Species and Structural Diversity of Coniferous–Broadleaf Mixed Forests of the Pshekha River

This article presents the species and structural diversity of coniferous–broadleaf forests of the Pshekha River, the largest tributary of the Kuban River. In total, seven main types of forest have been identified and described: fir–beech fern–forb, fir–hornbeam blackberry–forb, aspen-hornbeam honeysuckle–small-herb, hornbeam–black alder nitrophilic–tall-herb, hornbeam–oak rhododendron–blackberry, hornbeam–beech blackberry–forb, and hornbeam honeysuckle–blackberry forests. The forest flora of the Pshekha River consists of 270 species, including 221 species of vascular plants and 49 species of mosses. The floristic diversity of coniferous–broadleaf forests of the Pshekha River is inversely related to the stand canopy density and the proportion of oriental beech (Fagus orientalis). The hornbeam–black alder nitrophilic–tall-herb forest type is characterized by the highest species saturation, while the fir–beech fern–forb forest is characterized by the lowest. The ecological and coenotic structure of coniferous–broadleaf forest types of the Pshekha River depends on the altitude, which determines the average annual precipitation and average annual temperature: with a decrease in altitude, the proportion of boreal species in the composition of the flora decreases, while the proportion of nemoral and meadow–edge species increases. In the coniferous–broadleaf forests of the Pshekha River, 11 species of earthworms have been identified. They belong to four morphoecological groups: epigeic, epi-endogeic, endogeic, and anecic. In forests with a high quality of litter (hornbeam-dominated), the greatest contribution to the biomass is made by epigeic (up to 41%) and epi-endogeic (up to 45%) earthworms. In forests with low quality of litter (fir- and beech-dominated), the proportion of endogeic earthworms is high (up to 66%). Anecic earthworms are mostly confined to forests on moist soils. In all types of forests, Crimean–Caucasian endemics significantly contribute to biomass and abundance (represented by polymorphic D. schmidti and anecic D. mariupolienis) as well as Mediterranean species (epigeic D. attemsi, which often inhabits oak and hornbeam deadwood, and endogeic A. jassyensis). Cosmopolitan species (D. r. tenuis and D. octaedra) are numerous among the epigeic worms and often inhabit coniferous deadwood.