Wednesday, November 15, 2006
298-1

Fire Frequency Effect on Greenhouse Gas Emissions and Belowground C and N Processes in Chaparral Shrublands.

Urszula Norton, Univ of California Davis, One Shields Ave, Davis, CA 95616, Jay B. Norton, Dept of Renewable Resources, Univ of Wyoming, 1000 E University Ave, Laramie, WY 87072, and William Horwath, Univ of California Davis, LAWR, 3226 PES Bldg, Davis, CA 95616-8627.

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. However, the information on the contribution of greenhouse gases (GHG) to the atmosphere from this biome is lacking. Historically, fire played a critical role in shaping the autosuccession of chaparral ecosystems, returning every 20-30 years on average in Sierra Nevada foothills. 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.  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. We hypothesize that fire-induced type conversion from dense brush to grass-shrub mosaic caused by repetitive short-recurrence-interval fires (every 4 years) in high fire hazard zones provides ecological benefits, which in turn, reduce flux of GHG to the atmosphere. The purpose of this research was to define the effects of 3 different fire return intervals (20-year, 4-year, and fire suppressed) in two predominant soil types (granitic and metabasic) on soil C and N dynamics and GHG flux. We will present a summary of 2-year seasonal inventory of GHG and soil C and N and assess its seasonal dynamics. Our preliminary data indicate that frequent, low intensity fires may not only reduce fire hazard but also lower the estimates of spring and summer GHG contributions.  However, extending the fire frequency to 20-years may not generate desirable effects on soil.  In addition, soils under chaparral at least double the capacity to consume methane during hot and dry seasons.