How does landscape use influence small mammal diversity, abundance and biomass in hedgerow networks of farming landscapes?

Over the last decades, profound changes in agricultural practices in the world have led to modifications of land-use as well as landscape structure and composition. Major changes resulted in enlargement of parcel size, increase of cultivated areas and drastic reduction of permanent elements such as woods, hedges or natural meadows. In this context we chose to investigate the composition and structure of small mammal communities in the hedgerow networks of three landscape units of Western France (Brittany) differing by their level of agricultural land-use intensity and hedgerow network density: a slightly intensified dense hedgerow network landscape unit (BOC1), a moderately intensified and fragmented hedgerow network landscape unit (BOC2) and a highly intensified landscape unit on an area reclaimed from the sea (POL). Characterization of small mammal communities was performed using live trapping on permanent habitats (eight hedges per landscape unit). In each of the 24 trapping units, a standardized method was used consisting of a baited 100-m trap-line. Diversity indices were used to compare the three communities. Species richness didn't vary across landscapes whereas Shannon's index of diversity underlined a clear difference between, on the one hand, the most intensified landscape unit (POL) which displayed the lowest diversity and, on the other hand, the two other less intensified units. The abundance of small mammals differed between the three sites: they were significantly more numerous in the hedges of the most intensified site than in hedges of the two other sites. Differences between species also appeared: for example, the Bank vole (Clethrionomys glareolus) was very characteristic of POL, whereas the Pygmy shrew (Sorex minutus) was much more associated with BOC sites. Within hedges, like for abundance, small mammal biomass was the highest in the most intensified site (POL > BOC2 = BOC1). On the contrary, at the landscape scale, biomass was the lowest in POL (BOC1 > BOC2 > POL) because of the fragmentation of the hedgerow network.