Invasive Plants Brought to Maui by Colonists Helped Fuel the Wildfires

There are a lot of things that have made the Maui wildfires—which have so far claimed a confirmed 111 lives—so widespread and deadly: drought conditions that have prevailed in the state since the end of May; hurricane Dora, which lashed the islands with 45 mph winds; and downed power lines—blown over by Dora’s gusts and suspected of sparking local blazes. What’s gotten less attention—but likely played a significant role—is Hawaii’s large and spreading population of non-native, invasive grasses, which grow fast, burn easily, and are covering more and more of the island chain, with climate change partly to blame.

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The Hawaii Invasive Species Council lists no fewer than 79 non-native plants that were brought to the islands as early as 1793, when Europeans, and later Americans, moved to the islands. The cattle that ranchers brought with them preferred the non-native grasses as food. Other immigrants brought other non-native species to be used for erosion prevention or decorative purposes. Of all of the invasive plants now thriving on the islands, the U.S. Department of Agriculture points to 18 specifically that contribute to Hawaii’s wildfire risk, including buffel grass, molasses grass, and especially guinea grass. This last one can grow an astonishing 6 in. in a day during the rainy season, and may reach a height of 10 ft.

Non-native grasses and shrubs currently grow on nearly 25% of Hawaii’s surface area. Part of what makes them so pervasive and such a peril is their life-cycle. “They tend to dry out very early in the season,” says Erica Fleishman, director of the Oregon Climate Change Research Institute and professor in the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University. “They also … decompose less quickly than other types of plants and so you wind up with a lot of dry, standing, dead plants and those can burn really easily.”

Non-native grasses also tend to be both drought-tolerant—sprouting even when rainfall is scarce—and fire-adapted, quickly bouncing back after a blaze and taking advantage of the torched and empty land around them. That’s a bad combination.

“They are the first things to regenerate after a fire,” says Lissa Strohecker, spokeswoman for the Maui Invasive Species Committee. “Native species’ seeds may be destroyed by fire, whereas invasive species’ seeds tend to survive; sometimes they’re even released by fire. If you’re the first plant to regrow in a cleared landscape, then you’ll have an advantage.”

Read more: How to Help Those Affected by the Maui Wildfires

It’s not fire alone that has exposed so much landscape to invasive plants in Hawaii. The island chain used to be home to a booming pineapple and sugar cane industry. But high local costs for land and labor led growers to move their operations out of Hawaii. The state’s last pineapple plantation closed in 2009, with sugar cane following in 2016. The sprawling tracts of land they left behind have been largely untended since. Without humans managing that land, says Fleishman, plants can take over, and “non-native invasives are really good colonists.”

“When you have an agricultural system, you often have a lot of active human management,” says Fleishman. “You have irrigation, you have people removing plants that are considered weeds. If those areas are no longer receiving that level of human attention, the plants that can colonize them are going to take advantage of that situation. Non-native invasives are really good colonists.”

Non-native grasses and the fires they contribute to have been a problem in Hawaii for most of the nearly 250 years Europeans and Americans have been coming to—and living on—the islands. But in the era of climate change, things are clearly growing worse. 

“Many of these plants do pretty well in high temperatures,” says Fleishman. “Many of them do pretty well with dry conditions. In general, a lot of non-native plants are doing very well as the climate changes.”

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