Habitat restoration involving the removal of invasive acacia trees from land owned by Audubon Canyon Ranch in Inverness last week irked a few local residents, who sounded the alarm that a toxic herbicide was being applied close to Tomales Bay.
The nonprofit acquired the two-acre parcel after longtime resident Helen McLaren bequeathed the land upon her death in 2012, with the stipulation that it be returned “to the birds.” Part of the restoration work involved treating about a half-dozen acacia stumps with triclopyr, an herbicide that has the potential to contaminate groundwater and has proven toxic to some fish species such as coho salmon. A contractor working on the property Friday afternoon daubed thin coats of Garlon 4 Ultra—one of the brand names for triclopyr—onto the stumps by using a sprayer wrapped in a rag, leaving behind a blue dye to mark the herbicide’s presence.
Pesticide application has long been a sensitive subject in West Marin, where many worry that substances such as RoundUp and Garlon 4 Ultra risk disrupting pristine ecological preserves and organic ranches. West Marin’s mosquito council has even negotiated a separate contract with the county mosquito-control that bans triclopyr from the region.
Triclopyr keeps trees and other broadleaf plants from re-sprouting by mimicking plant growth hormones, called auxins, causing abnormal growth and death. Grasses that surround plants treated with triclopyr are not affected because they can quickly transform the herbicide into compounds that do not affect plant hormones, according to the Journal of Pesticide Reform.
Audubon Canyon’s director of stewardship, Jeanne Wirka, said that triclopyr is applied during conservation projects as a “last resort” to fend off fast-spreading invasive species which tend to resist manual removal. She noted that acacias were the only non-native plants not hand-removed by the contractor, a Sonoma-based company named Hanford ARC that focuses on stream and wetlands restoration.
“Our contractor as well as other organizations that do invasive species control haven’t found any other successful way to control invasive acacia species,” Ms. Wirka said. “What the research does show is that, with proper application, there’s very little risk of it entering the environment beyond the target organisms.”
Audubon Canyon has also applied RoundUp—which contains the herbicide glyphosate—for vegetation-management projects at other properties, but staff is reviewing its policy in light of recent findings by an agency of the World Health Organization that glyphosate may possess carcinogenic qualities. Nonetheless, Ms. Wirka said the Hanford worker took care to keep the herbicide from coming into contact with the soil or surrounding areas.
But one Inverness resident, Tom Kent, pointed out that the worker applied triclopyr on stumps not only adjacent to Tomales Bay, but also abutting and even within a culvert that slices through the property and drains rainwater into the bay.
“They’re a conservation organization, and they’re poisoning vegetation in a wetlands,” Mr. Kent said. “It just makes no sense.”
Mr. Kent, a member of the Pacific Slope Tree Cooperative, also questioned the need to knock down the trees in the first place. He reasoned that Sir Francis Drake Boulevard and a shield of willows along the bay’s bank would contain the acacias’ spread. Ms. Wirka could provide no factual data to address Mr. Kent’s assertion.
Audubon Canyon Ranch conducts periodic shorebird counts near the property, which fronts a salt marsh. The nonprofit is planning for the restored land to enhance shoreline habitat for birds and help the wetlands adapt to sea level rise.
Over the summer, Audubon Canyon completed the first phase of restoration work with the removal of the property’s home, outbuildings, driveway, and all septic, gas and electrical systems. This fall, the nonprofit will plant native trees, grasses and shrubs, such as willows, alders and coffeeberry.
“That particular environment is fertile and very fast-growing,” Ms. Wirka said. “Nature will do most of the work for us. I suspect in a year’s time it will look very different from the way it does now.”