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The increased deposition of nutrients from the atmosphere has contributed to widespread changes in wet heathland ecosystems throughout Europe. As a result, management measures are nowadays considered a tool with which to mitigate impacts of atmospheric nutrient loads by reducing nutrient stores in the above-ground biomass and soils. A burning experiment was carried out in order to evaluate the effects of prescribed winter burning on the nutrient budgets of an extensive wet heathland complex in NW Germany (with particular reference to growth limiting N and P, but also Ca, K, and Mg). Changes in nutrient budgets were calculated by analysing the current input (atmospheric deposition), the output due to biomass combustion, and N losses due to denitrification. In the study area, atmospheric inputs amount to 3.31 g m -2 yr -1 for N, and -2 yr -1 for P. Mean N stores in the above-ground biomass are 9.34 and 9.66 g m -2 (in Calluna-Erica- and Calluna-dominated wet heaths, respectively), and biomass P contents in both vegetation types amount to 0.43 g m -2. From these stores, 47-68 % (for N) and 2-16% (for P) were removed by burning (taking into consideration the return of nutrients as a result of ash deposition). Nitrogen losses owing to denitrification range between 0.5 and 1.6 g m -2 yr -1 and may, thus, compensate for about 15-48% of the atmospheric input. However, calculations of input/output-ratios show that prescribed burning is insufficient to counterbalance present-day atmospheric nutrient loads since management cycles usually exceed a 10-year interval. Our results suggest that wet heaths managed by means of prescribed burning will accumulate nutrients, particularly N, in the long term. As a means of preserving a balanced nutrient budget on a long-term basis, high-intensity measures (e.g. high intensity mow), applied in combination with low-intensity measures, will be an indispensable instrument in wet heathland preservation.

We hypothesize that plant species diversity is favoured when actual resource supply ratios are balanced according to the optimum resource supply ratios for the vegetation as a whole. This ‘resource balance hypothesis of plant species diversity’ (RBH) follows from two different mechanisms of plant species coexistence, namely: ‘differential resource limitation’, which allows species to coexist in a competitive equilibrium in a homogeneous environment and ‘micro-habitat differentiation’, which builds on spatial heterogeneity. Both mechanisms require that resource supply ratios are intermediate between the optimum supply ratios of the species present in the species pool. Additional conditions, concerning the resource acquisition and requirement ratios of the species, are easier to meet for the second mechanism than for the first. To test the RBH we measured species diversity parameters in 74 grassland plots, as well as the N, P and K concentrations in the above-ground biomass. We used a new ceiling detection algorithm to examine the relationship between maximum observed diversity and the N/P-, P/K- and K/N-ratios in the biomass. Most of these ceiling relationsips could be described by parabolic curves with significant quadratic terms. This indicates that high diversity does not occur at the extremes of the observed ranges of nutrient ratios. This supports the RBH.