Invasive plants in park a growing threat

02/12/2020

In the dunes at Abbotts Lagoon, the Western snowy plover is nesting, the Tidestrom’s lupine is germinating, and the sand is flowing.

At most other beaches in the Point Reyes National Seashore, the dunes are steep, continuous ridges infested with iceplant and European beachgrass. These invasive plants stabilize the sand, eliminating wildlife habitat and crowding out native plants.

The lagoon, which has been the subject of a restoration project since 2011, shows the benefits of ridding an area of invasive plants. But the restored area is miniscule compared to the immense scale of invasive plants across the seashore. Streams, roadsides and ranches are also inundated with hundreds of different species of invasive plants, and the problem is growing. 

According to a natural resource conditions assessment of the seashore released last year by the National Park Service, invasive plans are being introduced at an unprecedented rate—replacing native species, changing ecosystems, altering soil chemistry and reducing agricultural productivity. 

Each year, an average of 2.8 species are added to the park’s list of species targeted for removal, which now includes 167 different plants. This includes data only from along roads and trails, and the report acknowledges gaps in understanding in remote wilderness areas.

The assessment examined eight natural resources and scored them based on how much concern is warranted. Invasive plants were the only resource of significant concern. Amphibians, birds and rare plants are doing well, while forests, grasslands (threatened by non-native plants) and steelhead could be doing better. Not enough information was available to determine the condition of coastal dunes.

The 300-page report gives four stressors in the park that correlate with invasive plant abundance: pests and pathogens, climate change, an altered fire regime, and land use. 

“Point Reyes is an unusual unit in the National Park Service in that it incorporates livestock grazing and associated agriculture into management goals,” the report states. “Because of these and other potential human activity vectors for the spread of invasive plants, Point Reyes has a great interest in understanding how invasive plants occur on the landscape.”

The battle against weeds is best fought early, so the park service deploys an invasive species early detection program across Bay Area parks. At least once every three years, a botanist, a biological technician and two interns complete a survey along roads and trails in the seashore.

“Early detection and rapid response is second only to prevention as the most cost-effective and efficient method of invasive-species management,” said Eric Wrubel, a biologist for the park service. “The invasive species early detection team in Point Reyes is a good example. [The team] has detected numerous small infestations of invasive plants species at Point Reyes that were quickly contained or eradicated before they were able to spread.”

The team prioritizes plants based on the ability to manage them. The highest-priority plants are highly invasive and typically not widespread, making eradication feasible. The lower-priority plants are either ubiquitous and beyond control, or rare and unlikely to persist. 

Last year, the early detection team discovered Poroporo, also known as New Zealand nightshade, at Chimney Rock and along Sir Francis Drake Boulevard. The shrub is characterized by deeply lobed leaves, blue-violet flowers and round, green fruits. Each fruit contains hundreds of seeds, and the plant can reach up to 12 feet high.

With an internal park service grant, the team cut the limbs, collected the seeds, and uprooted the plants. As the team was finishing up at a bird viewing area near A Ranch, a birder asked what they were doing. The team explained they were eradicating the last known populations of Poroporo in the park, and the visitor said he saw more plants on the other edge of the area. Sure enough, the team found a very dense, very healthy population, which the team left because the size of the infestation called for significant treatment.

The park service largely relies on volunteers to manage invasive plants. Through the habitat restoration program, volunteers can drop in one Sunday a month to pull up plants, rotating between active projects. The Third Thursday Weeders, an outside group, is also dispatched, and a group called the Stream Team is dedicated to improving fish habitat.

Two school groups—one from Utica College in New York and the other from the University of Utah—plan to be here in March for an alternative spring break filled with invasive-plant removal and dune restoration.

The park service takes many measures to slow the spread of invasives, but it is not alone in the battle. The seashore is included in the Marin-Sonoma Weed Management Area, a collection of about 20 organizations cooperatively fighting weeds and invasive plants. The weed management area was re-established last year after a hiatus of eight years because the state ceased funding it. 

“All of the organizations had to strap down and use their own resources,” said Stefan Parnay, the county’s deputy agricultural commissioner, “which isn’t nearly enough to deal with the issue. With invasive weeds, they don’t just go away, they continue to get worse.”

The California Invasive Plant Council successfully lobbied state lawmakers to put $2 million towards weed management areas, and last year, the program started awarding grants again. 

Marin’s first grant went toward an ongoing effort to remove Japanese knotweed from the San Geronimo Valley watershed; another round comes in July. 

The Japanese knotweed project was chosen partly because of its threat to the natural ecosystem, but weeds are also targeted for their economic impacts.

Ranchers deal with a variety of weeds, including woolly distaff thistle, which encroaches on grazing land. Like other thistles, woolly distaff grows dense, is extremely spiny, and cows won’t eat it. It will readily spread over dozens of acres, and it takes multiple years to eradicate because the seeds can germinate for up to eight years.

“If too much [pasture] becomes unpalatable, you’re either going to have to reduce the number of your herd, or you’ll have to supplement and buy feed,” said David Lewis, the director of the University of California Cooperative Extension for Marin County.

For nonorganic farms, conventional herbicide is the most effective method for removing the thistle. Organic farms have to take the extra step to mow before applying organic herbicide to be effective. Mr. Lewis has said that in some cases, he has seen farms come out of organic certification for a period to allow for stronger herbicides.

“It may seem ironic to people,” he said. “That’s the nature of some of these weeds.”

 

Restoration workdays are scheduled for Feb. 20, Feb. 23 and March 8. Check the seashore’s calendar for details at nps.gov/pore/planyourvisit/calendar.