• Pacific Invasion

    New technologies combat super weeds that threaten Kaua’i's forests.
    By Matt Jenkins
    Photographs by Ethan Welty


ust inland from the Hawaiian Island

of Kaua‘i’s famed Na Pali coast, Jim Hobbs flies a Hughes 500 helicopter high over sharply serrated ridges that are draped with a million shades of green. To the north, the breakers of the blue Pacific sparkle.

“I knew it was gonna be a good day when I walked out the door this morning,” Hobbs says from the pilot’s seat, his voice crackling through the helicopter’s intercom system.

Every bit of good weather here is welcome. Home to some of the most rugged terrain on the planet, Kaua‘i is also one of the rainiest spots on Earth, and flying in the island’s canyons is extremely challenging. In the helicopter’s backseat, Stephen Ambagis monitors a pair of cameras as they create a finely detailed map of the ground below, while Hobbs flies the helicopter 1,000 feet over the landscape—the exact altitude necessary for the cameras to work correctly.

When Wainiha Valley suddenly opens below, the diminutive helicopter shudders mightily as Hobbs drops elevation to keep the required 1,000 feet above the ground. “I’m going down as fast as I can,” he says, but even the nimble Hughes 500 can’t keep up with the precipitous topography.

Kaua‘i is rugged and beautiful, but it is also threatened by a host of invasive plants and animals. One of those invaders is the Australian tree fern, a fast-reproducing ornamental that was brought to Kaua‘i almost half a century ago to prettify resorts on the island’s North Shore. It rapidly grows frond to frond and crowds out native plants.

“I’ve been fighting weeds for 20 years and I’ve never seen anything like the Australian tree fern,” says Trae Menard, The Nature Conservancy’s director of forest conservation in Hawaii. “It’s a pretty bad weed.”

The Conservancy and several other organizations that make up the Kaua‘i Watershed Alliance manage about 144,000 acres here in the heart of the island, and today’s flight is a recon mission to assess their fight against the weed. The flight will yield a photo mosaic of Wainiha Valley with one-centimeter resolution—fine enough to reveal the individual leaflets, known as pinnae, on a fern frond. But this is just one part of an all-out campaign to map and eradicate invasive interlopers—from strawberry guava to wild pigs—that imperil the native forest, which harbors a trove of endemic species and the island’s main source of water. This is not an easy place to fight an invasion, and the Conservancy has deployed helicopters, herbicide-loaded guns and smartphone-controlled pig traps to stanch the onslaught.

Sheer doggedness doesn’t hurt, either. Mapping flights like this one—running cameras back and forth across the landscape—can be repetitive and grueling. But the pilot, Hobbs, who seems to subsist solely on energy drinks, is indefatigable.

“This is as exhausting as it gets,” he says from the pilot’s seat. “But when we get a weather day like today, we’ve gotta go, baby.”
On an island in the middle of the ocean, water is never far from people’s minds. In fact, it is at the heart of native culture here: The wai in Hawaii means water, and in the Hawaiian language, to be “waiwai” is to be rich.

In that sense, Kaua‘i is an aquatic mother lode. After traversing 3,000 miles of ocean, the steadily eastward-blowing trade winds hit the island laden with moisture. Cloud-wreathed Mount Wai‘ale‘ale, which rises more than 5,000 feet, wrings all that water from the sky. And in the native forests of the surrounding Alaka‘i Plateau, an exquisitely layered suite of plants, from delicate ferns to moss-covered trees, catches the water like a giant sponge. The plateau—a swirling realm of constantly shifting light and cloud—is a natural waterworks, feeding deeply incised streams that carry millions of gallons of water out of the highlands every day, charging the island’s aquifers.

But invasive plants and animals are destroying this finely tuned system. Weeds like Australian tree ferns, kahili ginger and strawberry guava have infested the heart of the island, taking hold in the footsteps of wild pigs. The pigs rip up the ground while rooting about for food, speeding erosion on steep inclines. These invaders also trample level ground and compress the soil, preventing rain from percolating to the water table. All of this destroys the water-generating function of the native forest, which discharges hundreds of millions of gallons of water a day.

“You’re getting less water recharging your aquifer, and you’re getting more water being blasted down the streams during heavy rainfall events,” says Menard. “That’s bad.”

In 2001, The Nature Conservancy launched its program to fight the invaders. One prong of the campaign has been aimed squarely at wild pigs. Since 2005, the Conservancy has built nearly 5 miles of fence, strategically linked with several impassable “pali,” or cliffs, to exclude pigs from 8,000 acres of the most sensitive land on the Alaka‘i Plateau and the neighboring Wainiha Valley. With those areas fenced off, the organization has subsequently been trapping and clearing pigs from the enclosures.

Given the wet weather, rugged terrain and other challenges of working here, Menard and his partners realized that the program would be important as a proving ground for innovative technologies to fight invasive species. “The amount of land that the Conservancy manages in this state is pretty small—minuscule—compared to the whole landscape,” says Menard. “But we realized that our niche was to restructure the whole program to be more like R&D people.”

And, he says, the Conservancy can play an important role in pioneering new but unproven control technologies that government agencies are reluctant to consider. “They don’t really have much appetite for risk,” he says. “It’s really difficult for them to say, ‘Hey, we want to try out something new, and we want to use taxpayer money to do it.’”
When they first started working on the problem in 2006, one-meter-resolution satellite imagery was the best that was possible. Today, a specially developed computer algorithm allows the system to create maps with one-centimeter resolution. That’s fine enough to identify not only individual Australian tree ferns but also smaller species like strawberry guava, which is among the targets for the next round of weed busting.

“You can zoom in all the way,” says Menard, “target the plant, put the cross hairs on it, make a map—and go kill it.”

