Variability of tree transpiration across three zones in a southeastern U.S. Piedmont watershed

Johnny Boggs; Ge Sun; Jean‐Christophe Domec; Steve McNulty

doi:10.1002/hyp.14389

Treesearch

Variability of tree transpiration across three zones in a southeastern U.S. Piedmont watershed

Formally Refereed

Authors:

Johnny Boggs, Ge Sun, Jean‐Christophe Domec, Steve McNulty

Year:

2021

Type:

Scientific Journal

Station:

Southern Research Station

DOI:

https://doi.org/10.1002/hyp.14389

Source:

Hydrological Processes

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Abstract

Quantifying the spatial variability of species-specific tree transpiration across hillslopes is important for estimating watershed-scale evapotranspiration (ET) and predicting spatial drought effects on vegetation. The objectives of this study are to (1) assess sap flux density (J_s) and tree-level transpiration (T_s) across three contrasting zones a (riparian buffer, mid-hillslope and upland-hillslope, (2) determine how species-specific J_sresponds to vapour pressure deficit (VPD) and (3) estimate watershed-level transpiration (T_w) using T_sderived from each zone. During 2015 and 2016, we measured J_sin eight tree species in the three topographic zones in a small 12-ha forested watershed in the Piedmont region of central North Carolina. In the dry year of 2015, loblolly pine (Pinus taeda), Virginia pine (Pinus virginiana) and sweetgum (Liquidambar styraciflua) J_srates were significantly higher in the riparian buffer when compared to the other two zones. In contrast, J_srates in tulip poplar (Liriodendron tulipifera) and red maple (Acer rubrum) were significantly lower in the buffer than in the mid-hillslope. Daily T_svaried by zone and ranged from 10 to 93 L/day in the dry year and from 9 to 122 L/day in the wet year (2016). J_sresponded nonlinearly to VPD in all species and zones. Annual T_wwas 447, 377 and 340 mm based on scaled-J_sdata for the buffer, mid-hillslope and upland-hillslope, respectively. We conclude that large spatial variability in J_sand scaled T_wwas 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.

Keywords

forest hydrology, sap flux, soil moisture, water balance

Citation

Boggs, Johnny L.; Sun, Ge; Domec, Jean‐Christophe; McNulty, Steven G. 2021. Variability of tree transpiration across three zones in a southeastern U.S. Piedmont watershed. Hydrological Processes. 35(10): 932-. https://doi.org/10.1002/hyp.14389.