USING GEOLOGIC MAPS AND HYDROLOGIC MONITORING TO ADDRESS LEGACY GRAZING IMPACTS ON EROSION IN CHANNEL ISLANDS NATIONAL PARK, CALIFORNIA

Channel Islands National Park, California experienced ~150 years of livestock grazing converting vast areas of perennial-dominated native plant communities to exotic, largely annual-dominated vegetation. Pre-European native perennial scrub was typified by deeper, larger diameter and hence stronger roots relative to exotic annuals and grasslands that now cover most of the landscape. This conversion changed the mass wasting regime elevating sediment transport rates. Decreased trapping efficiency of grasses and increased sediment transport preclude the establishment of soil and vegetation cover, resulting in an inability to store organic matter carbon and reduced infiltration and groundwater delivery. As a result, steep uplands and some road segments are unstable and at heightened erosion risk, archaeological sites are exposed and vulnerable, natural recovery of native vegetation is hindered, and infiltration of rainfall and surface water percolation into groundwater sustaining base flow in streams and island operations is decreased. Although ranching has ended, introduced grazing animals are extirpated, and the islands are now managed for conservation and ecosystem recovery, the legacy of heightened erosion remains.

Land use managers benefit from knowledge of where mass wasting processes are concentrated, what processes transport sediment, how vegetation and their associated root structure influence shallow landslide susceptibility, and what controls the presence of surface water for ecosystem health. The U.S. Geological Survey assists National Park Service colleagues to identify and manage erosion-prone areas and restoration strategies with maps of Quaternary surficial geology, bedrock geology, and vegetation. New Quaternary geology maps, portraying spatial regolith cover with estimates of relative thickness, provide constraints of where soil substrate for plant growth is present. A key component of restoration employs fog moisture to sustain juvenile plants during the dry Mediterranean summer climate. The U.S. Geological Survey provides monitoring arrays measuring rainfall, fog delivery, soil water content and water suction to evaluate relative effectiveness of fog-water harvesting strategies for naturally sustainable restoration.