HR: 14:10h
AN: B12E-03    [PDF]
TI: Effect of Climate Variability and Management Practices on Carbon, Water and Energy Fluxes of a Young Ponderosa Pine Plantation at the Blodgett Forest Ameriflux Site
AU: * Misson, L
EM: lmisson@nature.berkeley.edu
AF: University of California, Berkeley, 151 Hilgard Hall, Berkeley, Ca 94720-3110 United States
AU: McKay, M
EM: megan@nature.berkeley.edu
AF: University of California, Berkeley, 151 Hilgard Hall, Berkeley, Ca 94720-3110 United States
AU: Goldstein, A H
EM: ahg@nature.berkeley.edu
AF: University of California, Berkeley, 151 Hilgard Hall, Berkeley, Ca 94720-3110 United States
AB: Our research at Blodgett Forest in the Sierra Nevada mountains of California seeks to better understand how fluxes of CO2, H2O, and energy in a mid-elevation, young pine plantation change interannually in response to climate variability, and how they are impacted by management practices such as shrub removal and thinning. Ecosystem scale fluxes have been measured by the eddy covariance method since 1997, along with meteorological parameters. During winter, the young Ponderosa pine plantation at Blodgett acted mainly as a sink of carbon. Strong variations in winter carbon sequestration occurred due to changes in leaf area index and frequency of freezing temperatures. Interannual variations in springtime carbon flux occurred mainly due to differences in the timing of seasonally increasing temperatures. Drought is a regular feature of the California climate, making water availability the major controller of gas exchange in summer and fall. In late summer 2001, drought stress reduced ecosystem carbon uptake by 1/5, while the Bowen ratio increased by 1/3. Thinning is a widespread procedure in plantation management carried out to reduce stand density, improve forest health, and optimize tree growth. In spring 2000, 2/3 of the trees were removed by mastication, the process of mechanically chewing up unwanted trees, which is becoming a widespread method for pre-commercial thinning in the U.S. During and after thinning, the plantation remained a sink of carbon. Thinning at the Blodgett site reduced the leaf area index from ~3 to ~1.5 m2 m-2, and created branch and stem debris of 400-500 g m-2. During summer 2000, mastication decreased ecosystem carbon uptake by 1/3. Ecosystem water use efficiency decreased by 1/5 and the Bowen ratio increased by 1/3. This indicates the increasing heat lost as sensible versus latent heat as the water flux decreased due to the reduction in leaf area index. After thinning, leaf area index rapidly increased to ~2.5 m2 m-2 by the end of 2000, and to ~3.5 m2 m-2 in 2001. As a result, the uptake of carbon by the ecosystem increased by 1/3 in early summer 2001 in comparison to the pre-thinning value. By summer 2001 the Bowen ratio returned to its pre-thinning value, and the ecosystem water use efficiency increased by 1/3. Higher ecosystem water use efficiency was maintained in summer 2002 and 2003, indicating that the thinning led to better optimization of ecosystem water use for at least the following three years, increasing the ratio of carbon gained to water lost over the growing season.
DE: 0315 Biosphere/atmosphere interactions
DE: 0322 Constituent sources and sinks
DE: 0400 Biogeosciences
DE: 1630 Impact phenomena
DE: 1803 Anthropogenic effects
SC: Biogeosciences [B]
MN: 2003 Fall Meeting