Invasive species are as bad as they sound. Non-native organisms can do serious damage to an ecosystem and its native wildlife, and can also negatively affect a visitor's experience. And it’s not a rare thing either—about half of the country’s national parks have reported issues with some type (or types) of invasive species. The National Park Service reported 1,500 populations of invasive animals as of 2016. Invasive plants cover 1.4 million acres of agency-managed land and water. A study found that more than 300 of the invasive animal species seriously threaten our parks.

So what can be done? The National Park Service is battling invasive species on multiple fronts. From feral hogs and frogs to extra-large pythons and quagga mussels, here are some of the most serious threats, the strategies for getting rid of them, and what you can do to prevent the spread of invasive species.  

Grand Canyon National Park 

Invader: Tamarisk 

The problem: Tamarisk was introduced to the Southwest in the late 1920s to help battle erosion and stabilize riverbanks, but it spread rapidly and soon dominated the environment—crowding out native cottonwoods and willows. The trees grow in dense stands along rivers and streams and can reach 15 to 50 feet tall. A mature tamarisk can use up to 200 gallons of water per day, and over time tamarisk (also called saltcedar) changes the salinity of the soil on which it sits, which further repels native plants. 

It gets worse: The seeds of the tamarisk are low in nutrients, so they’re not sufficient to sustain native species, like birds, and the rampant spread of tamarisk has increased the risk of wildfire. The pervasive plant exists in the Grand Canyon as well as other parks, from Dinosaur National Monument to Arches National Park, and Canyonlands National Park to Glen Canyon National Recreation Area. 

The plan: In the Grand Canyon alone, 270,000 tamarisk trees have been removed (at last count, in 2009) in order to allow the natural vegetation to recover. Crews cut the trees down with chainsaws, bulldoze them, or use chemical controls. Other land managers in the Southwest introduced the tamarisk beetle, which feeds on tamarisk leaves, killing the trees. However, the beetle is also non-native, and it has spread faster and farther than expected, causing unintended consequences, like threatening the endangered southwestern willow flycatcher in Arizona.

Congaree National Park 

Invader: Feral Hogs

The problem: Feral hogs aren’t just a national park problem, they run rampant in dozens of states (at least 42 of them) and their population is estimated at more than 6 million. The hogs have been here for hundreds of years, arriving in the 1500s as a food source for European settlers. According to the USDA the hogs cause about $2.5 billion in damage per year: plowing through crops, tearing up roads, spreading disease, contaminating water, and pushing out native species. This highly destructive species runs rampant at Congaree, where they threaten the park’s forest ecosystem and floodplain. Feral hogs create trail networks, root up the forest floor, reproduce quickly, eat almost anything, are incredibly adaptive, and are aggressive competitors with the park’s native animals like wild turkey and white-tailed deer. 

The plan: The park is working on two fronts. Federal trappers hunt and kill the animals in an ongoing removal effort. But there’s no hope of completely eradicating them, so scientists are also planning strategies to reduce the impact of the feral hogs—adapting to the reality that they’re here to stay. 

Hawaii Volcanoes National Park 

Invader: Coqui Comun Frogs

The problem: The coqui, native to Puerto Rico and a beloved creature there, is thriving in Hawaii (traveling there in the 1980s via potted plants), where it has no predators and tons of insects to feed on. In its home country the frog has predators that keep the population in check, but in Hawaii its population has grown exponentially—with densities ranging between 10,000 and 40,000 per acre. 

The frogs are only about the size of a quarter, but have an outsized impact: they’re damaging the ecosystem and feeding on native insects, which threatens the food source of bird populations. In addition to that, they’re incredibly loud. Their chirp has been measured at a staggering 70 to 90 decibels. The lower end of that range is comparable to a washing machine, but given their density that’s like running thousands of washing machines at once. 

The plan: The park is working to remove the frogs from the most sensitive areas of Hawaii Volcanoes, but due to the lack of predators and the frog’s adaptability, eradication is unlikely. 

