Rooting and Foraging Effects of Wild Pigs on Tree Regeneration and Acorn Survival in California's Oak Woodland Ecosystems

Wild pigs (Sus scrofa) have been widely distributed by humans and significant populations now occur in oak-dominated ecosystems in California. Because they are omnivorous and forage by rooting, wild pigs have the potential to impact a wide variety of plants and animals directly by consumption and indirectly through disturbance. In 1998, we initiated a long-term study of the ecological effects of wild pigs on oak woodland ecosystems in California using multiple exclosures with paired control plots targeting four oak communities in the north and central coast region of California that vary in population density of wild pigs. Soil disturbance by wild pigs was significantly higher in areas where wild pig densities are high. Rooting significantly reduced aboveground plant biomass in oak grassland and oak woodland habitats, and may therefore reduce forage availability for herbivores in areas with widespread rooting. Rooting disturbance may be significantly reducing survival of tree seedlings, thereby limiting tree regeneration in oak woodlands. Experimental plots associated with high masting oak trees indicated that wild pigs significantly reduced acorn survival and, therefore, reduced the availability of acorns for germination and consumption by native wildlife.