Short-term effects of different management regimes on the response of calcareous grassland vegetation to increased nitrogen

摘要

The short-term (4-year period) effects of different management regimes on the response of calcareous grassland vegetation to increased nitrogen were investigated. Four levels of nitrogen and two levels. of management were applied in a factorial design. Besides, the effects of management practices alone on species diversity were also studied. Species diversity was investigated at different levels of sub-sampling using a nested plot design. In this way, both species saturation and accumulation curves could be established. The effect of community structure, as reflected by the light regimes at various heights in the vegetation, on species diversity was also investigated. Species diversity at all levels of sub-sampling decreased significantly with management regimes and nitrogen supply rates. Percent light penetration differed significantly among management regimes and nitrogen supply rates. Grazing proved to be most efficient in countering the negative effects of nitrogen supply, but could not prevent competitors from becoming dominant. In the absence of any form of disturbance, species diversity decreased relatively rapidly. Decreased light availability, the loss of gap formation, a decrease in small-scale environmental heterogeneity and proliferation of strong competitors, all may have contributed to the observed decrease in species richness. The results of this study highlight the importance of management in maintaining high species diversity in the studied calcareous grassland.