Future droughts will have a more detrimental impact on larger trees

Larger trees suffer most during drought in forests worldwide

by Amy C. Bennett, Nathan G. McDowell, Craig D. Allen, Kristina J. Anderson-Teixeira

Abstract

The frequency of severe droughts is increasing in many regions around the world as a result of climate change^1,​2,​3. Droughts alter the structure and function of forests^4,5. Site- and region-specific studies suggest that large trees, which play keystone roles in forests⁶ and can be disproportionately important to ecosystem carbon storage⁷ and hydrology⁸, exhibit greater sensitivity to drought than small trees^4,5,9,10.

Here, we synthesize data on tree growth and mortality collected during 40 drought events in forests worldwide to see whether this size-dependent sensitivity to drought holds more widely.

We find that droughts consistently had a more detrimental impact on the growth and mortality rates of larger trees. Moreover, drought-related mortality increased with tree size in 65% of the droughts examined, especially when community-wide mortality was high or when bark beetles were present. The more pronounced drought sensitivity of larger trees could be underpinned by greater inherent vulnerability to hydraulic stress^{11,​12,​13,​14}, the higher radiation and evaporative demand experienced by exposed crowns^4,15, and the tendency for bark beetles to preferentially attack larger trees¹⁶.

We suggest that future droughts will have a more detrimental impact on the growth and mortality of larger trees, potentially exacerbating feedbacks to climate change.

See the text: Nature

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• Nepstad, D. C., Tohver, I. M., Ray, D., Moutinho, P. & Cardinot, G.Mortality of large trees and lianas following experimental drought in an Amazon forest. Ecology 88, 2259–2269 (2007).
• Phillips, O. L. et al. Drought-mortality relationships for tropical forests.New Phytol. 187, 631–646 (2010).
• Stahl, C. et al. Depth of soil water uptake by tropical rainforest trees during dry periods: does tree dimension matter? Oecologia 173, 1191–1201 (2013).
• McDowell, N. G. & Allen, C. D. Darcy’s law predicts widespread forest mortality under climate warming. Nat. Clim. Change 5, 669–672 (2015).
• Allen, C. D. et al. A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests. For. Ecol. Manag. 259, 660–684 (2010).
• Mueller, R. C. et al. Differential tree mortality in response to severe drought: evidence for long-term vegetation shifts. J. Ecol. 93, 1085–1093 (2005).
• Doughty, C. E. et al. Drought impact on forest carbon dynamics and fluxes in Amazonia. Nature 519, 78–82 (2015).
• da Costa, A. C. L. et al. Effect of 7 yr of experimental drought on vegetation dynamics and biomass storage of an eastern Amazonian rainforest. New Phytol. 187, 579–591 (2010).
• Mattson, W. J. & Haack, R. A. the role of drought in outbreaks of plant-eating insects. BioScience 37, 110–118 (1987).