Rethinking 'Invasive' Species

Experts Suggest Less Emphasis on Non-Native Plants

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Toby Query is a natural resources ecologist for the city of Portland, Ore.

Mark Davis is Dewitt Wallace professor and chair of biology at Macalester College in St. Paul, Minn.

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Posted: Wednesday, May 13, 2015 12:00 pm

It’s generally accepted that invasive plants and animals are bad for biodiversity and should be eradicated. Many individuals, organizations and municipal leaders have enlisted in the battle against these non-native species - plants in particular.

Millions of dollars, not to mention hours, are spent yanking, cutting or applying herbicides to certain species, while simultaneously nurturing others. However, without an understanding of their repercussions, these efforts can do more harm than good. Some experts in urban ecology warn that labeling plants as native or non-native, bad or good, and allowing those labels to direct policy, could be the wrong approach.

Toby Query has worked as a natural resources ecologist for the city of Portland, Ore., Watershed Revegetation Program since 1999, and manages several hundred acres of forests and wetlands in the city. Under his watch, more than 3 million native seedlings and many tons of native grass and wildflower seeds have been planted. He also is the founder of Portland Ecologists Unite!, a monthly discussion group working to improve land management practices and increase the resiliency of the community of ecologists.

Through the years, Query said, he has slowly shifted his thinking from one that “combats evil invasives” to a more nuanced approach. When managing natural areas, it is first important to know what you have living in them by surveying the plants, birds and animals, he said, then documenting and assessing their status on a routine basis.

“The most important thing is to then line out specific goals that you have for them,” Query said, adding that the goals, especially in urban areas, need to be flexible to deal with what the needs are, and specific enough to highlight certain species managers want to recover.

Query learned this lesson first-hand when his team was trying to remove an invasive reed canary grass, as well as clear out non-native blackberry bushes, from an area. They wanted to instead plant hawthorn and other native trees. However, during the process of removing the plants they no longer desired, they realized a rare bird, the willow flycatcher, liked to nest in the blackberry bushes. Before realizing what was occurring, they cut out the blackberry bushes in the middle of bird nesting season. Query’s team destroyed some nests in the blackberry bushes, not realizing they were habitat for a species of concern.

“Early in my career I didn’t know about that bird. Now with the help of other biologists we’re trying to assess natural areas and tailor our treatments and interventions to do the least amount of damage and to make those treatments move the natural area in the direction we want them. That is, to make the environments more sustainable and healthier for all species that are there,” he said.

Overly simplistic approaches to the natural world can create harm, Query said, as began to happen with his blackberry bush project.

“It is not as simple as bad and good,” he added. “It is a lot more complex than that. For example, there are certain species that ecologists love to revile, such as garlic mustard,” which many people will do anything to get rid of because it is considered a non-native that will change forest dynamics.

But “we’re moving toward dialogue that tries not to label plants or animals as good or bad, as invasive or not,” Query said. “Various species have different capacities for adapting to change, some faster than others.”

Plants like garlic mustard do quite well on disturbed soil, he said. They propagate quickly and their seeds live for a long time. But he pointed out an important set of questions that should be asked, such as the underlying causes of why a non-native plant is thriving there. Is it because of the disturbed ground? Because of climate change? Because of earthworms in soil?

“We need to look at the underlying drivers of ecological change and realize that a plant or animal isn’t bad or good,” he said. “It is just living its life. It is up to us whether it fits in with our goals or not.”

The city of Portland has a broad, long term assessment map of the Portland Area Watershed, Query said. It looks at specific randomized points mostly in riparian areas to assess the bio-community, streams, plant community, bird community and long-term trends. Then it ranks those communities on what is doing well and how they can work on other areas to make them healthier. But of course, nature doesn’t always follow a predictable path, since weather patterns and many other variables are constantly changing.

“There’s a lot of basic biology we don’t know about including soils and insects. The ecosystem is almost infinitely complex. There is too much information to know,” Query said. “There are multiple examples of where we tried something but it didn’t necessarily work, but that’s the nature of sites — each site we manage is kind of its own problem to solve, so failures are part of what we need to learn. We start trials here and there to see if it works. If it does, we expand, if not we abandon. It’s a constant learning process.”

