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Data from repeated measurements of predawn and midday water potentials on Quercus agrifolia and Quercus douglassi trees at Sedgwick Reserve, CA, USA from 2022 - 2024. The data includes the following columns: Column name Description individual_id Unique numeric ID for individual tree site Name of site location, represents a spatially distinct group of trees species Quercus agrifolia and Quercus douglassii date date of data collection, in YYYYMMDD pd_md Indicates whether measurements were taken at predawn (pd, 1-3 hours before sunrise) or midday (md, within 1.5 hours of solar noon) water_potential_mean Mean water potential measurements for each tree/date/time (MPa). water_potential_sd Standard deviation of water potential measurements for each tree/date/time (MPa) water_potential_n Number of water potential measurements for each tree/date/time latitude Location of individual tree, latitude in decimal degrees longitude Location of individual tree, longitude in decimal degrees coord_system EPSG:4326-WGS 84 For details on collection methods, see: Boving I, Allen J, Brodrick PG, Chadwick KD, Trugman A, Anderegg LDL. The Unstable Relationship Between Drought Status and Leaf Water Content Complicates the Remote Sensing of Tree Drought Stress. Glob Chang Biol. 2025 Apr;31(4):e70188. doi: 10.1111/gcb.70188. PMID: 40249004; PMCID: PMC12007071. 

ABSTRACT Remote sensing holds promise for ecosystem‐level monitoring of plant drought stress but is limited by uncertain linkages between physiological stress and remotely sensed metrics of water content. Here, we investigate the stability of relationships between water potential (Ψ) and water content (measured in situ and via repeat airborne VSWIR imaging) over diel, seasonal, and spatial variation in two xeric oak tree species. We also compare these field‐based relationships with ones established in laboratory settings that might be used as calibration. Due to confounding physiological processes related to growth, both in situ and remotely sensed metrics lacked consistent relationships with stress when measured across space or through time. Relationships between water content and physiological drought stress measured over the growing season were stronger and more closely related to established laboratory‐based drydown methods than those measured across space (i.e., between wet trees and dry trees). These results provide insight into the utility of “space for time” approaches in remote sensing and demonstrate both important limitations and the potential power of high temporal resolution remote sensing for detecting drought stress.