Exotic invaders besiege U.S. parks
Published 4:00 am, Sunday, April 29, 2007
The fallow deer of Point Reyes National Seashore are regal animals, tall and muscular with spotted fur and antlers like moose. They're easy to spot on the meadows and hillsides of the park, grazing in large herds.
But they don't belong there.
They are invaders from central Asia, introduced three generations ago for the benefit of hunters. Scientists fear they are driving out native black-tailed deer that have been there for centuries but could vanish within our lifetime.
From Point Reyes to Everglades National Park, many experts say, invasive species of every size and description are changing the very ecology of America's parks and public lands. The National Park Service says it is bound by law, including the statute that created the agency in 1916, to act.
It is of acute concern at Point Reyes, which is among the most biologically diverse places in the world. Seventeen percent of California's plant species, 45 percent of all bird species on the continent and 30 percent of the world's marine mammal species live in a park just three times the size of San Francisco.
That complex ecosystem is under attack from within. Foreign species introduced over the past century are pushing out endemic plants and animals at an increasing pace, and they are moving beyond the park into Marin County.
Beach grass from Ireland has pushed the western snowy plover from coastal dunes. Eastern bullfrogs and mosquito fish from the American Southeast kill endangered red-legged frogs. A European sea squirt that has blanketed vast tracts of the North Atlantic now lives in Tomales Bay.
Individually, invasive species are a nuisance. Collectively, they threaten to reshape within decades ecosystems that evolved over millennia.
"We're at a moment in history where we must save California's natural heritage," said park Superintendent Don Neubacher. "If we don't address this in the next 20 to 50 years, a significant part of that heritage will be lost forever."
Critics argue Neubacher is an alarmist. They say ranching, development and the 2.5 million people who visit the park each year do far more harm than a few hundred fallow deer or a pond full of bullfrogs.
Evidence suggests ecosystems can thrive for decades with invasive species before reaching a tipping point beyond which the invaders expand exponentially. The ecosystem becomes homogenized, dominated by a few hardy species in the environmental equivalent of suburban strip malls filled with big-box retailers.
It's happened on islands in the South Pacific. There are signs it's happening in Bodega Bay.
Ecologists call invasive organisms the greatest threat to endangered species after habitat loss -- a significant concern at Point Reyes, home to at least 27 species of threatened or endangered plants and animals.
Nationwide, about 400 of the 958 species protected by the Endangered Species Act as of 1998 are at risk primarily because of predation by, or competition with, invasive species, according to a study published in the journal Bioscience. The number of protected species has since grown to 1,285, according to the U.S. Fish and Wildlife Service.
Humans have moved plants and animals around the world for eons. The U.S. Geological Survey says there are at least 6,500 nonnative species in the United States. Cornell University researchers place the figure closer to 50,000.
The issue goes beyond the National Park Service. Studies show that invasive species cost the nation $138 billion annually in economic losses and environmental damage.
Point Reyes spends $750,000 annually combatting invasive species and will spend $20 million during the next five years restoring the Giacomini wetlands and other habitats to protect endemic species like the red-legged frog.
It is one of many parks grappling with the issue. But it typifies the many ways the pests are introduced, the challenge of removing them and the opposition many people have to government tinkering with the environment.
A rancher introduced fallow deer and the less commonly seen axis deer to the area in the 1940s. Their numbers have ebbed and flowed with the effort to control them; park officials estimate there are about 1,100 roaming the park.
Fallow deer are voracious eaters and more aggressive than the endangered tule elk, and they carry Johne's disease, an intestinal disorder often fatal to native deer. They have few Northern California predators. A study by the U.S. Geological Survey found Point Reyes would have 900 more black-tailed deer without the invasive deer.
That worries park biologist Natalie Gates and other biologists because black-tailed deer are a keystone species critical to the park's health. They control vegetation and are the primary prey for mountain lions.
Park rangers shot 2,700 exotic deer between 1976 and 1994, when park superintendent Neubacher scuttled the practice pending a formal management plan. The plan approved in December calls for sterilizing some deer and shooting others. The 15-year campaign is to begin later this year; the goal is to eliminate the invasive deer by 2027.
