©istockphoto/Jeff Goulden

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.

©istockphoto/Jeff Goulden

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
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
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.


Zebra Mus­sels
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.


Scot’s Broom
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.


Euro­pean Starling
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.

Pitch in
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.