Dramatic Recovery Seen at Maui Preserve After Pigs, Goats Removed

Fourteen-year study shows 300 percent increase in native plant cover  

HONOLULU, Hawaii | July 23, 2009

Native species in the shrubland and forest of Waikamoi Preserve on the north slope of Maui's Mount Haleakalā have staged a dramatic recovery after hooved animals were fenced out—in some cases increasing native plant cover by 300 percent or more.

The Nature Conservancy of Hawai‘i said work at the site confirmed that strategic conservation efforts, like fencing and feral animal removal, can help restore damaged ecosystems.

The Conservancy conducted two surveys, one immediately after fencing and removing goats and pigs from part of its Waikamoi Preserve in 1994, and another survey last year.

The results surprised scientists. When they went back for the second survey, they found the land was far denser with native plants than it had been. As an example, in the test plots surveyed, in 1994 botanists found seven native māmane trees. In 2008, in the same test plots they counted 65 māmane.

“The message is that it's really worth protecting important native forests and watersheds from invasive animals. You really do get remarkable results,” said Mark L. White, Maui program director for The Nature Conservancy.

Native trees and ferns sprang up. Native shrubs and forest-floor mosses and lichen exploded. And remarkably, several grasses including an invasive grass, declined.

“This was one of the most beat-up areas when we started. There was a three-fold increase in native shrub cover and a 50 percent reduction in a dominant alien grass,” White said.

The survey covered a 1,000-acre area between 6,000 and 8,600 feet in elevation, running north from near Hanakauhi peak, which is also known as Hana Mountain. The upper parts of the area are a subalpine habitat with few large trees, while the lower regions are densely forested. The area where the two habitats meet is called the treeline.

It is a little-visited, remote part of the island, and yet both types of habitat had been severely affected by grazing animals, primarily feral goats and pigs immediately before fencing. Local hunters assisted conservation teams in removing the animals once the area was fenced.

Guy D. Hughes III, plant ecologist with the Kalaupapa National Historical Park on Moloka‘i, who conducted both surveys, said the terrain clearly looks different and is continuing to change as it recovers from the goats and pigs.

In the 1994 survey, the upper subalpine areas were open and dominated by grasses, both native an alien. By the time of the 2008 survey, grasses and soft-bodied (herbaceous) plants were reduced in number. In their place were native woody shrubs and ferns.

“We found that the native shrubs... pūkiawe ‘ōhelo, māmane and the native fern ‘ama‘u significantly increased,” Hughes wrote in a report on the surveys.

Among the species that declined were invasive alien velvetgrass, and the native alpine hairgrass, Deschampsia nubigena.

“There was a hundred years of goats, and then pigs. The pigs are rototilling the forest, plowing up large areas, and the grasses are the first to invade and establish themselves,” White said.

On removing goats and pigs, the shrubs have a chance to recover. 

“Weather could be playing a role... but we attributed the greatest magnitude of change to be a release from extensive ungulate browsing, trampling, and rubbing. The data clearly indicated native subalpine shrubs and ferns increased at the expense of native and alien grasses on the mountain across years. These patterns of change are what one expects from a normal succession process from more open animal-occupied habitat to denser, wooded habitat in the absence of animals,” Hughes' report said.

The lack of trampling also let mosses and lichen recover, which Hughes said he took as a sign of a recovering ecosystem.

The results of removing ungulates from this region are impressive, but not entirely unexpected, said Lloyd Loope, a veteran research biologist with the U.S. Geological Survey. At an upland bog on Haleakalā, pigs had reduced vegetation cover to 5 percent by 1981. After their removal, the bog responded to 90 percent cover within six years, he said. 

Waikamoi Preserve: The Nature Conservancy's 5,230-acre Waikamoi Preserve is part of the East Maui watershed, which covers more than 100,000 acres and is home to 63 species of rare plants and 13 kinds of native birds. The preserve was established in 1983 when Haleakalā Ranch conveyed to the Conservancy a permanent conservation easement. It is managed in partnership with the state Department of Land & Natural Resources' Natural Area Partnership Program. 

The Nature Conservancy is a leading conservation organization working around the world to protect ecologically important lands and waters for nature and people. The Conservancy and its more than 1 million members have protected nearly 120 million acres worldwide. Visit The Nature Conservancy on the Web at

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