EFFECT OF LIMING AND ITS ASSOCIATION WITH FERTILIZATION ON THE BIOGEOCHEMICAL CYCLE OF NUTRIENTS IN A DECLINING SPRUCE STAND (PICEA-ABIES KARST) IN THE VOSGES (FRANCE)

Effect of liming and its association with fertilization on the biogeoc hemical cycle of nutrients in a declining spruce stand (Picea abies Ka rst) in the Vosges (France). The forest decline observed in the 1980s showed a complex interaction between biological, edaphic, climatic and silvicultural parameters. The effects of the edaphic constraints were studied using in situ fertilization experiments, which demonstrated b oth the origin of some of the forest decline symptoms observed an spru ce stands (Picea abies Karst) in the Vosges and the efficiency of the treatments applied. Liming restored the green growth and foliation of severely declining trees within 2 years independently of whether it wa s associated with complete fertilization (NPK). A detailed quantitativ e study of the mineral function of a spruce ecosystem which reacted po sitively to liming was set up in an experiment situated at Le Col du B onhomme (Vosges). The soil is very acidic and its current geochemistry is dominated by nitrate and aluminium. Acidification is still an acti ve process and the soil cannot neutralize acidify from external (atmos pheric input) or infernal origins. This acidity must be neutralized at depth in the sub-soil since the water in the catchment stream is neut ral. Input-output budgets, even if they were not very accurate, always showed a Mg deficit whatever the time-scale considered (seasonal, yea rly or over several years). This element is often cited as the cause o f forest decline. Liming neutralized the soil acidity, particularly it s Al component, and increased the Ca and Mg tree nutrition of the tree s; nitrates decreased in the gravitational solutions of the liming tre atment. Addition of fertilizers to liming, which did not clearly incre ase tree health and accelerated the depletion of Ca and Mg caused by l iming, did not seem suitable in this situation. This experiment demons trates clearly the role of edaphic parameters in this particular case of forest decline.