Getting Ahead of Large Rangeland Fires in the Great Basin

Annual fire probability map layers help managers better plan and prepare for rangeland fire season in the Great Basin

The sprawling geography of the Great Basin covers most of Nevada and parts of Utah, Oregon, California, and Idaho. Large wildfires — those burning thousands of acres in one fell swoop — have increased over recent decades in this region, impacting wildlife habitat, water quality, recreational opportunities, livestock production, and more.

Accurately predicting the likelihood of a large fire in this remote and rugged region, particularly ahead of the upcoming fire season, would provide land and fire managers with critical insight that could help prevent or minimize lasting impacts to the region’s imperiled sagebrush habitats.

New research funded by the USDA’s Agricultural Research Service (ARS) and supported by Working Lands for Wildlife (WLFW) does just that.

We sat down with Joe Smith, WLFW researcher, and Jeremy Maestas, sagebrush ecosystem specialist with the USDA’s Natural Resources Conservation Service (NRCS) West National Technology Support Center, to learn more about how sagebrush rangeland fires differ from forest fires, how Smith led the creation a new fire probability map for the Great Basin, and how this tool can be used to better manage fire risk across the region.

This research focuses on wildfires in the Great Basin. Tell us more about how wildfires have changed in the region over the last few decades? 

Jeremy: According to the National Interagency Fire Center, in the U.S. today, there are more acres cumulatively burned in rangelands than in forests, and most of those rangeland fires are in the Great Basin. But, when people think of fire, they tend to think of forest fires. The reality is that more acres are burning in rangelands than in forests.

Joe: Data from the Monitoring Trends in Burn Severity [a fire information clearinghouse maintained by the U.S. government] shows the 12 largest fires on record in the Great Basin have occurred since 2000, and, of those, eight occurred since 2010. So, there’s growing evidence that fires in the Great Basin are increasing in size and impact over the last 20 years.

Jeremy: When we talk as a society about wildfire, almost all the conversation is focused on forests. This data tells us that fires in rangelands also need to be addressed. The Great Basin is one of the largest expanses of sagebrush range in the country, and it’s been experiencing larger fires. If we don’t focus on rangeland fire and only focus on forest fires, we’re only addressing one-half of the problem.

What sort of impact do these larger fires have on rangelands?

Joe: Sagebrush shrublands aren’t as fire-adapted or resilient as forests are. Large fires often have significant and long-lasting ecological consequences in sagebrush country. Many forests, especially those in the West, evolved with regular fire with tree species dependent on fire to reproduce. Sagebrush is different. It’s killed by fire, and when it’s lost, it may be lost for a long time as sagebrush re-establishes only by wind-blown seeds from nearby plants.

Vegetation communities in the Great Basin can be so slow to recover from fire due to aridity of the region. Their vulnerability to invasive species, like cheatgrass, further exacerbates the consequences of fire by disrupting natural recovery processes.

Jeremy: Invasive annual grasses are a game-changer. We don’t have the luxury of just letting fires burn in the Great Basin’s sagebrush ecosystems, even when they’re not threatening infrastructure. Not all fire is bad, even in sagebrush range. But when you lose hundreds of thousands of acres of sagebrush habitat in a matter of days, and you have invasive annual grasses just waiting in the wings to grow after a fire comes through, you start to change entire landscapes that will take a 100 years or more to recover — if they recover at all. The pace and scale of fire in the Great Basin is unsustainable for sagebrush-dependent wildlife and threatens other ecosystem services that we depend on.

In what other ways are fires in sagebrush rangeland different from fires in forests? 

Joe: To put it simply: forests are a moisture-limited system. There’s always enough fuel in a forest to burn, and that fuel load is relatively stable over time. How much moisture is in that fuel determines whether a fire starts after an ignition. If the vegetation and litter are dry when there is an ignition source, then it’s likely the forest will burn. If the fuel is wet, then there’s less likelihood it will burn.

