Scientists and academics say they have been warning for several years that invasive grasses covering a quarter of the Hawaii islands are a major fire risk.
Untamed grassland helped fuel the spread and intensity of last week’s deadly fires on the island of Maui, according to experts. The fires, which broke out last Tuesday, have killed at least 106 people and destroyed the island’s historic town of Lahaina.
A July 2021 report on wildfire prevention by a Maui government commission warned that non-native grasses are making Hawaii more vulnerable to destructive fires, saying their presence, particularly on abandoned sugarcane fields, provides a source of “combustible, rapidly burning fuels” that “needs to be addressed”.
Hawaii’s last sugarcane mill, HC&S, which covered 14,570 hectares (36,000 acres) on Maui, closed in 2016. “The lands around Lahaina were all sugarcane from the 1860s to the late 1990s. Nothing’s been done since then – hence the problem with invasive grasses and fire risk,” said Clay Trauernicht, an ecosystems and fire specialist at the University of Hawaii at Mānoa.
Asked if the non-native grasses made the Maui fire worse, Trauernicht said that any form of “land use or land care would have made the situation safer”, given that the grasses were “completely left unmanaged”.
The 2021 report quotes Trauernicht describing the wildfire season in Hawaii as a “one-two punch” of wet then dry conditions. During the wetter part of the year, “a lot of vegetation and particularly grasses … grow and grow very fast,” he said. Then, in the dry period, the grasses turn “from green to yellow to brown pretty quickly … making us way more vulnerable to these big, destructive fires”.
The non-native grass species include fountaingrass (Cenchrus setaceus) and Guinea grass (Megathyrsus maximus), both of which have “adapted to thrive with fire”, according to a factsheet from the Pacific Fire Exchange (PFX), a Hawaiian fire science communication project. The grasses, PFX said, were originally introduced to feed cattle and provide ornamentation.
“The early part of 2023 was wet, which helped grass growth, and then we have had quite a dry summer, with a moderate drought on Maui for about a month now,” said Prof Abby Frazier, a climatologist who studied in Hawaii and is now at Clark University in Massachusetts. Frazier was on the nearby island of Oahu when the Maui fires broke out.
Frazier said the Maui fires were no surprise, although the human toll was shocking. “I never expected it to be this bad in terms of lives lost. It is shocking and gut-wrenching, but the fire itself was not a surprise.”
The exact ignition source has yet to be determined, and the risks were heightened by the strong winds associated with Hurricane Dora, but Frazier said “the overall cause of this fire being so large was the invasive grasses”.
Non-native grasses now cover about 25% of the state of Hawaii, Frazier added, and grow well on the drier, leeward side of Maui where Lahaina lies.
Frazier and Trauernicht said it was impossible to know what would have happened if the grasses had been removed. But reducing the coverage – using grazing animals, for example – could have tamed the fire’s intensity, they said, while farming activity, reforestation or fire breaks might have slowed its progress.
“It’s the speed of the fires through these grasslands that is and continues to be the problem here,” Trauernicht said.
Another problem, said Camilo Mora, an environment professor at the University of Hawaii, Mānoa, is the failure to tackle the climate crisis. “Yes, the grasses were a disaster waiting to happen, but … the silver bullet [solution] is reducing GHG [greenhouse gas] emissions,” he said.
“These people in Lahaina did not deserve to die. For a smart species like us to let this happen … as a scientist, I feel like crying.”
Mora said the invasive grasses grow faster than native plants, and are benefiting from increasing CO2 emissions. “The more CO2 that’s in the air … it’s like more food for the plants. CO2 feeds photosynthesis of these grasses, and that helps them grow.”
Maui County’s governor’s office did not immediately respond to a request for comment on the role of the grasses or the 2021 report which identified them as a risk.
Katie Kamelamela, an ethnoecologist at Arizona State University, said that non-native grasslands cover a quarter of Hawaii, dominantly to the west where many tourist destinations, including Lahaina, are located. The grasses include kikuyu grass (Cenchrus clandestinus), fountaingrass (Cenchrus setaceus) and molasses grass (Melinis minutiflora).
With small seeds that disperse on wind during winter months, Guinea grass can grow six inches a day in spring and reach up to 10ft tall. In summer, these grasses dry out and become a tinderbox. When wildfires break out, the area is cleared, the seeds grow, and the grass fire cycle starts all over again.