HR: 0800h
AN: B41A-0177    [Abstracts]
TI: The Influence of Thinning on Components of Stand Water Balance in a Ponderosa Pine Forest Stand During and After Extreme Drought
AU: * Simonin, K
EM: ksmonin@berkeley.edu
AF: University of California Berkeley, Dept. of Integrative Biology, Valley Life Sciences Building, Berkeley, CA 94720-3140 United States
AU: Kolb, T
EM: Tom.Kolb@nau.edu
AF: Northern Arizona University, School of Forestry, Flagstaff, AZ 86011-5018 United States
AU: Helu, M
EM: Mario.Montes-helu@nau.edu
AF: Northern Arizona Univeristy, Department of Biological Sciences and Merriam Powell Center for Environmental Research, Flagstaff, AZ 86011-5018 United States
AU: Koch, G
EM: George.Koch@nau.edu
AF: Northern Arizona Univeristy, Department of Biological Sciences and Merriam Powell Center for Environmental Research, Flagstaff, AZ 86011-5018 United States
AB: To understand the effect of restoration thinning of ponderosa pine forests of the southwestern U.S, we compared the components of water balance between an unthinned plot and a thinned plot using a paired water balance approach. Forest overstory transpiration was estimated from tree sapflow scaled to the plot level. Understory herbaceous evapotranspiration was estimated from throughfall precipitation and changes in soil water content measured in trenched plots that excluded tree roots. The thinning treatment in 2001 reduced plot basal area by 82% and leaf area index by 41%. Stand-level evapotranspiration (ET), which includes overstory transpiraion and understory evaporation and transpiratio, was 72% higher in the thinned than the unthinned plot in 2002 when soil moisture was low due to drought. In spring 2003, when soil moisture was high due to recharge from late fall and winter precipitation throughfall (PT), ET of the thinned plot was 56% lower than the unthinned plot. Thinning also influenced the partitioning of ET between understory herbaceous evapotranspiration (ETU) and overstory transpiration (TO). During periods of low soil moisture (July 2002), ETU accounted for 92% of stand-level ET in the thinned plot compared to 74% in the unthinned plot. When soil moisture was higher (August 2002), ETU accounted for 75% of stand-level ET in both the thinned and unthinned plots due to increased TO. The following spring under wetter conditions (May 2003) ETU accounted for 48% of stand-level ET in the thinned plot compared to 28% in the unthinned plot. Our results highlight the importance of moisture availability and climate as factors determining the impact of thinning on water balance in southwestern ponderosa pine forests.
DE: 0495 Water/energy interactions (1878)
DE: 1813 Eco-hydrology
SC: Biogeosciences [B]
MN: Fall Meeting 2005