Earthworms (Ologochaeta, Lumbricidae) of the Hyrcanian Forests of Azerbaijan

Hyrcanian forests are a relict forest massif in Iran and southeastern Azerbaijan preserved since the Tertiary period. To the best of our knowledge, earthworms of the Azerbaijani part of the Hyrcanian forests have not been studied. The aim of this work is to study the fauna, population structure, and biotopic distribution of earthworms in natural and disturbed biogeocenoses of the lowland Hyrcanian forests of Azerbaijan. The material was collected in the Hyrkan National Park. We studied occurrence, average and relative abundance, dominance, and biodiversity of earthworms, evenness indices, and variation coefficients of synecological characteristics. The core of the earthworm fauna in the Hyrcanian forests is formed by Transcaucasian and Turanian Lumbricidae species as well as species of Mediterranean origin. In forests with the chestnut-leaved oak as the tree layer edificator species, earthworm taxocenes are characterized by a stable species composition, low total abundance, and significant variability of synecological indices. The structure of meadow taxocenes of Lumbricidae depends on the localization of the biogeocenosis: in areas surrounded by oak forests, it is formed by forest species, while the edge communities are influenced by steppe inhabitants and a sharp increase in the total abundance of earthworms is noticeable; moreover, the participation of endogeic group of lumbricids in the edge communities is more pronounced. Meadow taxocenes are characterized by the lack of epigeic species, Mediterranean species are rare and their abundance is low, however cosmopolitans have been identified. In secondary forest biogeocenoses, compared to the meadow ones, the representation of Mediterranean taxa tend to increase and that of cosmopolitan taxa increased statistically significantly in the chorological structure of earthworm taxocenes, and among morpho-ecological groups they are represented by epigeic species. The structures of hornbeam, pecan, and black-walnut taxocenes are balanced, diverse, include rare species, while autochthonous elements of the fauna are less represented.