Impact of different cutting regimes on the performance of Brachypodium pinnatum in Dutch chalk grassland

Abstract

During the past decade the usual management in Dutch chalk grassland, hay making in autumn, has not prevented a sharp increase of Brachypodium pinnatum and a drastic decrease in species diversity. To optimize management, the impact of different experimental cutting regimes in controlling Brachypodium was investigated in three- and five-year experiments in two chalk grassland sites. Dominance of Brachypodium was reduced within three years by cutting the vegetation in mid-summer. Relative phytomass of this species decreased from 80% to less than 35% during five years of summer cutting. Forb phytomass doubled in these stands, although total above-ground phytomass markedly decreased. Cutting in summer prevented Brachypodium from effectively overtopping other species. Due to this change in vegetation structure, light penetrated more deeply int he conopy and species number and Shannon index of diversity increased considerably. Many characteristic chalk grassland species, especially short-lived forbs or plants with low stature, benefited from this cutting regime. Analyses of N and P in the above- or below-ground plant material of Brachypodium did not demonstrate nutrient deficiencies due to summer cutting. No relation between N removal by cutting and the reduction of dominance of Brachypodium was found. It is suggested that the decrease in non-structural carbohydrates in the rhizomes of Brachypodium is an important factor in the observed growth reduction. It is concluded that cutting the vegetation in mid-summer with removal of the plant parts is adequate to control Brachypodium. It restores a characteristic forb-rich chalk grassland vegetation within five years.