America, they say, is a nation of immigrants. On a human level, it’s led to vibrant cultural exchange, economic growth, and a broader worldview. When it comes to natural ecosystems, however, the story is a bit different. Invasive species—plants and animals that are recent arrivals—can disrupt ecosystems and wreak havoc on native species.
How Do They Get Here?
Non-native species get to the Pacific Northwest in a variety of ways. Some ride ocean currents, some hitchhike in shipping containers, and some latch on to car tires. Others were brought here on purpose by well-intentioned but ultimately foolish humans. Once established, these species have a heyday, spreading further through the use of birds, car tires, hikers’ boots, and their own aggressive resilience to the preexisting ecosystem.
What Makes Something Invasive?
Not all non-native species are disruptive. The daffodils in my front yard originated in Spain and Portugal, not North America. But they don’t spread aggressively, choke out native species, or disrupt the ecosystem. The most wanted species are aggressive turf-expanders who threaten to upend what’s already in place.
Bullfrogs are a welcome part of ecosystems in the American southeast, but in the northwest they’re a big, loud, hopping problem. They grow fast, and are particularly effective at taking over ponds with warm water, a frequent occurrence in disturbed areas where trees are scant. They will voraciously devour anything: native frogs, birds, fish, and even baby ducks. The best solution? Keep ponds shady to keep the water cool, and keep the pond vegetation complex to support many native species. An even better solution—frog legs taste like chicken…seriously.
Himalayan blackberry is so common that many people think it’s native. At least it produces delicious berries. It grows so fast on sunny, disturbed sites that it often forms a thorny wall. If it’s pulled or dug up, it can still grow back from small chunks of the plant left in the soil. Tackle blackberry with a plan for how to keep it from re-growing (shade is your biggest ally) and cart off all the stems. And be sure to wear thick clothing.
Japanese knotweed first showed up in the Northwest after the flood of 1996. It moves down rivers with floodwaters, and is a voracious spreader. Like blackberry, it regrows from small bits of plant, and is phenomenally difficult to remove. Pulling or cutting just seems to aggravate it, making it grow even faster. The best solution is reserved for professionals with the right training: injecting a chemical directly into the plant stem.
If you’ve ever driven across the Oregon border and happened upon a pull-off that says “boat cleaning station,” you’ll notice that it’s all about trying to catch Zebra Mussels before they establish themselves. Their larva spread from their home in southern Russia into the ballast water of ships that eventually took them to The Great Lakes. In the lakes, they created a massive monoculture that covered docks, dams, water intakes, and blocked hydropower facilities. They are also a common source of avian botulism, which can decimate bird populations. The boat wash stations are to make sure that boats don’t arrive with larva clinging to their hulls.
You’ve no doubt seen the deep-green leaves and array of yellow flowers on Scot’s Broom, which lines the sides of highways. Scot’s Broom thrives on sandy, disturbed soil, and very quickly establishes deep, woody roots. For this reason, it used to be planted by road crews to hold soil after construction, but then it went wild. Scot’s Broom adds massive amounts of nitrogen to the soil and since nitrogen is a key factor in plant growth, this massive addition changes plant communities for the worse. Scot’s Broom also produces a ton of seeds, which can last in the soil for half a century, making the removal of Scot’s Broom a grueling, long-term effort.
An aquatic rodent, the nutria is often mistaken for its larger native cousin, the beaver, or its smaller one, the muskrat. The South American nutria was brought to the Northwest for fur farming between the 1920s and 1950s. Some escaped, and when farms failed, many were simply released. Comfortable in urban areas, very quick to reproduce, and aggressive, they’ve forced out the native muskrats and become a huge problem.
In Shakespeare’s Henry IV, a character named Hotspur utters the line “I’ll have a starling shall be taught to speak nothing but ‘Mortimer.’” That’s unfortunate, both for Mortimer (whoever he was) and for North America, because in 1890, a man named Eugene Schieffelin decided it would be great to introduce all the birds mentioned in Shakespeare to North America. He released 60 starlings in New York’s Central Park. What a mistake it was. The street brawlers of the avian world, European Starling’s are aggressive, nest-grabbing expansionists that now number 200 million and span the continent.
What Can You Do?
We can all play some role in keeping invasive critters and plants at bay. While removing them is often a job for professionals, or at least someone with some knowledge and a plan, there are still three things you can do:
Make Your Yard Wildlife-Friendly
Your yard can become a healthy refuge for native wildlife, and organizations like Portland Audubon Society can help you do it.
Organizations that manage native landscapes—from environmental organizations to park districts—often rely on the hard work of many volunteers to keep a handle on invasive species.
Be on the Lookout
When you’re out hiking, keep an eye out for these species, especially when it looks like they’re moving into a new area. If you see a new infestation, let the park or forest manager know.