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.