Communities of soil mites (Acarina) in planted birch stands compared with natural forests in central Finland

The aim of the study was to compare the soil mite communities in anthropogenous birch stands of different origin with each other and with natural forests at the same latitude. Nine sites were investigated: three birch stands (Betula pendula Roth) planted ca. 30 years prior to the study after clear-cutting of spruce stands ("birch after spruce"), three birch stands planted ca. 30 years earlier on arable soil that had been under cultivation until reforestation ("birch after field"), and three natural deciduous forests. These were sampled twice, and microarthropods were extracted, counted, and identified. There were clear differences between birch stands established after spruce forest and after cultivation and between these and natural deciduous forests. The communities of birch after spruce were rather similar to those of natural spruce forests, but the population densities were lower. The populations in birch after field were generally very low. There were also conspicuous differences among replicates of the same kind of forests. All the dominant species in the study sites are common members of the forest soil fauna. The communities of birch after field could be characterized as impoverished forest communities. Soil pH and the removal of the litter layer by earthworms were regarded as the most important factors explaining the observed differences.