There will always be individuals concerned about changes in a habitat area they see on a regular basis. Where there are natural spaces, there will be creatures. In the wooded area around Portland, that might include black-tail deer, a rare bear or mountain lion, and on local golf courses, the ever-present Canada goose.

Although Query doesn’t work directly with these sorts of animal species, he understands that their prospects are directly tied to what is occurring in the woodlands he manages.

“It is important to communicate with the public that we’re trying to do what is best for the health of the ecosystem and what is good for the public,” he said. “We want people to be able to enjoy nature. When we do an ecological restoration treatment, we know we are impacting negatively some part of that ecosystem and positively some other part. We all are trying to figure out the best timing, best treatment, best target sites. That’s a learning process.”

Mark Davis agrees with Query about ecological practices and the nuanced use of language to describe them. He is the Dewitt Wallace professor and chair of biology at Macalester College in Saint Paul, Minn., and was once Query’s professor. Davis considers words like “invasive species” to be a value-laden term.

“People, including conservationists and scientists, apply these terms indiscriminately," he said. "It is best to call them ‘recent arrivals’ or even ‘non-native and native.’ But words like ‘invasive,’ ‘alien’ and ‘exotic’ suggest these are bad things and shouldn’t be there.”

Davis worries we’ve somehow gotten into an armed conflict with nature that we can’t possibly win.

“A problem that arises is that a lot of money is spent to eradicate them (non-native species) through the use of chemicals,” Davis said. “The recognition that species are doing desirable ecological services will be overlooked. We could be getting rid of species that are providing benefits.”

A change of perspective about these plants and animals is the new reality, he said.

“That is not saying just don’t worry about anything but let nature take its course, because some things cause problems,” he said, using the example that too many stinging bees make a city less attractive and public parks less usable, and too many deer can cause safety issues when they are hit by cars.

“When it comes to human safety, a city needs to intercede. Best practices will vary by community and what their key issues are,” he said, and just like with most other decisions made by government officials and other leaders on behalf of the larger community, it is best when the decisions are made by many people.

Most cities only have the resources to focus on a few things and should get input from as many stakeholders as they can, Davis said, “but the herbiciding of non-native plants should be stopped. A lot of the public does not like having chemicals sprayed, and a lot of these plants go back a long time. Continuing to think of them as non-natives and therefore something that shouldn’t be here is stupid.”

Some non-native species even provide a sense of place for local residents, Davis said, because these plants have been there longer than any individuals currently alive.

Ultimately, it’s very hard to manage nature so it “is just enough but not too much,” Davis said. Not too hot or cold, not to buggy or too humid, not overrun with nuisance wildlife but not barren and sterile.

“That’s the natural world out there,” he said. Deer don’t have predators. Raccoon populations have exploded. Coyotes are adaptable. Wild turkeys were reintroduced or introduced to new places and now wildlife managers get complaints that turkeys cause problems when they eat crops and gardens. “There is a fantasy out there that we have the ability to create an environment with everything at the desired level. If you think that way, you will be perpetually unhappy.”

Davis advised urban ecologists, conservation advocates and even backyard gardeners to realize they can only focus on a few things.

“It makes people feel good to be out waging war against a diabolical enemy,” he said. "But, it's not really a war because the other side isn’t fighting. Humans brought them over, they’re just here living because that’s where we put them. It is a one-sided war.”

If we really want something to fight, Davis has a few suggestions.

“You should worry about introduced pathogens, viruses, bacteria and fungi,” he said. “Besides harming people, they can decimate food production crops, livestock and wild populations. Then next on the list is the introduced insects that can devastate and threaten society. There is not enough emphasis on that and way too much preoccupation worrying about non-native plants.”

Anyone who has witnessed the pine beetle invasion in our western landscapes, or the emerald ash borer currently chewing through the tree stock of many American cities, will understand Davis’ point. According to the National Invasive Species Council, these and other destructive species cost the U.S. $100 billion per year.

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