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Last month, a heat wave persisted for days in the Chilean coastal city of Viña del Mar. The landscape, already affected by an El Niño-supercharged drought, was baked dry. So, when wildfires sparked, they ripped through densely populated and mountainous terrain. In just a few days, the fires — the deadliest in Chile’s history — burned 71,000 acres and killed at least 134 people.
Devastating wildfires like these are becoming increasingly common. Climate change is partly to blame — while research has found that both El Niño and climate change have contributed to intense wildfires in Chile in recent years, scientists disagree whether climate change had a statistically significant impact on these particular February fires. But the Chilean fires also underscore another ominous dynamic: Grasses, shrubs, and trees that humans have introduced to new ecosystems are increasing wildfire occurrence and frequency.
In central Chile over five decades, timber companies have converted natural forests to homogenous, sprawling plantations of nonnative eucalyptus and Monterey pine that grow rapidly in the country’s Mediterranean climate. These trees contain an oily resin that makes them especially flammable but coupled with hotter and drier conditions due to climate change, they can be explosive, says Dave McWethy, an assistant professor at Montana State University.
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Our relationship with such nonnative species is fraught. We enable the spread of nonnatives by purposely transporting species to landscapes that haven’t previously existed with them. Take English ivy, a popular choice for stabilizing soil as an ornamental plant. Or the Norway maple, which was introduced to the East Coast of the US in 1756, quickly becoming popular for the shade it provided. In the process, such nonnatives can displace local ecologies and native species, disrupt agriculture, or transmit disease. Once a critter or a plant is introduced, either accidentally or purposefully, it can spread rapidly and outpace efforts to catch them at checkpoints or, as is the case for Florida’s state-sponsored “rodeos” for species like pythons, kill them.
A report from the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) estimates that the approximately 3,500 geographically invasive plants and animals worldwide cost the global economy $423 billion annually.
Climate change is also shuffling the ecological deck: As Vox has reported, ecologists expect climate change to create “range-shifting” or “climate-tracking” species that move to survive hotter temperatures. Perhaps some of those species will be more fire-prone. “Fires in places that are not used to fires are going to become much worse because of invasive species,” said Anibal Pauchard, co-author of the IPBES report and a professor at the University of Concepción and director of the Institute of Ecology and Biodiversity in Chile.
Such trends are causing wildfires to burn in unexpected places in the US as well. Last summer, for example, a wildfire — fueled by guinea grass, molasses grass, and buffel grass — killed at least 101 people in Maui.
According to research published in the journal PNAS, eight species of nonnative grasses are increasing fire occurrence by between 27 and 230 percent in the US.
This means, due in part to the spread of nonnative species, millions of people in the US will be affected by more frequent wildfires and the unhealthy smoke they produce. As the research shows, invasive grasses are altering historic fire activity and behavior in a variety of locations across the US. This includes those living in the arid West (especially the Great Basin and the Southwest) but also those in more humid parts of the country, particularly people living near eastern temperate deciduous forests, which cover the eastern US, and pine savannah ecoregions from central South Carolina to central Florida.
The nonnative grasses driving wildfire risk in the US
While no one factor causes a big fire to happen on its own, nonnative grasses have played a more important role in recent decades — especially in low-elevation regions without much fire historically, said Seth Munson, an ecologist with the Southwest Biological Science Center in Flagstaff, Arizona.
The annual invasive grass cheatgrass, known for its hairy tops, is found in an estimated 50-70 million acres nationwide, mostly in the Great Basin states. Lands with at least 15 percent cheatgrass are twice as likely to burn as those with a low abundance of the grass, and four times more likely to burn multiple times, according to researchers at the University of Massachusetts Amherst, University of Idaho, and University of Colorado.
According to the latest data, eight of the largest fires on record in the Great Basin have happened since 2010. That includes Nevada’s Martin Fire, which burned over 435,000 acres in 2018 and destroyed large swaths of grazing pastures for cattle and habitat of the federally protected sage grouse.
Another invasive grass, cogongrass flourishes across Florida and the Gulf States, infiltrating traditional pine woodlands. These landscapes are already burning, with harsh human consequences. Wildfires in northwest Florida in recent years have scorched homes, prompted the evacuation of over a thousand people, and cost millions of dollars.
The largest wildfire in Texas state history, only recently contained, damaged or destroyed hundreds of homes, killing at least two people and thousands of cows. Hundreds of wildfires in Louisiana last summer also resulted in two deaths. Buffelgrass is taking root all over Arizona’s Sonoran Desert, and red brome is spreading in the Mojave and other deserts.
Highly flammable tamarisk shrubs have taken root in thick stands near streams in the western US, and eucalyptus — one of the primary invasive trees blamed for worsening Chile’s recent wildfires as well as fires in Portugal — increases wildfire risk in California.
What can be done?
Limiting the introduction of nonnative plants, when possible, addresses the problem at its root. But many invasive species already have a foothold somewhere nearby. In that case, early detection of invasive species, by satellite imagery or by people on the ground, is the best way to stop invasives with a variety of removal techniques, be that herbicide or something else, in an attempt to keep them somewhat contained.
Federal agencies across the country, like the one Munson works for, as well as states, tribes, nonprofits, and others, are already monitoring for the movement of invasive species on the landscape and attempting to manage them as they inevitably spread. Work is also underway to help native plants reestablish faster after fires, giving them a chance against invasives angling for the same open space.
You can do your part by finding out which nonnative plants exist in your area, especially those that increase wildfire risk. And if you’re looking to spruce up your home’s landscaping, don’t plant them; consider a native alternative instead.
