THE LAST CAST
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ASHLEY RUST, PHD
How Will The Wildfires of 2020 Impact Colorado’s Trout Fisheries? Colorado, along with many states in the Rocky Mountain West, experienced a record-breaking fire season in 2020; over 650,000 acres burned in our state. How will the trout populations in nearby streams be impacted? What should anglers expect to see in the rivers this year?
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Yes, 2020 was an unprecedented year. Colorado experienced three of the largest fires in the state’s history: the Cameron Peak fire, the East Troublesome fire and the Pine Gulch fire-- each burning well over 100,000 acres apiece. And this is after the Grizzly Creek fire had engulfed forest areas around I-70 and caused highway closures. With climate change, our fire season each year is two months longer on average, starting a month earlier in the spring and lasting a month longer in the fall. Combine a longer, drier season with current forest management practices, and more people living in the wildland-urban interface, and we are observing fires that are larger, more severe, and more costly than ever before. We are reckoning with our attitude of fire suppression, which has been a warfare on fires, allowing forests to age and fuels to accumulate. However, fires are a part of the forest landscape. Fires are a natural disturbance, and the inhabitants of the West, including our beloved trout, have evolved with fire. Native plants, insects and fish have all adapted to return after fire. If you take the “long-view” fires generally help revitalize ecosystems, acting as a natural re-set in climax communities. I have spent much of the last decade studying
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High Country Angler • Spring 2021
how wildfires disrupt water quality, impact water supplies and affect aquatic life. I have been on the ground sampling aquatic insect and fish populations immediately after and many years following fires in Colorado. And I have utilized public data to evaluate the most common water quality responses in streams disturbed by hundreds of wildfires. My main observation is that the earth is incredibly resilient and ecosystems recover healthier after fire when enough time has passed. I hope to convince you to be patient, remain hopeful, and observe some remarkable landscape scale changes and recovery. Wildfires are evaluated by their burn severity, a spectrum where foresters consider how much of the vegetation was combusted. Low severity fires leave much of the vegetation intact, are more like crown fires, and do not disrupt the hydrology, water quality, insect or fish populations in the streams within and below the burn scar. Moderate and high severity fires, where vegetation is completely combusted and the ground is scorched, result in higher streamflows and compromised water quality for 1-5 years after the fire. The greatest impacts on streams have been observed after rainstorms. In moderate to high severity burn scars, the forest floor becomes hydrophobic because the organic material has been cooked, reducing infiltration capacity of the soil, preventing rainwater from percolating into the ground and causing rain to accumulate as surface runoff, delivering more water to the streams after rain. The higher flows can scour stream bottoms, flushing fine sediment and material from the system. During Colorado’s monsoon season late in the summer, short intense rain-events also physically dislodge soil from burned landscapes, increasing erosion and delivering soil to streams. The eroded soil carries nutrients, like nitrates and phosphates, and absorbed heavy metals from ash and minerals to the stream. But www.HCAezine.com
