Soil fauna and microbiological activity

Few organisms of the macro – and mesofauna live in the raw soils. The pioneer sites are still free of earthworms. Generally, no microbiological ac­tivity was found on these sites (average soil respiration: 0.04 mg O2/100 g dry matter/h). In the shrub and woodland sites, the level of microbiological activity ranged between mean moderate and high (average soil respiration from 0.1-1.2 mg O2/100 g TS/h). Due to ongoing acidification, a reduction in microbiotic activity is to be expected. This would enhance fungi instead of bacteria and would subsequently decrease the decomposition rate of lit­ter.

In the shrub site SR and woodland site WZ, the population density of lumbricids is still low with 6-12 individuals per square meter (Fig. 3). The lack of litter consumers, particularly big, deep-digging earthworms, leads to a “decomposition jam” and an accumulation of litter and thick raw hu­mus forms. Such raw humus forms are typical of the acidic, low-nutrient soils that are found at the site WZ. The lumbricid presence at WR is com­pletely different. Here, big, deep-digging earthworms occur abundantly throughout the mineral soil although they live under the same acidic condi­tions as the previous cases (pHCacl2<4). In contrast to the lumbricids, the enchytraeids indicate a future change in the composition of the soil macro­fauna in response to acidic soil conditions. The dominant species Cognet – tia sphagnetorum and Marionina clavata are typical micro-annelids of acidic top layers.

At the rubble site SA, the number of lumbricids is typical of moderately alkaline pH values. Surprisingly, there is a clear dominance of animals that usually live in humus layers over those living in mineral-soil layers, al­though we recorded no significant humus layer at this site.