In contrast, sagebrush rangelands are fuel-limited systems. There is less burnable vegetation overall, and also more variability in fuel load each year, which means there isn’t always enough fuel to carry a large fire despite an ignition. The sagebrush range is made up mostly of perennial grasses and forbs, sagebrush and other shrubs, and, unfortunately, fine fuels like cheatgrass. But there is also bare ground in between those plants that makes it harder for fire to move across the landscape, especially in dry years. There must be enough fuel (grasses, forbs, and shrubs) to burn and enough fuel continuity to carry that fire across the landscape for a large fire to get going.

Walk us through your research and how vegetation data helped inform the maps you produced.

Jeremy: Joe is a wildlife biologist by training, not a fire specialist. He essentially modeled a habitat that was suitable for large rangeland wildfire, like one might model habitat suitability for a wildlife species. It was a clever way to get at this challenge.

Joe: Prior research had shown that wet years create periodic flushes of vegetation productivity in rangelands that lead to more fire the following year. But those analyses were fairly coarse in scale and didn’t approach the problem with forecasting in mind. We also didn’t have spatial vegetation datasets that would allow us to model these relationships and map fire risk at ecoregional scales until very recently.

Because rangeland fires have high consequences for sagebrush, I wanted to see if I could combine new, fine-scale and dynamic vegetation data from the Rangeland Analysis Platform (RAP) with historic fire data from the MTBS and weather data to develop a model that could accurately predict the likelihood of a large fire across the Great Basin in advance of the fire season.

We were able to build a fairly accurate model, thanks largely to the RAP.

RAP gave me the dynamic, fine-scale vegetation data I needed; the MTBS data provided the historical fire data, and by using a “hindcasting” process, I was able to test the predictive ability of these forecasts at scale.

How can these maps help managers better plan and prepare for rangeland fires in the Great Basin?

Jeremy: Joe’s work highlights that herbaceous fuels drive the potential for large rangeland fires. To date, most fuels management in rangelands has been focused on woody species, which from a fire behavior standpoint makes sense. Woody species do produce hotter, more intense fires with higher flames that are harder to control and more dangerous for firefighters. But they don’t increase the potential that a large fire might occur in the first place.

Not only did Joe’s work highlight the importance of fine “grassy” fuels, but he also homed in on the fact that it’s really the previous year’s vegetation accumulation that drives large fire risk.

So right away, you have two important management shifts to consider: 1) fuels management should be focused not only on woody species, but also on herbaceous vegetation and fine fuels like cheatgrass, and 2) the current year’s vegetation growth doesn’t necessarily impact whether a rangeland fire might become large, it’s mostly about what happened the previous year.

Fire behavior is influenced by three factors: topography, weather, and fuel. We can’t manage topography, and while we can monitor weather, we can’t manage it. We can manage fuels. Joe’s research helps us better understand what fuels to manage and where to manage them. That is huge.

Beyond those basic shifts in how we think about managing large fire risk on rangelands in the Great Basin, we can start to integrate Joe’s fire probability maps into pre-fire preparedness and fuels management efforts. For example, with Joe’s preseason fire probability forecast maps,  managers can line up fire-fighting resources and position them where fire risk is highest or surgically implement fuel treatment practices like targeted grazing or cheatgrass eradication that can help reduce fuel loads. Public land managers also might implement closures or fire restrictions to help reduce the likelihood of human-caused ignitions in high-risk areas.

Since Joe’s research spans back to 1988, we gained additional perspective on which areas of the Great Basin are chronically at risk of large fires year after year and which ones aren’t. So, at broader, strategic-planning scales, we can leverage Joe’s maps to target treatments like roadside fuel breaks in areas that have a consistently high probability of a large fire. In areas where fire risk is typically low, we might implement different fuel management activities with a lighter touch on the land, such as early detection and rapid response to cheatgrass invasions. Implementing the right actions, in the right places, at the right time improves stakeholder buy-in and public support for the fuel management activities needed to reduce the odds of losing more sagebrush country to fire.

---