Weather underground: Subsurface hydrologic processes mediate tree vulnerability to extreme climatic drought

Blair C McLaughlin; Rachel Blakey; Andrew P Weitz; Xue Feng; Brittni J Brown; David D Ackerly; Todd E Dawson; Sally E Thompson

doi:10.1111/gcb.15026

Weather underground: Subsurface hydrologic processes mediate tree vulnerability to extreme climatic drought

Glob Chang Biol. 2020 May;26(5):3091-3107. doi: 10.1111/gcb.15026. Epub 2020 Mar 24.

Authors

Blair C McLaughlin¹, Rachel Blakey², Andrew P Weitz³, Xue Feng⁴, Brittni J Brown⁵, David D Ackerly³, Todd E Dawson³, Sally E Thompson^{6

7}

Affiliations

¹ Hampshire College, Amherst, MA, USA.
² La Kretz Center for California Conservation Science, Institute of the Environment and Sustainability, University of California Los Angeles, Los Angeles, CA, USA.
³ Department of Integrative Biology, University of California, Berkeley, Berkeley, CA, USA.
⁴ Department of Civil, Environmental, and Geo-Engineering, University of Minnesota, Minneapolis, MN, USA.
⁵ Department of Natural Resources and Society, University of Idaho, Moscow, ID, USA.
⁶ Department of Civil, Environmental and Mining Engineering, University of Western Australia, Crawley, WA, Australia.
⁷ Department of Civil and Environmental Engineering, University of California, Berkeley, Berkeley, CA, USA.

PMID: 32056344
DOI: 10.1111/gcb.15026

Abstract

Drought extent and severity have increased and are predicted to continue to increase in many parts of the world. Understanding tree vulnerability to drought at both individual and species levels is key to ongoing forest management and preparation for future transitions in community composition. The influence of subsurface hydrologic processes is particularly important in water-limited ecosystems, and is an under-studied aspect of tree drought vulnerability. With California's 2013-2016 extraordinary drought as a natural experiment, we studied four co-occurring woodland tree species, blue oak (Quercus douglasii), valley oak (Quercus lobata), gray pine (Pinus sabiniana), and California juniper (Juniperus californica), examining drought vulnerability as a function of climate, lithology and hydrology using regional aerial dieback surveys and site-scale field surveys. We found that in addition to climatic drought severity (i.e., rainfall), subsurface processes explained variation in drought vulnerability within and across species at both scales. Regionally for blue oak, severity of dieback was related to the bedrock lithology, with higher mortality on igneous and metamorphic substrates, and to regional reductions in groundwater. At the site scale, access to deep subsurface water, evidenced by stem water stable isotope composition, was related to canopy condition across all species. Along hillslope gradients, channel locations supported similar environments in terms of water stress across a wide climatic gradient, indicating that subsurface hydrology mediates species' experience of drought, and that areas associated with persistent access to subsurface hydrologic resources may provide important refugia at species' xeric range edges. Despite this persistent overall influence of the subsurface environment, individual species showed markedly different response patterns. We argue that hydrologic niche segregation can be a useful lens through which to interpret these differences in vulnerability to climatic drought and climate change.

Keywords: Quercus douglasii; climate change; drought; hydrologic niche; hydrology; lithology; oak woodlands; subsurface; water.

MeSH terms

Droughts*
Ecosystem
Hydrology
Trees*
Weather

Abstract

MeSH terms

Grants and funding