Long-term effect of sheep and goat grazing on plant diversity in a semi-natural dry grassland habitat

Abstract

Semi-natural dry grassland sites are of great importance for nature conservation because they support high species diversity and the abundance of "Red-List" species. Grazing has proved to be a successful management tool in terms of maintenance and restoration of biodiversity. For a deeper understanding of the effects of different grazers on species biodiversity in dry grasslands, it is necessary to study the long-term effects of major changes in grazing management. In a semi-natural dry grassland habitat, which was formerly grazed by cattle, we investigated the changes in plant species composition due to long term grazing by sheep and goats. Specifically we asked: a) How does long-term grazing by sheep and goats change the composition of all plant species and particularly those that are on the Red-List? Are changes caused mainly by species turnover? b) How does long-term grazing by sheep and goats influence the fertility and acidity of the soil? To address these questions, we compared the composition and diversity of plants as well deriving Ellenberg indicator values of the species. Long-term grazing by sheep and goats subsequent to a year-round cattle grazing changed the plant species composition of the dry grasslands resulting in a high species turnover rate. It did not, however, lead to an increase in plant species diversity even though Red-List species were considerably more abundant in 2013. Overall, the grazing regime studied positively influenced vegetation composition. The effects on local species composition due to species turnover might further be influenced by local factors like soil nitrogen availability.

Keywords: Ecology; Environmental science.

Fig. 1

Non-metric multidimensional scaling (NMDS) using Bray-Curtis dissimilarity for binary (i.e. presence-absence) data showing dissimilarity of species composition before and after 15 years of grazing management by sheep and goats (2013: circle, 1995: triangle). Distances between transects in the two-dimensional NMDS plot represent dissimilarities in species composition: (A) All plot sizes as pooled data (N = 32; stress = 0.120), (B) 6–8 m² plot size (N = 10; stress = 0.121), (C) 10–12 m² plots size (N = 9; stress = 0.135), (D) 16–20 m² plot size (N = 13; stress = 0.176).

Fig. 2

Non-metric multidimensional scaling (NMDS) using Bray-Curtis dissimilarity for binary (i.e presence-absence) data showing dissimilarity of species composition of all Red-List plant species (categories 1, 2, 3, V) before and after 15 years of grazing management by sheep and goats (2013: circle, 1995: triangle). Distances between transects in the two-dimensional NMDS plot represent dissimilarities in species composition: (A) All plot sizes as pooled data (N = 32; stress = 0.211), (B) 6–8 m² plot size (N = 10; stress = 0.124), (C) 10–12 m² plots size (N = 9; stress = 0.139), (D) 16–20 m² plot size (N = 13; stress = 0.176).

Fig. 3

Box-whisker plots showing mean Ellenberg's indicator values (EIV) for all plant species per plot for soil fertility (A) and soil acidity (B) in 1995 and 2013. N = 32 (pooled data). Significant results from Mann-Whitney U test are included in the graphic: *p = 0.031, z = −2.155, r = −0.381.