As the helicopter descended beneath a thick band of clouds, conservation worker Michael Ade scanned the horizon of a dense native Hawaiian forest, looking for an old base camp where he and another worker would spend several days eradicating the latest alien plant invader — a pampas grass called Cortaderia jubata.

The flights and campouts are familiar to conservationists like Ade who work for the Maui Invasive Species Committee. In the past decade, workers have taken dozens of helicopter rides and spent millions of dollars to reduce the presence of Miconia calvescens — a plant that ruined about two-thirds of the Tahitian rain forest and was threatening Maui’s watershed.

As Hawaii continues with costly extraordinary efforts to rid pristine native forests of one invasive plant after another, environmentalists and scientists here and elsewhere are beginning to criticize the U.S. Department of Agriculture’s system of protecting the country from destructive alien plants.

Critics say the system of screening for noxious weeds used by the department’s plant inspectors is inefficient and ineffective, costing taxpayers tens of millions of dollars annually. It also threatens native vegetation and agriculture and lacks a balanced approach to conservation, they maintain.

As federal and state agencies spend millions of dollars annually in Hawaii to try to control stifling weeds, the USDA allows some of the same destructive alien plants to enter the country and to be distributed and sold between states.

Harm from alien, invasive plants in the United States amounts to $3.6 billion to $5.4 billion annually in pesticide control efforts and crop losses,according a congressional study by the Office of Technology Assessment.

The report was done in 1993, two years before Congress defunded the office, impeding further scientific reports.

In the 20 years since the report, not much has changed as far as screening out undesirable alien plants, said Florida biologist Don C. Schmitz, the coordinator of the scientific group North American Species Network.

"About a fourth of U.S. agriculture’s gross national product is lost to foreign plant invaders and the cost of controlling them," Schmitz said.

California spends about $82 million annually to fight invasive plants, according to the California Invasive Plant Council.

In the past 20 years, Florida has spent more than $40 million trying to eradicate a single tree — the Melaleuca quinquenervia — from its southern wetlands.

And here in Hawaii in the past five years, about $17.7 million has been spent to fight invasive plants alone, according to the National Resource Conservation Service.

The costs of battling invasive species will continue to escalate as long as there is a lack of accountability in the USDA’s screening system, critics and observers say.

For example, the agency has the power to determine whether plants enter the country, and should an import become a problem in wildlife and watershed areas, USDA defers responsibility for addressing it to other federal agencies or to states.

"The big problem is no one’s really in charge," Schmitz said. "There’s a lack of leadership."

The Star-Advertiser sought more information and comments from both the office of U.S. House Agriculture chairman Frank Lucas and U.S. Senate Agriculture chairwoman Debbie Stabenow but received no response to email requests.

USDA Plant Quarantine Division spokesman Ed Curlett would not comment on the agency’s leadership.

THE CONSEQUENCES of a broken system when it comes to dealing with harmful plants can be devastating in Hawaii, sometimes called the "endangered species capital of the nation."

Of the 853 plants on the federal endangered species list, 395 (or 46 percent) are native to Hawaii, according to the U.S. Fish and Wildlife Service.

In the past 37 years of having a Federal Noxious Weed List that could be key in protecting Hawaii’s native species, the USDA has banned only 120 of more than 250,000 known plant species in the world.

Although a federal noxious weed list exists, states like Hawaii have developed their own lists of undesirable alien plants which they believe are more comprehensive.

The last time the USDA added to its list was in December 2010, when nine species brought the total to 120. By comparison, there are more than 206 on California’s noxious weed list alone.

"The list is too short," said Mark Fox, the Nature Conservancy of Hawaii’s director of external affairs.

"More work needs to be done to evaluate plants that not only threaten Hawaii but also the rest of the country."

Environmentalists note that getting a plant on the federal noxious weed list often takes several years — enough time to allow it to effectively become a permanent resident.

Since the Federal Noxious Weed List was created, officials have added species "carefully and deliberately, considering not only the impacts of the species, but also the impacts of the regulations themselves," Curlett said. "The initial FNW list had 22 species on it. Since then we had added many more."

If a plant is not on the federal list, the danger lies in nurseries, botanical gardens, arboreta and plant collectors assuming it presents no problem to agriculture or the environment.

Although states have developed their own noxious weed lists, they do not carry the same authority as the federal government’s. For example, while Hawaii can launch multimillion dollar campaigns to clear invasive plants, the state lacks the power to force a landowner to eradicate a plant on its list.

