“The pines are forming an insidious lei around the summit.”
Alison Cohan, TNC Maui Nui Forest Program Director
By Jan TenBruggencate
A century ago, foresters were trying to cover the slopes of Haleakalā with stands of introduced pine. Today wildlife managers are trying to turn back their advance across Maui’s great mountain.
Pine growth on Haleakalā has been rapidly increasing for the past decade. Pines have spread into native forest areas and stark volcanic landscapes, where they form dense stands that shade everything else out and create severe fire hazards.
“The pines are forming an insidious lei around the summit,” said Alison Cohan, director of the Conservancy’s Maui Nui forest program. “The threat is serious because pines can outcompete native species such as silversword inside the crater.”
“We’ve seen record growth,” added Keahi Bustamente, field crew supervisor for the Leeward Haleakalā Watershed Restoration Partnership. “If we leave it like it is, you won’t be able to see the sky, the clouds, the stars.”
A Partnership Effort
The Nature Conservancy is part of a multi-agency partnership working to control the pines. The partnership’s efforts range from volunteers who pull up small pines to experts with chain saws who chop larger ones. Where necessary, small, targeted amounts of herbicide are applied.
“This is one of the park’s highest natural resource priorities,” said Woody Mallinson, natural resources program manager for Haleakalā National Park. “The pines represent a persistent threat.”
Hawai‘i foresters began planting hardy pine species in the early 1900s to protect watersheds and create the raw material for a timber industry. Of the several species planted, two are causing the most trouble: Monterey pine (Pinus radiata) and Mexican weeping pine (Pinus patula), which now cover tens of thousands of acres of the crater and its outer slopes.
Pines are not native to the Islands, but they thrive on high volcanic summits. “They will fill that whole niche if not controlled,” said Jordan Jokiel, vice president for land management at Haleakalā Ranch.
There are two invasion patterns. One is a slow advance out of several hundred acres of existing planted pine forest at Hosmer Grove, Polipoli Springs State Recreation Area, parts of The Nature Conservancy’s Waikamoi Preserve and neighboring lands.
The other is the development of outlier populations, the result of a massive 2007 wildfire at Polipoli that burst open the cones of the Monterey pines, lifting their seeds on clouds of smoke and spreading them across the crater and its exterior slopes. Monterey pine cones are serotinous, meaning the seeds stay trapped inside the cones until set free by fire.
Stopping the Spread
As a result, there have been pine seedlings sprouting from the crater floor, the crater walls, the volcano’s steeper outer slopes and even on cliffs. In the subalpine region, at 6,000 to 7,000 feet elevation, the pines are transforming native habitat for eight endangered plants, four endangered birds and untold numbers of endemic invertebrates into alien pine forest. They also provide fuel for wildfires, which can severely damage Maui’s watershed.
The team battling the invasion includes Haleakalā National Park, The Nature Conservancy, Haleakalā Ranch, Leeward Haleakalā Watershed Restoration Partnership, East Maui Watershed Partnership, State Division of Forestry and Wildlife, State Natural Area Reserves System, Maui Invasive Species Committee, University of Hawai‘i and Windward Aviation. Volunteer groups and other Maui watershed partnerships also help.
Some of the work involves simply pulling up young seedling pine or sawing them off below the lowest branch. On larger trees, a series of holes is drilled in the trunk and a small amount of herbicide dripped into each hole. “We use very small amounts, from a dropper bottle,” Bustamente said.
In remote and inaccessible areas like cliff faces, a helicopter is deployed with a pilot-controlled applicator that shoots a very targeted herbicide spray.
While many of the dispersed pine seedlings from the Polipoli fire have been controlled, the estimated footprint of the seed dispersal area is over 15,000 acres, so incipient satellite populations are still being discovered. Work on the slow-spreading pines is ongoing. Eradication teams work with maps set by satellite data points to ensure nothing is missed, and helicopters are guided to pine targets by GPS locations.
We’re trying to get to those trees before they have a chance to regenerate,” Cohan said. “We want to prevent fire and preserve Haleakalā’s native ecosystems.”