Fast-growing plant threat to habitat of Lanai petrels
Invasive strawberry guava ‘cancer that’s taking over’ watershed, says biologist
By ILIMA LOOMIS, Staff Writer
LANAIHALE – For decades, researchers thought the last major colony of Hawaiian petrels in the islands nested on the slopes of Haleakala.
Then about a decade ago, wildlife biologist Fern Duvall was working on Lanai when he noticed a petrel burrow. He kept the discovery in the back of his mind for six years, until he was able to return to the island to follow up.
“We just went to see if we could detect any birds at all,” Duvall said. “It turned out that not only could we find birds – there were thousands of them. We think it’s the second-largest known concentration of Hawaiian petrels.”
Duvall suspects that the birds have thrived on the slopes of Lanaihale – Lanai’s only large mountain – because the island has so little development and few urban lights.
The night-flying birds depend on starlight to navigate and often become disoriented and crash in urbanized areas.
“Lanai disappears after dark,” Duvall said. “We think the birds cue in on this absolute darkness.”
The qualities that attracted the birds to Lanai also helped them go unnoticed for decades – and still makes it tough to get an accurate estimate of the population, said researcher Jay Penniman.
“It’s pretty difficult when you have a night-flying species that nests in burrows underground,” he said, noting that the birds like to nest in areas where their burrows are hidden by ferns.
Penniman said his current estimate was a population of about 4,000 birds. That’s a significant number for a species that 30 years ago was estimated to have only about 20,000 birds left.
But while the island’s dark nights may have made Lanai a haven for petrels that have been under increasing pressure from urban lights on Maui and across the rest of the state, an “invasive species invasion” on Lanaihale is now threatening to drive them from the island, Penniman said.
Introduced plants and weeds, especially the aggressive strawberry guava plant, have been encroaching on the native plants and ground ferns the petrels depend on for habitat.
The birds, which are awkward on land, look for clearings in the forest to make their burrows. On Lanai, they also prefer to nest under native uluhe ferns, which help protect the burrows from cats and other predators.
But the fast-growing strawberry guava has been moving farther and farther up the mountain, filling in the forest clearings and choking out the uluhe and other native plants.
“It’s like the cancer that’s taking over that watershed,” Duvall said.
Now Penniman, Duvall and a crew of Lanai conservationists are hoping to turn back the invasion and reclaim the forest tree by tree.
Earlier this month, Christine Costales of the Lanai Native Species Recovery Project showed off her group’s 3-acre clearing high on Lanaihale. On either side, a 30-foot-high wall of dense strawberry guava trees marked the boundaries of the project’s work site. She proudly waved a hand over an open patch of uluhe ferns.
“This is what we want to see,” she said. “The birds look for these patches, but they cannot get here when they have to fly through the strawberry guava.”
Work on the site started in 2008, when Castle & Cooke Resorts set aside the area and provided funding for habitat restoration as a condition of approval to install meteorological towers to measure wind conditions for the company’s proposed wind farm on the northwestern end of the island.
Costales said she and her crew spent two years clearing the 3-acre site, before they began planting native vegetation in the area in March 2010. Since then, they’ve cleared another acre, and hope to eventually expand the site to 6 acres.
While the original funding from Castle & Cooke has run out, the project also receives some funding through the Department of Land and Natural Resources’ Maui Nui Seabird Recovery Project, which Penniman oversees. It has also received some grants from the Office of Hawaiian Affairs and the Hawaii Invasive Species Committee.
“We’re committed to continue to try to find the funding to expand the site,” Penniman said.
Costales said conservationists have cultivated native plants from seeds gathered on Lanaihale, and so far have planted koa, maile, manono, kopiko, hoawaa, ohe mauka, mountain naupaka, hala pepe, as well as other species.
Like Costales, Penniman said he’s hoping the state moves forward with a proposal to use biological controls to limit the spread of strawberry guava.
Penniman said the insect proposed to fight the strawberry guava would not be a “silver bullet” that would eradicate the plant, but would only slow its spread and act as a deterrent.
“There’s no way we could ever eradicate it,” he said. “It’s such a successful plant that we need the full array of tools to be able to limit it.”
The project has enlisted the help of community groups and Lanai High and Elementary School students to clear brush and plant the native vegetation, and crew members maintain the site by watering the seedlings during droughts and fencing off the native plants to protect them from hungry deer.
Although deer-proof fencing encloses around 4,000 acres of the mountain summit to keep out ungulates that graze on native plants, deer and sheep continue to wander the area because they were never eradicated from the protected area after the fence was installed.
Deer eat native grasses and shrubs, and they kill fragile native trees by rubbing their horns against them, Costales said.
While much of the project’s focus has been on restoring habitat for the Hawaiian petrels, Costales, Penniman and Duvall said they’re all acutely aware that the mountain’s watershed is also under threat.
With little rainfall and no known natural surface water sources, more than 65 percent of the water that recharges the island’s primary aquifer is believed to come from fog that accumulates on the leaves of forest trees and drips onto the ground.
Native plants like koa trees are natural fog collectors that once formed a “cloud forest” on the summit of the mountain. But the invasive strawberry guava trees don’t have the same ability.
Last year, the county’s Lanai Water Use and Development Plan warned that the island’s watershed is so fragile that a loss of the Lanaihale cloud forest could reduce water levels in the island’s only viable aquifer by 50 percent.
While Penniman said he’s been glad to be involved in clearing habitat for Hawaiian petrels on Lanai, he believed that getting the island’s watershed partnership more organized and restoration projects under way would be “really the most important thing to get going over there right now.”
“What’s really good for the birds would also be really good for the watershed,” added Duvall. “They’re the canary in the coal mine.”
* Ilima Loomis can be reached at iloomis@mauinews.com.