In less than a week the fire-blackened ridges above Nanakuli Valley will sprout pale green tentacles of grass — infant shoots growing rapidly among the charred corpses of the parent plants.

This is not an example of Mother Nature replenishing native flora, said Pauline Sato, O'ahu program director for the Nature Conservancy.

"Those are invasive species," she said. "Weeds."

As the fires burn again and again, the weeds encroach farther into the native forests higher on the ridge, permanently displacing them and forever changing the character of O'ahu's landscape.

The non-native plants are invigorated by fire, Sato said, growing back dense and healthy after the blaze and serving as excellent fuel for the next burn.

Native plants exposed to fire simply die, she said.

It's not just plants. Hawaiian short-eared owls, or pueo, would have been living in the areas where the fire burned this week.

"Hopefully they are all right," Sato said. "There were some in the area, but they can fly away."

On Monday, conservationists watched nervously as the flames licked at the Nanakuli Forest Reserve, inching closer to three of the four wild native gardenias in the state. On Monday night that part of the fire seemed contained, and the conservationists took a tentative breath. It was premature.

On Tuesday, the ridge area where the gardenias grow burned.

"We think they were consumed by the fire," Sato said of the three gardenias there.

The fourth wild gardenia grows farther up the ridge, on the Nature Conservancy's Honouliuli Forest Preserve. Offspring plants have been cultivated from seeds from the wild plants, but unless conservationists find something near-miraculous when the burn cools enough for them to explore the blackened areas of Nanakuli Forest Reserve on foot, the Honouliuli gardenia stands as the last wild version of the plant.

Pat Costales, O'ahu branch manager for the Department of Land and Natural Resources' Division of Forestry and Wildlife, said the perimeter of the fire overlapped the area where the native plants grow, and what he saw Tuesday during a helicopter tour did not look promising.

"I saw a lot of blackened forests," he said.

Sato explored the opposite side of the ridge yesterday and said she was shocked by the number of burned areas that have stained the mountainside this fire season.

She said those areas and the area where the gardenias once bloomed are likely to be overtaken by guinea grass, a common invasive species.

The weed, which can reach 7 feet in height, was introduced in the mid-1800s as a failed experiment at developing a food source for cattle.

"It spreads up the mountain and grows in thick, and nothing else can grow there," she said.

Native trees, including lama and sandalwood trees, were killed in the fires, she said. The individual plants were not the last of their kind, but the forest community in which they grow is rare.

"That type of native Hawaiian dry forest is rare all over the island," she said.

Wayne F. Ching, state protection forester for the Department of Land and Natural Resources, said removing the forests affect other aspects of the environment as well.

Without the plants to hold it in place, soil along the mountainside poses a hazard to humans and to ocean life.

"For example," he said, "right after a fire we had in Waikoloa (on the Big Island), the wind picked up and created a dust storm like something right out of the Sahara desert.

"Then, three days later, we had a storm with a lot of rain, and that caused runoff into the ocean. You can imagine what that does to the reef."

Landslides and rockslides also are more likely to occur on denuded areas, he said.

Leslie Au, a toxicologist with the state Department of Health, said those who have allergies or other respiratory disorders can suffer increased difficulties during and after a fire.

"During the fire, people with pre-existing conditions are going to be aggravated," he said. "Not just allergies but other conditions, including emphysema and others with decreased lung capacity."

After the fire, he said, the breathing problems may persist as the bare soil blows away.

"Bacteria live in the soil," he said. "Fungus and mildew. For people with allergies, it is like someone just opened a pollen field upwind."

Ching, the state protection forester, said he hopes Leeward residents will remain vigilant in protecting their property from fire damage, including clearing an area 30 feet out from the property line, and making sure there is space between homes and wilderness areas that allow firefighters to move in and take a stand.

Sato, from the Nature Conservancy, said she hopes homeowners on the Leeward side will help hold the line against invasive species by growing more native plants that thrive in dry environments, such as pili and kawelu grasses, and 'ilie'e, a native plumbago.

Reach Karen Blakeman at kblakeman@honoluluadvertiser.com.