From the Ashes: Complex Changes in Wildfire Patterns Detailed in Great Basin's History

Wildfire patterns in the West are changing, but according to new research, the trend in the Great Basin hasn’t necessarily been a simple increase.

Exploring differences between current wildfire patterns and those from the past can help researchers pinpoint trends in the complex shifts in the region, according to new work from Mark Brunson from the Quinney College of Natural Resources, Eva Strand from the University of Idaho, and other collaborators.

“The narrative we tend to hear is that fires are getting bigger, hotter, and more destructive,” Brunson said. “In the Great Basin fire is certainly increasing, but the story is more complex. Some plant communities are burning less than they once did, especially on relatively cooler, wetter mountain slopes.”

The project compared wildfire patterns in the Great Basin from the past 60 years with those before the 1900s and found that wildfires in many vegetation types have become larger and more frequent over the past three decades compared to the decades before. Wyoming big sagebrush and basin sagebrush burned more frequently, as did long-established juniper and pinyon woodlands — even potentially pushing them beyond recovery in some places.

But while fire now occurs more often in aspen and higher-elevation sagebrush-scrublands than it did 30-60 years ago, fires are still less frequent than in prior centuries.

“There is still a fire deficit in many forests from decades of over-suppression — but that’s not true for rangelands,” Brunson said. “It’s a complicated story, but one we have to understand if we are going to find a way to help these lands recover.”

In valleys and the lower slopes of Great Basin’s mountain ranges, fires are more frequent, and sagebrush struggles to recover from repeated impacts.

“In those places we're seeing conversion to invasive annual grassland,” Brunson said. “But moving up the slope of the mountain to cooler, moister sagebrush communities, natural recovery after a fire is still happening and is much more likely. We're actually seeing fewer fires than there had been historically.”

The devil is in the details, and the complexity of the pattern makes it tricky to communicate. The team created an interactive story map to illustrate these big-picture shifts. Understanding how natural and human-caused fires have shaped ecosystems over time offers key insights into the challenges now facing the region, Brunson said.

This information offers an important baseline for understanding the complex dynamics and for prioritizing management actions across the region, he said.

Major culprits for changes in wildfire patterns are the explosion of invasive cheatgrass and human ignitions, he said. Climate change is also exacerbating fire risk, with drier and hotter fire seasons increasingly common.

Nonnative annual grasses like cheatgrass continue to be major drivers of increased fire frequency and size. Human-ignited fires are also a significant factor contributing to increased frequency of wildfire, especially in those areas with a high abundance of nonnative annual grasses and places where human populations are growing the fastest, such as on Idaho's Snake River Plain.

The increasing frequency of wildfires may eventually lead to major changes in these landscapes; converting ecosystems to nonnative, fire-adapted plant communities. But understanding the nuance of variation in fire regimes across landscapes and over time can help land managers to prioritize how they use limited resources to protect ecosystems and human values most effectively, Brunson said.

A focus on strategies that tackle non-native grasses and human-caused ignitions can be a good use of resources while considering the specific fire ecology of different vegetation types and the overarching influence of climate change allows for longer-term change. Protecting persistent and old-growth woodlands should be a management focus, he said.