Effect of mono- and mixed grazing of cattle and sheep on grassland diversity patterns

Plant diversity is linked to a multitude of important ecosystem functions such as productivity. Intensive agricultural management results in a decrease of grassland diversity. In this study, the effect of different grazer species on the vegetation composition and diversity patterns of an extensively managed semi-natural grassland sward was investigated. The hypothesis was that grazing cattle and sheep affect vegetation composition and diversity patterns in different ways because of differences in forage selectivity. Mixed grazing should, therefore, lead to a greater evenness of the vegetation, which might be beneficial for the maintenance and enhancement of diverse grassland. The experimental site is a moderately species-rich Lolio-Cynosuretum in the Solling Uplands, Germany. The inital diversity of the grass sward was manipulated by the use of a herbicide, resulting in a low diversity sward compared to the untreated sward (control). Both diversity treatments were either grazed by sheep, by cattle or by both. The six combinations of plant diversity and grazing treatment were replicated three times in blocks that were grazed rotationally. Data on plant species diversity and botanical composition of three years were analysed. Grazing with cattle led to a significantly different vegetation composition than mono-grazing by sheep, which seemed to be related to differences in forage selectivity.