Spatial Distribution of Pine Forests in the Caucasus

An effective approach to studying the factors of distribution of forest-forming species of the Caucasus in conditions of orographic inaccessibility of mountainous areas is a combination of the use of geoinformation systems and the theory of ecological niche in SDM distribution models. Many aspects of this approach remain controversial, including the choice of ecological predictors, the collinearity of variables, the scale effect of the study area, the formalization of biotic factors and the dispersal capacity of species in models. The aim of this study has been to identify patterns of spatial distribution of pine (Pinus sylvestris L.) forests of the Caucasus depending on the area of the analyzed territory. To formalize the biotic factor of pine forest distribution, a method has been proposed for including probability distribution maps of the detection of competing species (birch (Betula pendula Roth and B. litwinowii Doluch.) forests) in the SDM model of P. sylvestris as biotic layers. The factor of pine dispersal capacity (accessibility of territories) has been formalized through the distance from the optimal habitats of the species (areas with a sustainability threshold of 0.8), where the probability of its detection remains above 0.5. A comparative analysis of different sets of abiotic predictors with and without multicollinear variables have revealed the advantages of the model based on the ENVIREM (Environmental Rasters for Ecological Modeling) dataset limited by the VIF (Variance Inflation Factor) test. At the local level (Central Caucasus), the main predictor of the location of pine forests is the accessibility of territories of 0–3 km from optimal habitats (the contribution to the model is about 72 %). At the regional level (Caucasus as a whole), interspecific competition is of great importance (the contribution to the model is about 37 %). The least significant factors in the distribution of pine forests are the main abiotic factors (orography of the area and the temperature and water regime of the driest quarter), the equity particlpation of which in the final models does not exceed 16 %. The species has been found to have a potentially wide distribution in the Caucasus in areas with diverse climatic and orographic conditions (about 21 thousand km2). The centre of the Caucasian pine range is predicted to be in the Central Caucasus (96 % of the optimal habitat area).