Native plant advocates claim that native wildlife benefits from native plant restorations. There is an intuitive logic that native animals require native plants. After all, didn’t they “evolve together?” In this post we will evaluate this claim, using our own eyes and what little scientific evidence is available about interactions between plants and animals. The scientific literature informs us that wildlife does not necessarily benefit from native plant restorations and sometimes they are harmed by them. The assumption that native animals are dependent upon native plants underestimates both the ability of animals to adapt to changing conditions and the harm caused by methods used to eradicate non-native vegetation.
Art Shapiro (UC Davis) has been studying California butterflies for over 35 years. His observations as well as the work of other scientists have informed him that “…the extensive adoption of introduced host plants has clearly been beneficial for a significant segment of the California butterfly fauna, including most of the familiar species of urban, suburban and agricultural environments. Some of these species are now almost completely dependent on exotics and would disappear were weed control more effective than it currently is.” (1)
He explains that this is particularly true on the coast of California because this is where the highest concentration of introduced species of plants is naturalized and the butterfly population is less diverse because of the cool, foggy climate. There are apparently few non-native plants in the desert and alpine regions of California and so butterflies in those regions have not had the opportunity or need to adapt to new plants.
The most conspicuous example of a butterfly making use of an introduced plant is the migrating Monarch which overwinters in eucalypts in many locations on the coast of California. A study of 180 of those locations found that 75% of the trees in which monarchs roost in the winter are eucalyptus.
Professor Shapiro also speculates that other insects have adapted to non-native plants as well: “Introduced hosts, having a broader geographic range than native hosts, may permit the expansion of the insect population geographically.”
Birds have also adapted to non-native plants and trees. Researchers at UC Davis surveyed over 1,000 ornithologists in 4 states, including California, about their observations of native birds and non-native plants. Responses from 173 ornithologists reported 1,143 “interactions” of birds with introduced plants considered invasive. Forty-seven percent (47%) of those interactions were birds eating the fruit or seeds of those non-native plants and trees. Other interactions were nesting, perching, gleaning (eating insects), etc. (2)
Interactions were frequently reported in non-native blackberry, which is found in most parks in San Francisco. It is one of the most productive food sources for birds in San Francisco. Unfortunately, it is being eradicated in many parks because it is non-native. Since the birds eat it in one location and “deposit” its seeds in other locations, complete eradication of this important food source for wildlife seems unlikely.
The non-native blackberry also provides cover for wildlife. It is an impenetrable bramble both physically and visually. Birds and small mammals hide and make nests and dens in these thickets. Coyotes are resident in San Francisco. The thick undergrowth which has been removed in some parks by the Natural Areas Program now allows unleashed dogs to pursue them in areas where they were protected before. If the safe havens of urban wildlife are destroyed, the animals may seek shelter elsewhere, a move that may be dangerous for them. For more information about the rich family life of coyotes in San Francisco and what you can do to protect them, visit the CoyoteYipps blog.
Native plant restorations also require the use of herbicides to eradicate non-native trees and plants. Herbicides are sprayed on the blackberries that are a major food source for wildlife. UCSF, when announcing its intention to destroy much of the forest and its understory on Mt. Sutro, has said that herbicides (Garlon and Roundup) must be used to implement their plans. (Update: UCSF recently made a commitment to NOT using herbicides on Mount Sutro.) Herbicides are used by most managers of public land to eradicate non-native plants, including by the Natural Areas Program in SF, the East Bay Regional Park District, and federal lands in the Bay Area such as GGNRA and Pt Reyes National Seashore.
We have described in other posts the harmful effects of herbicides on the environment and the animals that occupy it so we won’t repeat that information here. We will only add that one study performed by the US Forest Service for the EPA reported that exposure to Garlon significantly reduced the reproductive success of birds. (3)
The Natural Areas Program in San Francisco is committed to the restoration of native plants to the city’s parks. It is not designed to benefit the animals that most urban dwellers call “wildlife.” Their management plan categorizes native raccoons and skunks as “subsidized predators,” along with a long list of non-native wildlife such as opossums. They recommend “control” of all of these animals if they have an effect on native wildlife populations. “Control” in this context should be interpreted as extermination.
Legally protected species such as Red-Legged Frog, San Francisco Garter Snake, Mission Blue Butterfly, and Western Pond Turtle are the only wildlife of interest to the Natural Areas Program. Extensive efforts are made to reintroduce these legally protected species to the parks of San Francisco. Why? Because the legal protections for rare animals are much stronger than the legal protections for plants. If a population of legally protected animals can be established, drastic measures are required to maintain them. For example, toxic herbicides that are otherwise banned by the SF Department of the Environment are permitted on Twin Peaks because the Mission Blue Butterfly has been reintroduced there. Prescribed burns are required on San Bruno Mountain because the Mission Blue exists there. Trees are being destroyed on Hawk Hill in Marin County because habitat for the Mission Blue is being restored there. The migrating raptors that use these trees do not have the legal status of the endangered butterfly, so their needs are secondary.
In other words, the native plant movement is selective about its interest in wildlife. Their interest is primarily in rare, native animals. Animal competitors of legally protected animals are eradicated. Animals that have adapted to non-native vegetation must move or die if their food source is destroyed by native plant “restorations.”
Micro-managing nature benefits few animals, least of all humans who watch their parks being torn apart by an ideology that is destructive at its core.
(1) SD Graves and AM Shapiro, “Exotics as host plants of the California butterfly fauna,” Biological Conservation, 110 (2003) 413-433
(2) CE Aslan and E Rejmanek, “Avian use of introduced plants: Ornithologist records illustrate interspecific associations and research needs,” Ecological Applications, 20(4), 2010, 1005-1020
(3) Marin Municipal Water District, Herbicide Risk Assessment, page 4-24.