Improved assessment of dryland riparian vegetation water use at leaf- to landscape-scales using unmanned aerial vehicle (UAV)-based thermal remote sensing
Abstract
Dryland rivers provide access to otherwise scarce water resources for biodiversity and are increasingly under pressure from anthropogenic disturbance, livestock grazing, and expansion of invasive species, amongst other threats. These pressures can alter the hydrologic regime, leading to changes in riparian forest composition that further alter the ecohydrological and geomorphological structure of the landscape. Accurate estimates of water use in riparian ecosystems are critical for understanding patterns of vegetation distribution, catchment water balance, and groundwater fluctuations and availability. Methods for measuring riparian vegetation water use include either highly individualistic approaches at leaf or stem scales, such as porometers or sap-flow probes, or large-scale (0.01-10 ha) tools such as eddy covariance measurements from flux towers or thermal imagery acquired from satellites. Individual and leaf-level methods require broad assumptions to upscale to stand and/or canopy scales. Flux towers provide average values over integrated areas much larger than typical riparian corridors, often confounding riparian communities with other distinct shrub and grassland functional types.
We compare these existing methods for estimating evapotranspiration and vegetation water use to a near-surface remote sensing approach using thermal and multispectral imagery acquired from an unmanned aerial vehicle (UAV) platform across select dryland ecosystems. Imagery from UAVs provides high spatial and temporal resolution data that show promise for calculation of transpiration and stomatal conductance across leaf, canopy, and landscape scales, specifically isolating riparian species from other vegetation types. Further, we explore the use of Structure-from-Motion (SfM) to resolve three-dimensional (3-D) canopy structure and improve estimates of temperature and transpiration across the 3-D structure of individual trees and plant communities. Such research provides an opportunity to improve estimates of riparian vegetation water use in drylands and understand mechanisms driving changes in vegetation distribution, composition, and responses to groundwater fluctuations in riparian environments.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B53P2616M
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES;
- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 0476 Plant ecology;
- BIOGEOSCIENCES