Tuesday, 8 November 2005
4

Assessing Seasonal Greenhouse Gas Emissions and Belowground C and N Processes under Different Fire Frequencies in Soils of Sierra Nevada Chaparral Shrublands.

Urszula Norton1, William R. Horwath1, Jay B. Norton2, and Timothy A. Doane1. (1) LAWR University of California Davis, Davis, CA 95616, (2) Univeristy of California Cooperative Extension Tuolomne County, 2 South Green Street, Sonora, CA 95370

Chaparral shrubland covers over 13 million acres in California, accounting for 13% of the total land area. It spans a wide geoclimatic range from the southern and central coast to the Sierra Nevada foothills. Unlike many other biomes in California, carbon and nitrogen dynamics in this ecosystem are poorly characterized. Specifically, information on the contribution of greenhouse gases to the atmosphere is lacking. Historically, fire played a critical role in shaping the autosuccession of fire-adapted chaparral ecosystems, returning every 30-40 years on average in central and southern California chaparral. The Sierra Nevada foothills probably had significantly shorter fire intervals because of somewhat higher incidence of lightning. However, as this ecosystem undergoes rapid human population growth and increasing commercial and residential development, often coupled with strict fire suppression policies, there is need for better understanding of how resulting ecological changes impact chaparral ecosystem resiliency and sustainability. Seasonal measurements of trace gas emissions across predominate fire-management-derived vegetation scenarios and soils of the Sierra Nevada foothills provide much needed information that can vary greatly during the year and across the landscape. Trace gas measurements are not only sensitive to management, but can also change depending on specific attributes of different soils. Predominate soils in the foothills formed in several distinct parent materials associated with the complex geology of the west slope of the Sierra Nevada. Soils vary markedly in texture, porosity, organic matter content and other attributes. We will present initial phase of the inventory of trace gas emissions from the foothill chaparral ecosystem across a variety of Sierra Nevada soils and assess its seasonal dynamics. We hypothesize that fire-induced type conversion from dense brush to grass-shrub mosaic caused by recent repetitive short-recurrence-interval fires provides ecological benefits, such as improved soil quality, which in turn, reduces flux of greenhouse gases to the atmosphere.

Handout (.pdf format, 1452.0 kb)

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