Document: BRI-3-30-31

Modeling tree stem temperature to estimate wood respiration.

KLOEPPEL, B.D.* 1, M.C.FREEMAN 2 and P.V.BOLSTAD 3

University of Georgia, Athens, GA 30602 USA 1
Wesleyan University, Middletown, CT 06459 USA 2
University of Minnesota, St. Paul, MN 55108 USA 3

Abstract:
Forest carbon cycling has received increasing attention as hypotheses related to global climate change are tested to predict long-term environmental effects. While forest carbon pools at the stand level are relatively easy to estimate, forest carbon fluxes remain difficult to estimate due to multiple driving variables. The woody respiration of southern Appalachian forests has been estimated by invoking a stratified random sampling design including forest stands in three topographic positions (ridge, midslope, and cove) and three age classes (200+ years, ~100 years, ~20 years). Allometric relationships were developed and used to scale measurements to the tree level. Stand biometric data were used to scale respiration estimates to the stand level. Relationships relating stem temperature to air temperature were needed to estimate stem wood respiration flux. Four sites measuring air temperature and stem temperature on 25 or more trees were established on north and south facing slopes in mature and old growth study sites. Four potential models were evaluated to predict stem temperature from climate station air temperature data: Lag, sinusoidal curve, single tree regression, and whole site regression. Single tree analyses indicated that up to 94.8 % of the variation in stem temperature data was explained by air temperature whereas sensor aspect, tree height, tree diameter, and topographic position explained only minimal variation. Previous data sets indicate that stem respiration Q10 values ranged from 1.63 in red maple to 2.57 in chestnut oak. Summarized calculations of woody respiration for nine southern Appalachian forest stands ranged from 305 to 770 g m-2 soil year-1.

Keywords: tree stem temperature, tree stem respiration, air temperature

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This abstract is being presented at: 10:30 AM in session:
Oral Session #9: Respiration and Isotopes.