Small Mammals in Farm Woodlands: The Effects of Habitat, Isolation and Surrounding Land-Use Patterns

Abstract

1. The results of this study, which surveyed 38 farm woods ranging in size from 0.05 to 4.45 ha, demonstrated clearly that the dynamics of wood mice Apodemus sylvaticus and bank vole Clethrionomys glareolus populations in small woods are strongly influenced by the landscape around the woods, for example the distance to neighbouring woods, abundance of hedges and types of crops grown, as well as the habitat within the wood. 2. In terms of the habitat features of the woods, the maturity of the wood and the amount of understorey and overstorey cover were important for both species, while the availability of herbaceous plants influenced bank vole abundance. 3. Wood mice, in particular, were influenced by the types of crops grown in neighbouring fields. Their abundance in spring, the proportion of juveniles in the autumn and the extent to which the population increased from spring to autumn were all influenced by the proportion of adjoining fields that were planted with wheat and/or oilseed rape. 4. Isolation variables, such as the distance to the nearest large wood and the extent of adjoining hedgerows, influenced both wood mice and bank vole populations. Populations of both species increased more from spring to autumn in more isolated woods. This was probably because of reduced opportunities for dispersal and the shortage of alternative woodland habitat for animals moving off the fields after harvest. Woods well connected with hedges supported higher densities of both wood mice and bank voles. 5. Within the size range of woods examined here, no effect of woodland size was found on the probability of catching wood mice or bank voles or their abundance in either spring or autumn. The data suggest that even very small farm woods are important as refuges for small mammals, particularly after harvest when arable fields provide little cover.