L’avifaune nicheuse de la succession écologique du Sapin de Douglas en Morvan (France)

In Morvan, one of the regions of France with the most numerous introduced Douglas-fir plantations, birds settle in the stands as early as the first preliminary clearcutting. The bird community then changes progressively during the cutting cycle, according to an ecological succession roughly similar to those observed in other analogous plantations (e.g. pines, beech). Schematically, this ecological succession goes through three main stages : (1) a pioneer phase (during the first ten years) when spontaneous vegetation develops vigorously among young Douglas-firs : open-space and low vegetation birds such as pipits, Stonechat, Yellowhammer, then Dunnock, Bullfinch and warblers, enter such places ; (2) an intermediate phase defined by Douglas-fir very strongly dominant over all other vegetation and pioneer species disappearing ; at that stage (which lasts several dozens of years) the bird community is reduced both in species and individual numbers and is mainly based on generalist (e.g. Song Thrush, Robin) or conifer-specialist (e.g. Gold-and Firecrests, Coal and Crested Tits) forest birds ; (3) in old stands (rare), the bird community becomes rich again because Douglas-firs are well grown and allow grasses and bushes to recover. The ornithological poverty of the intermediate stages (which is also observed in other similar types of even-aged plantations) seems best explained by the sylvicultural treatment (i.e. almost single-cohort stands) than by Douglas-fir per se. The phenomenon is however more pronounced with Douglas-fir because of its very important domination over grassy and bushy vegetation. Moreover one observes that in these dense stands of intermediate age the smallest edge effect (either on edges or in gaps) goes with an increase in bird species richness. These observations allow one to expect better conditions for birds in Douglas-fir plantations if they were harvested in less dense, mixed-species or uneven-aged stands.