The war on so-called “invasive species” continues to escalate. One of the indicators of this escalation is the recently revised California Invasive Plant Council’s (Cal-IPC) inventory of “invasive” plants. Nearly 100 plant species were added, a 50% increase in the inventory.
More alarming is that most of the additions to the list are not considered “invasive” in California. Rather, a new category of “potentially” invasive plants was created, based on their behavior elsewhere. Many of the plants in the new category are considered invasive in Hawaii, a place with a distinctly different climate than California. Hawaii is a tropical climate, hotter than much of California and wetter and more humid than everywhere in California.
The big increase in the number of plant species now designated as “invasive” in California is a concern partly because of the herbicides that are usually used to eradicate them. Not only do we lose that plant species in our landscape when it is added to the hit list, we can also expect to see an increase in the use of the herbicides that are used to kill it.
Increased use of herbicides
Native plant advocates are aggressively defending the use of herbicides. Policies and practices are being developed to accommodate increased use of herbicides on our public lands.
East Bay Municipal Utilities District (EBMUD) is evaluating its Integrated Pest Management Program (IPM), including practices and policies regarding pesticide use. The first draft of EBMUD’s revised IPM program was made available to the public in July 2017. The draft adds several new goals to the IPM program: “habitat protection and restoration,” reducing populations of “invasive plant species,” and “use of alternative vegetation such as native plants.” EBMUD is the supplier of our drinking water in the East Bay and the quality of the water they supply should be the top—if not the only—priority. If destroying non-native plants requires greater use of herbicides, that goal contradicts EBMUD’s obligation to providing safe drinking water.
San Francisco’s IPM program has also changed some policies to accommodate use of herbicides in parks on plants the Natural Resource Division of the parks department considers “invasive.” The parks department restricts all park access to the established trails in the 33 “natural areas” where non-native plants are eradicated and replaced by native plants. The new IPM policy permits the spraying of herbicides without posting pesticide application notices in places that are “publicly inaccessible.” In other words, pesticide application notices are no longer required in the “natural areas” unless herbicides are sprayed on the trails. One way to reduce the public’s opposition to pesticides is to hide their use and this policy seems designed to do that.
Update: The San Francisco Forest Alliance (SFFA) has informed me that Chris Geiger, head of San Francisco’s IPM program, has given assurances that the IPM program will no longer offer City departments a blanket exemption to apply herbicides without posting in areas the department considers “publicly inaccessible”. Previous to this, each land manager was empowered to make their own decisions as to which areas they considered “publicly inaccessible”. The IPM group did not provide oversight of the decisions or keep records of which areas were exempted. Now specific exemptions will be issued and recorded on the IPM exemptions webpage. Chris Geiger reports RPD will not be requesting any posting exemptions. SFFA is still waiting for formal written documentation of this change.
San Francisco’s IPM Program is also demonstrating its commitment to native plants and the eradication of non-native plants by sponsoring a webinar on October 5th, 2017, featuring Doug Tallamy: “The Plant-Pollinator Connection: Why Pollinators Need Native Plants.” Tallamy is the academic entomologist who has devoted his career to the promotion of native plants based on his claim that insects at the base of the food web are dependent upon native plants. He has said in many publications that non-native plants will cause the collapse of our ecosystems. Many of the statements he makes in support of his dire theory are not accurate.
This post will focus on the intersection of these symptoms of the escalating war on “invasive” plants: the expansion of California’s inventory of “invasive” plants and the closely associated claim that non-native plants must be eradicated because they compete with the native plants required by wildlife. We use buddleia, commonly known as butterfly bush, as an example.
Butterfly Bush (Buddleia): friend or enemy of butterflies?
Buddleia is one of 87 plant species recently added to Cal-IPC’s inventory of “invasive” plant because it is considered invasive outside of California. Buddleia is called butterfly bush because it produces large quantities of nectar that attract swarms of butterflies. Since buddleia is very appealing to butterflies, it is popular with gardeners who like to see butterflies in their gardens.
Since buddleia is obviously useful to butterflies and Doug Tallamy claims to be concerned about the welfare of our pollinators, why is he telling gardeners to quit planting buddleia? His advice is based on the fact that buddleia is considered invasive in some places and his belief that it will eventually be invasive everywhere. In fact, that’s his belief about all non-native plants: they may not be invasive now, but he predicts that eventually they all will be invasive.
Secondly, Tallamy argues that although buddleia provides food for butterflies, it is not a host plant for butterflies. The host plant is where butterflies lay their eggs and where the caterpillar feeds when the eggs hatch. The choice of host plant species is much smaller than the number of food plant species available to butterflies, but it is not as small as Tallamy thinks it is. Tallamy does not seem to realize that many plants are chemically similar, which enables butterflies to make a transition from a native plant to a chemically similar non-native plant. Here in California, many butterfly species have made that transition and a few butterfly species are dependent upon abundant non-native plants that are available year-around because their original native host plant is dormant much of the year.