Thanks to breakthroughs like that, as well as integrating the data in an online portal, Menard’s team has become “the go-to techies for conservation here in Hawaii,” he says. And, he adds, “all the Indiana Jones stuff aside, the mapping is probably going to be the most important part of this.”

But the most important spinoff from the program will be the aerial mapping technology. Originally, Menard and his team members essentially mapped the ferns by hand, leaning out of the helicopter with a hand-held GPS and recording the location of each plant. Over the past several years, however, Stephen Ambagis and Dana Slaymaker, who run a company called Resource Mapping Hawaii, have worked to develop the aerial mapping system.

Much of the research and development has focused on the Australian tree fern—“an ecosystem dominator,” as Menard puts it—that has exploded across the island. Menard and his team have deployed a wide-ranging arsenal that includes “the Stinger,” a precision herbicide dispenser slung underneath the helicopter, which Hobbs and other pilots use to spray individual Australian tree ferns. The team has also tested herbicide-packed pellets that can be fired by a crew member in the helicopter with a paintball gun. That kind of precision targeting, along with a formula tailored to the Australian tree fern, has allowed the weed fighters to kill a lot of plants with extremely small quantities of Imazapyr, a relatively short-lived herbicide that has almost no effect on animals. 

“We treated over 4,000 tree ferns in a 5,000-acre area over a three-year period,” says Menard, “and we only used 11 gallons of herbicide.”

The ultra-high-resolution mapping will allow resource managers—not just on Kaua‘i but elsewhere, too—to see whether the weed-eradication program is keeping pace with the invasion. That, in turn, could open the door to a new era of more effective weed warfare.

Menard’s goal is for Wainiha Valley to become an Australian tree fern-free buffer zone that will prevent the weed’s wind-borne spores from reaching the water-generating Alaka‘i Plateau downwind. The weeds will come back—even in treated areas, Menard acknowledges, but they are rebounding at a slow rate that can be easily monitored and suppressed by the mapping and weed-busting technology.
“Doing any kind of weed control is pretty pointless unless we have a way to map it, at a big scale,” says Menard. Otherwise, “we could just be pouring money down the drain.”
The day after Jim Hobbs’ flight into sunshine, Mount Wai‘ale‘ale’s legendary weather has closed back in. Hobbs tiptoes his helicopter just under the wild cloud and across a knife-edge ridge to the high Alaka‘i Plateau—a skill Menard refers to as “flying by Braille.” Hobbs eases the helicopter into an impossibly tight spot under the branches of an ‘ohi‘a tree, planting the landing skids on a large rock in a little grotto with a stream tumbling through.

Hobbs may be fueled by Red Bull, but he can be surprisingly thoughtful in the backcountry. As he throttles down the helicopter’s engines, he appraises the lush vegetation hugging the grotto. “It’s another world—the native world,” he says. “It’s from 100 years ago; an untouched forest.”

Once the rotors stop, Menard eases out of the helicopter. Minutes later, he’s walking along the stout hog-wire fence line that snakes down from the summit of Mount Wai‘ale‘ale. The plateau is thick with healthy stands of ‘ohi‘a trees and ohelo bushes, low-growing verdure such as ‘ala‘ala wai nui and pa‘iniu, lapalapa trees softly shimmering in the wind and a spongelike carpet of moss.

“This is what really provides the water for the island,” says Menard. “This is the thing that we’re trying to save.”

But there is much more at stake here than water and erosion. “The thing that makes Hawaii so special from a biodiversity standpoint is its endemism,” Menard says. “Because it’s the most isolated landmass in the world, the things that did evolve here, on their own, occur nowhere else in the world.”

The Alaka‘i Plateau and Wainiha Valley are home to 220 species of endemic Hawaiian plants, including 92 found only on Kaua‘i. Most of those plants are not only ecologically important but also culturally significant to native Hawaiians.

Canen Ho‘okano is a member of Na Pali Coast ‘Ohana, an organization working to restore native plants on Kaua‘i. He tells of the rich tradition and lore of plant use on the island and its slow disappearance in the modern era. “Every species of native plant that we lose, we lose a piece of our culture,” Ho‘okano says. “And there’s no amount of money in the world that can get that back once it’s gone.”

But the tide may be turning in the fight to save Kaua‘i’s native forest. More than 90 percent of the mapped Australian tree ferns in Wainiha Valley have been treated and killed, and Menard’s team is now preparing to attack ferns in neighboring Lumaha‘i Valley. The Conservancy has almost completely removed feral pigs from the Alaka‘i Plateau, and Conservancy staffers are now working to clear the animals from Wainiha Valley as well.

The efforts being pioneered on Kaua‘i are being expanded. Hawaii’s Department of Land and Natural Resources has used the helicopter-mounted Stinger and has also adopted the mapping system. In 2011, the department announced a 10-year plan to fence 25,000 acres on Kaua‘i, more than tripling the pig-free areas on the island. Throughout the entire state, the department plans to fence another 90,000 acres over the next decade.

When clouds roll in, Menard hikes back to the helicopter. The pilot powers up and backs the aircraft out from under the tree. As the helicopter speeds home over the Alaka‘i, Hobbs marvels at the resurgent vegetation from his open door.

“It’s super, super important work,” he says, and then adds: “It’s kind of intense, but it’s kind of fun.”

"We've become the go-to techies for conservation here in Hawaii, and all the Indiana Jones stuff aside, the mapping is probably going to be the most important part of this."

Trae Menard, The Nature Conservancy’s director of forest conservation in Hawaii
Kauai Map 60x60
The Conservancy is killing invasive weeds and removing feral pigs from two of Kaua’i’s central valleys in order to safeguard the island’s rare native plants and a key source of its fresh water.