SREL Reprint #3737

Evapotranspiration partitioning of Eucalyptus benthamii and Pinus taeda during early stand development

Seth E. Younger1,2,3, C. Rhett Jackson1, Mackenzie J. Dix1,2, Peter V. Caldwell4, and Doug P. Aubrey1,2

1Warnell School of Forestry and Natural Resources, University of Georgia,
180 E Green Street, Athens, GA 30602-2152, USA
2University of Georgia’s Savannah River Ecology Lab, PO Drawer E, Aiken, SC 29802, USA
3The Jones Center at Ichauway, 3988 Jones Center Drive, Newton, GA 39870, USA
4Southern Research Station, Center for Integrated Forest Science, USDA Forest Service,
3160 Coweeta Lab Road, Otto, NC 28734, USA

Abstract: Increasing demand for bioenergy from intensively managed woody crops raises concerns of increased evapotranspiration and potential decreases in water yield. Pinus taeda (loblolly pine) is currently the most cultivated species in the southeastern USA, the country’s wood basket. However, Eucalyptus species could achieve greater productivity but with unknown ramifications for water budgets. To address the knowledge gap, we determined annual water budgets of loblolly pine and Eucalyptus benthamii (eucalypt) from growing years 3 through 5 in a replicated (n = 3) two-factor design comparing species and groundwater depth. Paired plots were established across a depth-to-groundwater gradient from shallow (~2 m) to deep (~8 m). Hydrologic budgets were constructed by measuring precipitation, interception, soil evaporation, and transpiration. Eucalypt evapotranspiration and above-ground biomass production for growing years 3 through 5 were on average 25 and 14% greater than pine, respectively; however, evapotranspiration did not differ across groundwater depths. At the end of growing year 5, eucalypt had higher transpiration and evapotranspiration per unit area than pine. Soil evaporation was substantial in young plantations (nearly 500 mm) in growing year 3 but declined as the canopy closed. Partitioning of evapotranspiration components in developing bioenergy plantations was dynamic due to canopy development driven decreases in soil evaporation and increases in transpiration and interception; total evapotranspiration was less variable from year to year. Water use efficiency (WUE, kg biomass/m3 H2O) per unit evapotranspiration was similar between species, but WUE per unit transpiration was higher in pine. Considering total evapotranspiration in young plantations can affect WUE interpretations.

Keywords: Transpiration; Sap flow; Evaporation; Evapotranspiration; Biomass; Bioenergy; Water use efficiency

SREL Reprint #3737

Younger, S. E., C. R. Jackson, M. J. Dix, P. V. Caldwell, and D. P. Aubrey. 2023. Evapotranspiration partitioning of Eucalyptus benthamii and Pinus taeda during early stand development. BioEnergy Research.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).