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 sylvestris L.) and applied to a transect of six meteorological stations in Europe. 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 phenology to the local climate differed up to 20% from simulations using the same phenology parameter values for all locations.

3. A temperature increase of 3°C and a doubling of the CO₂ concentration, while adjusting the photosynthesis parameters to give approximately the observed changed photosynthesis of +30%, also increased the length of the growing season by 23–42%. Combination of increases in the rate of photosynthesis 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 simulated increases in GPP was similar for locations representing boreal, temperate and mediterranean climates.