Over the past 10 years, some Dutch chalk grasslands have experienced pronounced increases in tor grass (wood-brome) Brachypodium pinnatum dominance and drastic decreases in plant species diversity. This is despite continuance of the usual management of hay making in autumn, under which herb-rich sward was previously maintained. Experimental cutting regimes were initiated in an attempt to reduce Brachypodium dominance.
In two chalk grasslands, the impact of cutting and removal of the cut vegetation in mid-summer (as opposed to the traditional autumn cut) was investigated in 2- and 5-year experiments. Biomass of Brachypodium and forbs were recorded in sample plots. Nitrogen (N) and phosphorous (P) in above- and below-ground Brachypodium plant material was analysed.
Cutting in mid-summer reduced Brachypodium dominance within three years, and Brachypodium biomass decreased from 80% to less than 35% over five years of summer cutting. In contrast, forb biomass doubled. Summer cutting effectively prevented Brachypodium from ‘overtopping’ other species, thus light penetrated more deeply. Many characteristic chalk grassland species, especially short-lived forbs and smaller species benefited, and species diversity markedly increased.
N and P in above- or below-ground Brachypodium did not demonstrate nutrient deficiencies due to summer cutting. There was no correlation found between N removal by cutting and the reduction of Brachypodium dominance. It is suggested that a decrease in carbohydrates in Brachypodium rhizomes is an important factor in its reduction.
It is concluded that at these sites, mid-summer cutting/removal reduced Brachypodium dominance and restored forb-rich chalk grassland vegetation within five years.
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