Testing scenarios for assisted migration of forest trees in Europe

One approach to compensating for rapid climate change and protecting biodiversity is assisted migration (AM) of key tree species. However, tools for evaluating the sensitivity of target sites and identifying potential sources have not yet been developed. We used the National Forest Inventories of Spain and France to design scenarios for AM between and within both countries. We characterized sensitivity to climate change as the expected changes in volume and mortality of Pinus halepensis Miller and Pinus pinaster Aiton between the present and 2050. Target zones were selected from provenances with high sensitivity and seed zones from provenances with low sensitivity to climate change; the latter can be considered "seed refugia" as the climate changes. Three plausible scenarios for translocation to the target zone were developed on the basis of volume simulations calibrated with different planting strategies: (1) seeds only from foreign provenances; (2) foreign provenances plus local seeds; and (3) only local seeds. The results for both species show that models based on foreign "top-three" provenances always increased the standing volume of the target zone. Models run with only local seeds predicted increased volume for P. halepensis but not for P. pinaster. Our results suggest that volume and mortality trends are not always correlated with seed sources and targets, that projected provenances mortality do not follow always a southern-northern pattern and that seed refugia, if any, may be useful for compensating for the effects of climate change only in a subset of provenances.