Artikkelit kirjoittajalta Ilkka Markkula

The numbers of soil mites, springtails and enchytraeid worms were compared on virgin and forest-ameliorated parts of a bog in Lammi commune, southern Finland (N 61o 02’ E 24o 58’). The study site was an ombrotrophic raised bog with Calluna vulgaris - Empetrum nigrum - Sphagnum fuscum-hummocks and Eriophorum vaginatum - Sphagnum angustifolium-hollows. Part of the bog was drained in 1966 and fertilized in 1970 with urea (100 kg/ha) and PK-fertilizer for peatlands (400 kg/ha). The drainage had lowered the ground water level by 10-15 cm. The vegetation of the ameliorated site had also changed. Sphagnum-mosses had decreased but Eriophorum, Culluna, Empetrum and Pinus sylvestris growed more vigorously than on the virgin site. Samples were taken from both virgin and ameliorated part of the bog in may-november 1975 and may-september 1976. In the seasonal fluctuation of the three mite groups (Oribatei, Prostigmata and Mesostigmata) maximum numbers occurred generally in spring and autumn (figs. 1 and 2) with the exceptions of mesostigmatid and prostigmatid mites in the hollows of the virgin study site. No clear trends were found in the seasonal fluctuations of the numbers of Collembola and Enchytraeidae (figs 2 and 3). During the winter 1975-76 a severe decline occured in the numbers of enchytraeid worms. The reason was most probably the hard frost in early winter 1975 when the snow cover was thin and could not protect the animals. The oribatids did not suffer from the frost. In the mean numbers of oribatid mites there was no significant difference between virgin and ameliorated site. The numbers were slightly smaller in the hollows than in the hummocks (table 1). The numbers of mesostigmatid mites in the hollows were greater at the ameliorated site than at the virgin one. In the hummocks there was no difference between the sites. Upon the all remaining groups, Prostigmata, Collembola and Enchytraeidae, the forest-amelioration had a similar effect. These animals had increased in the hollows but at the same time decreased in the hummocks. At the virgin site, the hummocks seemed to be preferred microhabitat but at the ameliorated site more prostigmatid mites, springtails and enchytraeid worms lived in the hollows. A probable reason of the general decrease in the animal numbers in hummocks is that drainage makes the environment too dry for the animals. In the hollows, on the other hand, drainage and fertilizing probably had caused changes favourable for the animals. The oxygen content of the peat had increased and the quality of the litter improved from the viewpoint of soil invertebrates (more Eriophorum instead of Sphagnum-litter). Because five years had passed since the fertilization, the direct "shock-effect" of fertilizers most probably had no significance any more.

• Markkula, Sähköposti: ei.tietoa@nn.oo

Vertical distribution of soil mites, springtails and enchytraeid worms was studied in virgin and forest-improved parts of a raised bog Laaviosuo in Lammi in 1975 and -76. The forest-improving practices were drainage in 1966 and NPK-fertilization in 1970. The drainage had lowered the ground water table by 10—15 cm (Table 1.). In both the virgin and the drained study sites, the water table was deeper in the Sphagnum /uscu/n-dwarf shrub-dominated hummocks than in the S.angustifolium-Eriophorum-dominated hollows. Those micro-relief structures were considered as separate microhabitats. The ground water table was closely correlated with the topsoil moisture and it also stated the lower limit of aerobic conditions in the peat. In the hollows the animals were relatively more restricted to the uppermost soil layers than in the hummocks (Fig. 1). This was most probably due to the high water table and thin aerobic layer in the hollows. The distribution of enchytraeids and prostigmatid mites had changed after drainage so that a greater portion of animals lived in the deeper soil layers in relation to the virgin site. In the other animal groups no such difference was observed. The vertical distribution of enchytraeids and ori-batids is plotted against the ground water table in Figs. 2 and 3. The very significant correlations result from great differences between the microhabitats. Inside the microhabitats there were no close correlations (Table 2). In the samples taken from frozen soil most enchytraeids and oribatids were usually found in the deeper soil layers (Tables 3 and 4). This most probably resulted from active migration to avoid coldness. However, in the virgin site hollows the oribatids stayed in the topsoil, possibly because the waterlogged and anaerobic conditions in deeper layers are unsuitable for their overwintering.

• Markkula, Sähköposti: ei.tietoa@nn.oo