FERTILIZATION OF ADULT CONIFEROUS STANDS IN THE VOSGES - MINERAL-COMPOSITION OF NEEDLES IN RELATIONSHIP TO NEEDLE LOSS AND YELLOWING

Fertilizer experiments were set up in 8 more or less declining stands of spruce (Picea abies Karst) or fir (Abies alba Mill) in the Vosges mountains in 1985 (table I). Five treatments, ie a control, Ca, CaMg, NPKCaMg, and KMg were applied. Needle yellowing and needle loss were recorded from 1986-1990 as well as needle mineral composition. Needle loss and yellowing decreased spontaneously from 1986-1990 in the control plots (tables II, III) while the Ca and Mg contents of the needles increased (tables VI, VII, VIII). These improvements were reinforced by Ca, CaMg or NPKCaMg fertilizers (tables II and IV). The strong defoliation and yellowing in 1985-1986 were probably due to the climatic conditions: very wet springs and hot and dry summers in 1983 and 1984. Correlations between Ca and Mg concentrations in the needles and needle loss or yellowing were higher during the climatic crisis period in 1985-1986 than later in 1989-1990 (table IX, figs 1, 2). Correlations between Ca and Mg concentrations in the needles in 1989 and needle loss or yellowing in 1986 might be used to determine which stands it is advisable to fertilize if one intends to avoid severe decline in the case of another climatic crisis (figs 3-5). For instance, stands with < 0.47% Ca in current-year needles and < 0.08% Mg in the 4th yr needles in 1989 should be fertilized to avoid, in the event of a future crisis, an average needle loss and a percentage of yellowing trees of > 20% and > 15% respectively.