moisture and is of great environmental importance (Panevin, 2006). Relatively harsh climatic conditions determine the rather limited species composition of forests. The most common types of forest formers are common pine, Siberian cedar, Siberian spruce, Siberian fir, saggy and fluffy birch, Siberian aspen, and larch (Panevin, 2006; Gorina, 2008).

The fire danger of the Tomsk Region forests is determined by the presence of a significant proportion of coniferous forests, developed high-temperature ground cover and hot, dry summers. The climate of the Tomsk Region is sharply continental of the boreal type (Gorina, 2008). In territories with a continental climate, conditions especially favorable for the occurrence of forest fires are created (Kurbatsky, 1964). Depending on weather conditions, all three peaks of seasonal incidence are expressed in the forests of the region: a spring wave of fires, summer steady fires and autumn fires (Panevin, 2006).

A feature of the forests of the Tomsk Region is the presence of combustible material in all stands. Mostly surface fires develop in the region (98.5%); 1.1% of incidents and 12.5% ​​of the burned-out area are accounted for by crown fires, and underground fires occur even less frequently (Panevin, 2006). The share of fires caused by anthropogenic reasons is quite stable over the years, and fires from a lightning discharge are cyclical. Periods with massive thunderstorms give way to calmer fires. The combustibility of the region’s forests also varies significantly over the months of the fire danger season. The most “burning” months are June and July. The duration of the fire danger season according to the weather conditions is from 137 to 161 days (Panevin, 2006). According to Rosleskhoz, the statistics of forest fires in the Tomsk Region suggests that approximately 200 forest fires are caused by anthropogenic factors and about 75 forest fires result from thunderstorm activity (as for 2016). Part of the fires arises as a result of the transition of agricultural burnings to forested areas.

Annually, field observations and collection of forest fuel samples for experimental studies are carried out in the Timiryazevskiy forestry of the Tomsk Region. The specified forestry of the Tomsk Forest Management is located between two large rivers (Ob and Tom) in the territory of three administrative districts of the Tomsk Region – Tomsky, Shegarsky, and Kozhevnikovsky. The length of the forestry territory from North to South is 64 km, from West to East 50 km. Forests of the forestry are mainly represented by a single forest, except for the isolated near-village pine forests of the settlements of Zorkaltsevo, Nizhne-Sechenovo, and Gubino (Matsenko et al., 1999).

According to the forest vegetation zoning of Western Siberia, the territory of the Timiryazevskiy forestry of the Tomsk Region belongs to the zone of the southern taiga (the Ob-Tomsk pine and pine forest-growing district). According to the agroclimatic zoning of the Tomsk Region adopted by the Tomsk branch of Sibgiprozem, the forestry area is classified as a moderately humid area. The growing season is 120 days. The predominant main breed is pine (39.6%), aspen (26.2%) and birch (21.2%); cedar, larch, spruce, and fir account for 13% (Matsenko et al., 1999). For several years, the former Kaltayskoye Forestry as the Kaltayskoye Local Forestry was part of the Timiryazevskiy forestry.

MATERIALS AND METHODS

The experimental facility and methodology described in detail in (Zakharevich et al., 2008; Kuznetsov et al., 2008) were used. The experimental facility is illustrated in Figure 1.

Figure 1. Scheme of the experimental facility: 1 – heating device, 2 – tripod, 3 – chromel-alumel thermocouple, 4 – ceramic rod, 5 – temperature control device UKT38, 6 – metal particle, 7 – working surface of the experimental setup, 8 – fireproof platform, 9 – radiation detector and flame recorder, 10 – emitter, 11 – vertical glass cylindrical vessels, 12 – analog-to-digital converter (ADC), 13 – personal computer (Zakharevich et al., 2008; Kuznetsov et al., 2008).

The sources of heating during forest fuel ignition were modeled by parallelepiped-shaped particles made of graphite with characteristic dimensions in three coordinate directions (14 mm, 8 mm, 8 mm). The weight of such a graphite particle was 1.3 g. The experiments were carried out in the initial temperature range T₀ from 1113 K to 1273 K. This range was chosen in order to single out, firstly, the lower ignition limits of the investigated forest fuel. The upper temperature limit was chosen based on the conditions of ignition of a graphite particle in the air (a burning particle upon precipitation onto the forest fuel layer always caused its ignition). Numerical analysis shows that at a low separation height, the particle retains its maximum heat content to the maximum and cools down only in the surface layers. The central massive part of the particle during the deposition period does not cool down regardless of the separation height. As a result of the sedimentation of such a particle on a layer of ground forest fuel at the contact point, heat will flow into the surface layers of forest fuel. At subsequent times, the thermal decomposition and gas-phase ignition of forest fuel layer can occur. As a result, a surface forest fire may occur (Grishin et al., 1998; Podur et al., 2003).

