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Local groundwater decline exacerbates response of dryland riparian woodlands to climatic drought

Williams, Jared, Stella, John C., Voelker, Steven L., Lambert, Adam M., Pelletier, Lissa M., Drake, John E., Friedman, Jonathan M., Roberts, Dar A. and Singer, Michael Bliss ORCID: https://orcid.org/0000-0002-6899-2224 2022. Local groundwater decline exacerbates response of dryland riparian woodlands to climatic drought. Global Change Biology 10.1111/gcb.16376

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Abstract

Abstract: Dryland riparian woodlands are considered to be locally buffered from droughts by shallow and stable groundwater levels. However, climate change is causing more frequent and severe drought events, accompanied by warmer temperatures, collectively threatening the persistence of these groundwater dependent ecosystems through a combination of increasing evaporative demand and decreasing groundwater supply. We conducted a dendro‐isotopic analysis of radial growth and seasonal (semi‐annual) carbon isotope discrimination (Δ13C) to investigate the response of riparian cottonwood stands to the unprecedented California‐wide drought from 2012 to 2019, along the largest remaining free‐flowing river in Southern California. Our goals were to identify principal drivers and indicators of drought stress for dryland riparian woodlands, determine their thresholds of tolerance to hydroclimatic stressors, and ultimately assess their vulnerability to climate change. Riparian trees were highly responsive to drought conditions along the river, exhibiting suppressed growth and strong stomatal closure (inferred from reduced Δ13C) during peak drought years. However, patterns of radial growth and Δ13C were quite variable among sites that differed in climatic conditions and rate of groundwater decline. We show that the rate of groundwater decline, as opposed to climate factors, was the primary driver of site differences in drought stress, and trees showed greater sensitivity to temperature at sites subjected to faster groundwater decline. Across sites, higher correlation between radial growth and Δ13C for individual trees, and higher inter‐correlation of Δ13C among trees were indicative of greater drought stress. Trees showed a threshold of tolerance to groundwater decline at 0.5 m year−1 beyond which drought stress became increasingly evident and severe. For sites that exceeded this threshold, peak physiological stress occurred when total groundwater recession exceeded ~3 m. These findings indicate that drought‐induced groundwater decline associated with more extreme droughts is a primary threat to dryland riparian woodlands and increases their susceptibility to projected warmer temperatures.

Item Type: Article
Date Type: Published Online
Status: Published
Schools: Earth and Environmental Sciences
Additional Information: License information from Publisher: LICENSE 1: URL: http://creativecommons.org/licenses/by-nc/4.0/
Publisher: Wiley
ISSN: 1354-1013
Date of First Compliant Deposit: 2 September 2022
Date of Acceptance: 6 June 2022
Last Modified: 10 Nov 2022 11:55
URI: https://orca.cardiff.ac.uk/id/eprint/152309

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