Five decades of growth in a genetic field trial of Douglas-fir reveal trade-offs between productivity and drought tolerance

Abstract

To select suitable planting stock for reforestation under uncertain future climates, information about tolerances of genotypes to different climate conditions is necessary. One useful approach is to combine dendrochronological research with common garden experiments to quantify genotype by environment interactions observed over time. Here, we assess the response of Douglas-fir provenances planted in a common environment to climate variation over five decades using tree-ring analysis and historic height data. A rare drought event that affected growth in the year of 1985 provided the opportunity to study how mature Douglas-fir provenances differ in resilience and resistance to drought conditions and whether there are trade-offs with long-term productivity. We found that overall growth performance of provenances originating from drier and colder environments within the coastal range was below average and correlated with interannual variation in temperature. Productive provenances originated primarily from moist and warm areas and their annual increments covaried strongly with summer precipitation and summer drought indices. Further, provenances with below average growth were able to recover more quickly from the drought event of 1985, but did not show stronger drought resistance than coastal sources. Our results provide evidence for trade-offs between productivity and drought resilience and show that sources originating from moist locations are more dependent on favorable growing conditions in the summer. We conclude that selecting drought-resilient planting stock as an adaptation strategy for climate change is possible, but it would entail reductions in productivity.