Importance of dead wood for soil mite (Acarina) communities in boreal old-growth forests

Abstract

We studied the importance of dead wood (coarse woody debris; CWD) for the mite (Oribatida and Mesostigmata) communities by comparing samples from CWD, soil under/beside CWD, forest floor outside CWD, and from living trunks of the same species (Picea abies, Betula pubescens, Populus tremula). Four spruce-dominated sites in old-growth forests in southern Finland were sampled. Our
hypotheses were that (1) presence of CWD increases the diversity of the community, (2) the communities are influenced by state and kind of CWD, and (3) species assemblage in CWD is distinct from that on living trunks. Total numbers of Oribatida under/beside CWD were twofold as compared both with CWD and forest floor outside CWD, while the numbers of Mesostigmata close to and apart from CWD did not differ but were higher than in CWD itself. Community structure differed between trunks and stumps, and even more between CWD and forest floor, while it did not differ between soil under and away from CWD. No differences in community structure were found between the tree species in Oribatida, but in Mesostigmata the communities in birch and aspen stumps differed from those in spruce stumps and trunks of all species. The results indicate that CWD supports the diversity of the mite community of forest
floor, the state (trunk/stump) and vicinity of CWD are more important than its origin (tree species), and the species assemblage on living trunks is distinct from that of dead wood.