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Weed Mapping

Hi-Tech Breakthrough for Invasive Plants

"This is a huge breakthrough for our conservation efforts.  This changes everything."

Trae Menard, Kaua'i island director for the Nature Conservancy of Hawai'i

By Grady Timmons

Imagine that it’s your job to protect the ancient forests that helped inspire the movie Avatar. The most immediate threat is an introduced ornamental gone wild: the invasive Australian tree fern.

Imagine also that you have adapted existing technology for use on the conservation battlefield — technology that dramatically boosts your chances of victory. 

That’s the position Trae Menard, Kaua‘i island director for The Nature Conservancy of Hawai‘i, finds himself in.

Menard is leading an alliance of Kaua‘i landowners who are working to defend a 144,000-acre watershed known for its abundant rainfall and extreme terrain.  

Halt the spread of the prolific tree fern and Kaua‘i can avert a future crisis, one that over time could drastically alter the island’s native forests and their ability to capture and store water.

“There is a real sense of urgency, because right now we have a 10-year window to get in there and control it,” Menard warns. “If we don’t, this invasive plant is going to take over.”

Weed Warrior

In 2008, the Conservancy began using a hi-tech aerial camera system to map Australian tree fern and other major weeds across 50,000 acres of the island’s steep interior.

More recently Menard has been testing the application of a safe and effective herbicide at the Conservancy’s Wainiha Preserve — using a helicopter to lower a 100-foot cable weighted with a spray ball directly over the plant and deliver a dose with near surgical precision.     

Menard calls the combination of tools a “game changer” — not only for Hawai‘i but conservation in general. Last fall, he eliminated almost half of the 3,500 tree ferns he had mapped in Wainiha, and this spring he will finish up and continue on.

The ultimate goal: to protect a 12,000-acre core wilderness area of rare birds and plants, many of them endangered and struggling to survive.

Cradle of Diversity

A combination of age, isolation and topography has made Kaua‘i a botanical marvel, home to more than 400 species of plants and animals found only in Hawai‘i. The Garden Isle has almost half of Hawaii’s endemic flowering plants and natural communities, and more than half of its native bird species. 

Six million of years of rainfall have eroded the single-shield volcano that formed the island, creating deep verdant valleys, magnificent canyon gorges and razorback sea cliffs. Mt. Wai‘ala‘ale, at 5,148 feet, is one of two summit peaks and one of the two wettest spots on Earth. 

The island’s greatest biological treasure, however, is the Alaka‘i, a mile-high plateau cradled between the mountains.

The Alaka‘i lies at the very center of the island — on the flank of Mt. Wai‘ale‘ale and at the head of Kauai’s five largest aquifers — and its native ecosystems include Hawaii’s oldest bog and most diverse high-elevation rain forest.

In all, it contains 105 endemic plant species, 87 of which are found only on Kaua‘i. Ken Wood, a prominent biologist with the National Tropical Botanical Garden and a key partner in the Kaua‘i alliance, calls it “the most important biodiversity conservation site in the entire archipelago.” That’s why alliance members are so determined to protect it.

Superweed

Chipper Wichman, director of the National Tropical Botanical Garden, calls the Australian tree fern a “superweed” because it releases millions of windborne spores that can be dispersed miles from the source plant.

Once the spores sprout, the tree ferns grow quickly, forming a dense canopy that chokes out the layers of native forest that capture rainfall and prevent erosion. The result: a ‘monotypic forest’ of one dominant species that increases sedimentation and is prone to landslides. 

Menard didn’t realize the extent of the problem until he began surveying Kauai’s backcountry in 2006. Hanging out of a helicopter while flying low over the canopy, he and his staff spent 80 hours identifying major weeds by eye and marking their location with a hand-held GPS device. 

“By the time we were done I realized Australian tree fern was everywhere and that the tools we had to map and fight it were inadequate,” he says.  

Hi-Tech Breakthrough

That’s when he contracted Dana Slaymaker of Resource Mapping Hawai‘i, whose genius was to adapt existing aerial mapping technology for conservation use and make it affordable.

Slaymaker developed a three-camera system that he mounted in the belly of a Cessna 182. From 2,000 feet above the forest floor, the camera snaps digital images so detailed that weeds are easily identified and their precise coordinates mapped and adjusted for changes in terrain.  

“All this for about $5 dollars an acre,” says Menard, who can download three-dimensional files that identify and show the location of virtually every invasive plant.   

Menard says the technology can be used to monitor progress, track new invasions and document changes to natural areas over time, including the impacts of feral animals and climate change.  

“This is a huge breakthrough for our conservation efforts,” he says. “This changes everything.”

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