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Goal: Apply Knowledge Globally Does forest water use increase with stand age?

Old growth forests in the southern Appalachian Mountains are made up of large trees capable of transpiring large volumes of water. However, a variety of factors, such as stem density, species composition, and stand structure, affect total evapotranspiration. Researchers examined forest water use across a range of stand ages to understand and predict how forest management affects evapotranspiration and streamflow.

Equipment that measures sap flow velocity in trees
Researchers measured sap flow velocity with heat ratio sensors installed on trees of different ages and species. USDA Forest Service photo by Chris Oishi.

Forest age and species composition vary widely in the southern Appalachian Mountains, due to legacies of land use and disturbances like repeat harvesting, fire exclusion, and invasive pests. In this highly productive region, leaf area recovers rapidly after harvesting, typically within five to ten years, while biomass accumulates more slowly and reaches peak basal area between 25 and 80 years.

Although tree-level water use should generally increase with size, age-related differences in transpiration rates are unknown for many species. To address this knowledge gap, researchers measured sap flow, throughfall, and evapotranspiration across a mesic cove forest: a young stand, a 15 year postharvest stand, a 35 year postharvest stand, and a ~200 year-old stand.

Total stand water use, or evapotranspiration, was similar among the 35 and 200 year-old stands but lower in the youngest stand. Among the two older stands, the 35 year-old stand had higher water use by trees, due to a large proportion of heavy water consuming species like red maple and tulip poplar. In contrast, the 200 year-old stand was dominated by lower water consuming oak species but compensated in total water use through precipitation intercepted by canopy leaves. These results suggest that predicted increases in the atmospheric demand for water and observed trends showing a decreasing proportion of oaks in this region could lead to greater forest water use in the future.

Principal Investigators
Christopher Oishi, Acting Team Leader, Research Ecologist
4353 - Center for Forest Watershed Research
Strategic Program Area
Water, Air, and Soil
Quantifying the effects of stand age on components of forest evapotranspiration
Research Partners
Chelcy Ford Miniat - Rocky Mountain Research Station
External Partners
Sander O. Dehnam - Indiana University
Steven T. Brantley - The Jones Center at Ichauway
Kimberly A. Novick - Indiana University
Paul V. Bolstad - University of Minnesota