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 treering 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 tradeoffs 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.

The impacts of increasing drought on forest dynamics, structure, and biodiversity in the United States

“…Successful regeneration during drought depends on microsite conditions, including competition from nonpreferred species. However, current practices and guidelines for seed transfer may need to be reconsidered given the potential for locally maladapted genotypes, as well as the possibility of planting more heatand drought-tolerant genotypes (Aitken et al, 2008;Joyce & Rehfeldt, 2013;Montw e et al, 2015). After all, decades of horticultural practice have clearly shown that growth and reproduction of many species well outside their native ranges is possible, suggesting 'assisted migration' is a viable diversity conservation option (e.g., Schwartz et al, 2012).…”

“…Changing temperatures and precipitation patterns will produce novel combinations of drought frequency, intensity, and seasonality (Wehner et al, 2011;Dai, 2012). Tree populations can disperse and adapt to local climates, including drought stress (Savolainen et al, 2007;Aitken et al, 2008;Montw e et al, 2015). As tree populations arrive in new locations, they interact with existing populations and form new communities.…”

Drought tolerance and growth in populations of a wide‐ranging tree species indicate climate change risks for the boreal north

“…As productivity and drought tolerance was negatively related in the US population, we had expected a similar growth versus drought tolerance trade-off in the northern population. Recent research has indicated a link between cold adaptation and drought adaptation in seedlings (Bansal et al, 2015a,b) and mature trees of Douglas-fir (Montw e et al, 2015). Cold-adapted trees also invest into thicker cell walls and narrower lumen sizes that are more resistant to freeze-thaw-induced embolisms (Schreiber et al, 2013a,b).…”

Cold adaptation recorded in tree rings highlights risks associated with climate change and assisted migration

“…Assisted migration involves changing the genetic composition of plant populations by moving seed material to climate regions where they are anticipated to be well adapted in the future 2 , 3 , 10 , 11 . For example, transferring seeds from southern, drought-tolerant tree populations may help more northern forests adapt to drier, warmer conditions 2 , 3 , 13 , 14 . However, there are concerns that assisted migration may not be successful and lead to unintended consequences 15 , 16 .…”