Tree species explain only half of explained spatial variability in plant water sensitivity

Area of Science:

• Ecohydrology
• Plant Physiology
• Remote Sensing

Background:

• Plant water uptake, loss, and storage critically influence photosynthesis and evapotranspiration.
• Species-specific traits (stomatal closure, xylem conductance, root traits) are traditionally studied in plant water stress responses.
• Ecohydrological factors like soil hydraulics, water redistribution, climate adaptation, and vegetation density also play significant roles.

Purpose of the Study:

• To determine the relative importance of dominant tree species in regional woody plant responses to water stress.
• To map plant water sensitivity (PWS) and assess factors influencing it.

Main Methods:

• Developed a plant water sensitivity (PWS) map using remotely sensed live fuel moisture content and hydrometeorological data via an auto-regressive model.
• Analyzed 21,455 U.S. Forest Service Forest Inventory and Analysis plots in the western United States with known dominant species.
• Employed a random forest model incorporating vegetation density, climate, soil properties, and topography.

Main Results:

• A species-specific mean PWS value explained only 23% of PWS variability.
• Environmental factors (vegetation density, climate, soil, topography) explained 43% of PWS variability using a random forest model.
• Dominant species accounted for 53% of the explainable variation in PWS, highlighting the greater influence of environmental context.

Conclusions:

• Environmental factors significantly influence woody plant water stress responses, often more than the dominant species identity.
• Future studies on inter-species differences in water stress should account for the specific environmental conditions where data are collected.
• Mean climate and normalized difference vegetation index (NDVI) also showed significant impacts on PWS.