Vegetational gradients in relation to environmental conditions in northwestern European mires

Abstract

Floristically characterized gradients related to (i) mire surface microtopography, (ii) marginal versus central areas, (iii) ombrotrophy and minerotrophy ("poor and rich mires"), and (iv) distance from the sea can be recognized in the mire vegetation of northwestern Europe. Along these gradients variation occurs in (i) oscillations in the water level, (ii) origin and flow of water, and (iii) supply of minerals. These conditions influence the decay processes and the resulting peat accumulation rate, pH, mineral nutrient supply, and productivity. The differences between marginal and open areas result from differences in nutrient supply (N,P,K), while the differences between "poor and rich" mires are due to differences in the reactions of the peat. In Sphagnum-dominated vegetation, most floristic variation results from effects of differences in peat accumulation rates. Climatic conditions, other than atmospheric supply of minerals, are most important in establishing the regional floristic differences in the bog vegetation.