Evolution of climate responses could alter forest dynamics under climate change even over short time-spans

Climate change is imposing new selective pressures on organisms, including trees, which may lead to enhanced survival via evolutionary adaptation. Such evolutionary rescue may in turn alter interspecific interactions. We incorporated heritable variation in climate responses into the individual-based forest simulator SORTIE-ND, enabling the modeling of evolutionary change under several potential future climate scenarios over a multidecadal timescale in the Sierra Nevada of California. We find that including heritability of climate responses can indeed influence forest dynamics, but not in a way that can be simply described as “rescue”. This is in part because some species increased their basal area (BA) or stem density under climate change in the no-heritability scenarios; including heritability in some cases increased mortality or otherwise reduced the gains in BA or density of these species. The level of heritability of mortality and growth responses to climate (h² = 0.1 vs. 0.7) usually mattered less than the presence or absence of heritable variation itself. Overall, including heritability in the climate change simulations led to greater increases in BA at the low and mid-elevation sites and less increase at high elevation, and greater decreases in density at the mid and high-elevation sites. The effects of selection may also interact with competition in complex ways. At the high-elevation site the increase in BA was reduced when white fir had a higher heritability than the others or red fir (the most common species and the one driving the BA increase) had lower heritability, but was maintained when the least common species had the highest heritability or white fir had the lowest, both of which likely moderated competitive interactions. These results suggest that where changes in forest composition, more than overall BA, is the response of interest, it may be worth further investigating how individual differences and evolutionary responses in trees may affect climate change responses even over timespans of less than 100 years.