Drought timing and local climate determine the sensitivity of eastern temperate forests to drought

Abstract

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. 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 ψ ) 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.

Drought legacies are dependent on water table depth, wood anatomy and drought timing across the eastern US

“…Previous work has documented the role of site climate and soil texture in controlling drought effects on ring width (D'Orangeville et al . ). Here, we find that legacy effects were less affected by these factors, and instead were larger at sites with a deep water table.…”

“…), underscoring the value of site‐specific factors to assist in explaining variation in tree drought sensitivities (D'Orangeville et al . ). However, most previous investigations of legacy effects have been global in scale and span vast climate gradients (Anderegg et al .…”

Linking drought legacy effects across scales: From leaves to tree rings to ecosystems

“…The temporal asynchrony between stem growth versus C uptake (Galiano et al, 2017;Mitchell, O'Grady, Tissue, Worledge, & Pinkard, 2014;Sala, Woodruff, & Meinzer, 2012) could also decouple legacy effects in tree rings from GPP, since radial growth tends to peak in late spring to early summer while C uptake occurs more uniformly throughout the growing season, at least in temperate and mesic forests (Čufar, Prislan, Luis, & Gričar, 2008;D'Orangeville et al, 2018;Delpierre, Berveiller, Granda, & Dufr, 2016). The temporal asynchrony between stem growth versus C uptake (Galiano et al, 2017;Mitchell, O'Grady, Tissue, Worledge, & Pinkard, 2014;Sala, Woodruff, & Meinzer, 2012) could also decouple legacy effects in tree rings from GPP, since radial growth tends to peak in late spring to early summer while C uptake occurs more uniformly throughout the growing season, at least in temperate and mesic forests (Čufar, Prislan, Luis, & Gričar, 2008;D'Orangeville et al, 2018;Delpierre, Berveiller, Granda, & Dufr, 2016).…”

Contrasting resistance and resilience to extreme drought and late spring frost in five major European tree species

“…As a consequence, drought can terminate the xylogenesis prematurely (Fernández‐de‐Uña et al, ) and can also affect radial growth in subsequent years (Anderegg et al, ). However, depending on intensity and exact timing of the ECE, impacts on tree growth might be very different and species dependent (D'Orangeville et al, ). Severe droughts in spring and/or early summer are expected to have the strongest impact on the current year's growth and tree functioning as they occur at early season peaks in radial growth, when soil water and nutrient availability are normally available in excess and do not limit growth (D'Orangeville et al, ).…”