ULUPALAKUA, Maui — In an effort to keep two-thirds of Ulupalakua Ranch's 18,000 acres preserved forever as agricultural lands, the Erdman family has donated an easement to the Maui Coastal Land Trust.

Details of the agreement were still being worked out Wednesday by attorneys on both sides, but it was expected to be signed tomorrow, said ranch owner Pardee Erdman.

The ranch will go on as if nothing occurred. The easement will protect ranch lands from being sold off piecemeal by future generations and turned into real estate developments such as condominiums.

Pardee and his son, ranch President Sumner Erdman, said they pursued the complex deal with the nonprofit land trust to ensure that nearly 12,000 acres of prime real estate — from a mile of coastline south of Makena to the 6,000-foot elevation of Polipoli Spring State Park — would never be developed.

The 165-year-old ranch has been in the Erdman family since 1963 and has 5,000 head of cattle, a winery, a country store and grill as well as horseback riding and clay skeet shooting. As a result of the agreement with the land trust, the property will not become a resort or residential subdivisions or shopping centers, Pardee Erdman said.

On Wednesday, the 78-year-old patriarch looked up at the misty green lands, hands on his denim-covered hips, and said he intends to preserve the property for agriculture only for generations to come.

He said he approached the Maui Coastal Land Trust almost two years ago, when it became increasingly apparent that Upcountry — and its sweeping ocean views — was being developed, often for giant homes or exclusive subdivisions.

"We saw development creeping up, and we didn't want it to happen here," he said, adding that the trust's new deeds preclude most development in perpetuity.

However, the owners reserve the right to develop renewable energy projects, and agriculturally appropriate commercial and noncommercial ventures, said Dale Bonar, executive director of Maui Coastal Land Trust.

For instance, Sempra Energy recently leased land for a 12- to 15-turbine, 20-megawatt wind energy farm on the Auwahi portion of the ranch.

The transaction involves two parcels of land that form a dog-leg shape on the slopes of Haleakalä.

One parcel of approximately 6,000 acres is used primarily for livestock grazing and farming, according to the trust.

The property is mauka of Kula Highway and extends from the ranch headquarters to the boundary of the state park.

The second parcel is the entire Auwahi ahupua'a, a 5,328-acre, rectangular property running lengthwise from the ocean.

The mauka portion of the property is home to the Auwahi Habitat Restoration Project led by conservationist Art Medeiros and is part of the Leeward Haleakala Watershed Restoration Partnership.

Sumner Erdman said the family, which includes his brother, Christian, and three granddaughters, will have the flexibility to pursue a variety of agricultural options, such as growing lumber, exotic vegetables and fruits and pursuing more renewable energy sources.

He called the agreement "fantastic."

While the family retains ownership, including responsibility for land management, property taxes and liability insurance, the agreement wipes out any rights to develop the land, beyond a 20 percent increase in the footprint of existing buildings.

The owners will receive some benefits, such as a charitable tax deduction and lower property value, the latter of which will make it easier to keep in the family, Bonar said.

When asked why he chose to pursue a perpetual agricultural easement, Pardee Erdman said: "I was driving in Kíhei one day, and I looked up those green hills, and I was proud of the land, and I decided I wanted it to stay the way it is."