Carbon Balance Studies in Chaparral Shrubs: Implications for Biomass Production1

Research Professor, Systems Ecology Research Group, San Diego State University, San Diego, Calif., 92182. Abstract: Photosynthesis and respiration rates were determined for chaparral shrubs as a function of temperature and/or light intensity. In mature stands at Echo Valley, Calif., net seasonal carbon assimilation by leaves ranges -2 from a dry weight equivalent of 673 g m -1 in -2 pure stands of Rhus ovata to 1439 g m y in Arctostaphylos glauca. Net accumulation of dry -2 matter ranges from 261 g m y for R. ovata to -2 525 g m y for A. glauca. Stem respiration utilizes about 30 percent of the assimilated carbon; total respiration accounts for about 60 percent of the carbon assimilated. This data and growth models are used to calculate optimal harvest intervals and productivity of shrubs. There is considerable energy available for harvesting in chaparral biomass. Each year, on the average, about 3 percent of California's 3.3 million hectares of chaparral burns. Using values from Riggan and Dunn (In press), at an average biomass of 50 m tons per hectare this 100,000 hectares burned represents the gross energy equivalent of 18.2 x 10 barrels of oil or 546 million dollars at current oil prices. This is roughly the energy equivalent of 2 Hoover Dams or 1/2 of the on shore oil production of the central California coast (2 X 10 kcal of renewable energy, McCartor 1976).