Forests play a key role in global ecosystems, hosting the majority of terrestrial biodiversity and acting as a net sink for atmospheric carbon. Numerous studies have documented responses of forest ecosystems to climate change and variability, including drought-induced increases in tree mortality rates and declines in growth. However, the sensitivity of forests to climate variability – in terms of both tree species composition and biomass carbon storage – has yet to be quantified across a large geographic region using systematically sampled data. Here, we use systematic forest inventories from the 1980s and 2000s across the eastern USA to show that tree species composition and forest biomass responds to decadal-scale changes in the Palmer Drought Severity Index – a widely-used index of water stress.
Results/Conclusions
We found that the tree species composition and biomass of eastern USA forests respond to decadal-scale climate variability in a predictable manner. The mean drought tolerance of forests (quantified as a community-weighted species drought tolerance index) tended to increase from the 1980s to the 2000s in locations that experienced increasing water stress. Forest biomass carbon storage responded directly to climate variability (decreased biomass due to water stress) and also indirectly (decreased biomass due to a shift in tree species composition towards more drought tolerant but lower biomass species). These results demonstrate a high sensitivity of forest species composition and biomass carbon storage to climate variability, and show that species turnover amplifies the sensitivity of forest carbon storage to water stress.