The Nature Conservancy on Thursday announced the creation of the largest private nature reserve in Hawaii, a move that nearly doubles the size of the Waikamoi Preserve on the slopes of Haleakala and protects a remote Maui rain forest with at least 20 rare native plants and two highly endangered birds.

The conservation group said it closed on a conservation easement agreement with East Maui Irrigation Co., a subsidiary of Alexander & Baldwin Inc., to take control of 3,721 acres that will be combined with the 5,230-acre Waikamoi Preserve, resulting in nearly 9,000 acres of protected rain forest.

"This area has been one of The Nature Conservancy’s highest priorities for more than two decades," Mark White, director of the conservancy’s Maui Nui Program, said in a statement. "The land lies at the core of the 100,000-acre East Maui watershed and is one of the most intact pieces of native forest in the state."

The land sits high above Makawao in the dense native rain forest of windward Haleakala at elevations from 3,600 to 9,500 feet above sea level and near the 7,500-acre Hanawi Natural Area Reserve to the east.

The rugged acreage is so remote that no roads and few trails lead to the area, which harbors at least 20 threatened or endangered native plants and two rare native forest birds — the akohekohe, or crested honeycreeper, and the kiwikiu, or Maui parrotbill.

Despite the isolation, sections of the land are being encroached upon by a range of invasive species, including feral pigs, cattle, strawberry guava, pampas grass and Himalayan ginger, said Francis Quitazol, the conservancy’s Maui natural resources manager. Controlling those threats, he said, will create safer habitat for the akohekohe and kiwikiu birds, whose declining populations have stabilized in the original Waikamoi Preserve.

"These are some of the rarest birds on the planet," Quitazol said.

Quitazol said the first order of business will be to erect a 3-mile, $600,000 fence to block pigs and cattle from the new acreage. One mile of fence has already been constructed with funding from the U.S. Environmental Protection Agency, state Department of Health and Maui County Department of Water Supply.

Once the fence is up, the pigs, cattle and weeds can be removed, allowing the natives to multiply, he said.

Garret Hew, president of EMI, said the agreement gives the company an opportunity to tap into The Nature Conservancy’s expertise and capacity to protect the land. The conservation work, he said, will enhance the water-holding capacity of the rain forest and help to preserve Maui’s water supply.

The conservation easement was valued at $190,000, and 75 percent of the acquisition costs came from the U.S. Fish and Wildlife Service Recovery Land Acquisition Program, through the state Department of Land and Natural Resources. A&B offered the easement at a discounted price of $142,500, donating 25 percent in matching private funds, or $47,500 worth of value.

Since 1991, EMI has participated in the conservation of the lands as part of the East Maui Watershed Partnership. The other partners include The Nature Conservancy, Haleakala Ranch, Hana Ranch Partners, Haleakala National Park, the Maui Department of Water Supply and DLNR.

"The EMI conservation easement was the result of great teamwork, bringing together the federal government, the state, the private landowners and the conservancy," said Suzanne Case, the conservancy’s executive director in Hawaii. "It took a long time to pull it together, but this area lies at the heart of the East Maui watershed, and native forest just doesn’t get any better."

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