Grazing is often used for conservation management of grasslands. A study was undertaken to assess the effect of livestock grazing on plant species richness and communities across a soil acidity gradient at different spatial scales on five dry dune grasslands (3.1 km or less from the coast) in western Belgium and north-western France.
Cattle, ponies and/or sheep, were introduced (free-ranging and mostly remaining year-round) in the late 1990s to control expansion of dominant grasses (primarily wood small-reed Calamagrostis epigejos) and invading woody plants, in four dune reserves (Ghyvelde, Cabour, Westhoek, Ter Yde) and one privately owned Dutch grassland (Oostvoorduinen).
Data were collected in summer 2006. Two or three representative areas were selected within each site. Within each area, two (8 x 8 m) plots were established randomly, one grazed and one non-livestock-grazed. These were subdivided into 0.25 × 0.25 m sub-plots. Cover of each vascular plant species was estimated within at each of five spatial scales from 0.25 x 0.25 to 2 x 2 m (10 random replicates) and 4 x 4 m (four replicates). Soil samples were taken and pH measured.
A rarity index classifying species as ‘very rare’, ‘rare’ or ‘common’, was used to assess rare species diversity response to grazing.
In total, 132 plant species were recorded (88 present in both grazed and ungrazed plots, 42 only in grazed plots and three only in ungrazed plots). Overall, species richness responded positively to grazing and scale, grazing increased the number of rare species, and there was no effect of soil acidity. However, looking at the results in greater detail indicates that interpretation of grazing impact depends on the scale considered and on soil pH.
Grazing had a mostly positive effect on plant species richness in all habitats at the smallest scale. However, at the largest scale it had only positive effects on vegetation on soils of higher pH (6.0-7.4). Grazing resulted in more uniform grassland vegetation at lower pH, while variation increased with grazing on higher pH soils.
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