| Popis: |
1. We tested whether patterns of species density are controlled not only by variations in community biomass but also by variations in environmental conditions, which may be related or unrelated to community biomass. Environmental variables (soil characteristics, acidity, water regime, nutrient availabilities) were measured in 46 sites in wet meadows and fens, and related to above-ground biomass and to densities of all vascular plants and of threatened species. 2. Both meadows and fens showed a hump-backed species density-biomass relationship, although there was much variability and the study did not include very highly productive sites. In fens a significant quadratic relationship was observed (R2 = 0.42). 3. Environmental factors could explain 57øin meadows) and 40øin fens) of variation in species density. The majority of the variance explained was attributable to factors that were not related to community biomass (increasing pH in meadows) or the organic soil-mineral soil gradient in fens. 4. Density of threatened species vs. biomass was also consistent with a hump-back curve covering a narrow biomass range. Density of threatened species increased with decreasing P availability, regardless of whether P availability was related to biomass (as in meadows) or not (fens). |
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