The plan is supported by the Sierra Club, the Marin Conservation League and others. But it is opposed by many local residents, naturalist Jane Goodall, the Marin Humane Society and In Defense of Animals. They argue the park is exaggerating the problem and say the deer can be managed with contraceptives or by sending them to a preserve.
"Parks are not static things. They're constantly changing," said veterinarian Elliot Katz, president of In Defense of Animals. "The thinking is a new species has moved in, it's causing a problem, so let's kill it. We should try to see if there is another way to solve the problem."
Few people objected when the park cleared beach grass by the ton in recent years from 50 acres of coastal dunes near Abbott's Lagoon at a cost of $400,000.
In their natural state, Northern California's coastal dunes are mostly open sand dotted by about a dozen species of plants. Seventy years ago the U.S. government recommended planting beach grass and other exotic plants to keep sand from blowing around.
Greater environmental awareness brought a re-examination of that policy. Beach grass dominates the landscape, eliminating most native vegetation and robbing shorebirds of nesting grounds. Nothing eats beach grass, so there's nothing to remove it.
Eradicating it is straightforward: Yank it out and let nature run its course.
Within six months of the restoration of Abbott's Lagoon, endangered plovers returned and raised 11 chicks, said Jane Rodgers, a vegetation ecologist at the park. Beach layia and Tidestrom's lupine, two threatened plants, and seven other species of native vegetation returned as well.
Given that success, park officials hope to restore the remaining 750 acres of coastal dunes, beginning with a $2.2 million campaign to restore 300 acres of dunes south of Abbott's Lagoon in 2010.
Eastern bullfrogs and mosquito fish are harder to eradicate.
Bullfrogs, introduced to California as food after the Gold Rush, live in ponds and marshes throughout the park. And nonnative mosquito fish have started turning up in recent months, said biologist Gary Fellers of the Geological Survey.
When they aren't eating red-legged frogs and tadpoles, bullfrogs compete with them for food. Mosquito fish -- introduced to California to control mosquitoes -- prey on the red-legged frog, Pacific tree frog and endangered California newt tadpoles.
Removing all the bullfrogs and mosquito fish -- both likely introduced by people who couldn't predict their consequences -- is all but impossible. However, biologists hope they can keep them from spreading to other areas, Fellers said.
Possibly more problematic is a sea squirt called clonal tunicate. The invertebrate looks and feels like a dirty sponge. It turned up in Tomales Bay four years ago, most likely in ballast water dumped from freighters.
Clonal tunicate envelops and suffocates almost everything it touches and is almost impossible to eradicate. It has blanketed more than 88 square miles of the Georges Bank fishing grounds in the North Atlantic since its discovery there in 2003, according to the Geological Survey.
That alarms marine biologists in California because some 2,000 species, from the smallest invertebrate to harbor seals, live in Tomales Bay. If the tunicate establishes itself, it could disrupt the entire food chain, said Ben Becker, a marine ecologist at the park.
"If it establishes itself on the floor of the bay, it will have grave impacts," he said.
Studies suggest ecosystems can tolerate some level of infestation before reaching what ecologists call invasional meltdown -- a point at which an invasive species grows so dominant that the natural system collapses and the invaders take over exponentially.
"We know that some of these species can change a habitat significantly and make it hospitable to other species," said Ted Grosholz, a UC Davis ecologist. "You can reach a point where the system is so overloaded, so compromised that it becomes easier for invasives to move in."
Grosholz has seen the nonnative eastern gem clam live for decades in Bodega Bay alongside two species of native clams, Nutricola confusa and Nutricola tantilla, until the European green crab arrived in the mid-1990s. The crabs have decimated the native clam population, and the gem clams now dominate.
Grosholz and other ecologists credit the park service for its assertive approach but complain that the issue of invasive species has gone largely unnoticed in the years since President Bill Clinton signed an executive order in 1999 directing federal agencies to minimize the number of invasive species in the country and their impact on both commerce and the environment. They say there must be greater cooperation among the agencies charged with addressing the issue, and the government must be more proactive.
Chris Dionigi, assistant director of the National Invasive Species Council, said the government is trying to be more aggressive but will be playing catch-up for years to come because there are so many species migrating into, and out of, the country.
"We're at the point where we need to get serious about addressing this issue," he said. "The sooner you act, the smaller the impact and the lower the cost. The longer we wait, the more difficult it becomes."