Year of Award

2023

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Systems Ecology

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

Kelsey G. Jencso

Committee Co-chair

Zachary H. Hoylman

Commitee Members

Anna Sala, Ashley Ballantyne

Keywords

Ecohydrology, soil water potential, VPD, semi-arid, soil, Montana

Subject Categories

Hydrology | Soil Science | Terrestrial and Aquatic Ecology

Abstract

Knowledge of vegetation’s response to soil water availability and atmospheric demand is critical to understanding the impact of climate change on semi-arid ecosystems. However, limited field-based research has been conducted to assess the relative importance of these drivers and previous research has simplified the assessment of soil water availability by relying on soil volumetric water content (VWC) as a primary control on plant growth, which, as opposed to soil water potential (Ψsoil), does not account for the effects of soil texture on plant available water. To address these gaps, we compared remotely sensed indicators of vegetation response to field based measurements of VWC (at 20 cm depth), relative humidity and temperature (used to calculate the vapor pressure deficit, VPD) and soil temperature from 52 sites in Montana. Soil samples were collected at each site and were used to generate continuous time series of soil water potential (Ψsoil). We utilized statistical analysis to assess the relationship of our biophysical metrics to satellite-derived estimates of vegetation health and vigor, including the Enhanced Vegetation Index (EVI), near-infrared reflectance vegetation index (NIRv), and solar-induced fluorescence (SIF). Results from this analysis suggest that Ψsoil is a better biophysical indicator that VWC for driving seasonal vegetation productivity in semi-arid regions, while VPD emerges as a secondary driver in the absence of Ψsoil limitations. Finally, anomalies in subsurface soil moisture were the dominant driver for explaining anomalies in vegetation response. These findings emphasize the importance of soil water potential as the first order control on vegetation water stress across semi-arid landscapes.

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© Copyright 2023 Kayla R. Jamerson