Natives Crowded Out : Species That Run Amok: A Quiet War

GERBODE VALLEY, Calif. —  It was no ordinary stakeout. But then, this was no ordinary crime.

The man crouched behind the bushes was not a cop, and he was not tracking a robber. He was a volunteer ranger in the Golden Gate National Recreation Area, and he was on the trail of cagier prey. He was stalking a rogue gardener.

Someone, for some reason, has been seeding the park north of San Francisco with South African capeweed. Rangers, required by law to keep the park in a natural state, have been scrambling to tear out the thick, fast-growing pest before it chokes out native grasses, bushes and berries.

So far, the capeweed is winning.

Battle Against Exotics

A small problem in a out-of-the-way part of California? Perhaps. But it is also the latest battlefront in a quiet world war against undesired non-native, or exotic, species that are killing off less hardy but more interesting--and maybe ecologically more important--native plants and animals.

Park rangers, scientists and others around the country, and worldwide, are locked in combat with unrelenting armies of exotics. Not only do they battle South African capeweed, but also the Australian melaleuca, Japanese grass, Himalayan raspberries and Russian thistle.

The National Park Service says exotic plants are the most widespread threat to the natural resources of the parks. Park Service rangers recently ranked exotic plants ahead of such other problems as wildfires, overcrowding, pollution, vandalism, oil drilling and off-road vehicles.

“People don’t realize it, but the problem is enormous,” said Cliff Smith, a University of Hawaii botany professor and an exotic species scientist at the National Park Service.

Flourish as Pests

Plants and animals need not be striking or fascinating or even unusual to qualify as exotic. Scientists consider species exotic after they move from one place to another, sometimes between continents, and flourish as pests in their new homes.

Thus, mongooses are exotic in Hawaii, but so are mountain goats in parts of Washington and rainbow trout in Tennessee. So, too, is the capeweed--ordinary freeway-median ground cover--in California, and feral house pets everywhere.

The problem is not just one of aesthetics. Scientists warn that exotics can impinge on agriculture, push endangered native species closer to extinction or in runaway cases restructure entire ecosystems with unknown consequences.

National Park Service biologist Gary Johnston cited as one example the case of mongooses being introduced to Hawaii and the U.S. Virgin Islands as a means to control exotic rats.

“But mongooses operate mainly during the day while rats go out at night,” Johnston said. “As a result, they rarely met. In the meantime, those mongooses have had a tremendous impact (by eating) ground-nesting birds and reptiles, including two endangered species.”

In Hawaii, Smith said researchers have found 4,000 plants not native to the islands. Of those, nearly 850 thrive and reproduce without human cultivation--and spread like weeds. By comparison, there are 892 native Hawaiian plants.

“What we are essentially saying is that half of all our . . . flora has been (artificially) introduced,” he said. “It (the spread of exotic species) is a remarkably invasive and intrusive problem.”

Problems Across Nation

Other states are less severely affected than Hawaii, but exotics are a headache from wetlands in Florida’s Everglades to forested mountains along Washington’s Olympic Peninsula and from the Great Smoky Mountains to the Mojave Desert.

Johnston and others said exotic species can thrive at the expense of native plants and animals because the exotics usually lack natural enemies in adopted environments. Without predators or diseases to thin their numbers, they simply crowd out not-so-fortunate native species.

“I do not believe that there is any such thing as a bad plant,” said Greg Archbald of the Golden Gate National Park Assn., which recruits volunteers and raises money to supplement the park’s funding. “They (exotics) are living things, and they are on our planet. But when you come right down to it, this is a managed natural area and we are supposed to manage it to keep it natural.”

“The point of having national parks is to preserve areas as distinct parts of America, just as the Everglades are a living example of the natural history of southern Florida,” said Peter Doren, an Everglades National Park scientist and vice chairman of the Miami-based Exotic Pest Plant Council. “If melaleuca takes over, what will people see? Whatever it is, it won’t be the real southern Florida.”

Beyond that, scientists worry that exotics often so successfully out-compete native species that they create areas called monocultures in which only one type of vegetation or one kind of animal survives.

“The species (in one particular area) originally have developed there over hundreds of thousands of years and have adapted to all the area’s stresses,” Smith said. “Species introduced artificially in the last 100 years generally have not. . . . These very large monocultures can crash, and when they crash, they leave nothing behind them.”

Some exotic species were introduced to these areas out of ignorance, others out of carelessness. Apparently, few species are inflicted on an area with the malicious intent that investigators attribute to the man suspected of planting capeweed near San Francisco.

Strawberry guava came to Hawaii as a commercial venture, but Smith said its attractive fruit now is usually eaten by feral hogs, which later excrete guava seeds over more and more of the state.

Melaleuca trees were imported from Australia by developers eager to use the species’ remarkable thirst to drain Florida swamps for farms and houses. Doren said the trees instead threaten to drain Everglades National Park.

Pampas grass came to California as an ornamental plant for landscaping. But feathery seeds from its distinctive panicles, or plumes, have long since spread the tenacious plant widely. English ivy is another ornamental plant headache.

Mountain goats, meanwhile, were transported to the Olympic National Park as game animals. Johnston said the goats consume much of the available forage and trample the rest, disrupting native plants and starving native animals.

One surprising example is the Russian thistle. Cowpokes call it tumbleweed, and as such it evokes romantic images of the unspoiled West. Botanists see the humble tumbleweed as just another pest in Death Valley and the Grand Canyon.

Many of these exotic pests are so pervasive that the Park Service is trying to find some way to control or eliminate them without resorting to essentially weeding millions of acres of public land with hand tools and volunteer labor.

Biological controls are the preferred method, but they can take up to 15 or 20 years to develop because scientists try to make certain that by introducing a new exotic species to an area they will only control a pest and not wipe out any more native species.

Despite the difficulty of being absolutely certain of all the consequences, scientists say safe biocontrols can be isolated and used. In Redwoods National Park, for example, biologists are controlling the exotic Tansy ragwort, a tiny herbaceous plant, with exotic moths and beetles that feed on it.

Often, however, such solutions have not yet been found. Volunteers wielding razor-sharp tools are the only way to cope with the capeweed left behind by the Golden Gate National Recreation Area’s rogue gardener.

That person, whom park volunteer Tom Ness of San Francisco has shadowed and reported to federal prosecutors, is believed to have spread the capeweed along “virtually every trail up here,” Ness said--a distance of 20 miles or more. Eight volunteers recently needed an entire day to rip up thick, tenacious mats of capeweed from about 50 feet of trail.

Ness said the person he reported to prosecutors has a grudge against the government stemming from past tax problems.

Archbald, his hands muddy and cut from wrestling capeweed from the soil and unknotting it from native berry vines, said his volunteers are not discouraged from their seemingly Sisyphean task.

‘Going to Lose This Battle’

“He (the phantom planter) is going to lose this battle eventually because people will care about the park a lot longer that he will live,” he said. The biggest problem, he added, is that capeweed distracts volunteers from clearing out the 28 other problem exotics that have accidentally invaded the park.

Volunteer Sophia Sparks of San Francisco said the capeweed caper may seem like an eccentric prank but is more akin to arson.

“This is kindling here,” she said, holding a length of capeweed, “but if left alone, in 100 years it will lead to the equivalent of a wildfire. Habitat will be destroyed. Rodents can’t eat it, so they would be driven out, and with them would go the hawks that prey on the rodents, and so on and so on.”