Colonization, riparian habitat selection and home range size in a reintroduced population of European beavers in the Loire

1. Colonization in a reintroduced population of European beavers in the Loi re Valley was studied between 1974 and 1999. It followed a discontinuous re moteness model and a scattered distribution, beavers occupying only 25% of the river system over the 2800 km explored. 2. After 5 years, the colonization rate reached 104.2% year(-1) of new site s occupied (SD 75% year(-1)), before dropping over the next 20 years. Never theless, the number of new colonies per km (0.125) remained stable througho ut the years. 3. Populus nigra, Salix alba and Fraxinus angustifolia were the dominant wo ody species in beaver sites, often associated with some herbaceous species. 4. The length of willow grove dominated by S. alba and P. nigra (x) was the best predictor of beaver home range (y), fitting the equation y = -0.742x + 5.9. Long-term maintenance of the population requires a minimum of 1.79-k m of willows per colony. 5. In cutting tree trunks, beavers stimulate shoot development from the rem aining stumps. They rejuvenate riparian forests, increase the number of tre e stems and help stabilize the banks. Their effect on woody plant morphogen esis may have consequences for the helophyte communities used as food or ha bitat by other aquatic species.