The experiments were carried out according to the classical plan with randomization due to the fact that up to now no mathematical model has been defined that describes the relationship between the delay time of forest fuel ignition and the initial temperature of a local heating source. At a constant value of T₀, 5–7 experiments were performed, the standard deviation and confidence intervals for determining t_ign were calculated with a confidence probability of P=0.95 (Ventsel, 1999). The normal distribution of the measured quantity (ignition delay time) was assumed. The experiments were carried out with a group of graphite particles identical in size and manufacturing conditions. Before the experiments, heat treatment of heating sources in an induction furnace was carried out to “burn” volatile compounds. Each particle was used in only one experiment, because its state (shape, size, and the structure of the surface layers) changed after the experiment. These changes were generally insignificant, but the particles were not reused to reduce the errors in the studies performed.

It should be noted that the carbonaceous particle ignition process is different from a similar process with a steel particle as a source of ignition. Single carbonaceous particles at high temperatures are characterized by a gasification process that occurs during the intense penetration of gas reagents through the porous structure of a particle (Vilensky and Khzmalyan, 1978; Golovina, 1983; Morell et al., 1990). That is, diffusion processes are important (it was shown (Samuilov et al., 2004) that diffusion phenomena have a significant influence on the gasification process for large particles and the transformation of components inside the particle, which leads to a change in the porous structure itself (Jones et al., 1999).

The type of global gasification reaction is as follows (Samuilov et al., 2004): C + CO₂ → 2CO. According to (Laurendau, 1978), this process involves a chain of reactions on the surface of pores:

C_f+CO₂C(O)_L+CO,

C(O)_L→C_f+CO,

C(O)_LC(O)_S,

C(O)_S→C_f+CO,

where C_f, C(O)_L, C(O)_S are free active carbon centers, an oxygen atom connected to a carbon atom by a mobile ionic bond, and an oxygen atom forming a fixed carbonyl bond with a carbon atom, respectively. To date, new approaches to the study of the mechanism and laws of heterogeneous combustion and carbon gasification reactions have been developed (Golovina, 2002). If in the framework of the diffusion-kinetic theory of heterogeneous combustion and gasification of carbon, the laws of the process were judged by the behavior of only the gas phase, then now, along with the gas phase, changes in the solid phase are also taken into account. For this, the concept of active surface areas (ASAs) or, more broadly, reactive surface areas (RSAs) is introduced. The reactive surface is determined by the concentration of active carbon atoms, on which a carbon-oxygen complex is formed, which gives a gaseous product upon decomposition (Golovina, 2002; Lizzo et al., 1990).

The preliminary placement of graphite particles in an induction furnace showed that in the temperature range 1113-1273 K, a graphite particle burned in a flame mode. The sedimentation of such a particle on the forest fuel layer also unambiguously leads to ignition. It is likely that the initial heating of a graphite particle is accompanied by the release of any volatile compounds that burn in the gas phase. The subsequent heating of the particle is not accompanied by the appearance of a flame around the particle. A series of preliminary experiments showed that a carbonaceous particle is characterized by its burnout over time. This can be explained by the processes of gasification of a carbonaceous particle considered above, as well as by the heterogeneous oxidation of carbon itself.

The object of the study was the model layers of a typical forest fuel (spruce needles with branches), which were formed in a refractory cuvette by means of a random stacking of branches with needles in a uniform layer. The characteristics of forest fuel:

a) the needles in appearance are green with a slight gray-brown tint;

b) the needles and branches of the current collection are practically not decomposed;

c) pre-dried material;

d) the main fraction consisted of needles with a size of (1.5-2) cm in the longitudinal and (0.7-1.3) mm in the transverse direction;

e) the fraction of twigs different from the main part of the needles was about 25%.

RESULTS AND DISCUSSION

The following patterns of the process under study were established. Two options for the implementation of the ignition conditions are possible:

a) Initially, the mechanism of the occurrence of ignition as a result of the impact of a burning graphite particle was investigated. A carbonaceous particle, accompanied by a flame torch of combustion of volatile compounds, falls on the forest fuel layer, which is heated by three heat transfer mechanisms: conduction, convection, and radiation (most likely, convective and radiant transfer are the main ones in this ignition mechanism). Individual needles warm up and begin to thermally decompose with the release of gaseous pyrolysis products. The injection of gaseous combustible products and the ignition of forest fuel in the gas phase occurs. For the moment of ignition, the appearance of a second flame is characteristic (the first is formed as a result of the combustion of volatile products released by the particle). Then there is a combination of torches and the subsequent spread of flame along the forest fuel layer.

b) Fig. 2 shows typical video footage of the process of forest fuel layer ignition by a carbonaceous particle heated to high temperatures (flameless mode). After the initial stage of a short period of inert heating of the forest fuel layer, the thermal decomposition of the material begins with the release of gaseous pyrolysis products. In the contact zone, the needles from the heterogeneous layer of forest fuel decompose almost completely with a small coke residue that falls on the substrate. Thin branches are thermally decomposed in a thin surface layer. In a porous forest fuel medium, gaseous pyrolysis products are filtered to the heated surface of the layer and mixed with an oxidizing agent, and the gas mixture is heated, followed by ignition. In most experiments, a flame torch formed over a heated particle.

a)

b)

Figure 2. Typical video footage of the forest fuel ignition by a particle heated to high temperatures at different points in time: a) t=0.08 s – inert heating of the forest fuel layer; b) t=0.24 s – the appearance of a microtorch of flame.

