Vegetation structure and interactions on mires

Abstract: The distribution of sloping fens in southern Sweden was mapped, their vegetation sampled and related to the environmental variables recorded. This mire type is distributed further to the east than previously reported, namely around the highest post-glacial limit of the sea level. Calluna vulgaris, Narthecium ossifragum, Erica tetralix, Molinia caerulea, Carex panicea and Sphagnum spp. or, e.g., Campylium stellatum and Calliergonella cuspidata were prominent, mainly forming a mire lawn vegetation. Four community types can be distinguished, each with its own characteristic environmental variables. Three vegetation gradients are evident. The first, a poor - rich one, is correlated with pH, the second is a slope gradient, and the third, a mire expanse - spring fen gradient, was revealed by the species composition. In the habitat studied, the characteristic lawn vegetation acts as an indicator of its specifically soligenous water supply. Interactions between vascular plants and Sphagnum are concluded to be less important than those between hepatics and other bryophytes, which appear with several positive or negative associations. Narthecium ossifragum supports the growth of Sphagnum, whereas the vascular plant suffers from the competition for light with the peat mosses. The intensity of this competition may be higher at sites more favourable to N. ossifragum. However, interactions between the vascular plant and Sphagnum are less important to structuring vegetation than edaphic factors, particularly on less productive sites. Similar to other plant taxocenes, mire hepatic species highly vary in their ecological amplitudes and preferences. Hepatics make use of the mire habitat with two different strategies. Some species, e.g. Aneura pinguis and Cladopodiella fluitans, compromise between benefiting habitats created by other living bryophytes and keeping pace with their growth. Other hepatics, e.g. Calypogeia integristipula and Cephalozia connivens, instead avoid growing among mosses and frequently occupy peat or litter. Mostly sterile Cephalozia spp. frequently grow among Sphagnum, whereas those commonly fertile keep away from peat mosses.