Structure of Earthworm Complexes in Forest Deadwood of Forest-Steppe of the Ob Region during the Temperate and Arid Summer Seasons

The investigation evaluates the species and functional diversity of earthworm complexes inhabiting the deadwood of the main tree species in two forest types during the time of conducive and dry summer seasons. The objects of the studying are the mixed-grass pine forest and birch-aspen fern forest in the forest-steppe Ob region of the Novosibirsk area, the deadwood Pinus sylvestris and Betula pendula of the 2–3 stages of decomposition, respectively. Quantitative counts of earthworms were carried out using manual analysis of deadwood in the field, according to accepted methods. During the research we found nine species and subspecies of earthworms belonging to five living forms, most of which are cosmopolitan. The main part of the population in Pinus sylvestris deadwood is made up by epigeic earthworms; a full-fledged earthworms complex has been found in the Betula pendula deadwood. During the conducive summer season earthworm complexes in each type of forest maintain their structure with slight fluctuations of population density and biomass. During the dry summer season the Pinus sylvestris earthworm complex retains its structure but changes in the composition of the predominant epigeic species and sharp fluctuations in population density and biomass are observed. The Betula pendula deadwood earthworm complex significantly changes its structure at the beginning of the dry summer season, which gradually recovers in the following period but there are no statistically significant differences in population density and biomass of the complex. The age structure of individual species in earthworm complex in both types of forest in a conducive season is characterized by an equivalent ratio of juvenile and adult individuals or a greater proportion of juvenile ones; at the beginning of the dry season the proportion of adults in the complexes is high, the proportion of juvenile individuals increases only towards the end of the season. Comparing the interannual data of earthworm complexes population density and biomass it was found that the Betula pendula deadwood is a more drought-resistant habitat for earthworms, unlike the Pinus sylvestris deadwood.