Fig. 3 shows the dependence of the ignition delay on the initial particle temperature with confidence intervals. The lower ignition temperature limit is highlighted. Unlike pine litter, the studied sample was characterized by an ordered distribution of individual needles, thin branches and often a fixed distance between them. The structure of the sample was characterized by porosity due to the ordered structure of the needles, as well as a large pore space due to the morphology of spruce branches, which led to rather high values ​​of the standard deviations of the measurement results t_ign from the average values. Due to this, in each particular experiment from a series of experiments at the same initial temperature, the heat exchange conditions between the ignition source and the forest fuel layer also differed.

An analysis of Fig. 3 shows that the dependence of the ignition delay on the initial particle temperature can be approximated, as a first approximation, by a straight line. However, a more qualitatively obtained experimental data describes a parabolic dependence. Earlier, a similar fact was established when studying the ignition processes of dry grass with a packing density corresponding to natural conditions. However, its further increase led to a linear dependence of the ignition delay on the initial temperature of the heated particle. The difference from the linear dependence was probably due to the non-identity of the processes of heat and mass transfer in a complex structurally inhomogeneous material. This is probably the reason for the deviation from the linear dependence in the case of studying spruce branches with needles.

It should be noted that the performed experimental studies showed the high stability of the ignition of forest fuel with multiscale porosity by a single carbonaceous particle heated to high temperatures. The development of the ignition process is fairly well demonstrated by the typical videogram of the experiment.

It should be specially noted that the experimental values ​​of t_ign (Fig. 3) at T₀ 1273 K can be compared with the values ​​of the ignition delay of a typical liquid fuel – kerosene under adequate heat exposure conditions (Zakharevich, 2008). For kerosene, t_ign is more than two times higher than the similar value for the litter of conifers. In this case, the lower limit values ​​of the ignition temperatures of kerosene are almost 100 K higher than those shown in Fig. 3. The correlation between the characteristic ignition delays of the litter of coniferous trees and typical liquid fuels established by the experimental results is due to the peculiarities of heat and mass transfer in the heated layer and on the surface of these combustible substances under local thermal exposure. For example, the research results (Kuznetsov and Strizhak, 2008; Kuznetsov and Strizhal, 2009; Kuznetsov and Strizhak, 2009) show that when heating both films and large masses of liquid fuels, a significant part of the supplied heat energy is spent on an energy-intensive process of formation of fuel vapor. The heat of phase transition (the evaporation of any liquid fuel) is significantly (more than 10 times) higher than the heat spent on the gasification of forest fuel (thermal decomposition). Accordingly, a longer heating time of liquid fuel is required in comparison with forest fuel in order to initiate a chemical combustion reaction.

CONCLUSION

Additional experiments were conducted with a typical forest fuel of the Tomsk Region (spruce branches covered with needles), which showed the need for the further improvement of the mathematical models of forest fuel ignition by a local heating source. An analysis of the results shows that for forest fuel samples with large pore spaces, the linear dependence of the ignition delay time on the initial temperature of the heated particle is applicable only to a first approximation. At the next stage, an improved mathematical model of forest fuel ignition should be developed taking into account small and large pores in the forest fuel layer.

ACKNOWLEDGEMENTS

The study was supported by the Russian Foundation for Basic Research and the Administration of the Tomsk Region. Scientific project No. 16-41-700831.

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Reviewer: PhD in technology, associate professor Goman P.N.

Original Russian Text © 2019 R.Kh. Pshegusov, F.А. Tembotova, Yu.M. Sablirova, published in Forest Science Issues Vol. 2, No. 3, pp. 1-11

R.Kh. Pshegusov^*, F.А. Tembotova, Yu.M. Sablirova

Tembotov Institute of Ecology of Mountain Territories of the RAS

I. Armand st. 37a, Nalchik, KBR, 360051, Russia

^*E-mail: p_rustem@inbox.ru

Received 10 June 2019

The paper presents a comparative analysis of spatial localization parameters of coniferous and coniferous-deciduous forests in various landscape and climatic conditions of the Western Caucasus. During the study, we set the task of determining parametric variables that would reflect the most significant factors of distribution of coniferous and coniferous-deciduous forests of the Western Caucasus based on the synthesis of field and remote data. In 2016–2018, 76 trial plots for research and material collection were laid in the Western Caucasus. The research resulted in presentation of a typological scheme of coniferous and coniferous-deciduous forests of the research area, and identification of 13 types of forests, that are distributed into 7 groups. The forest stands in the studied forest types are mainly of different ages, multi-storeyed, highly closed, of medium or high density. Conclusions are made about the high accuracy of the spatial distribution model based on the parametric values of discriminant functions and average values of predictors.

Key words: Western Caucasus, coniferous forests, remote sensing data, spatial analysis

Figure 1. Variable importance plot to the construction of the forest type classification tree model

Reviewer: PhD in biology, senior researcher N.E. Shevchenko