Effects of grazing intensity on small mammal population ecology in wet meadows

Abstract

Summary Livestock grazing is common management practice in wet grasslands. However, knowledge of its effects on small mammals is limited. We studied the influence of grazing intensity on small mammals in general and field voles Microtus agrestis in particular in two Danish wet meadows, 1998–2000. Generally, grazing livestock had a negative effect on the peak biomass of small mammals, and the negative effect increased with grazing intensity, irrespective of whether pens were grazed by cattle or by sheep. More detailed analyses, however, revealed that an intermediate grazing intensity (approximately 400 kg ha −1 as maximum livestock biomass) actually seemed to benefit small mammals. This grazing intensity generally held small mammal biomasses and field vole population sizes that were similar to or larger than those on the ungrazed control, and markedly larger than those on the more heavily grazed pens. Additionally, field voles in the intermediate grazing intensity had more foetuses. Though a number of parameters may contribute to the observed patterns, we suggest that these primarily are caused by the livestock removing vegetation cover, thereby influencing the number and size of patches with high, dense vegetation in the vicinity of grass that is rejuvenated by grazing.