Effect of land-use on small mammal abundance and diversity in a forest–farmland mosaic landscape in south-eastern Norway

Abstract

During the last century the boreal forests of south-eastern Norway have been converted into patchworks of agricultural areas, clear-cuts and even-aged conifer monocultures. Even though Scandinavian forest ecosystems are strongly influenced by small mammals’ dynamics, the effects of anthropogenic changes on these communities are still debated. We conducted an extensive capture–mark–recapture study to examine the relative abundance and distribution of 11 species of small mammals during the reproductive season with respect to all available landscape-scale habitat types and fine-scale vegetation characteristics. At the landscape scale, the highest abundance and diversity of small mammals was recorded in abandoned meadows. The community was dominated by Myodes glareolus in old abandoned meadows sparsely colonized by trees and bushes, and by Microtus agrestis in younger grass-dominated meadows, likely reflecting inter-specific competition and niche separation. Notwithstanding the remarkably low availability of both types of meadows, these habitats sustained by far the highest abundance of small mammals. Intensively managed forest monocultures at logging age and cultivated fields sustained the lowest abundance of small mammals. However, while the former also supported the lowest species diversity, the latter unexpectedly sustained the highest number of species. Only Apodemus sylvaticus attained highest densities in cultivated fields, but its marked association with forest edges clearly indicates its need for landscape-scale complexity. Contrary to previous theories, clear-cuts and forests overall did not support the highest abundance of M. agrestis and M. glareolus. Both young and mature forests failed to explain a significant amount of variation in community structure when taking into account other habitat types. However, a few old clear-cuts characterized by higher vegetational complexity, and a few stands preserving characteristics typical of late successional stages (moss, berries, woody debris) were able to support relatively high abundance of small mammals. Our study shows that sampling in all available habitats at different spatial scales is essential for a comprehensive understanding of community dynamics in forest–farmland ecosystems, as even habitat types that are under-represented at the landscape scale might play a significant role for the community dynamics. Forest–farmland mosaic landscapes with a high degree of heterogeneity at both large spatial scale ( e.g. meadows, shelterbelts) and at fine-scales ( e.g. varied and multi-layered ground cover) allow for the conservation of small mammal diversity and abundance in human-dominated areas. Nonetheless, the low number of Myodes rufocanus trapped in this highly fragmented mosaic landscape supports the hypothesis that habitat fragmentation negatively affects the dynamic of this forest specialist.