HR: 14:15h
AN: H32E-02    [PDF]
TI: Interannual Variation in Stand Transpiration is Dependent Upon Tree Species
AU: * Ewers, B E
EM: beewers@uwyo.edu
AF: University of Wyoming, Department of Botany 16th and Gibbon, Laramie, WY 82070 United States
AU: Mackay, D S
EM: dsmackay@buffalo.edu
AF: State University at Buffalo, Department of Geography 105 Wilkeson Quad., Buffalo, NY 14261 United States
AU: Burrows, S N
EM: sburrows@ascendanalytics.com
AF: Ascend Analytics, 221 Stonehaven Circle, Newfield, NY 14867 United States
AU: Ahl, D E
EM: deahl@wisc.edu
AF: University of Wisconsin, Dept of Forest Eco. & Mgt. 1630 Linden Dr., Madison, WI 53718 United States
AU: Samanta, S
EM: ssamanta@wisc.edu
AF: University of Wisconsin, Dept of Forest Eco. & Mgt. 1630 Linden Dr., Madison, WI 53718 United States
AB: In order to successfully predict transpirational water fluxes from forested watersheds, interannual variability in transpiration must be quantified and understood. In a heterogeneous forested landscape in northern Wisconsin, we quantified stand transpiration across four forest cover types representing more than 80 percent of the land area in order to 1) quantify differences in stand transpiration and leaf area over two years and 2) determine the mechanisms governing the changes in transpiration over two years. We measured sap flux in eight trees of each tree species in the four cover types. We found that in northern hardwoods, the leaf area of sugar maple increased between the two measurement years with transpiration per unit ground area increasing even more than could be explained by leaf area. In an aspen stand, tent caterpillars completely defoliated the stand for approximately a month until a new set of leaves flushed out. The new set of leaves resulted in a lower leaf area but the same transpiration per unit leaf area indicating there was no physiological compensation for the lower leaf area. At the same time, balsam fir growing underneath the aspen increased their transpiration rate in response to greater light penetration through the dominant aspen canopy Red pine had a thirty percent change in leaf area within a growing season due to multiple cohorts of leaves and transpiration followed this leaf area dynamic. In a forested wetland, white cedar transpiration was proportional to surface water depth between the two years. Despite the specific tree species' effects on stand transpiration, all species displayed a minimum water potential regulation resulting in a saturating response of transpiration to vapor pressure deficit that did not vary across the two years. This physiological set point will allow future water flux models to explain mechanistically interannual variability in transpiration of this and similar forests.
DE: 1818 Evapotranspiration
DE: 1851 Plant ecology
DE: 1890 Wetlands
SC: Hydrology [H]
MN: 2003 Fall Meeting