How Swaths of Invasive Grass Made Maui’s Fires So Devastating

Researchers are still looking for answers as to what started last week’s fires in Maui that have killed at least 99 people to date and decimated the historic tourist town of Lahaina. Investigators do know, however, one factor that made the fires so deadly: invasive grass that had transformed the island into a giant tinderbox.

For nearly 200 years, Hawaii’s economy was highly dependent on sugar cane and pineapple agriculture. But plantations began declining in the 1990s as the state transitioned to a tourism-dominated economy, report Simon Romero and Serge F. Kovaleski for the New York Times. Vast swaths of farming acreage were abandoned, and in 2016, Hawaii’s last sugar cane plantation shuttered.

Without farmers tending that land, nonnative brushes such as guinea grass, molasses grass and buffel grass moved in. These species are native to Africa and were introduced to Hawaii in the late 18th century by European ranchers who wanted a steady supply of drought-resistant livestock forage. Today, almost a quarter of Hawaii’s land cover consists of these invasive shrubs. They run amok on the tens of thousands of acres of plantations on which sugar cane and pineapple plants once flourished. Hardy, voracious and opportunistic, they invade roadside shoulders and encroach on urban housing areas.

“Those fire-prone invasive species fill in any gaps anywhere else—roadsides, in between communities, in between people’s homes, all over the place,” Elizabeth Pickett, co-executive director of the Hawaii Wildfire Management Organization, tells Wired’s Matt Simon.

Hawai'i firefighters have been telling me for several years they're seeing fires burn hotter and faster than in the past - and I trust their knowledge. But fire and land use histories tell us fallow lands and grassy fuels are the key issue - and one we can deal with locally pic.twitter.com/91CTqMXQSg

— Clay Trauernicht (@claytrau) August 15, 2023

The nonnative grasses spread easily during the rainy season and dry out during droughts. At a time such as this summer, when the landscape is arid, the plants’ desiccated and dormant state makes them highly flammable. And after a fire burns through, some of these species are adapted to recover quickly—as a result, they are first to repopulate the scorched Earth, crowding out native plants as they proliferate. This “grass-fire cycle” makes the invasive grasses more prevalent after a blaze, leaving the land more susceptible to another fire, write Scott Dance and Kate Selig for the Washington Post.

Scientists have long known about these invasive species’ potential to burn. In 2018, fires broke out on West Maui and destroyed 21 homes, in part thanks to these grasses. Researchers estimate 85 percent of the razed areas in the 2018 fire were nonnative shrub lands, per the Post. After that disaster, one of the island’s most prominent fire experts, University of Hawaii plant ecologist Clay Trauernicht, published a letter asserting “all that grass” could fuel future incidents. In 2021, a Maui County report also warned about the rampantly spreading shrubbery and called for its reduction.

Now, five years after that destructive event, history is repeating itself.

Worsening matters today is a confluence of weather patterns that make for a perfect storm of fire risk. For one, Hawaii is in the thick of its dry season, with more than a third of Maui County facing drought. Secondly, 80-mile-per-hour gusts have been sweeping across the island, fanning the flames of Maui’s blazes. Those powerful winds were likely caused in part by Hurricane Dora, which passed by the state in the Pacific Ocean last week.

Although the storm skimmed roughly 500 miles off the island’s coast, it created a pocket of low air pressure that contrasted sharply with a high-pressure area from another storm north of Hawaii. This stirred up southbound, high-speed gales that promoted the advance of the flames.

It doesn’t help that the winds also suck moisture from the vegetation they touch, further parching the landscape and exacerbating dangerous conditions where fires can spread.

#Dora tracks past Hawaii pic.twitter.com/k5AaU8w9II

— Zoom Earth (@zoom_earth) August 9, 2023

Less rainfall and thinner cloud cover—on top of higher temperatures in today’s era of global warming—have made wildfires in a tropical island like Hawaii not just a possibility, but a probability. And the incidence of wildfires will only grow more common, unless local officials take action to mitigate fire risks, experts say.

Trauernicht tells Spectrum News’ Michelle Broder Van Dyke that a good first step for fire mitigation is to reduce the fuel for future blazes. That means reverting the overrun plantations back into tended agricultural lands. Grazing animals can also be valuable allies to tamp down these invasive grasses. This method is as simple as letting sheep, cattle or goats do what they do best on grass-dominated spaces, so they can trim the unruly kindling.

Moreover, fire breaks, or gaps between flammable vegetation, can also help contain a blaze once it gets going. Instead of allowing fires to spread untrammeled on grasslands, Trauernicht recommends planting rows of pineapples, bananas, dragon fruit or taro to cut off a fire’s potential path of spread.

“Just like with climate change, we know what steps will reduce the risk of wildfire,” Trauernicht wrote in his 2018 letter. “But actually taking these steps will require reinvesting in and, frankly, reimagining our individual and collective responsibility for the larger landscape.”

Shi En Kim | | READ MORE

Shi En Kim is a Washington, D.C.-based freelance science journalist. Her work has appeared in National Geographic, Scientific American, the Atlantic, Popular Science and others. In 2021, she interned at Smithsonian magazine as an AAAS Mass Media Fellow.