Wildfire in Nanakuli this month took a toll on native plants

A wildfire that scorched 2,500 acres in Nanakuli Valley earlier this month threatened the last remaining wild nau tree on Oahu.

“It barely escaped the fire,” said Susan Ching, coordinator of the Oahu Plant Extinction Prevention Program. Noting that some leaves and fruit on the nau tree, believed to be at least 100 years old, were singed by heat from the blaze, she said, “That’s how close the fire was.”

The nau is among scores of rare native plants and animals in the Waianae mountains, where wildfires pose an ongoing, significant threat.

In the aftermath of the blaze, which ignited on March 17 and burned for several days, conservationists are asking the public to step up efforts to help protect native species. The cause of the wildfire has yet to be pinpointed.

At a news conference Wednesday at Lyman Ranch, Pauline Sato, executive and program director of the Malama Learning Center, said, “What we see around here is not acceptable. We can’t let this keep going on.” Behind her was a panoramic view of charred lands caused by the blaze.

Pointing out that a majority of the wildfires in Hawaii are caused by people, conservationists are urging the public to help prevent wildfires by keeping cigarettes, vehicles, fireworks and any other ignitable items away from the forest reserve area.

Marigold Zoll, acting Oahu forestry and wildlife manager of the state Department of Land and Natural Resources Division of Forestry and Wildlife, described the wildfire as the second-largest on Oahu in the past 10 years. It burned private and public lands and scorched portions of the state’s Nanakuli Forest Reserve. Some rare plants, such as the mehamehame, kului and ahakea, were destroyed.

With drought conditions predicted to worsen as summer approaches, worries tied to the threat of more wildfires in the area are growing. “It could all go. Most people don’t know what we’re losing,” Sato said.

The valley is home to the last remaining wild nau or Hawaiian gardenia (Gardenia brighamii) on Oahu. The 20-foot tree, located in the upper region of the valley, is one of only 16 wild nau trees statewide. Fifteen of the trees are on Lanai. Zoll and Ching, who conducted an assessment of the charred Nanakuli Valley lands, were relieved to find its nau tree still standing.

Sato recalled watching a wildfire burn the back of the valley 10 years ago. “I was really fearful that it was going to take the native forest of Palikea. This time, (the wildfire) has gotten even higher. And my concern is, 10 years from now, what’s going to be left as the fires go higher and higher?”

Some 60 rare and endangered plants and animals are located along the top of the ridgeline in the Palikea area of the Honouliuli Forest Reserve. The reserve is home to the Hawaiian tree snail (Achatinella mustelina), which is found only in the Waianae Mountains.

Sam Ohu Gon III, a senior scientist and cultural adviser at the Nature Conservancy of Hawaii, describes the mountains, particularly the southern half of the range, as the “single richest botanical region in the state.”

Regarding the cultural significance of the nau, Gon said, a bright orange pigment found inside the tree’s walnut-size fruit is said to represent a Nanakuli sunset, and has been used to create dye.

The tree’s flowers were once used for lei. Traditional uses for the wood ranged from structural housing posts to anvils used to create kapa or cloth.

Sometime in the early 2000s, two other nau trees in the upper valley were killed either by a previous wildfire or by non-native weeds, insects or drought conditions.

Plans in the works for planting more trees involve using viable seeds extracted from a charred fruit taken from the nau tree. Ching said they will likely plant near the area where the last remaining wild nau tree is.

Zoll added that the Division of Forestry and Wildlife also has a program to collect common native seeds for a large seed bank “so when things like this happen, we can come in and do large re-seedings of areas to help the natives get a leg up on the invasive species and try to out-compete them.”