A primary purpose of the Department is to preserve the state's extraordinary biological diversity by restoring, maintaining, and protecting native species and natural communities. Invasion by exotic species is a threat to native species and natural environmental complexes.

Exotic species are those that occupy or could occupy State Park System lands as a result of deliberate or accidental human activities. Exotic species are also referred to as non-native, alien, or invasive species. When an exotic species does not evolve in concert with the species native to a particular place, it is not a natural component of that particular ecosystem. For example, Monterey pine is native to a restricted section of the California coast, but acts as an aggressive exotic plant outside its natural range. By contrast, native species are those that occur on State Park System lands as a result of natural processes. Native species have evolved together for thousands of years and are continuing to evolve together.

Some exotic species have the ability to significantly alter native environmental complexes. Exotic vegetation often competes aggressively and successfully with the natural vegetation, upsetting ecosystems, supplanting native plants, and altering natural scenes. Exotic vegetation may occur in either the terrestrial or aquatic environment. Similarly, exotic animals may also occur in the terrestrial or aquatic environment. They may out-compete native species for food or habitat, may prey upon native species, or parasitize their nests causing the decline or extirpation of the native population.

California State Park's resource management policies call for preservation and restoration of native plants and animals and systematic removal of populations of exotics in wildland settings in the State Park System. Using a variety of methods, and often a helping hand from volunteer organizations, the Department strives to protect sensitive species and preserve examples of the unique and diverse ecosystems that make up the rich natural history of this state for present and future generations.