Long-Term Changes in the Structural and Functional Сomposition of Spruce Forests in the Center of the East European Plain

Norway spruce (Picea abies [L.] Karst.) is a primary forest-forming species in the European part of Russia, both in terms of its distribution and economic importance. A number of studies indicate that one of the reasons for the disturbance of spruce forests is linked to rising temperatures, particularly the detrimental effects of extreme droughts. In our study, we propose a hypothesis regarding the critical condition of mature spruce forests within the coniferous-broadleaved vegetation zone at the center of the East European Plain, the decline of which is escalating each year due to global climate change. The studies were conducted in intact spruce forests using resurveyed vegetation relevés within the Smolensk-Moscow Upland by repeating relevés after 40 years. We estimated beta diversity of species composition using the Mann-Whitney U test to study succession processes. Interspecific relationships were estimated using the Spearman criterion. The functional significance was assessed using the species activity index. Interpretation of the species composition of communities of different time periods based on indirect ordination methods (NMDS). Results showed that significant disturbances of the tree layer have led to changes in the vegetation of subordinate layers. An analysis of the complete species composition of spruce forests based on scoring assessments using Ellenberg's scales revealed changes in the ecological conditions of habitats over 40 years. A noticeable trend was observed towards an increase in the proportion of thermophilic species and those favoring less soil reaction, indicating a shift towards a nemoral vegetation spectrum. It is expected that without implementing additional forestry measures such as silviculture and thinning, the next 40 to 60 years will see a decline in the proportion of spruce within mixed stands, potentially culminating in the complete collapse of monospecific spruce forests in the center of the East European Plain.