Douglas-fir root biomass and rooting profile in relation to soils in a mid-elevation area (Beaujolais Mounts, France)

Douglas-fir is the main reforestation species in the French Massif Central area (14 000 ha), but little is known about its rooting strategy in differe nt soil conditions. This information has important implications for the cho ice of better soils for settling Douglas-fir, and consequently limiting ris ks of failure, pests or diseases. As a result, the influence of edaphic con ditions on rooting patterns of dominant Douglas-fir was studied over a larg e range of ecological conditions in a mid-elevation area of the French Mass if Central (Beaujolais Mounts). Root systems were studied extensively using the trench profile wall technique and the sector method in 74 pure and eve nly aged Douglas-fir stands. The stands were chosen as being representative of soil conditions among 165 stands in an auto-ecological study. The rooti ng patterns were related to seven typical soil profiles, and to root profil e groups. Results stressed that edaphic constraints due to substratum and s oil structures have a strong influence on root system morphology. Important variations in root biomass and vertical distribution were highlighted amon g soils. Small fine root biomass is maximal for soils with no major edaphic constraints. The vertical distribution of fine root biomass is positively correlated for some soil types with organic C, total N, and most cations. F or some types it was negatively correlated with the amount of exchangeable aluminum and coarse fragments, and with constraining rock facies. Harsher s oils however, showed no correlation between soil chemical variables and fin e-root biomass. A practical implication is that Douglas-fir seems to be a p liable and adaptive species: variation in habit and root system biomass are considerable within a study area which was presumed uniform.