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Larger trees suffer most during drought in forests worldwide

Amy C. Bennett·Nathan G. McDowell·Craig D. Allen·Kristina J. Anderson-Teixeira
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Abstract

The frequency of severe droughts is increasing in many regions around the world as a result of climate change . Droughts alter the structure and function of forests . Site- and region-specific studies suggest that large trees, which play keystone roles in forests and can be disproportionately important to ecosystem carbon storage and hydrology , exhibit greater sensitivity to drought than small trees . 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 , the higher radiation and evaporative demand experienced by exposed crowns , and the tendency for bark beetles to preferentially attack larger trees . 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.

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Amy C. Bennett, Nathan G. McDowell, Craig D. Allen, Kristina J. Anderson-Teixeira. 2015-09-28. Larger trees suffer most during drought in forests worldwide. https://doi.org/10.1038/nplants.2015.139

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