Invasive plants brought by colonists exacerbated wildfires on Maui

Invasive plants brought by colonists exacerbated wildfires on Maui

THere are many of the things that made the Maui wildfires — which have claimed 111 lives so far — so widespread and deadly: the drought conditions that have gripped the state since the end of May; Hurricane Dora, which struck the islands with winds of 45 miles per hour; And downed power lines – broken by storm surges and suspected of sparking local fires. What has gotten less attention — but likely played an important role — is Hawaii's large and widespread population of non-native and invasive grasses, which grow quickly, burn easily, and are covering more and more of the island chain, with climate change partly to blame.

The Hawaii Invasive Species Council lists at least 79 non-native plants that were introduced to the islands as early as 1793, when Europeans, and later Americans, moved to the islands. The cattle that ranchers brought with them preferred non-native grasses as food. Other immigrants brought other non-native species for use in erosion prevention or decorative purposes. Of all the invasive plants now thriving on the islands, the USDA cites 18 plants specifically that contribute to Hawaii's wildfire risk, including buffalo grass, molasses grass, and especially guinea grass. The latter can grow a staggering 6 inches in a single day during the rainy season, and may reach 10 feet in height.

Non-native grasses and shrubs currently grow on approximately 25% of Hawaii's surface area. Part of what makes them so widespread and such a danger is their life cycle. “It tends to dry out very early in the season,” says Erica Fleishman, director of the Oregon Climate Change Research Institute and a professor in Oregon State University's College of Earth, Ocean and Atmospheric Sciences. “They also decompose less quickly than other types of plants, so you end up with a lot of dry, dead plants that can easily burn.”

Non-native grasses also tend to be drought-tolerant – germinating even when rainfall is scarce – and fire-adapted, bouncing back quickly after a fire and taking advantage of the burned, empty land around them. This is a bad combination.

“They're the first things to regenerate after a fire,” says Lisa Strohecker, spokeswoman for the Maui Invasive Species Commission. “Seeds of native species may be destroyed by fire, while seeds of invasive species tend to survive; sometimes they are released by fire. If you are the first plant to regrow in a clean area, you will have an advantage.”

Read more: How to help those affected by Maui wildfires

It's not just fire that has exposed much of Hawaii's landscape to invasive plants. The island chain was home to a thriving pineapple and sugarcane industry. But high local costs of land and labor prompted farmers to move their operations outside Hawaii. The state's last pineapple plantation closed in 2009, and sugarcane followed in 2016. The sprawling tracts of land they left behind have remained largely neglected ever since. Without humans controlling that land, plants can take over, and “non-native invaders are really good colonizers,” Fleishman says.

“When you have a farming system, you often have a lot of active human management,” Fleishman says. “You have irrigation, you have people removing plants that are considered weeds. If these areas no longer receive this level of human attention, the plants that can colonize them will take advantage of this situation. Non-native invaders are really good colonizers.

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

“Many of these plants do well in higher temperatures,” Fleishman says. “A lot of them do well in dry conditions. In general, a lot of non-native plants do very well with climate change.”

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    (Tags for translation) Extreme weather 

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