The UC Hill Area Fire Management Plan is a long-range (1987-1991) plan designed to reduce the fire hazard in the hill area by reducing the fuel volume as well as restoring a more "natural" vegetative community such as existed prior to the arrival of Spanish settlers. The plan is to use prescribed bums, pruning, and selective herbicide treatment to reduce north coastal scrub and eucalyptus sprouts and subsequently seed these areas with native perennial grasses. The cdnversion of brush and eucalyptus to grassland should result in increased groundwater recharge in the hills which could subsequently beneficially increase the baseflow of Strawberry Creek.
Specific vegetative management prescriptions vary according to the vegetative cover type. In conifer stands, 50% of the duff will be removed by burning and a minimal understory will be maintained. North coastal scrub areas invading grasslands will be limited to 20% cover mainly on rocky areas of shallow soil. This will be acheived by prescribed bums and subsequent seeding with native perennial grass. North coastal scrub on wet north aspects will be replaced with coast redwood in areas of convex topography. Eucalyptus sprouts will be eliminated by felling the boles and treating the stumps with herbicide. Cutting will be concentrated from September through January and slash will be burned as soon as practicable. Native perennial grass will be seeded after the burn. In mature eucalyptus stands, the shrub tree understory will be eliminated by burning and seeded with native perennial grass. No burning will be done below the lower fire trial.
The Hill Area plan presents several water quality concerns. The primary concern is that increased soil erosion will occur. The hill area soils are generally heavy clay soils that have high runoff and erosion potential. Numerous landslide and colluvial bodies are also located in the canyon. Erodibility of these soils is primarily a function of vegetative cover. The Hill Area plan will result in a reduction of canopy cover and shrubby ground cover as well as a reduction in the depth of the litter or duff layer in some areas. All these factors will serve to reduce the amount of woody vegetation and organic material available to intercept rainfall. The overall effects of these practices will generally be to increase rainfall energy at the ground surf ace resulting in soil compaction and increased surface runoff. Therefore, infiltration will decrease and the soil erosion potential will increase.
The roots of woody vegetation increase the cohesiveness of the soil which in tum increases the shear strength of the soil. The rotting of root systems and stumps over time could decrease the shear strength of the soil, resulting in higher erosion and landslide potential. In addition, the stems of woody vegetation tend to break up the velocity of overland flow more effectively than grass which could result in greater distances of relatively unimpeded surf ace flow causing higher erosion potential.
Prescribed burning also poses some hazards. Burning may consume the litter or duff layer and expose bare soils, especially if the fuel is heavy and/or conditions are quite dry. Extremely hot fires can possibly result in hydrophobic soil conditions where soils become more impermeable because of condensation of volatile organic compounds during burning which leaves a thin waxy impervious layer in the soil. Although prescribed burning is a valuable vegetation management tool, its improper or untimely use can result in increased surface runoff and subsequent soil erosion.
Vegetative cover such as seeding of native perennial grasses should be established as soon as possible after prescribed burning or other vegetative removal. Areas where management activities have occurred should be carefully monitored for soil erosion and appropriate actions including ongoing evaluation of the management practices should be undertaken. Prescribed burning should be conducted under carefully controlled conditions to prevent the exposure of bare soil. Finally, management activities resulting in removal of vegetation should be avoided during the rainy season to allow time for revegetation before heavy rainfall occurs.