Buddleia “starves” butterflies?
This is Tallamy’s apocalyptic prediction about the fate of butterflies if gardeners continue to plant buddleia:
“It’s no exaggeration to say that when you choose which plants to include in your garden, even the beautiful, seemingly harmless butterfly bush, you’re deciding if members of your community’s local food web will be nourished or unintentionally starved. And to get to that mind frame, which is a way of thinking that truly benefits nature, including its butterflies, you’re going to have to come to a harsh realization: You need to stop planting the butterfly bush—forever.” (1)
Ironically, this harsh verdict on buddleia was published by a blog entitled, “Organic Life.” Is Organic Life unaware of the fact that the most widely used method of eradicating non-native plants is spraying herbicides? The consequence of adding more plant species to the long list of “bad plants,” is more pesticide use. That’s not very “organic.”
What amoral, selfish gardener would plant buddleia in their garden after such a severe scolding? First, let’s stop and think about the logic of the claim that buddleia will disrupt the “food web” and starve butterflies. Since buddleia is an excellent source of nectar and swarms of butterflies are observed nectaring on buddleia, how could we be “starving” them? Professor Art Shapiro (UC Davis), our local butterfly expert, said when asked about this article, “The ‘disrupting food webs’ argument is ludicrous. It’s equivalent to saying that if you eat popcorn rather than apples, you’re contributing to unemployment in the apple-picking industry.”
Is buddleia a host plant for butterflies?
Now let’s consider the argument that we should not plant buddleia in our gardens because although it feeds butterflies, it isn’t their host plant where they lay their eggs. The problem with that argument is that it isn’t true!!
In 1940, Charles M. Dammers reported that the Variable Checkerspot (Euphydryas chalcedona) “can use” buddleia as a substitute for its usual native host in southern California desert-mountain areas, based on a laboratory study of the larval stages of its caterpillar on buddleia. In 2001, chemical analysis of buddleia found that it is chemically similar to the native host of the checkerspot, which confirmed the potential for such a substitution.
The first actual observation of checkerspot butterflies breeding spontaneously and successfully on buddleia was in Mariposa County, California in the Sierra Nevada foothills. “Mariposa” is Spanish for butterfly. Mariposa County was named by an early Spanish explorer who saw many butterflies near Chowchilla.
Checkerspot bred successfully on buddleia in 2005 and in subsequent years. This colony of checkerspot on buddleia was reported in 2009: “We conclude that buddleia davidii [and other species of buddleia] represents yet another exotic plant adopted as a larval host by a native California butterfly and that other members of the genus may also be used as the opportunity arises.” (2)
More recently, a gardener in Mendocino County also reported the use of buddleia as the host plant of checkerspot:
“By now I am questioning how it was that butterfly larvae were using my butterfly bush as a host plant, completely against everything I’d ever heard. How was this possible? I emailed Art Shapiro, a very well-known butterfly expert and author, sending him a pic. He wrote back to confirm they were butterfly larvae, but added, ‘These are not mourning cloak butterflies. They are checkerspots. And the only time I’m aware this has happened [like, ever, except one in a lab in 1940…] is in Mariposa County.’” (3)
Bad rap for non-native plants
When the native plant movement began some 30 years ago, native plant advocates promoted their agenda with a straight-forward claim that they are superior to non-native plants. The public was initially resistant to that argument because non-native plants have been around for a long time and people have become fond of them.
Native plant advocates began to fabricate stories about the evils of non-native plants to convince the public that eradicating them was necessary because they are harmful to wildlife and they damage the environment. The Million Trees blog was created to address those claims.
But Doug Tallamy’s active participation in the crusade against non-native plants is a special case because he is an academic entomologist, credentials that make him more influential with the public. For that reason, Million Trees has critiqued several of his publications. We publish this critique of Tallamy’s opinion of buddleia for several reasons:
- Buddleia is very useful to butterflies. The loss of buddleia in our gardens would be a loss to butterflies.
- San Francisco’s IPM program is using Doug Tallamy’s mistaken theories to promote the use of herbicides to eradicate non-native plants in San Francisco.
- Buddleia is one of 87 plants that have been classified as “invasive” by the California Invasive Plant Council despite the fact that it is NOT invasive in California. The expansion of the list of “invasive” plants in California to include plants that are NOT invasive in California, will increase the use of herbicides and will eliminate plants that are performing valuable ecological functions.
- https://www.rodalesorganiclife.com/garden/never-plant-butterfly-bush (N.B. The butterfly in the photo in this article is European Small Tortoiseshell, found in Britain and in Europe. The caterpillar in the photo is the monarch caterpillar on its host plant, milkweed. Buddleia is food for both of these butterfly species.)
- Arthur M. Shapiro and Katie Hertfelder, “Use of Buddleja as Host Plant by Euphydryas chalcedona in the Sierra Nevada foothills, California,” News of the Lepidopterists’ Society, Spring 2009