Wednesday, November 15, 2006

Soil Carbon Storage, Fuel Loads, and Runoff in Four Fire Regimes in Chaparral Shrublands of the Sierra Nevada Foothills.

Jay B. Norton, Dept of Renewable Resources, Univ of Wyoming, 1000 E University Ave, Laramie, WY 87072-3354, William R. Horwath, Univ of California, Davis, Dept of Land, Air, & Water Resources, One Shields Ave, Davis, CA 95616-8627, and Urszula Norton, Univ of California, Davis, Dept of Land, Air & Water Resources, One Shields Ave, Davis, CA 95616-8627.

With cessation of frequent “rancher burns” – prescribed fires to improve forage – in the 1960s due to increased residential development, the occurrence of dangerous fuel loads increased dramatically in foothill chaparral shrublands. While prescribed fire is the only feasible way to reduce fuel loads in rugged and isolated terrain, concerns about smoke and ecological impacts make burning increasingly difficult to achieve. But the ability to manage vegetation in strategic zones, on steep slopes below forest communities for instance, is crucial for fire management agencies. Our objective was to measure sustainability, fuel loading, and ecological impacts of four recent fire frequencies. We analyzed soil organic matter (SOM) fractions, plant community composition, and runoff/erosion across four fire history scenarios: 1) long-term fire-suppressed; 2) 20-year wildfire frequency (1950-1972-1992); 3) four-year wildfire frequency (1997-2001); and 4) one-time wildfire (2001). We replicated these sampling areas on two soil types ubiquitous to Sierra Nevada Foothills chaparral: soil derived from residuum of granite, and basic igneous and metamorphic rocks. Results of vegetation analyses show that a second fire four years after the first killed many resprouting shrubs and resulted in herbaceous ground cover in a grass-shrub mosaic. Compared to fires in dense, decadent growth of fire-suppressed shrublands, fires in this type of vegetation cover are much easier to control from the air. Prescribed burning to maintain lower fuel loads is much easier to achieve in such grass-shrub mosaics. Increased diversity in plant species and growth form relative to fire-suppressed shrublands may be beneficial to wildlife and may decrease smoke production during fires. Initial results of SOM fractionation suggest that the four-year treatment increased slow and passive pools, which should improve resistance to erosion. Runoff and erosion rates were variable, but runoff from fire-suppressed sites was much richer in dissolved nitrogen, carbon, and phosphorus.

Handout (.ppt format, 1857.0 kb)