Weather underground: Subsurface hydrologic processes mediate tree vulnerability to extreme climatic drought
Blair C McLaughlin1, Rachel Blakey2, Andrew P Weitz3
1Hampshire College, Amherst, MA, USA.
Global Change Biology
|February 15, 2020
Summary
Subsurface water access significantly impacts tree drought vulnerability, mediating species responses to climate change. Understanding these hydrologic niches is crucial for forest management and predicting future forest composition.
Area of Science:
- Ecology
- Forestry
- Hydrology
Background:
- Droughts are increasing globally, necessitating research into tree vulnerability.
- Subsurface water's role in tree drought response is under-studied, particularly in water-limited ecosystems.
Purpose of the Study:
- To investigate tree drought vulnerability in California using the 2013-2016 drought as a natural experiment.
- To examine how climate, lithology, and subsurface hydrology influence drought vulnerability across four co-occurring woodland species.
Main Methods:
- Utilized regional aerial dieback surveys and site-scale field surveys.
- Analyzed drought vulnerability in blue oak, valley oak, gray pine, and California juniper.
- Assessed the relationship between climate, lithology, groundwater, and stem water stable isotopes with canopy condition.
Main Results:
- Both climatic drought severity and subsurface processes explained tree dieback variation.
- Blue oak mortality correlated with specific bedrock types and reduced groundwater.
- Access to deep subsurface water, indicated by isotope composition, improved canopy condition across all species.
Conclusions:
- Subsurface hydrology mediates species' drought experience, with channel locations acting as potential refugia.
- Hydrologic niche segregation helps explain differential species vulnerability to drought and climate change.
- Understanding subsurface water access is vital for effective forest management in a changing climate.
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