Study of Salicaceae x European beaver (Castor fiber) interactions following modification of Populus nigra resources by fluvial maintenance operations in the mosaic of islands of Mareau-aux-près (Loire, France)

The European beaver is a ‘keystone species’ of Loire riverine ecosystem and present in the islands of Mareau-aux-prés (Loiret, France) since 1982. Our study is located in a mosaic of five islands (13 hectares) within the National Nature Reserve of St-Mesmin (Loiret, France), constituting the first Conservation Unit of the national programme of conservation of genetic resources of Populus nigra. The central island constituted the main source of food, with young shoots coming from stumps of black poplar (Populus nigra). In september 2012, the vegetation of such island was uprooted and the bar level lowered in order to maintain the flow capacity of the river.Modification of such feeding habitat is at the origin of our study, with a particular view of the consequence on genetic resources of Populus nigra, especially on mature trees located in the other four islands. Scientific questions focuss on (i) what were the feeding habits of the beaver family (4 to 6 individuals) before maintenance operation? (ii) how have they changed their feeding habits after such fluvial work, and what will be the impact on other vegetated islands? (iii) what is the impact of foraging activity by beavers on the genetic diversity of black poplar?To answer these issues, we have recorded data on Salicaceae vegetation (species, circumference, density of trees), presence of beaver (slides, lodges) and herbivory pressure (fresh or old traces on the bark, girdling percentage of these trees, cut trees). All of these data are georeferenced and were recorded before and after fluvial works (in september 2012). The results will be presented and discussed in terms of species selectivity, circumference of the tree, density of poplar and willow stumps acting as barrier to the consumption of adult stems, feeding tracks and forest composition and structure (in competition with underneath non-preferred Acer negundo).