Remote sensing of plant-groundwater relations in riparian forests during the 2011-2017 California drought
Abstract
Semi-arid riparian forests are important habitats that are assumed to rely on groundwater availability to maintain ecosystem structure and function. Prolonged drought can cause the water table to drop below the rooting depth of riparian trees and shrubs, which may induce water stress and can ultimately lead to plant mortality. In this analysis, we used remote sensing imagery to monitor riparian vegetation health during the 2011-2017 California drought. We examined 12 sites in the Santa Clara River watershed, an important multi-use river basin in Southern California that supports agriculture, urban development, and natural ecosystems. Spectral mixture analysis was used to quantify the fractional cover of green vegetation across the watershed from remotely sensed imagery. Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) imagery was used to calibrate the mixing models and Landsat imagery was used to monitor vegetation change over a time series spanning the drought. Our analysis revealed significant spatial variability in vegetation signatures for willow (Salix) forest stands in response to the drought. In one stand of Salix laevigata near Fillmore, California, there was complete mortality of the riparian forest: vegetation cover decreased from approximately 75% to 0% between 2011 and 2017. In another stand of S. laevigata near Santa Paula, California, plant health improved during the drought: vegetation cover increased from approximately 80% to nearly 100%. Differences in riparian forest responses to drought in the Santa Clara basin can be explained by site-based trends in groundwater table elevation. Specifically, steep declines in water tables disconnect the roots from a key water source leading to forest die-back, while sustained water tables enable forest growth, even during drought. Water table trends in the basin are associated with complex patterns of groundwater flow and local anthropogenic controls, leading to strong spatial differences in availability of plant-available water under drought conditions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B53N2588K
- Keywords:
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- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES;
- 1807 Climate impacts;
- HYDROLOGY;
- 1813 Eco-hydrology;
- HYDROLOGY;
- 1851 Plant ecology;
- HYDROLOGY