Nonnative Species are Posing Management Challenges in Parks Across the US

Problem exacerbated by climate change, which has plants and animals moving beyond their historical ranges

John Soltes

While heading to the Bear Lake parking lot in Rocky Mountain National Park, I was aware of the preserved, splendid wilderness in all directions. The road meanders from civilization in Estes Park, Colorado, to the deep environs of a vast wild land that sits 9,475 feet above sea level. My goal for the day was a hike from Bear Lake to the Fern Lake trailhead, a trek of nearly 10 miles that allows hikers a chance to experience cascading waterfalls, high peaks, and dense forests.

Photo by Justin Ratcliff

Breaking a sweat and taking in the environment were the objectives, but I would not have been opposed to some wildlife sightings. Elk, bighorn sheep, and moose are common distractions in the park, resulting in traffic jams and selfie-taking tourists attempting to snag a closer look. Perhaps an elusive mountain lion or black bear would be in the cards — from a safe distance, of course. In reality, the largest species I saw was a pika, a small mammal that looks like a cartoon mouse with adorably large ears. However, unbeknownst to me at the time was that one species could have be seen on the hike, and if the sighting occurred, it would have been a rare and historically inappropriate encounter.

Defenders of Wildlife estimates there are 100,000 mountain goats in North America. The shaggy, cliff-dwelling mammals are often found in the northern Rockies in and around Glacier National Park in northwestern Montana. However, on occasion, a mountain goat will stray into the boundaries of Rocky Mountain National Park in Colorado, and then the National Park Service has a predicament on their hands. The goats are listed as a nonnative species for the park, but because they were introduced in the Mount Evans area by Colorado Parks and Wildlife, the animals sometimes travel north and enter the national park, according to the RMNP website.

When a goat is found in Rocky Mountain, disease spread to the native bighorn sheep becomes a real possibility. “We’ve had a couple of instances where we’ve seen mountain goats come into Rocky Mountain National Park,” said John Mack, acting chief of resource stewardship for RMNP. “To tell you exactly where they came from, we wouldn’t know.”

Mack admitted that it’s pretty rare to find mountain goats in the park, but when they do turn up, there’s a process in place to deal with the animals and their potential to cause harm.

“The first [thing] that we do is we try and see if there are any photos or get a location of where it was spotted,” he said. “Then we would send up some of our park employees who, if you will, verify the sighting. Sometimes people make incorrect sightings. They’ll think that they see a mountain goat. It’s something else or maybe a bighorn sheep, and so we first try to actually get a positive identification of the animal. Once we get a positive identification, then we have to kind of do an assessment of where it’s located, and then we follow our own procedures and protocols to first [contact] Colorado Parks and Wildlife, because we work cooperatively with them, to see if they are maybe wanting the animal back. And that’s only if it’s maybe located in an area where we could safely anesthetize it, and safely transport it out and turn it over to Colorado Parks and Wildlife.”

On occasion, Rocky Mountain National Park officials have to use “lethal removal” when a mountain goat comes into park boundaries. Such a decision is based on the location of the animal. Because these goats can climb to some precipitous, dangerous heights, safe extraction is sometimes impossible. Mack has seen these fatalities occur in his career.

The concern among park officials is not only that the mountain goat will spread disease to bighorn sheep, but also that it would contribute to habitat degradation, or both. They don’t want a situation in which mountain goats are competing for the same resources as native species.

Human Encroachment

Photo by Tim Wilson

Life in a national park, both for the animals and the employees, has changed in recent years. Parks are seeing record visitors, and this can cause unique habitat problems and difficult management decisions. More crowds mean more opportunities for visitors to inadvertently bring exotic plant seeds as well. That situation is not as iconic as a mountain goat performing a balancing act on a snowy ledge, but it’s arguably more of a pressing issue. There’s evidence of these exotic plants at some trailheads and roadsides in the park.

“So we have a lot of concern dealing with invasive exotic plants like cheatgrass, and Canada thistle and, you know, some of these really bad exotic plants that 20 years ago or so were never really an issue, and due to a whole host of other environmental factors, and increasing visitation and maybe disturbed areas, we’re starting to see invasive plants show up in places that they never have before,” Mack said. “We also have concerns with what we call aquatic invasive species, so there’s ... the chytrid fungus that is really devastating to native amphibian and frog populations, and so we have a native boreal toad here in Rocky Mountain National Park. And all over the last couple of decades our research and information suggests that the population and the areas where they used to have been found from, let’s say 20 or more years ago, is probably only 10 percent of what it used to be.”

