PARENT SESSION
Oral Session #27: Fire Ecology.
Presiding: C. Allen
Tuesday, August 6. 8:00 AM to 11:30 AM. Graham Meeting Room, TCC.
Stand age and seasonal effects on chaparral ecosystem carbon flux.
Sims, Daniel*,1, Schmidts, Miriam1, Gamon, John1, 1 California State University, Los Angeles, CA
ABSTRACT- Frequent fires result in heterogeneous mosaics of stand age in Southern California chaparral. Observations of vegetation regeneration after fire have suggested that productivity increases during the initial regeneration phase, peaks around 20 years after fire and then slowly declines. We used a combination of remote sensing and physiological measurements to estimate variation in carbon flux over an annual cycle and across stand ages ranging from 0 to 40 years in the Santa Monica Mountains. Spectral reflectance was measured monthly along 100 m transects. In addition, leaf reflectance and photosynthetic rates were measured for Adenostoma fasciculatum and Ceanothus spp. Ecosystem carbon exchange was estimated directly from transect spectral reflectance using a model parameterized with eddy covariance data. Scaling of branch photosynthetic rates to the stand level was also used to estimate carbon exchange. Both methods indicated that peak ecosystem carbon gain occurred about 20 years after fire with some decline in older stands. Most of this variation resulted from changes in plant cover rather than changes in photosynthetic rates. There were no significant changes in photosynthesis with stand age for Adenostoma. However, Ceanothus photosynthesis showed a negative relationship with stand age in spring, when photosynthetic rates were the highest, but a positive relationship in fall when rates were lowest. The results will be discussed in terms of the potential for assessing stand age effects on regional carbon gain.
KEY WORDS: light use efficiency, PRI, NDVI