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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Hydrology and Remote Sensing Laboratory » Research » Publications at this Location » Publication #382289
Research Project: Integrating Remote Sensing, Measurements and Modeling for Multi-Scale Assessment of Water Availability, Use, and Quality in Agroecosystems

Location: Hydrology and Remote Sensing Laboratory

Title: Studying drought-induced forest mortality using high spatiotemporal resolution evapotranspiration data from thermal satellite imaging

Author
item Yang, Yun
item Anderson, Martha
item Gao, Feng
item WOOD, J. - University Of Missouri
item GU, L. - Oak Ridge National Laboratory
item HAIN, C. - National Aeronautics And Space Administration (NASA) - Johnson Space Center

Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2021
Publication Date: 8/18/2021
Citation: Yang, Y., Anderson, M.C., Gao, F.N., Wood, J.D., Gu, L., Hain, C. 2021. Studying drought-induced forest mortality using high spatiotemporal resolution evapotranspiration data from thermal satellite imaging. Remote Sensing of Environment. 265:112640. https://doi.org/10.1016/j.rse.2021.112640.
DOI: https://doi.org/10.1016/j.rse.2021.112640

Interpretive Summary: While forested landscapes tend to be more resilient to drought than are crops and grasslands, prolonged severe moisture stress can lead to enhanced potential for tree disease and mortality. For monitoring susceptibility to mortality, remotely sensed maps of water use or evapotranspiration (ET) provide an effective indicator of tree health. This paper explores the utility of a high-resolution (30-m) ET mapping timeseries for predicting spatial variations in tree die-off over a forested area in the Missouri Ozarks. Intensive measurements have been collected for many years in plots on the order of 30-m in dimension around the MOFLUX flux tower site. In this study, we find that anomalies in ET correlate well with recorded drought severity and with anomalies in measured leaf water potential, a signature of tree stress. ET anomalies were good predictors of tree mortality in the subsequent year, indicating a time-integrated relationship between stress and death. This work demonstrates an effective new tool for monitoring forest health at high spatial resolution.

Technical Abstract: Drought can have pervasive and wide-spread impacts to forest health, as evidenced in several severe events occurring over the recent decades. Extensive forest die-off due to drought can impair the ecological functioning of forests, impacting habitat, water yield and quality from forested lands, and altering forest fire dynamics and intensity. Satellite remote sensing provides an effective means for detecting and monitoring spatial patterns of forest mortality over large areas, exploiting free and open long-term image archives available at a range in spatial and temporal resolutions. While remotely sensed surface reflectance and vegetation indices have been widely used to study optical response of forest canopies to drought events, retrievals of evapotranspiration (ET) derived from thermal satellite imagery – particularly at resolutions approaching crown scale - can provide insights into cumulative tree stresses that can incite disease and trigger mortality. In this study, we applied a multi-sensor satellite data fusion approach to estimate daily 30-m resolution ET and an associated Evaporative Stress Index (ESI) to study drought-induced mortality in a temperate forest at the Missouri Ozark AmeriFlux (MOFLUX) site, located in the central United States. The study covered the period from 2010 to 2014, including an exceptional drought year of 2012. Modeled ET agreed well with eddy flux measurements from the MOFLUX tower, with average monthly relative errors of 15%. Plot-scale ESI, describing temporal anomalies in the ratio of actual-to-reference ET, was used as an index of relative forest health to investigate relationships between forest mortality and drought severity. ESI showed good agreement with observed predawn leaf water potential, especially during the drought year. Furthermore, plot-scale ESI was also correlated with the subsequent year’s tree mortality, suggesting the importance of considering the forest health condition prior to drought when studying drought-induced forest impacts. This study demonstrates the utility of multi-year ET remote sensing data at the stand or plot scale as an indicator of forest health and as a predictor of future mortality due to drought.