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Variability of tree transpiration across three zones in a southeastern U.S. Piedmont watershed
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  • Johnny Boggs,
  • Ge Sun,
  • Jean-Christophe Domec,
  • Steven McNulty
Johnny Boggs
USDA Forest Service Southern Research Station
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Ge Sun
USDA Forest Service Southern Research Station
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Jean-Christophe Domec
Duke University Nicholas School of the Environment
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Steven McNulty
USDA Forest Service Southern Research Station
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Abstract

Quantifying species-specific tree transpiration across watershed zones is important for estimating watershed evapotranspiration (ET) and predicting drought effects on vegetation. The objectives of this study are to 1) assess sap flux density (Js) and tree-level transpiration (Ts) across three contrasting zones (riparian buffer, mid-hillslope, and upland-hillslope), 2) determine how species-specific Js responds to vapor pressure deficit (VPD), and 3) compare watershed-level transpiration (Tw) derived from each zone. We measured Js and Ts in eight tree species in the three zones in a 12-ha forested watershed. In the dry year of 2015, loblolly pine (Pinus taeda), Virginia pine (Pinus virginiana), and sweetgum (Liquidambar styraciflua) Js rates were significantly higher in the buffer when compared to the other two zones. In contrast, Js in tulip poplar (Liriodendron tulipifera) and red maple (Acer rubrum) were significantly lower in the buffer than in the mid-hillslope. Daily Ts varied by zone and ranged from 10 to 93 liters in the dry year and 9 to 122 liters in the wet year. Js responded nonlinearly to VPD in all trees and zones. Annual Tw based on scaled-Js data was 447 mm, 377 mm, and 340 mm for the buffer, mid-hillslope, and upland-hillslope, respectively. We conclude that large spatial variability in Js and scaled Tw were driven by differences in soil moisture at each zone and forest composition. Consequently, spatial heterogeneity of vegetation and soil moisture must be considered when accurately quantifying watershed level ET.

Peer review status:UNDER REVIEW

28 Apr 2021Submitted to Hydrological Processes
29 Apr 2021Assigned to Editor
29 Apr 2021Submission Checks Completed
29 Apr 2021Reviewer(s) Assigned
10 Jun 2021Review(s) Completed, Editorial Evaluation Pending