Rocky Mountain officials also work with local guides to educate them about disinfection protocols for visitors who wish to fish the pristine backcountry lakes in the park. The guidelines call for removal of mud, snails, algae, and debris from nets, boots, waders, and other equipment. Anglers should wash the equipment and follow a host of rules, including soaking the equipment in a solution and freezing their gear.

Climate change is also a concern for species moving into areas where they have never been historically. “I think cheatgrass really wasn’t found in Rocky Mountain National Park much above 7,000 feet or so, and now we’re starting to see it in places up to 9,000 feet,” Mack said. “So we’re starting to get exotic plants at elevations that we’ve never seen before. We’re doing our level best to combat that, so where we find these invasives starting in small populations, we’re trying to eradicate them as quickly as possible using all the appropriate means and methods, but it’s becoming more of a concern for us in Rocky.”

It Came From the Land and Water

Over in upstate New York, Brendan Quirion, manager of the Adirondack Park Invasive Plant Program, doesn’t mince words when describing the invasive species that have wreaked havoc in the Adirondack Mountains.

“For New York in general, it’s a tremendous issue,” he said. “New York is really the gateway for many of the invasive species that we’re currently dealing with and for many more that are on their way. New York is kind of ground zero for invasive species into the rest of the country, so our efforts here are really focused on prevention and not only protecting New York but really the rest of the United States.”

The organization splits its efforts between two project coordinators, one for land-based species (Japanese knotweed, phragmites, giant hogweed) and one for aquatic species (Eurasian watermilfoil, water chestnut, spiny water flea, Asian clam).

From Quirion’s perspective, based on the evidence he has gathered, the most prominent reason behind the spread of these invasive species is “human-based movement.” The land-based species are spreading through road corridors and maintenance activity. Examples would be the movement of contaminated fill and mowing activities along the corridors, he said. In the water, the problem can be found with recreational watercraft that are not properly decontaminated.

“We’re actually focused more on prevention, early detection, and rapid response,” he said. “We do a little bit of research and partnership with local universities, but we’re really the boots on the ground, so to speak, actually doing the work to control infestations and prevent them from spreading.”

Lake Champlain Woes

Photo by Benjamin Scott Florin

On Quirion’s radar right now is the current status of Lake Champlain, along the border of New York and Vermont. The southern end of the lake has “very extensive water chestnut infestation.” The only way to keep the water clear for boaters is to go in with mechanical harvesters every summer and harvest the southern portion of the lake of water chestnut. “If they didn’t do that, it would just be a map of weeds across the entire surface of the water, so that’s one horror story,” he said.

The impacts to the ecosystem can be severe. Quirion called the nonnatives “bullies” because they come in and push out the native species of fish, wildlife, and other native plants.

“Managing invasive species currently is more difficult because you have increased global trade,” he said. “You have climate change in the wings that is really throwing a wrench on where species can establish and spread, and you just have more habitat disturbance as a result of urban sprawl. So the impacts that we’re seeing from invasive species are certainly exacerbated in this day and age, but they’ve been around for a long time.

“I mean, we’ve lost entire tree species from the landscape because of invasives that came in over 100 years ago. American chestnut used to be the most prominent tree species in northeastern forests, and it is essentially wiped out. Another example is the elm trees that we once had. Dutch elm disease came in, and we no longer have elm trees. So it’s not a new topic, but it requires a more urgent action because of the different exacerbating factors that we’re now faced with.”

The Adirondack Park Invasive Plant Program is funded through the New York Environmental Protection Fund. However, the outfit considers itself a private organization and is housed under the Adirondack chapter of The Nature Conservancy. This interesting structure allows for a quick response and sidestepping of governmental bureaucracy. The program has been prioritizing education to foster early detection and rapid response to tackling nonnative species as and when they appear because it’s easier to stall their spread when their populations are still small.

“What invasive species [cause] is a much slower death of the ecosystem or the species under consideration,” Quirion said. “What we often see is it’s almost so slow that people don’t realize it’s even happening until it’s too late, so it’s already killed off the trees on their property. It’s already taken over their yard, or their wetland that [they] care about, and at that point, it’s almost too late.

The work is paying off. In 2008, when Quirion was working for the state Department of Transportation, he mapped nonnative species along the Route 3 corridor from boundary to boundary of the Adirondacks.

“The park is 6 million acres in size, and at that time, I mapped hundreds of infestations along Route 3 of mostly phragmites and Japanese knotweed,” he said. “If you go back to that same road corridor now, you are taxed to try and find a phragmites infestation along that same road corridor. We’ve had response teams out since 2011 doing comprehensive management of our target species across the landscape, and we’re processing the data from this past season right now. But what we’ve been able to demonstrate is if you can catch these infestations while they’re still small, you have a really high chance of eradicating them, at least locally, from the landscape.”

