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Zusammenfassung:
Projected changes in temperature and drought regime are likely to reduce carbon (C) storage
in forests, thereby amplifying rates of climate change. While such reductions are often
presumed to be greatest in semi-arid forests that experience widespread tree mortality, the
consequences of drought may also be important in temperate mesic forests of Eastern North
America (ENA) if tree growth is significantly curtailed by drought. Investigations of the
environmental conditions that determine drought sensitivity are critically needed to
accurately predict ecosystem feedbacks to climate change. We matched site factors with the
growth responses to drought of 10,753 trees across mesic forests of ENA, representing 24
species and 346 stands, to determine the broad-scale drivers of drought sensitivity for the
dominant trees in ENA. Here we show that two factors – the timing of drought, and the
atmospheric demand for water (i.e., local potential evapotranspiration; PET) – are stronger
drivers of drought sensitivity than soil and stand characteristics. Across ENA, intraspecific
variation in drought sensitivity was equal to or greater than interspecific variation in
sensitivity in 17 of 24 species. Drought-induced reductions in tree growth were greatest when
the droughts occurred during early-season peaks in radial growth, especially for trees
growing in the warmest, driest regions (i.e., highest PET). Further, mean species trait values
(rooting depth and Psi50) were poor predictors of drought sensitivity, as intraspecific
variation in sensitivity was equal to or greater than interspecific variation in 17 of 24 species.
From a general circulation model ensemble, we find that future increases in early-season PET
may exacerbate these effects, and potentially offset gains in C uptake and storage in ENA owing to other global change factors.
