Forest sensitivity to extreme climate events such as drought has long been presumed to hinge on the hydraulic traits of dominant tree species. However, large intraspecific variation in sensitivity suggests the existence of underpinning environmental controls. We matched local site factors with the growth responses to drought of 10,753 trees in the temperate biome of eastern North America (ENA), representing 24 species and 346 stands.
Here we show that the timing of drought and the atmospheric demand for water (i.e., local potential evapotranspiration; PET) are stronger drivers of drought sensitivity than are soil and stand characteristics or plant traits. Across ENA, intraspecific variation in drought sensitivity was equal to or greater than interspecific variation in sensitivity in 21 of 24 species. The impacts of drought were greatest when the droughts occurred during seasonal peaks in radial growth. Further, trees growing in more arid areas (defined by their higher PET) showed the largest growth reductions during drought. We estimate that predicted changes in drought frequency and PET across ENA over the next decades may reduce C uptake by 4-7% annually. Such changes have the potential to offset the gains in C sequestration from longer growing seasons, land use change, rising atmospheric CO2 and/or nitrogen fertilization.