For aggressive plant species, herbicides are used. Sometimes even pulling plants out by hand is effective. On the aquatic side, hand harvesting is used primarily, though sometimes chemical treatments are unavoidable. The program has also experimented with biocontrol, a method of trying to find and use a natural predator to stop the nonnative species.

“Essentially you can go back to where the invasive species came from, somewhere else on the planet, and try and find a predator or a pest of the species there that you can bring back to the United States and release here to feed on it,” Quirion explained. “Now, you have to do a ton of research to make sure that the species you’re bringing over does not in itself become invasive when you release it, but we’ve been able to do that for certain species. For example, purple loosestrife; there’s now a beetle available that you can release on purple loosestrife, and it will feed only on the purple loosestrife and really keep it in check. So there’ve been some good success stories of biocontrol in just the past decade.”

Where are the Marsh Rabbits?

Photo by Holmes Palacios

The issue of nonnative species is not relegated to colder climates. Florida and Everglades National Park have long been dealing with a python infestation that has become legendary in habitat management circles.

Bryan Falk, research ecologist for the US Geological Survey at the Daniel Beard Center in the Everglades, is on the frontlines of tackling this threat lurking in the grass. “Invasive species in general are a big issue, so that term invasive means that they have a large ecological impact,” Falk said. “Pythons specifically have a large impact on a large number of mammal and bird species that they prey upon,” he said. “For example, in Everglades National Park, there used to be a lot of marsh rabbits. I’ve been here for about three years, and I’ve never seen a marsh rabbit in the park. And we think that’s because pythons have eaten all of them.”

There are a couple of theories on how the pythons made their way to different locations throughout Florida. Falk mentioned the infestation being the result of the pet trade. “Some people think that Hurricane Andrew in ’92 demolished an importer facility, and that’s how they were released,” he said. “[But] there was a study where they used a model, and they made some assumptions about demographic parameters. And that model suggested that the introduction probably happened in the ’80s or before, so we don’t know the specifics of it. And we probably will never know, but the general consensus is that they did ultimately come from the pet trade.”

There are several species of pythons present in the Everglades and other nearby regions, but Burmese pythons are certainly the most widespread and numerous among these, Falk said. There’s even one population of Burmese pythons closer to Miami that has been there for decades. A population of African rock pythons too, has been discovered near Miami and right outside the boundaries of the Everglades. A couple of yellow anacondas (a boa constrictor species that’s often confused with pythons) have been seen in southern Florida, but Falk hasn’t heard of a recent sighting.

“Initially a lot of the effort was focused on understanding the impacts,” Falk said. “Most herpetologists wouldn’t have thought probably at the time that Burmese pythons would be invasive, so early efforts were actually documenting the effect that they had on the environment. Now there’s a general consensus that they are having a negative effect, so most of our research is focused on how we can get rid of them.”

Falk and his team have agreements with Everglades National Park and other federal properties to conduct research on the snakes. He also corresponds with the Florida Fish and Wildlife Conservation Commission, state parks, the University of Florida, and other universities. “I would say in general there’s a consensus among people working on the problem that the problem crosses jurisdictional boundaries, and so we all try to work together to kind of cross over those hurdles as easy as possible,” he said.

Most of the specimens that Falk encounters are 8 feet or shorter in length. There have been a few larger ones at more than 15 feet, but those sightings are rare. During the month of August, the team often finds pythons in the 3-feet range because they have been recently hatched.

The average park visitor at the Everglades would be extremely lucky (or unlucky) to see a Burmese python. They are hard to find, even if they are located right off the road. Falk also said the snakes are generally not aggressive, and they could go undetected at close distances. Most sightings occur when the snakes cross a road.

One thought — a thought Falk doesn’t wish to entertain — is whether pythons and other nonnative species should be considered the “new” native. Is it possible that some of these species will be around their new ecosystems forever?

“The problem is all the other things that come along with that if you accept that,” he said. “If you think about an ecosystem, you think about all these little parts that are working together to keep it stable and functioning properly. And all the little parts are things that marsh rabbits do, and raccoons do, and possums do. We take those out, and the ecosystem works differently. And so if we accept that we’re just going to leave pythons there, leave invasive species there, it means that we also accept all the instability and ecosystem dysfunction now that we’ve introduced into the system with the invasive species. So I would say, in general, no, people do not want to just let them be and let them follow through because that means we have a dysfunctional ecosystem.”

Correction: An earlier version of this article identified the Adirondacks as 60 million acres in size. The park encompasses 6 million acres.