There are chemical and non-chemical approaches to native plant restoration. Neither succeeds. Non-chemical methods are labor-intensive, which makes them prohibitively expensive. Chemicals are cheaper and they kill non-native plants, but they don’t restore native plants because they kill them and damage the soil. Either strategy must be repeated continuously to be maintained. This article is the 25-year story of reaching the conclusion that neither chemical nor non-chemical approaches are capable of restoring native plants on a landscape scale. Where do we go from here?
In 2014, the California Invasive Plant Council (Cal-IPC) conducted a survey of land managers to learn what methods they were using to control plants they considered “invasive.” The Cal-IPC survey reported that herbicides are used by 94% of land managers and 62% use them frequently. Glyphosate was the most frequently used herbicide by far. In 2014, no other eradication method was used more frequently than herbicides.
We have learned a great deal about the dangers of herbicides since 2014.
- The World Health Organization has categorized the most frequently used herbicide—glyphosate—as a probable carcinogen.
- The manufacturer of glyphosate, Monsanto-Bayer, was successfully sued by terminally ill users of glyphosate. These product liability lawsuits resulted in multi-million dollar awards for damages. The awards were reduced on appeal but ultimately upheld. Monsanto has agreed to pay more than $10 billion to settle close to 100,000 product liability claims.
- The US Environmental Protection Agency has finally published its Biological Evaluation (BE) of the impact of glyphosate products (all registered formulations of glyphosate products were studied) on endangered animals (mammals, birds, amphibians, reptiles, fish, invertebrates) and plants. The BE reports that 1,676 endangered species are “likely adversely affected” by glyphosate products. That is93% of the total of 1,795 endangered species evaluated by the study. Both agricultural and non-agricultural uses of glyphosate products were evaluated by the BE. Although only endangered plants and animals were evaluated by the BE, we should assume that all other plants and animals are likewise harmed by glyphosate because the botanical and physiological functions of plants and animals are the same, whether or not they are endangered.
How have land managers responded to the dangers of herbicides?
San Francisco’s Recreation and Park Department has increased the use of herbicides in public parks every year since 2016. In 2020, herbicide use increased significantly from 243 applications in 2019 to 295 applications in 2020. SF RPD has been spraying herbicides on non-native plants for over 20 years. They have been using hazardous herbicides on some 50 target plant species year after year. The longer they use them, the more resistance to the herbicides the plant develops.
Chris Geiger, director of the integrated pest management program at the San Francisco Department of the Environment, told San Francisco Public Press that although the city has reduced its use of glyphosate outside parks, it won’t ban glyphosate because it hasn’t found a more efficient or safer alternative for controlling some weeds. He said, “In habitat management, there are certain plants you cannot remove from a natural area by hand.”
San Francisco’s IPM program recently published “Pest Prevention by Design Guide” that illustrates the bind they are in with respect to promoting native plants while trying to reduce pesticide use. On the one hand, the Guide promotes the use of native plants in landscape design plans by making the usual claim that “Native species are generally best suited to supporting local insect populations and ecosystems.” On the other hand, the Guide recommends the use of “pest resistant” species that are not eaten by insects and grazing animals and are capable of outcompeting weeds. Can’t have it both ways, folks!!
East Bay Regional Park District has made a commitment to phase out the use of glyphosate in developed areas such as parking lots, playgrounds and picnic areas. However, EBRPD remains committed to using glyphosate and other herbicides to eradicate non-native plants on undeveloped park land. In 2020, no glyphosate was used in developed areas, but about 23 gallons of glyphosate were used to eradicate non-native plants on undeveloped park land. Twenty-one gallons of triclopyr were also used to eradicate non-native shrubs and to prevent non-native trees from resprouting after they were cut down. They continued the 15-year effort to eradicate spartina marsh grass with imazapyr. A few other selective herbicides were used on other eradication projects. (2)
In the San Francisco Bay Area, most land managers are still committed to using herbicides, particularly in so-called “natural areas,” regardless of the damage herbicides do to human health, wildlife, and native plants. In fact, the City of Oakland is planning to begin using herbicides on 2,000 acres of public parks and open spaces for the first time to implement its vegetation management plan. The vegetation management plan is both a fuels reduction program and a “resource protection” program, which is a euphemism for native plant “restoration.”
