Published 2:11 pm Wednesday, May 28, 2025
Rangelands in much of the Snake River Plain are receptive to fire earlier than usual thanks to prolonged warm, dry conditions.
The area’s “peak of green” was in early to mid-May rather than the usual May 25 or thereabouts, mostly due to minimal rain and above-average temperatures, said Matt Reeves, fuel and forage specialist with the U.S. Forest Service Rocky Mountain Research Station.
“In theory this will lengthen out fire season by some,” he said. Grasses cured early, making them fire receptive longer.
“You can have fire now” in the Snake Plain, the Missoula, Mont.-based Reeves said. “Historically, it’s a little bit later when that is the case.”
In many rangeland areas, a dry spring leads to lower fuel production and smaller fires, he said.
“However, also in a drier spring, in very productive rangelands like the Snake River Plain, even though it has been drier than normal, there is still plenty of fuel to go around,” Reeves said.
About 24% of the non-forested, rangeland portion of the West has not produced enough fine fuel or did not have enough holdover from the last growing season to produce large wildfires most years, he said. Researchers look for 800 pounds per acre, “which seems to be a threshold where, below that number, large wildfires do not normally occur.”
In the Snake Plain west of Boise, yields of fine fuel are about 1,100 pounds per acre on average, while the average cover by invasive annual grasses such as cheatgrass is about 25%, Reeves said. “In addition, the fine fuels such as grasses are fully cured. But the region has not experienced excessive drought, so live fuel moisture should be near normal for this time of year.”
Fuel moistures in the Southwestern U.S., in contrast, are “anomalously low,” he said, particularly in shrubs.
“We don’t see the same anomalies in the Snake River Plain,” Reeves said. But on the Snake Plain, rangeland productivity and the presence of invasive annual grasses mean “even average years produce wildfires.”
U.S. Bureau of Land Management Boise District fire information officer Chad Cline said winter brought less low-elevation snow to pack down the previous year’s grass crop.
“That’s what you’re seeing — a lot of last year’s crop still standing,” he said.
Also in the West, the Forest Service’s Reeves is looking at California’s southwestern area, which is dominated by extremely flammable chapparal and supports fine fuels exceeding 2,500 pounds per acre in many cases, he said. Fuels have been cured in most of the region for a month or more, “so generally speaking, fine fuels are highly susceptible to ignition and rapid fire spread rates.”
He also is watching conditions in the northern Great Basin, in Oklahoma and parts of Texas, in southwestern South Dakota and in the area south and east of Phoenix.
The northern Great Basin is “supporting a much larger than normal herbaceous fuel yield” at more than 1,600 pounds per acre on average, Reeves said. This year’s average to below average production combined with the amount left from last year creates fuel bed conditions that can enable large wildfires, “accentuated by the relatively high cover of cheatgrass, especially in the lower elevations where cover of cheatgrass in excess of 30% is common.”
Invasive annual grasses such as cheat can increase fuel bed continuity and quicken the spread of fire.
