Sub-regional climate change impacts on the water balance, carbon balance and primary productivity of maritime pine in south-west France

The development of sustainable forest management practices must take into account the possible impacts of climate change at the spatial scales of interest to forest managers. We used a simple process-based model of pine forest growth (GRAECO) to examine sub-regional climate change impacts on the water balance, carbon balance and primary productivity of maritime pine in south-west France. GRAECO simulates the energy, water and carbon balances and growth of a monospecific, even-aged stand of maritime pine, represented by soil, understorey and tree layers. Standard and modified (2 x CO2) climate data were generated by the ARPEGE model of METEO-France over a 10-year period across a 60 x 60 km grid in south-west France. GRAECO simulated the behaviour of two stand age classes (8 and 18 yr) at seven representative grid points chosen to cover the range of climate conditions within this region. Under 2 x CO2 ARPEGE predicted a mean temperature increase of 2 degreesC, an increase in summer values of air vapour pressure deficit, and a shift in the seasonal distribution of precipitation from summer and autumn to winter. Regardless of age class, GRAECO then predicted a decrease in gross and net primary productivity at 6 grid points, but a slight increase in growth at the most coastal (and humid) site. The negative growth responses reflected increases in air and soil moisture deficits. Increased water stress more than offset the relatively small CO2-fertilisation effect, which was limited by the poor nutrient status of the sites considered. We conclude that sub-regional (approximate to 10 km) variations in the impact of climate change on forest growth may be significant, and should be considered in assessments of sustainable forest management.