Invasive species, such as these quagga mussels at Glen Canyon National Recreation Area, are poised to upend some ecosystems in the National Park System/David Rankin via NPS

Invasive species, not the maintenance backlog, not the annual budget, and not political differences, pose the greatest threat to America's Best Idea.

The gustatory delights that the small native mammal species of Everglades National Park and neighboring Big Cypress National Preserve have turned into for non-native Burmese pythons is evidence of that. So, too, are the lopa trees at National Park of American Samoa, the quagga mussels of Glen Canyon National Recreation Area, the wild hogs in Big Thicket National Preserve, and the lake trout at Yellowstone National Park.

These and other invading non-native flora and fauna species are not only threatening to overrun some ecosystems in the parks, but in the case of vegetation, they are transforming landscapes.

"The Lopa tree spreads aggresively by being a prolific seeder, which outcompetes the growth of native trees. Lopas are also nitrogen-fixed trees, which are a major risk factor, causing bleaching of the coral reefs," warns the park staff at National Park of American Samoa. "Our native forest provide habitats and home to many native birds. No food source, no more native birds. Invasive species have a negative affect in the following areas: Ecosystems, Biodiversity, Recreation, Health and Economics."

The maintenace backlog can be overcome...if Congress appropriates the dollars. Roads can be rebuilt, buildings reshingled and painted, trails and campgrounds restored. The National Park Service budget can be made whole, equal to the task the agency faces in managing 419 units...if Congress appropriates the dollars. And politicians come and go, and their questionable decisions can be righted.

But invasive species threaten to not just reorder, but rewrite, ecosystems, and cures remain elusive.

At Everglades, mid-sized mammals have turned into a favorite prey of pythons, according to a 2012 study published in the Proceedings of the National Academy of Sciences. 

"The most severe declines, including a nearly complete disappearance of raccoons, rabbits and opossums, have occurred in the remote southernmost regions of the park, where pythons have been established the longest," a USGS release about the report said at the time.  "In this area, populations of raccoons dropped 99.3 percent, opossums 98.9 percent and bobcats 87.5 percent.  Marsh and cottontail rabbits, as well as foxes, were not seen at all."

Since that study came out, pythons have only continued to ravage the park. Last week, Everglades Superintendent Pedro Ramos told the Traveler that the onslaught on small mammals in the park, as well as birds and bird eggs, continues unabated.

"We continue to see that decline. We continue to notice the absence of animals like rabbits and raccoons throughout the landscape," he went on. "And while we may not fully understand the direct correlation between the snake itself, the python, and that decline, we do know for sure that the python invasion has had a lot to do with it.”

Across the country in Utah at Glen Canyon National Recreation Area, home of Lake Powell, invasive quagga mussels are impairing beaches, encrusting some boats, and threatening the hydropower operations of the Glen Canyon Dam.

The invading hemlock woolly adelgid was the downfall of most Eastern hemlock forests in Shenandoah (pictured) and Great Smoky Mountains national parks/NPS

"They ruin a lot of recreation areas that people typically like to visit just because they’re no longer really usable," Nathan Owens, the aquatic invasive species coordinator for Utah's Division of Wildlife Resources, told the Traveler in August 2018. "That’s kind of what we’re starting to see in a few areas at Lake Powell for the first time. I’ve been told by boaters, they’ve tried to pull up to land but they didn’t want to walk out because it was covered in mussels and they didn’t want to get cut up. So they just ended up going somewhere else."

At Yellowstone, some non-native lake trout were dumped into Yellowstone Lake sometime back in the late 1980s or 1990s, and while it's no longer expected that they'll completely decimate the native Yellowstone cutthroat trout, they won't ever be completely removed from the lake. That means the Park Service will continue to spend money every year on removal operations. It's not only costly, but the big trout's appetite for the smaller cuts has upset spawning in the lake's tributaries, and that in turn has affected meals for grizzlies and other predators.

Bears that used to pull spawning cutthroats from the lake's tributaries have had to look elsewhere, as have osprey, which can't normally dive deep enough to snare a lake trout. The lake waters have become more clear because the downfall in cutthroat trout numbers led to a boost in zooplankton. The fallout of that, according to researchers, has been a slight increase in water temperature.

"I’d say of all these cutthroat trout consumers, the osprey are definitely the ones that took the hardest hit in the Yellowstone Lake area," Todd Koel, a fisheries biologist at Yellowstone, said during a conversation back in March. "Once the cutthroat declined in the 2000s, the osprey declined in the lake area dramatically with them. So before the cutthroat decline, before the lake trout invasion, we would have an average of 38 osprey nests every year, from 1987-1991. Now, the current condition is we have about three. So greater than a tenfold loss of osprey nesting.

"And the nesting success crashed, as well. So not only did the (sheer) numbers, but then their ability to produce young greatly declined as well. They’re not fledging chicks."

Look around the National Park System and you'll find other invasives:

* Tamarisk trees grow and crowd out native willows and cottonwoods along the Colorado, Green, and Yampa rivers in Dinosaur National Monument, Arches National Park, Canyonlands National Park, and Glen Canyon; 

* Chinese Mysterysnails have been confirmed in the waters of Voyageurs National Park and are a threat to native snails;

* The mottled shell of an Asian shore crab has been discovered in the waters of Acadia National Park, evidence of a small, so far at least, invasion;

* Predatory lionfish have been spotted at Everglades and Biscayne national parks, and likely swim the waters of Dry Tortugas and Virgin Islands national parks, too;

* At Santa Monica Mountains National Recreation Area in California, so invasive are non-native weeds that the Park Service has recruited volunteers to pull them out;

* Obnoxious, and painful, Little Fire Ants have been crawling about in Hawai'i Volcanoes National Park, and led to extensive spraying efforts;

* Garlic mustard is among the exotic species growing along the Appalachian National Scenic Trail, and;

* The deadly-to-ash-trees emerald ash borer has shown up in a number of parks, including Shenandoah National Park, where the hemlock woolly adelgid long ago brought death to grand stands of Eastern hemlocks.

Seed pod of the invasive lopa tree at National Park of American Samoa/NPS

That's just a good start of a list of invasive problems in the parks. What damage, dollar-wise, they're doing is unknown, though it is estimated that parks are spending about $10 million a year attacking the invaders. What the cost to the natural ecosystems amounts to is anyone's guess.

The latest tally by the Park Service shows there were 1,428 populations of 308 invasive animal species reported in the National Park System this year. Of that  total, 25 percent of the invasive animal species are accounted for in park management plans; just 11 percent are reported as being "under control."

“It definitely is a very daunting task," Jennifer Sieracki, the Park Service's invasive animal species coordinator, told the Traveler. "We are dealing with a number of species that actually do a lot of damage to our parks."

Elaine Leslie, who retired from the Park Service earlier this year, is well aware of the problems, having been chief of biological resources for the agency. From her point of view, the Park Service and other federal agencies that deal with plants and animals need to get extremely serious in their battles with invasives.

“It’s just time for the Park Service and Fish and Wildlife Service and others to not be so afraid of new approaches and technologies, because you’re not just losing the battle in Everglades," she said. "You’re losing the ecosystem, the very reason that the park was established."

And if you think overcoming the maintenance backlog is tough, imagine the cost and effort it would take to rebuild an ecosystem.