Current issue: 55(1)
Under compilation: 55(2)
According to studies following the development of vegetation of drained peatlands, it seems that they have transformed to a relatively stable plant communities during the succession. In earlier studies it was assumed that after drainage a mire type would develop to a corresponding forest site. This investigation studies what kinds of plant communities are formed during succession of different mire types on peatlands drained for forestry in the southern half of Finland. Understorey vegetation was studied in 18 sample plots established by Forest Research Institute on drained peatlands. In addition, sample plots were studied on peatlands in natural state.
The results suggest that understorey vegetation on peatlands drained for forestry have developed into plant communities, the most advanced of which are the so-called dry plant communities. They represent transformed site types, which are the following: drained peatlands with upland herb-rich vegetation, drained peatlands with upland grass-herb vegetation, drained peatlands with upland Myrtillus site type vegetation, drained peatlands with upland Vaccinium site type vegetation, and drained peatlands with upland Calluna site type vegetation. Drained peatlands with upland Cladonia site type vegetation seem to be a temporary type caused by incomplete drainage. The transition between Myrtillus and Vaccinium dominated dry plant communities is not clear, but especially the pure Vaccinium vitis-ideae communities justify its place as an independent plant community. The dry drwarf shrub plant communities are also stable.
The PDF includes a summary in German.
Severe climatic conditions promote gregariousness, because the number of species capable of surviving is small. Thus, it its more common in cold or arid regions. For instance, sands and gravels that are poor in nutrients, and subject to drying, are often characterized by pure crops of pine, whose seedlings are comparatively drought resistant. One example of gregariousness due to favorable conditions of seedlings, seed-dispersal and germination is birch. It produces seed abundantly from an early age, and the light seeds are dispersed widely by the wind. Gregariousness can also be induced by conditions which destroy all species except those specially adapted to resist extermination. One example of this is annual fires. A species may be gregarious in some conditions and sporadic in others.
The colonisation of a burned clear-cut by ants in southern Finland was monitored using pitfall traps, artificial nest sites, and direct nest sampling from the ground and stumps. Clearcutting and fire seemed to have destroyed wood-ant colonies (Formica rufa group), and also other mature-forest species suffered from fire. Myrmica ruginodis Nylander was able to survive only in less severely burned moist sites, whereas it benefitted from the enhanced light conditions in a non-burned clear-cut. The fire resulted in an essentially ant-free terrain into which pioneering species immigrated. The mortality of nest-founding queens appeared to be high. The results supported the hypothesis that the pioneering species tend to be those that are capable of independent colony founding, followed by species founding nests through temporary nest parasitism. The succession of the burned clear-cut differed from that of the non-burned one, suggesting that habitat selection in immigration and priority effects, i.e. competition, introduce deterministic components in the successional pathways of boreal ant communities.
The structural matter production of selected plant species of a ground cover community was determined in relation to light available for photosynthesis. The resulting functions were applied in a situation where the light reaching the ground cover was controlled by the dynamics of the tree crown strata, and the occurrence of different plant species at different stages of succession was determined on the basis of their production of structural matter in actual light conditions. The possible strategies involved in adaptation to a successional environment have been discussed.
The PDF includes a summary in Finnish.