Given what we now know about the dangers of herbicides, why are public land managers still committed to using herbicides? The City of Oakland explains in the EIR for its vegetation management plan why it is proposing the use of herbicides where they were prohibited in the past:
“It is estimated that if the City were to rely on hand removal and mechanical treatments in place of herbicide, it would cost the City up to 40 times more to treat these areas than under the VMP. The cost for herbicide treatments, not including any associated physical treatments, is approximately $250-$500 per acre. This reflects a range of potential vegetation conditions, vegetation types, and densities. The cost for hand removal and mechanical treatments is estimated at approximately $1,000-$4,000 per acre, using the same range of site-specific conditions.” (page 5-9)
In other words, herbicides are the preferred method of killing non-native plants because it is the cheapest method. However, there is another reason why herbicides are preferred to non-chemical methods. There isn’t a non-chemical method that is more effective than using herbicides.
Looking for an alternative to herbicides
As we should expect, new information about glyphosate has increased the public’s awareness of the dangers of pesticides. California Invasive Plant Council has responded to the public’s growing awareness and concern about the herbicides to which they are exposed in our public parks and open spaces. They recently published a comprehensive 300-page brochure entitled “Best Management Practices for Non-Chemical Weed Control.” (1) Many highly qualified land managers participated in the preparation of this credible publication. The Cal-IPC brochure is credible because it frankly admits that no method of eradication is without problems. Irrigation and intensive planting are required for good results, but without continuing regular maintenance the results are only temporary. Few land managers have the resources needed for success.
If you wonder why herbicides are the preferred method of eradicating non-native plants, reading Cal-IPC’s brochure about non-chemical methods will tell you why. There is no non-chemical method that achieves better results than using herbicide.
Herbicides are not a magic bullet
Herbicides are the most frequently used method of killing non-native plants, but using herbicides does NOT result in a native landscape. “Lessons learned from invasive plant control experiments: a systematic review and meta-analysis,” analyzed 355 studies published from 1960 to 2009 to determine which control efforts were most effective at eradicating the target plants and which method was most successful in restoring native plants. The analysis found that “More than 55% of the studies applied herbicide for invasive plant control.” Herbicides were most effective at reducing invasive plant cover, “but this was not accompanied by a substantial increase in native species,” because, “Impacts to native species can be greatest when programs involve herbicide application.” It’s not possible to kill non-native plants without simultaneously killing native plants and damaging the soil.
Reaching a dead—and deadly—end
Public land managers in the San Francisco Bay Area have been trying to restore native landscapes for over 25 years. Every project begins by eradicating non-native plants, usually with herbicides. Our public parks have been poisoned repeatedly, but native landscapes have not replaced the plants that were killed. Meanwhile, we have learned that herbicides are dangerous to our health and animals who live in our parks.
The only viable alternative to using herbicides to “restore” native plants is to change the goals for native plant restorations such that herbicides won’t be required:
- An exclusively native landscape cannot be achieved where native plants have never existed, such as the many parks along the bay waterfront that were built on landfill. It is an unrealistic goal.
- Given that no effective method of achieving this unrealistic goal has been found after 25 years and the most popular method is poisoning our environment, it is time to stop trying.
- Smaller, achievable goals must be set. Landscape scale projects should be abandoned and replaced with small scale projects where native plants already exist.
- Smaller areas can be managed without using herbicides because they will be affordable to manage with labor-intensive methods that are more expensive.
- If smaller projects are more successful, they will be less controversial. The projects are unpopular partly because they aren’t successful.
The native plant movement in the San Francisco Bay Area has bitten off more than it can chew. Native plant advocates need to back out of their dead end and regroup with plans that are less destructive and more realistic. As the Economist magazine said in 2015, “you can garden in a garden, but you can’t garden nature.”
(1) California Invasive Plant Council is offering free video training for non-chemical methods of killing “invasive” plants on May 4, 2021, 1-5 pm. Sign up HERE.
(2) 2020 IPM Report, East Bay Regional Park District available HERE.