Changes in mesofauna abundance in peat soils drained for forestry

Soil mesofauna community structure was studied in a drainage-succession con tinuum of peatland sites supporting Scots pine (Pinus sylvestris L.) domina ted stands in southern Finland. The numbers of Enchytraeidae, Collembola, O ribatida, Mesostigmata and Prostigmata in an g-cm-deep surface peat layer w ere compared among a pristine undrained pine mire site, comparable sites dr ained for forestry 12, 26 and 60 years earlier, and a 42-year-old drained s ite re-wetted two years earlier. Drainage and the consequent water-level dr aw-down clearly increased the numbers of all soil animals studied, the numb ers showing highly significant correlation with the water-table level of th e sites. On the older drained sites, the populations were generally about t en times higher than on the undrained site; for Collembola, almost 100 time s higher. After re-wetting, the numbers dropped abruptly, falling between t hose of the undrained and the youngest drained site. Oribatida were the mos t frequently found animals on the sites studied: on the undrained site almo st 60% of the total number were these mites, the relative proportion somewh at decreasing along the drainage succession. The proportion of Enchytraeida e also decreased slightly after drainage, whereas that of Collembola clearl y increased. Most of the soil fauna was found close to the soil surface. In general, >80% of Collembola, Oribatida, Mesostigmata and Prostigmata, and >60% of Enchytraeidae were found in the topmost 4-cm layer. In the course o f the drainage succession, the soil fauna community structure became more s imilar to that of upland sites with similar tree-stand growth potential. (C ) 2000 Elsevier Science B.V. All rights reserved.