Abstract <p>This article assesses the nutrient status of soils in the coniferous–broad-leaved forests of the North-West Caucasus, taking into account their mosaic structure. The relevance of this topic is driven by the increasing demand for assessments of supporting ecosystem functions based on the relationship in the soil–forest-vegetation system. The objects of study are coniferous–broad-leaved forests of the North-West Caucasus (Caucasian Biosphere Reserve and Absheron Forestry in the upper reaches of the Belaya and Pshekha rivers, respectively) at different stages of secondary succession of fir–beech forests. Parcels of forest gaps and closed canopy parcels have been identified in the studied biogeocenoses. At the intra-parcel level, structural units of biogeocenotic cover (elementary biogeoranges (EBGA) have been identified according to the boundaries of Ramenskii’s microcommunities. With the structural heterogeneity taken into account, change in the litter quality is characterized as a factor influencing the formation of the soil nutrient status. Taking into account the mosaic structure of the forest cover, the soil horizons have been analyzed for acidity and the content of carbon, nitrogen, and available mineral nutrient compounds using physicochemical methods. The most significant differences in the soil nutrient status have been recorded at the inter-biogeocenotic level. In young hornbeam forests, the differences in the soil nutrient status between forest-window parcels and closed-canopy parcels are more significant than the differences in the soils under trees of different species in parcels with closed canopy. Differences between different tree EBGA are observed in mixed coniferous–broadleaf forests as a result of the combined influence of fir and hornbeam. The article develops ideas about the mosaic structure of mountain coniferous–broadleaf forest biogeocenoses, determined by the influence of biota.</p>