Increasing dominance of Brachypodium pinnatum (L.) beauv. in chalk grasslands: A threat to a species-rich ecosystem

Chalk grassland is a semi-natural, species-rich vegetation which was once widespread in West Europe. Due to the high species diversity a number of remnants of this vegetation have been set aside as nature reserves and managed by man to prevent natural succession into woodland.

During the last decade an increase of dominance of the grass Brachypodium pinnatum has been observed in chalk grassland within the greater part of the distribution area. Increasing dominance is strongly negatively correlated with the species diversity. Increase of this species is observed in grassland with different management regimes, e.g. sheep grazing, mowing or burning. Brachypodium can gain 80% or more of the relative above-ground phytomass. In such vegetation the species number decreases to less than 50% of the original number within a few years-the low growing forbs especially disappear almost completely. It is argued that the impact of nutrients by air pollution, especially of nitrogen, causes the increasing dominance of Brachypodium. Further research will focus on the effects of this extra nutrient supply.

The aim of the present research is to formulate management strategies in order to prevent degradation of the species diversity in chalk grasslands.