Hawaii can, however, enter into cooperative agreements with landowners to remove undesirable plants, said Neil Reimer, state Plant Pest Control Branch manager.

The state noxious weed list has no impact on the sale or movement of plants, "crippling the program," Reimer said.

Curlett said it is not USDA policy through its Animal and Plant Health Inspection Service to evaluate banning plants that are bought and sold commercially and known to be widely prevalent, like pampas grass, sometimes used in floral arrangements.

The criteria used to determine if a plant is on the federal noxious weed list prevents many invasive plants that turn up in Hawaii from being banned, University of Hawaii biologist Curt Daehler said.

Under federal law, to be put on the list a plant must have the potential to be destructive to a large portion of the United States — a requirement that disqualifies tropical plants that cause serious problems, but only in a handful of states in warm, southern regions, critics say.

"Because Hawaii is generally a tropical environment, most of our problem species are tropical, and they cannot survive throughout most of the United States," Daehler said.

Also under federal law, a plant that has become too "pervasive" to be eliminated keeps it from being put on the federal list.

Because pampas grasses have become pervasive in many areas, none has been put on the federal noxious weed list. But two of them — Cortaderia jubata and Cortaderia Selloana — are listed as species that shouldn’t be planted in California by the state’s Department of Fish and Wildlife.

Native to South America, pampas grass is also pervasive in Oregon and Washington state, according to the Natural Resources Conservation Service.

Because pampas grasses aren’t on the federal noxious weed list, ornamental nurseries in East Coast states are able to distribute and sell them.

In fact, the North Carolina Nursery and Landscape Association has the pampas grass, Cortaderia selloana, on its Buyer’s Guide pick list of plant selections.

North Carolina weed specialist Rick Iverson said his state Plant Industry Division has done no risk assessment of the two pampas grasses, Cortaderia selloana and Cortaderia jubata, that are problems in Hawaii and on the West Coast.

Iverson said using the "pervasive" criterium to determine if a plant should be on the noxious weed list can be misleading and inappropriate.

He said a more meaningful basis for determining whether a plant is invasive is whether it can be quarantined.

Environmentalists and scientists say USDA officials have sometimes taken no action to ban the import of plants that could have a devastating effect in conservation areas.

For example, Hawaii has spent millions to battle Miconia calvescens. It, too, isn’t on the federal list, although National Park Service employees are battling to keep it out of native forests on Maui and Hawaii island.

Victoria Branson,chairwoman of the California Invasive Species Advisory Committee, said as a result of differing state and federal lists, USDA inspectors at borders allow entry of plants not on their list that could be on a state noxious weed list.

"So there is protection of invasive plants on the state list but not on the federal list," she said. "It would be really great if federal inspectors just expanded their scope and worked collaboratively with the state."

On Maui, where the state has spent hundreds of thousands of dollars to control pampas grass in the past 10 years, a property owner has refused to allow state officials to remove it from his land in light of there being no federal ban on the plant.

"They like them. They don’t see any reason to remove them … It’s frustrating," said Adam Radford, operations manager for the Maui Invasive Species Committee.

"Is the camp along the ridgeline?" the pilot asked.

"No," said Ade, a supervisor who had made numerous trips to the camp. "Just keep going in the direction you’re going."

The flight carried some risk, as clouds move in and out quickly on Maui, sometimes obscuring the landscape.

But the pilot picked a good day to fly, with less wind and rain, and touched down on one of the few flat spots on a ridge.

With the helicopter rotors still spinning, the environmental field workers scampered out.

Ade and fellow workers spend a week at a time in tents on wooden platforms in rainy wilderness at two separate camps in East Maui, using a combination of defoliants and physical labor to kill weeds.

In West Maui, the terrain is too steep and inaccessible in many areas to set up camp, so eradication efforts are conducted mostly from the air.

Program manager Teya Penniman said the workers, who receive extensive safety training, realize what they’re doing is critical to save the native environment.

"We wouldn’t be doing it if we didn’t think it was important," she said.

The latest alien plant invader, Cortaderia jubata, is declining in East Maui because of the work being done by invasive species workers.

On the other hand, they have found out from other expeditions that there is more Cortaderia jubata in West Maui than they initially estimated.

There is a sense of urgency for the conservation workers to get to work in problem areas of West Maui as soon as possible because delays increase the challenge ahead.

"If we can’t fly in for a year, we miss a whole reproductive season and the plants reproduce," she said. "It sets us back by years."