The effect of temperature and PAR on the annual photosynthetic production of Scots pine in northern Finland during 1906–2002

The annual photosynthetic production of Scots pine (Pinus sylvestris) was simulated for 1906-2002 for a location in northern Finland. We used the PhenPhoto model, which combines two key features of photosynthesis: the response to instantaneous radiation and the acclimation to the annual cycle. The input data for the PhenPhoto model include instantaneous photosynthetically active radiation (PAR) and temperature. The PAR values were generated from existing weather data and the instantaneous temperatures were interpolated from daily maximum and minimum values. The simulated annual photosynthetic production was at a low level during the the first two decades of the 20th century. No trend was observed for 1920-2002. The standard deviation of the annual photosynthetic production was 11.3% of the mean for the period 1906-2002. There were large differences in springtime recovery of photosynthesis: in 1964 over 30% of annual photosynthetic production had accumulated by 10 June, while at the other extreme (1917) the percentage was only 3.5%. A comparison of the simulated photosynthetic production with tree-ring indices of Scots pine showed a rather similar pattern of high-frequency variation.