EFFECTS OF DROUGHT AND PHENOLOGY ON GPP IN PINUS-SYLVESTRIS - A SIMULATION STUDY ALONG A GEOGRAPHICAL GRADIENT

1. A simple canopy model was developed for Scots Pine (Pinus sylvestri s L.) and applied to a transect of six meteorological stations in Euro pe. The model accounts for possible genetic adaptation of phenology of photosynthesis to the local climate and to decreases of gas exchange owing to drought. 2. Simulations accounting for adaptation of phenolog y to the local climate differed up to 20% from simulations using the s ame phenology parameter values for all locations. 3. A temperature inc rease of 3 degrees C and a doubling of the CO2 concentration, while ad justing the photosynthesis parameters to give approximately the observ ed changed photosynthesis of +30%, also increased the length of the gr owing season by 23-42%. Combination of increases in the rate of photos ynthesis and the length of the growing season resulted in increases of yearly Gross Primary Productivity (GPP) from 72 to 101%. Increases in transpiration were smaller.4. A decrease of the precipitation by 25% reduced this increase to 54-64%. 5. The relative magnitude of the simu lated increases in GPP was similar for locations representing boreal, temperate and mediterranean climates.