Structural Diversity of Vegetation Influencing the Soils' Nutrient Regime in Coniferous-Broadleaved Forests of the Northwestern Caucasus

The article provides an assessment of the soils’ nutrient regime in coniferous-broadleaved forests of the Northwestern Caucasus, taking into account their mosaic structure. The relevance of the topic is due to the increasing demand for assessments of supporting ecosystem functions, which are in turn based on the relationships within the “soil — forest vegetation” system. The objects of study were coniferous-broadleaved forests of the Northwestern Caucasus (the Caucasian Biosphere Reserve and the Apsheron Forestry Unit in the upper reaches of the Belaya and Pshekha rivers, respectively) at different stages of restorative succession of fir-beech forests. In the studied biogeocenoses, forest gap parcels and parcels with closed canopy were identified. At the intra-parcel level, structural units of the biogeocenotic cover were identified — elementary biogeoareals (EBGA) along the boundaries of Ramensky microgroups. Taking into account the structural heterogeneity, the changes in the litter quality were characterised as a factor influencing the formation of the soils’ nutrient regime. Then, an analysis of acidity, carbon, nitrogen content, available compounds of mineral nutrients was carried out within the soil horizons using physicochemical methods, taking into account the mosaic nature of the forest cover. The most significant differences in the soils nutrient regimes were identified on the interbiogeocenotic level. In young hornbeam forests, the differences in the soils nutrient regime between forest gap parcels and parcels with closed canopy were more pronounced than in soils under trees of different species in parcels with closed crown canopy. Differences between different woody EBGAs appeared in mixed coniferous-broadleaved forests due to the combined influence of fir and hornbeam. The article discusses ideas about the mosaic nature of mountain coniferous-broadleaved forest biogeocenosis being caused by the influence of biota.