Invasive grasses are fueling large fires in dryland ecosystems across the Southwestern U.S., including at Agua Fria National Monument in central Arizona. Photo by Katie Laushman, USGS.
BY SETH MUNSON, ERIN MCDUFF
Each year, as we hear about wildfires raging across the U.S., people often envision vast forests. However, much of the low-elevation Southwest is also experiencing larger, more destructive wildfires. These arid and semi-arid regions, known as drylands, can take a long time to recover, and the ecosystem can change in ways that make wildfires more likely to recur.
Researchers are trying to understand what is driving fires in these areas to become more extreme while exploring what we can do to promote recovery and reduce wildfire risk.
Seth Munson, Ph.D., is a research ecologist with the U.S. Geological Survey (USGS) Southwest Biological Science Center in Flagstaff, Arizona. During his thirteen years in this position, his research has focused on the impacts of climate change and land use on dryland ecosystems.
What happens to drylands after a wildfire?
Drylands are a challenging environment, and recovery from large wildfires tends to be slow. Some long-lived plants, like creosote bush, may take decades to re-establish. Intense fires can also damage soils, further delaying native plant regrowth.
The big question with drylands is how to bolster slow-growing native plants. If the ecosystem doesn’t recover fast enough, invasive species have an opportunity to move in. By invasives, I mean those plants found in an area that was not part of its historical range. Many invasive grasses in the Western U.S. were introduced intentionally from Eurasia or Africa in attempts to either stop erosion or increase forage for cattle. However, they can reduce food sources for wildlife and provide fuel for wildfires.
What impact do wildfires have on invasive plants?
A large wildfire essentially levels the playing field. The plant that grows back the fastest is most likely to take over, and invasives grow quickly.
In each major desert area of the U.S., at least one invasive grass has largely become dominant. For example, in the Great Basin, cheatgrass has become dominant over native sagebrush. Invasive grasses are now the primary wildfire risk in dryland areas because they are more flammable than native plants.
The story repeats itself throughout the West. The invasive grass may be different from one area to the next, but they are uniformly increasing the size and frequency of fires, which in turn create room for the invasives to spread further.
What role does climate change play in this cycle?
The Southwest is projected to experience increasingly dry conditions due to climate change, which can accelerate the growing season of some invasive grasses. One of the driest years on record was 2020.
Drylands are pretty well adapted to drought, but prolonged drought will eventually kill off native vegetation, as we’ve seen recently with juniper and piñon trees. It’s not widely covered in the news, but a lot of perennial grasses will die off as well.
Projections also show that climate change will cause less frequent but more intense summer storms in the Southwest. Because invasive grasses are opportunistic, they can take advantage of this irregular moisture, especially following prolonged drought that kills off native plants.
Once the storm passes, the invasive grasses will then dry out, creating the perfect conditions for wildfires, which in turn help the invasives to spread further.
How does the work you and others are doing address these challenges?
The first thing we contribute is detection. If we detect invasives early, we can eradicate them. We’ve developed methods that use remote sensing technologies, from coarser-scale satellite imagery to high-resolution imagery from drones.
Once invasives are detected, we help monitor them. We respond to a lot of requests from land management agencies to identify where invasives are, where they could go, and what environmental factors will drive their spread.
We also research the underlying factors that cause invasives to explode across the landscape. We’re working on a project right now to run fire and fuel treatment simulations to figure out how ecosystems will burn and what fuel treatments could reduce that risk.
Finally, we’re working on post-fire recovery by finding ways to jumpstart the growth of native plants and suppress invasive species.
What makes you hopeful for the future of these landscapes?
It’s easy for people hearing about these ecosystem changes to develop a doom-and-gloom mindset, but there’s a lot of reason to be optimistic. We’re having success in ecological restoration, both in getting rid of noxious plants that cause fires and in helping native plants recover.
Even large fires have presented an opportunity to reimagine how these ecosystems look and improve how they’ll perform amid climate change and increased land use pressure.
I have a lot of optimism from the work I see our land managers doing to adapt to our changing future.
Seth Munson, Ph.D., is a research ecologist with the U.S. Geological Survey (USGS) Southwest Biological Science Center in Flagstaff, Arizona.
Erin McDuff is a public affairs specialist with the Interior’s Office of Wildland Fire.