Effects of prescribed burning on plant available nutrients in dry heathland ecosystems

Heathland management is an important tool with which to modify ecosystem impacts caused by atmospheric nutrient deposition. Since changes in nutrient availability as a result of management measures affect the outcomes of heathland succession and species competition, studies on this issue are important from both a nature conservation and management point of view. This study reports the effects of prescribed burning on nutrient availability in dry heathland soils and the nutrient content of the two competing heathland species Calluna vulgaris and Deschampsia flexuosa, with particular reference to N and P. We hypothesise that winter prescribed burning leads to additional N availability, which enhances the importance of P in the context of nutrient limitation in heathland ecosystems. In the nature reserve “Lueneburg Heath” (NW Germany) we examined the availability of nutrients in the humus horizons and in the leachate as well as the relevant C:element ratios in Calluna and Deschampsia before and after a burning experiment. Our results show that prescribed burning resulted in drastically increased NH₄⁺ availability in the O-horizon. We observed only short-term effects (for NO₃⁻, PO₄³⁻, Mg) and insignificant effects on the availability of other nutrients (K, Ca). As a consequence of an increased nutrient availability in the humus horizons and a limited nutrient uptake by plants after burning, leaching increased significantly for N, Ca, K, and Mg after burning treatment. No significant changes were found in the foliar C:N ratios for either species after prescribed burning, although Deschampsia showed an increased deficiency for all the other nutrients, particularly for P, as expressed by increased foliar C:P and N:P ratios. By contrast, the nutrient content of Calluna did not change significantly, suggesting that prescribed burning favours the competitive capacity of Calluna as against Deschampsia. We assume that water shortage as a result of changes in the microclimate was mainly responsible for the deterioration of the nutrient content of Deschampsia. This gives Calluna a competitive advantage, enabling it to out-compete Deschampsia on burned heathlands, with respect to the key factor P-limitation.