Individual study: Short-term cutting and removal of tor grass Brachypodium pinnatum dominated vegetation on an abandoned chalk grassland encourages reinstatement of a species-rich sward at Bemelerberg, Limburg, the Netherlands
Bobbink R. & Willems J. H. (1993) Restoration management of abandoned chalk grassland in the Netherlands. Biodiversity and Conservation, 2, 616-626
After abandonment of sheep grazing of a chalk grassland in the Netherlands, tor grass (wood brome) Brachypodium pinnatum became very dominant with a dramatic decrease in plant diversity. Restoration of such sites is considered important because of former high diversity including many nationally endangered species. To restore the grassland vegetation, the impact of the introduction of different experimental cutting regimes was investigated over three years.
Study area: The study was undertaken at Bemelerberg (50º51'N, 5º45'E), on a chalk grassland slope situated near the city of Maastricht, Limburg province, the Netherlands. Sheep grazing ceased in the late 1930s from when the site remained unmanaged until the early 1980s when sheep grazing was re-introduced over most of the area. During the period of no grazing, a near monoculture of Brachypodium with a thick litter layer had developed. This present study was carried out in an ungrazed part of the site.
Methods: In May 1984, 16, 1 x 1 m plots were laid out on part of the slope dominated by Brachypodium and with much litter accumulation. Each plot was randomly selected for one of the following annual cutting treatments applied in 1984 and 1985:
i) no cutting (control);
ii) cutting and removal of cut material once/year (end of August/early September);
iii) cutting and removal twice/year (end of May and end of August/early September);
iv) cutting and removal four times/year (from the end of May every four weeks).
Vegetation was cut with an electric hand-mower at 3 cm above the soil surface. In August 1986, the central part each plot (25 x 50 cm) was cut and vascular plant samples were sorted into species. Species, density per plot and a Shannon index of diversity were calculated. Shoot dry weight of Brachypodium was determined per plot for 20 randomly selected shoots, and root samples were taken at random in the plots using a root auger (diameter 8 cm) to 10 cm depth.
In the laboratory, belowground parts were sorted into rhizomes and attached Brachypodium roots, non-Brachypodium roots, and fine rootlets of unknown species. Dry weight of the above- and below-ground plant material was measured.
The above-ground plant parts of each plot were pooled for nutrient (nitrogen and phosphorus) analyses in the following groups: Brachypodium, other graminoids (grasses, sedges Carex spp., wood rush Luzula spp.) and forbs.
Above-ground dry weight: Total above-ground plant dry weight decreased after two years of cutting compared with the uncut controls. All cutting regimes reduced the amount of litter to about one third of that in the controls. Whilst the number of Brachypodium shoots did not decrease, shoot weight did and the previously tall growth was markedly reduced by cutting.
The dry weight of some species groups was strongly affected by cutting. In all cutting treatments the average shoot dry weight of Brachypodium was reduced to a third of that of the control. It decreased in the once and twice cut treatment to c.115g/m² (48-55% of total above-ground dry weight); in the control treatment it was 225g/m² (c.80%); in the 4-times treatment it was only 90g/m² (c.45%). The total dry weight of other graminoids was much lower than that of Brachypodium, but was similar between treatments. In all cutting treatments, forb dry weight increased considerably compared to the control. This was especially pronounced in the twice cut treatment, where forb weight was almost as high as that of Brachypodium. The increase of forbs in the 2x and 4x cut treatments was partly caused by the strong growth of a few short-lived species (carline thistle Carlina vulgaris, fairy flax Linum catharticum, wild carrot Daucus carota and common centaury Centaurium erythraea).
Below-ground dry weight: Total below-ground dry weight was twice that of above-ground, but no significant differences between treatments were observed at the end of the experiment. In the 4 x cutting regime, non-Brachypodium root material tended to be somewhat higher, whereas that of Brachypodium tended to be somewhat lower, compared with the other regimes.
Nutrient concentrations: No significant differences between the plant material (shoot and root material of the different species groups) of nitrogen and phosphorus concentrations for the four cutting treatments were found.
Conclusions: The thick litter layer and the dominance of Brachypodium was strongly reduced after introduction of the cutting regimes. In all cutting treatments forb biomass increased considerably, especially in the twice-a-year cutting and species diversity increased. The number of short-lived forbs with a persistent seed bank, especially, increased markedly in the twice-a-year cutting treatment.
Cutting and removal twice a year was adequate to reduce the litter layer and abundant Brachypodium growth, and created a good starting point for more long-term management, whether mowing or grazing, to restore a species-rich sward.
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