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The effects of elevated CO2, climate variability, and fire on the functioning of the chaparral of Southern California

The effects of elevated CO2, climate variability, and fire on the functioning of the chaparral of Southern California

Presented at MEDECOS XII Conference, July 6-9, 2011, Los Angeles, CA.

Oechel, Walter1,2, Alessandra Rossi1, Patrick Murphy1, John Kim3, Tom Bell1, Hongyan Luo4, David Lipson5

1Global Change Research Group, San Diego State University, San Diego, CA 92182, USA
2Fondazione Edmund Mach (FEM), Centro Ricerca e Innovazione (CRI), Via Edmund Mach, 138010 – San
Michele all’Adige (TN), Italy
3Field Station Program, College of Sciences, San Diego State University, San Diego, CA 92182, USA
4The National Ecological Observatory Network (NEON) Science Office, Boulder, CO 80301, USA
5Department of Biology, San Diego State University, San Diego, CA 92182, USA

Three decades of research on fire, climate change, and elevated atmospheric CO2 in the chaparral, a Mediterranean-type climate ecosystem, at San Diego State University’s Sky Oaks Biological Field Station, has provided information and insights that are useful to understanding controls on Mediterranean-type ecosystem functioning of southern California under current, and likely future, conditions.

Results from atmospheric carbon dioxide manipulations show that long-term stimulation of NEE, carbon sequestration, leaf area, fuel accumulation, and VOC production occur and that ecosystem composition, species reproduction, soil microbial composition, and plant-animal interactions, are affected by increased atmospheric carbon dioxide levels. Suggested is the fact that at least these water stressed ecosystems see increased water use efficiency and increased NPP over the long-term from elevated atmospheric carbon dioxide. More than a decade of measurement of net ecosystem exchange by eddy covariance demonstrates the long-term pattern of carbon exchange with stand age, and the short term impacts of variation in climate, especially precipitation, on stand water use and NEE. Annual variability in rainfall has profound affects on NEE, the impact of variation in annual rainfall on NEE lasts more than one year. The functioning of this ecosystem adjusts more quickly than does the composition of the ecosystem. Similarly, the sink strength of NEE following fire recovers more quickly than does community composition and percent above ground cover. The combined impacts of anticipated changes in atmospheric carbon dioxide and climate suggests changes in species composition and NPP. Fire intensity and/or frequency are anticipated to increase due to increases in weather conditions conducive to fire and increases in fuel accumulation due to higher atmospheric carbon dioxide levels.

These data show that old chaparral stands can be significant sinks for atmospheric CO2. And that managing for old growth chaparral can increase carbon sequestration while increasing biodiversity and habitat diversity.

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