Landscape composition and vole outbreaks: evidence from an eight year study of Arvicola terrestris

This study investigates the relationships between landscape composition and the population dynamics of the fossorial water vole Arvicola terrestris. L and use patterns were studied based on agricultural and forestry data from the French Ministry of Agriculture collected in 1955 and 1988. In the Massi f Central. France, water vole populations were monitored from 1985 to 1993 by using index methods. Outbreaks of water vote populations occurred in man y dispersed epicentres and spread suddenly and widely over > 7500 km(2). At a regional scale, the fluctuation lasts six years on average with an outbr eak period lasting from two to three years. Density variation patterns are positively correlated with the proportion of permanent grassland to agricul tural land. A high risk of outbreak is linked to a high proportion of perma nent grassland (over 90%), whereas a low risk of outbreak is linked to a pr oportion of < 80%. Conversely. density variation patterns are negatively co rrelated with the proportion of temporary grassland to agricultural land an d with the proportion of forest to total land in the western (major) part o f the study area. Temporary grassland thus appears to be a marginal habitat for water voles and extensive forests could act as a brake on outbreaks. T he increase in the area of permanent grassland from 1955 to 1988 was appare ntly the major cause of chronic high densities of water voles. Therefore. l and use and landscape management could be one way to control water vole out breaks.