How non-native weeds turned Hawaii into a powder box

How non-native weeds turned Hawaii into a powder box

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Dried buffalo grass, an invasive species that causes faster-growing wildfires, appears on the side of a hill near a trail in Tucson, Arizona.

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Dried buffalo grass, an invasive species that causes faster-growing wildfires, appears on the side of a hill near a trail in Tucson, Arizona.

After catastrophic wildfires killed more than 100 people in Hawaii, attention has turned to an unexpected culprit: an invasive grass species that has spread widely over the archipelago for decades, serving as the perfect fuel.

They are drought-resistant, able to invade difficult terrain and gradually eliminate native species, and they pose a growing threat in the western United States, where destructive fires are increasing.

“Invasive weeds are very flammable. They change the landscape,” Carla D’Antonio, a professor of ecology at the University of California Santa Barbara, told AFP.

“They provide more favorable conditions for more fires, and all of a sudden, we have a lot of fires.”

Instead of decomposing when they die, they remain “standing there for a long time, dry as bones,” said D’Antonio, who has been studying these species for more than 30 years. They are also hardy, survive fires better than native species and are gradually replacing them.

Most of these grasses – buffalo grass, guinea grass, molasses grass – came from Africa, and were introduced as livestock pasture, without knowing the danger they would pose decades later.

In Hawaii, the demise of sugarcane plantations in the 1990s as a result of globalization had dire consequences: vast tracts of land were abandoned, creating an opportunity for invasive species.


Graphic showing a selection of invasive and flammable grass species in Hawaii that can serve as fuel for wildfires.

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Graphic showing a selection of invasive and flammable grass species in Hawaii that can serve as fuel for wildfires.

“Yes, many parts of Hawaii are headed toward drought conditions, but the fire problem is mostly due to the vast tracts of non-native grasslands that have been left unmanaged by large landowners as we enter the ‘post-agricultural era,’” Clay said. Fire ecology at the University of Hawaii at Manoa.

The annual area burned in Hawaii has increased by 300 percent in recent decades, Trawernicht said.

Maui County’s 2021 Fire Prevention Report describes fires as an increasing threat due to rising temperatures and longer dry periods as a result of climate change, and the growing threat of invasive weeds.

Hawaii, despite its tropical reputation, is becoming drier: A 2016 study found that 90 percent of the state received less rain than a century earlier.

The Maui County report recommended “a bold plan to replace these hazardous fuel sources with local plants to reduce combustible fuel while increasing water retention.”


This undated photo by Carla D’Antonio shows the invasive tumbleweed (Melinis minutiflora) filling in the gaps between remaining native shrubs and trees in burned areas of Hawaii Volcanoes National Park.

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This undated photo by Carla D’Antonio shows the invasive tumbleweed (Melinis minutiflora) filling in the gaps between remaining native shrubs and trees in burned areas of Hawaii Volcanoes National Park.

“There is nothing natural about it”

The problem is not limited to Hawaii. In the U.S. mainland, “in the deserts of the West and the conifer forests, and then the shrublands of the coastal region, the invasive grasses are here to stay, and are now part of the ecosystem,” D’Antonio said.

She herself spends some Saturday evenings weeding roadsides with neighbors in a mountainous area near Santa Barbara, California. Their goal: to prevent a fire from a cigarette butt or from a car overheating.

She says most of the major fires in the Mojave and Great Basin were fueled by invasive grasses, while also citing the 2018 Camp Fire, which devastated the small California town of Paradise, killing more than 80 people. It was started by a power line that ignited dry grass.

“(I) would not mistake it for a natural disaster because there is almost nothing natural about it,” the scientist asserts.

One invader, buffalo grass, also threatens the emblematic cactus in Arizona’s Saguaro National Park, by suffocating young saguaros and sparking fires in the area. Organizations regularly organize clearing operations. The same species is widespread in Mexico and Australia.


This undated photo by Carla D’Antonio shows fountain grass (cenchrus setaceum) covering large areas of the Kona side of Hawaii Island.

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This undated photo by Carla D’Antonio shows fountain grass (cenchrus setaceum) covering large areas of the Kona side of Hawaii Island.

According to a 2019 study, six invasive grass species have increased the frequency of fires by up to 150 percent in U.S. ecosystems.

For UC Santa Barbara’s D’Antonio, tragedies like the one in Hawaii are linked to many factors: landscape change by humans, invasions by alien species, droughts exacerbated by climate change, but also a lack of preparedness.

In the American West, extensive logging of conifer forests in the 19th century and a long history of excessive fire suppression in the 20th century contributed to the accumulation of combustible material on the forest floor.

“The potential for disaster is high,” D’Antonio said, leaving the community with difficult questions to address. “How do we plan for extreme fire? Not for medium fire, but for extreme fire?”

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