Frequency and diversity of worms in topsoil of degraded and reclaimed forest habitats of the Caspian region

Earthworms are considered as the most important characteristics in assessing the quality and soil health of forest ecosystems. Earthworms were identified according to their shape and appearance, and their biomass was measured at the laboratory. In order to study the earthworm's biodiversity, Simpson diversity and Margalef richness indices and Camargo evenness were employed. A total of 5 different types of earthworms were identified in the studied habitats. According to the results, all of the earthworms identified were belonged to a family (Lumbricidae), four genera (Lumbricus, Dendrobaena, Aporrectodea and Octolasion) and three ecological groups (Epigeic, Anecic and Endogeic). The Dredrobaena octaedra earthworms from the Epigeic ecological group in all studied habitats were observed in this study and have the highest frequency. The earthworm species belonging to the Anecic and Endogeic ecological groups were not found in the oak, cypresses and degraded areas. In general, ecological groups of earthworms under less degraded natural forest and alder habitats were the most frequent and they had positively significant relation with litter and soil nitrogen and also soil pH, whereas they were negatively related to litter and soil carbon and carbon to nitrogen ratio. As a conclusion, the degradation of forest habitats has reduced the frequency and diversity of earthworms, while the reforestation of degraded forests, especially alder plantation, has increased diversity and abundance of earthworms.