The 2000 Bitterroot fires gave researchers a chance to examine long-term impacts to fish populations.
Wildfire is a fact of life in western Montana. In summer, we resign ourselves to the smoke and trail closures that can change travel or recreation plans. Meanwhile, in winter, we analyze snowpack percentages and make wagers on how the snow (or lack thereof) might influence our wildfire season.
In our own way, Westerners are used to living with fire. And now, new research shows that native wildlife — namely, native trout — might also be adapted to fire. Studies suggest that natives are better equipped to withstand fire impacts, and are more likely to thrive in post-fire habitat conditions than non-native species.
In 2000, fires ravaged much of the Bitterroot National Forest and Ravalli County. Mike Jakober, Fisheries Biologist on the South Zone of the Bitterroot National Forest, explains that these widespread fires had substantial detrimental impacts on fish in the short-term.
“These (the 2000 fires) were high severity burns,” says Jakober. “We documented large-scale fish kills, lots of sedimentation, ash, black water, high flows, debris torrents, you name it. These were negative impacts, and were dramatically negative in the short-term for sure.”
Because of the range of damage, Jakober and other researchers surmised that the post-fire conditions would favor non-native fish, like brook trout, which typically do fairly well in streams that contain high sediment levels and warm water, both of which usually occur following a high severity burn. Managers braced themselves for a full-on invasion of non-native fish into the new habitat. But, the data soon began to reveal a different story: in fact, it appeared that native fish like westslope cutthroat trout were bouncing back in a robust – and unexpected – fashion.
New research shows that post-fire conditions favor native over non-native trout.
“By 2003, the native fish levels were at or close to pre-fire numeric abundance,” says Jakober. “And, at 30 study sites, only 1 showed a dramatic increase in brook trout. At the remainder of the sites, the vast majority of brook trout were very suppressed.”
Researchers Clint Sestrich, Thomas McMahon, and Michael Young from Montana State University conducted a number of fish surveys following the 2000 Bitterroot fires, and recently published a widely-read paper titled, “Influence of fire on native and nonnative salmonid populations and habitat in a Western Montana Basin.” Their study – which includes 11 years of pre-fire data and three years of post-fire data from nearly 30 streams in the Bitterroot National Forest – is now helping biologists, managers, and local citizens to more clearly understand how fire impacts native and non-native fish populations.
“At the time of the fires in 2000, not much was known about long-term impacts of fire,” Jakober explains. “We knew from the fires in Yellowstone that wildfire had a harmful short-term impact. But not much was out there about what came next.”
Today, Jakober continues to piggyback on this original research by monitoring the long-term impacts of fire on native fish populations. He’s found that the short-term trend – in which he witnessed a solid rebound in native trout numbers – has played itself out in the long-term, too.
“Even now, 10 years later, most brook trout populations are still suppressed,” says Jakober. “The brookies aren’t nearly as numerous as they were pre-fire. And, in places where the brook trout have recovered, there weren’t a lot of them to begin with, so they’ve remained at those low-density numbers.”
The research is telling. Studies indicate that after initial fish kills, fire actually creates improvements to fish habitat that bolster native trout populations. Indeed, long-term benefits to habitat seem to outweigh the high mortality rates seen in the short-term following a fire.
In fact, in the Bitterroot, areas affected by the 2000 fires now boast so much woody debris and shrub growth that the streams have become difficult to survey. And when Jakober and his techs do manage to get samples, they know it’s not the whole picture – with all the new and woody habitat, plenty of fish are likely hiding nearby, just out of sight from well-meaning managers.
So how might these findings affect management decisions down the road? Jakober says that, for now, not much will change on the ground.
“Even in 2000, increased ecological awareness coupled with low budgets caused the Forest Service to let a lot of fire burn,” explains Jakober. “We’ve had a lot of fire on our forest in the last 15 years, and we can see the benefits. We’ve got an incredible mosaic of habitat, different classes of vegetation, and lots of stages of development.”
Jakober hopes that the MSU research and his subsequent monitoring will help the public gain a fuller understanding of how fires affect ecosystems and create benefits for native fish populations.
“As a biologist, it doesn’t really bother me to see fire,” says Jakober. “Some areas are roasted for sure, but there are a lot of patchy areas – a lot of refugia in the unburned areas.”
Ask any angler, and he or she will likely say they prefer not to fish in a burn. Floating downriver next to a charred hillside, or wade fishing through thick shrub and debris doesn’t exactly fulfill the vision of a tranquil Montana fly-fishing experience. But it should be nice for any angler to know that — beneath the surface – the post-fire years are likely treating native trout just right.
In all, Jakober is confident that native fish are faring just fine in the post-fire years across the Bitterroot. Now, he’s got a different set of concerns on his mind — namely, climate change. The Bitterroot data shows that cutthroat can survive, and even out-compete brook trout, when fires cause short-term habitat disturbances. But, if average stream temperatures continue to rise, the natives might lose some of their natural advantages, particularly native bull trout, which are the most thermally sensitive trout species in western Montana.
“The only concern in all of this is how the climate is going to change in the future,” says Jakober. “If we could have a guarantee that we’ll maintain a stable climate, I wouldn’t be worried. But with temperatures going up, maybe by an average of five degrees Fahrenheit over next 20 years, these burned streams are going to get awfully warm, and it will take a lot longer for them to cool down.”
Protection and restoration of streamside vegetation becomes even more important in light of climate change.
In this light, preparing for climate change by mitigating for other negative impacts to native fish populations becomes even more important. Stream temperature surveys, protection and restoration of streamside vegetation, and increased species monitoring are several tools that can help biologists and managers take on the climate challenge. We’ll continue to track these issues on www.clarkfork.org — stay tuned.