Three major fires occurred in the foothills and mountains above the greater Santa Barbara area in 2008 and 2009, all within watersheds with on-going, multiyear measurements. Because high rainfall is expected during the El Nino conditions forecasted for 2009-2010, burned ecosystems will show their greatest responses this year and afford an excellent opportunity to examine the effects of fire on terrestrial and stream ecosystems. Measurements will be made of short-term changes in burned and unburned watersheds, comparing the influence of fires on a variety of ecological and environmental responses including: stream discharge and the export of sediment and nutrients, soil movement and landslides, re-growth of vegetation at the watershed-scale using high resolution remote sensing and at the transect-scale by direct measurements of re-sprouting plants, and stream biota and ecosystem processes.
Modeling will permit prediction of flooding, soil movements, and stream water quality across a range of climatic conditions during post-fire periods. This information will be of value to natural resource managers and public safety officials. Participation in public meetings will further disseminate the findings. In addition, three graduate and four undergraduate students will gain invaluable experience in watershed ecology, hydrology and management.
Wildfires are a common occurrence in southern California coastal regions. While impacts on vegetation are conspicuous, fires influence many other aspects of the environment. Subsequent to three wildfires in the foothills and mountains above Santa Barbara (California) between summer 2008 and spring 2009, an integrated study of vegetation, hydrology, geomorphology, soils, aquatic ecology and export of nutrients and suspended sediment to coastal waters was conducted. A series of images obtained with an airborne imaging instrument that remotely sensed reflected light in visible and near infra-red wavelengths allowed characterization of the vegetation and impacts of the fires over the whole area burned in comparison to unburned neighboring areas. To aid interpretation of the remotely sensed imagery, the species of plants and their coverage and biomass were sampled on the ground, though the steep terrain made access challenging. To obtain detailed information about erosion, an airborne laser detection and ranging system was deployed just after the largest fire in autumn 2009 and again after the rainy season in summer 2010. To determine the amount of material carried by streams to the coastal ocean, measurements of flow and concentrations of nutrients were made in the creeks draining the mountains. The remotely sensed imagery indicated that the type of shrubs had little impact on the spread of the fires, though moist vegetation, such as stream-side areas and orchards did restrict fire spread. The multiple wavelengths detected with the imaging system allowed clear identification of areas covered with ash and estimates of the severity of the fires. Plant regrowth within the burned areas was highly variable, though it was generally vigorous in most sites in the first year after the fires, except in areas that had burned twice and the highest elevation sites where burn intensity was high. Herbaceous vegetation accounted for between 5 and 90% of the biomass in the first year. Most of the percent cover in spring was a single species of native vine that was absent prior to the burn and also was absent in unburned areas. Shrub re-sprouting was vigorous with more than 60% of burned stumps re-sprouting even in high intensity sites. Exotic plants were mostly lacking across all sites. Fire-unaffected regions had very low erosion rates, but fire-affected regions had greater than 0.5 m channel incision in some places due to unobstructed overland flow that resulted in high flow velocities and low infiltration of water into the soil. Soil samples collected after fire and prior to the onset of rain were enriched in ammonium, presumably due to ash residue deposition. Rain storms then stimulated microbial activity that converted ammonium to nitrate. After fires, the concentrations of ammonium and nitrate in stream water increased dramatically. As the sequence of rain storms, typical of the rainy season, progressed though the season, the concentrations of nutrients decreased. Within streams located in and below burned areas, large amounts of sediment were deposited during the rainy season, but most of this sediment was washed out of streams during the second rainy season following the fire. Trout populations in burned basins nearly disappeared, but remained at fairly constant levels in unburned basins. The abundance of algae in streams in or below burned areas decreased during the first major storm after the fires, but after the rainy season ended, it was greater in streams where the stream-side vegetation had burned and the canopy was opened than in burned sites where the stream-side vegetation was not burned or in unburned sites. Aquatic insects in basins where upland but not stream-side zones burned were similar to those in unburned basins within 2 to 3 years after fires; however, assemblages in basins where both the upland and stream-side zones burned remained different from those in other basins after 2 to 3 years. Analysis of stable isotope signatures for hydrogen and carbon for leaf litter, algae, and invertebrates from streams draining basins in degrees of burning indicate that the effects of fire on stream food webs are driven by fire effects on stream-side vegetation, with algal-based food webs dominating in streams where the stream-side vegetation burned and detrital-based food webs dominating in streams where the stream-side vegetation remained intact.
