ИСТИНА

Spatial relations between forest and steppe communities are commonly highly sensitive to climatic changes. However, the result of their competition for space may be mediated by relief which can either enhance or smooth climatic signals. Since vegetation and soils have different characteristic time scales, discrepancy between their properties are believed to indicate possible expansion of communities following trends in heat or water supply. We tested the hypothesis that the movement of forest-steppe boundary in the Southern Urals, Russia, takes place and depends on topographic conditions. We calculated the set of relief morphometric attributes from DEM and classified multichannel Landsat 8 space image in SAGA software to relate occurrence of vegetation types (broad-leaved forests, shrub communities, and steppes) to topography. Discriminant analysis was used to calculate the posterior probabilities that the community at each pixel occurs in typical topographic conditions for each vegetation type. Field data was used to calculate probabilities that chemical and color properties of soils (Chernozems and Phaeozems) correspond to typical values for each vegetation type. We tested the hypothesis that if vegetation type occurs in untypical topographic conditions, soil properties correspond to another vegetation type and this indicated forest expansion to the steppe niche or vice versa. The results showed that at the north-facing slopes oak forests and shrubs more often occur on soils with steppe-related properties. This testifies decrease of steppe communities following current increase of winter precipitation in the region despite decrease of summer precipitation. On narrow ridges with shrubs forest-related soil properties occur frequently. Absence of forests in these habitats is most likely explained by fire events. Steppes are stable on flat plato with Chernozems.