Choppers made the difference Thursday in taming a 450-acre wildfire that threatens native plants and animals in the mountains above Waialua and Mokuleia, the first in at least 28 years.

Among the hidden gems in those native forests are the kahuli, the endangered native tree snail; the elaborately marked Hawaiian picture-­wing fly; and the rare mehamehame tree. Those trees, the redwoods of Hawaii, were once used to build canoes, but there are only 20 of them remaining, said Kapua Kawelo, natural resource manager for the Army’s Oahu Natural Resource Program.

The Army sent in a massive Chinook helicopter with a 2,000-gallon bucket — the same carrying capacity as a Honolulu Fire Department tanker — as well as two smaller Black Hawks with 660-gallon buckets.

The state Department of Land and Natural Resources contracted a small helicopter at a cost of $1,200 an hour. The Honolulu Police Department and the Honolulu Fire Department used their helicopters equipped with 100-gallon buckets.

By late Thursday afternoon the fire, which began Wednesday morning, was 50 percent contained.

“A lot of the fuel burnt up yesterday,” said Division of Forestry and Wildlife fire incident commander Jason Misaki. The helicopters, including the “Type 1, with a huge bucket,” made a difference, he said.

At higher elevations most of the fire is smoldering and continues to burn underground. Misaki said. Crews must use hand tools there to put out the fire because water drops alone cannot extinguish it, he said.

The lower fire front was contained by midday Thursday, and no structures were threatened, HFD said.

HFD reported the fire ignited from a work truck that had stopped in a grassy area. The truck was destroyed by fire, but its operators were uninjured.

Kawelo said the fire was extreme Wednesday with “massive flames cresting the ridge, out of control, and the helicopters were hitting it hard.”

The fire entered the Mokuleia Forest Reserve and threatens the Pahole Natural Area Reserve, said Marigold Zoll, DLNR Oahu Forestry and Wildlife manager. These areas are meant to preserve in perpetuity examples of native Hawaiian forests, including the dry forest and mesic or moist forest, where the majority of endangered plants and animals are located, she said.

Some are the host plants for endangered insects such as the Hawaiian picture-wing fly.

A flight over the area showed the fire already had destroyed some wiliwili trees, iliahi (native sandalwood) and lama trees.

Talbert Takahama, a nature ecosystem recovery specialist in the Waianae Mountains, said in his 28 years at DLNR, he had never experienced a fire there.

“I was hoping never to see one,” he said. “For us the worst thing that could happen is if the old-growth eucalyptus over 100 feet tall were to ignite.”

Had that happened, the fire would have scaled up the trees, and there would have been an intense fire. “We probably would not have been able to stop it moving,” he said.