Aboveground biomass and nutrient content of five Douglas-fir stands in France

International audience

English. Despite great interest shown in assessing nutrient removal by forest harvesting, little information is available concerning biomass and nutrient accumulation in French Pseudotsuga menziesii (Mirbel) France stands. Five even-aged Douglas-fir stands from three age classes (26-29, 36, and 54 years of age) were selected in several large wood production areas, Regression equations were developed for separate estimates, at the stand level, of stemwood, stembark, branchwood (wood+bark). needle biomass and nutrient contents (N, P, K, Ca, Mg). Soil pools (0-100 cm total N, BaCl2 extractable cations and Dyer's extractable P contents) were quantified for comparison with the corresponding tree nutrient data. For all stands and elements, mean nutrient concentrations increased in the order stemwood much less than stembark<branchwood<much less than>needles. Scheffe's tests indicated significant differences (P<0.05) between stands for most elements and components. The magnitude of the effect and the corresponding stand groupings, however, depended both on the elements and the components. The comparison between restricted and full regression models showed that no common biomass or nutrient content tables could be obtained at P<0.05. Total aboveground biomass increased with increasing stand age, from about 160 t ha(-1) in the youngest stands to 360 t ha(-1) in the 54-year old plot. Stemwood biomass predominated in each stand, ranging from 70 to 80% of total aboveground biomass. By contrast, the contribution of either stembark or needles to the total was always less than or equal to 10%. On account of concentration differences between components, biomass and nutrient content distributions differed drastically. For instance, the contribution of bark to total stem nutrient contents (bark+wood) ranged from 30 to 60%, for a corresponding biomass percentage of about 10%. Between-plot variability was much higher for soil nutrient contents (SNCs) (0-100 cm) than for the corresponding total tree aboveground contents. Both lower and upper estimates of SNCs, in this case as concerns potassium, were found to be less than the corresponding tree nutrient contents (TNCs) in only one stand. At a given age, however, no consistent relationship appeared between SNC and TNC for any element