Climate change is helping several resilient invasive plant species take root in Washington

TACOMA – Skye Pelliccia knows an invasive plant when she sees one.

“(They) could be (in) a development area, roadsides, somewhere that is being physically develped, like urban areas that just have soil availability,” she said.

Pelliccia knows these plants – more commonly known as weeds – aren’t harmless. Pelliccia is an education specialist for the King County Noxious Weed Control Board. Part of her job is to identify and remove invasive plants out in the field.

But she and others at the board have noticed a worrying trend that is making their work more challenging: Climate change is making it harder for native plants to thrive in their natural environment, giving invasive plants the opportunity to fill the niches native plants leave behind.

The King County Noxious Weed Control Board has been adapting in response to get a better grasp of the situation.

Washington has continuously battled invasive plants since 1881 with the passage of the first weed law, which said it was the responsibility of property owners to control the spread of invasive plants.

Yet climate change has made this struggle tougher by facilitating the spread of invasive plants into regions that were previously too cold for them to grow. This allows invasive plants to outcompete native plants, some of which do not thrive in hotter temperatures, and reduce biodiversity within an ecosystem.

The National Oceanic and Atmospheric Administration reported that 2024 was on track to be the hottest year on record.

The University of Washington Botanic Gardens is an organization that vigilantly monitors its gardens for invasive plants. Associate director and curator of living collections Ray Larson said they employ a strict checklist and testing process when introducing a plant species to their gardens. This is because they aren’t always sure how a species will react to Washington’s climate compared to that of other regions, as it could coexist normally with native plants or spread aggressively like an invasive plant.

The UW Botanic Gardens has been proactive about invasive species by tracking those plants in regions similar to Washington to determine how much of a threat they may become here.

Larson said the species that are becoming problems in California, such as pampas grass, are of particular concern to the UW Botanic Gardens.

Pampas grass is a reed-like grass species native to Brazil, Argentina and Chile that can grow up to 10 feet tall and features silvery-white plumes at the top.

“One nice thing about our graduate program in the past is we’ve had students that have taken on those topics, and it’s like ‘Hey, this is a problem in California or some similar region to ours,’ ” he said.

“We’ll study and see, OK, where is it occurring, and we work closely with various noxious weed boards and invasive plant councils to monitor where it is in the country and how it seems to be behaving.”

Larson said the Botanic Gardens has chosen to err on the side of caution.

It has proactively removed any species that are a problem in California and which experts think might be a problem in Washington in the future.

The King County Noxious Weed Control Board uses herbicide to kill invasive plants in the summer months. Herbicide, however, can be used only within a specific temperature range. Pelliccia said that in higher temperatures herbicide becomes less effective and the chemicals in it can vaporize, harming nearby plants. This is especially troubling during drought periods.

To deal with this, work crews who go to sites to remove invasive plants now have to be more conscious of the day-to-day weather and adapt their plans appropriately, Pelliccia said.

Funding these noxious weed control programs is becoming more of a challenge, said Anne Schuster, Washington State Noxious Weed Control Board education specialist.

“With climate change increasing, there’s so many more issues that need this funding, need resources, need education and outreach, and I feel like it’s sort of getting diluted,” she said. “How can we really fund and get attention on all the aspects of climate change that need attention, with invasive plants just being one of several?”

Schuster said that the funding issue is due also, in part, to the public’s lack of knowledge about invasive plant species and the unique problems they present.

Climate change is progressive, according to Schuster: Invasive plants reduce biodiversity by pushing out native plants. This makes ecosystems less healthy and more susceptible to climate change.

Schuster said invasive plants negatively affect urban areas like Seattle in various ways.

First, what little green space people can access gets degraded by invasive plants.

“So that can be more of a social justice issue where what might have been an accessible, maybe forgeable, native forest remnant is now a holly or blackberry bramble, and so now you don’t have the nice thimbleberries and salmonberries that might have used to be there,” she said.

Another potential impact most people wouldn’t think of: Invasive plants that grow along roadways pose a threat to humans by reducing visibility for drivers, which increases the likelihood of car crashes.

Brian Darst, president of the Society for Ecological Restoration UW, said teaching residents more about which plants are invasive to their area is one of the best ways they can help stop the spread.

“In an ideal world, everyone would educate themselves on the types of plants they should and should not purchase for any given region,” Darst said. “That’s a really quick Google search, and everyone has access to that knowledge to make sure that we’re choosing plants that can work well within our broader ecosystem in this area.”

For example, English ivy, which is non-native to Washington, is one type of plant that is legally allowed to be sold in the state despite being considered invasive, Schuster said. People can buy these plants and put them in their yards without knowing they are likely to take over and spread into neighboring yards and even further into the community.

The Washington State Noxious Weed Control Board’s website has a list for Western Washington of noninvasive alternatives to common invasive plants. Some of their recommended alternatives include cardinal flowers, golden rain trees, Japanese irises and climbing hydrangeas.

Pelliccia and Schuster recommended that residents who notice an invasive plant growing in their area report it through apps like iNaturalist or directly to their county’s Noxious Weed Control Board website. If the invasive plant is on a citizen’s own private property, however, Pelliccia said the owner should remove it themselves.

Darst described the restoration work the Society for Ecological Restoration does removing invasive species and planting native ones.

He said what motivates himself and others to continue participating in these efforts is the feeling they have made an impact in the face of climate change in just a few hours a week.

“It’s this very immediate, very tangible way that we can make a difference in our community and our local environment,” Darst said.

While climate change affects many aspects of the world around us, Larson wants people to notice the way invasive species fit into this challenge.

“If you are noticing more stress when you’re outside, walking around, (and you’re thinking,) ‘Gosh, it’s a lot hotter than last summer,’ it’s like, yeah, that also affects the environment,” he said.

“Just kind of keep an eye on how it affects the other living things in your life, not just yourself and your friends and pets, but plants.”