BIOMASS AND NUTRIENT CYCLING OF A HIGHLY PRODUCTIVE CORSICAN PINE STAND ON FORMER HEATHLAND IN NORTHERN BELGIUM

Biomass and nutrient cycling were examined in a 62-year-old highly pro ductive Corsican pine stand (Pinus nigra Am. ssp. laricio Poiret) grow ing on a coarse and dry sandy soil with low exchangeable nutrient pool s. Total aboveground biomass was estimated at 240 tons dry weight per hectare of which 201 tons concerned boles. The belowground biomass amo unted to 46 t ha(-1) (16 % of total standing biomass). The current ann ual volume increment was estimated at 20.6 m(3) ha(-1) year(-1). Root study emphasized the role of the rooting depth as an important growth factor. Calculated uptake rates for N, P, K, Ca and Mg were respective ly 50.5, 1.9, 38.2, 15.6 and 3.3 kg ha(-1) year(-1). Despite an abunda nt nitrogen deposition (46 kg inorg. N ha(-1) year(-1)) between 23 and 35 % of the nitrogen demand was supplied by internal transfers. Retra nslocation of phosphorus fulfilled 64 % of the annual requirement. The root uptake of potassium, calcium and magnesium were better coupled w ith the tree requirements. The uptake rates of Ca and Mg could be met by atmospheric deposition. The canopy leaching of potassium accounted for 70 % of the root uptake. The low uptake rates of P, Ca and Mg were inconsistent with the vigorous growth of the stand, which could only be maintained by a high nutrient use efficiency. The monitoring of the nutrient status between 1988 and 1995 revealed an obvious decline in the concentrations of Ca, Mg, K and P due to growth dilution. ((C) Inr a/Elsevier, Paris.).