Everglades National Park 

Invaders: Burmese Pythons & Invasive Trees

The problem: Burmese pythons, native to Southeast Asia, came to the U.S. through the pet trade and since then have been reproducing at high numbers and expanding their geographic range. The snakes, which can reach up to 14 to 16 feet long, are ravaging wildlife populations in Florida. According to estimates, there are tens of thousands of pythons across the state and they’re present in all of Everglades National Park.

The plan: The park has been working with researchers for over a decade to figure out how best to remove the pythons (either through euthanizing them or via live capture). In 2018, the park tripled the number of contractors it uses to remove snakes.

The problem: Pythons aren’t the only invasive in the Everglades. Australian pine, old world climbing fern, Brazilian pepper, and Melaleuca trees have also moved in. The Melaleuca tree, for example, was brought to Florida in the 1900s with the intention of drying up swampland. But the introduction did not go according to plan. The trees spread quickly, drive out native vegetation, disrupt water flows, and damage the swampland.

The plan: The park has worked for decades alongside other partners to introduce multi-faceted plans to combat the Melaleuca and the other species, employing everything from herbicides and prescribed burns to biocontrols or just cutting and removing them—and it’s working. Through their efforts they’ve managed to clear the majority of the Melaleuca from the park, and the species has continued to decline. 

Isle Royale National Park 

Invader: Quagga/Zebra Mussel

The problem: These mussels are not just an issue at Isle Royale—the species is pervasive in at least 52 National Park Service units. The infestation of these aggressive mussels was first found in Lake Superior in the late 1980s, and the aquatic invader can reproduce very quickly. The mussels are thought to have traveled to the U.S. via large European ships. 

There are multiple threats. According to the park, if zebra mussels were to enter inland lakes—Lake Whittlesey, Wood Lake, Siskiwit Lake, and Intermediate Lake—they could cover nearly every habitable surface of a lake floor in two to four years. The mussels cause damage to boats, drive out native mussels which affect the food source of fish, and their spiky edges can injure barefoot beach walkers and swimmers. 

The plan: To combat the spread of the mussels the park service relies heavily on educating visitors. Before traveling to Isle Royale, boaters must drain live wells on land and thoroughly clean their boat with high temperature water and soap or a disinfectant. Backpackers and anglers must also thoroughly clean their gear. While at the park, visitors should  clean gear and change fishing line spools before traveling from Lake Superior to an inland lake. 

Yellowstone National Park

Invader: Lake Trout

The problem: Lake trout were introduced to Yellowstone’s waters illegally sometime in 1994, and have since dramatically decreased the population of the native Yellowstone cutthroat trout. The Yellowstone cutthroats are an important food source for other native species, while the non-native trout is an aggressive predator. These newcomers dominate the waters and don’t spawn upstream like their native counterparts, meaning grizzly bears have less to feed on when they emerge from hibernation. These large trout can live up to 25 years and grow to 50 pounds, eating the native fish’s food supply and sometimes even eating the native cutthroats themselves. 

The plan: The park has been working to protect the natural ecosystem by removing the non-native lake trout population by capturing them with nets. To date, officials have removed more than 2.3 million lake trout and estimate that by 2025 they’ll no longer be a major threat. 

What You Can Do

Management agencies are tackling large-scale removal and eradication efforts, but we can all help prevent the spread of invasive species on public lands. Here are three key steps the National Park Service advises:

1. Be Smart about Pets: Many invasive animals started out as pets that escaped or were released into the wild (that’s true for 80% of the non-native reptiles and amphibians in Florida). Before acquiring a non-native pet, be sure to understand the care it needs and the consequences of it getting loose. 
2. Plant with a Purpose: When planning a garden or landscaping, avoid using non-native plant species (they can compete with natives and their seeds can easily blow in neighboring open spaces). Instead, plant native species that attract regionally specific pollinators. Get help with this free guide from the North American Pollinator Campaign.
3. Prevent Unwanted Travelers: Some invasive species hitch rides on boats, so be sure to comply with all state and federal regulations regarding cleaning and managing watercraft for your destination. Check with park rangers for local details. 

All articles are for general informational purposes.  Each individual’s needs, preferences, goals and abilities may vary.  Be sure to obtain all appropriate training, expert supervision and/or medical advice before engaging in strenuous or potentially hazardous activity.