Niko Silvan

Changes in mesofauna abundance in peat soils drained for forestry

Abstract Soil mesofauna community structure was studied in a drainage-succession continuum of peatland sites supporting Scots pine (Pinus sylvestris L.) dominated stands in southern Finland. The numbers of Enchytraeidae, Collembola, Oribatida, Mesostigmata and Prostigmata in an 8-cm-deep surface peat layer were compared among a pristine undrained pine mire site, comparable sites drained for forestry 12, 26 and 60 years earlier, and a 42-year-old drained site re-wetted two years earlier. Drainage and the consequent water-level draw-down clearly increased the numbers of all soil animals studied, the numbers showing highly significant correlation with the water-table level of the sites. On the older drained sites, the populations were generally about ten times higher than on the undrained site; for Collembola, almost 100 times higher. After re-wetting, the numbers dropped abruptly, falling between those of the undrained and the youngest drained site. Oribatida were the most frequently found animals on the sites studied: on the undrained site almost 60% of the total number were these mites, the relative proportion somewhat decreasing along the drainage succession. The proportion of Enchytraeidae also decreased slightly after drainage, whereas that of Collembola clearly 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 of the drainage succession, the soil fauna community structure became more similar to that of upland sites with similar tree-stand growth potential.

Effects of water level and nutrients on spatial distribution of soil mesofauna in peatlands drained for forestry in Finland

We investigated the within-site distribution of Enchytraeidae, Collembola, Oribatida, Mesostigmata and Prostigmata relative to varying water level and substrate quality on pine mire sites forming a drainage succession continuum. Collembolans were most intolerant of wetness, favoring drier locations at all stages of the drainage succession. In general, the effect of water level variation on the within-site distribution of the soil fauna was strongest when the site was at an early stage of either progressive or regressive water level change. When the average water level was below 20 cm, it no longer had a significant effect on the distribution of mites, but still affected that of Enchytraeidae and Collembola. Boron was positively correlated with faunal density in several cases, and thus may be the growth limiting nutrient affecting substrate quality for decomposers in these sites. The overall changes in the soil mesofauna in drained peatlands depicted here show that these peatland forests are converging ecologically on upland forests where decomposition in general is much faster than in pristine peatlands. The change caused by restoration shows how labile these ecosystems are also with respect to the mesofaunal community.