Protecting water resources is a common justification for conducting wildfire mitigation projects on our national forests. The concern is valid, as forestland provides “the cleanest and most stable water supply compared to other lands,” according to a 2022 Forest Service analysis conducted in support of the Agriculture Department’s Wildfire Crisis Strategy. The report demonstrates that 99% of people on municipal water systems in the lower 48 states receive water from forested lands. Wildfire is a direct threat to these water supplies, especially in the arid West.
“High severity wildfires increase runoff and erosion rates by two or more orders of magnitude, while low and moderate severity burns have much smaller effects on runoff,” according to Cumulative Watershed Effects of Fuel Management in the Western United States, a Forest Service technical report published in 2010 by the Rocky Mountain Research Station. Because soils absorb less water following wildfire, flows from precipitation increase at burn scars, causing erosion, sedimentation, and debris flows. The harmful effects to water quality from sediment, ash, and pollutants like heavy metals are felt far downstream. Sediment collects in reservoirs, lessening their storage capacities and shortening their lifespans. Water infrastructure maintenance and repair costs increase significantly, along with water treatment costs, following severe wildfire.
The Forest Service currently focuses billions of dollars on mechanical “fuel treatments” to reduce fuel loads and, therefore, minimize post-wildfire consequences for water resources. Like traditional logging, these tree-cutting projects require roads. Chapter 5 in the 2010 technical report, “Fuel Management and Erosion,” identifies these unpaved forest roads as chronic sources of erosion and sedimentation. Combined with the “impacts of fuel treatments, repeated at 10-20 year intervals,” the cumulative effects of fuel treatments “may be similar to the pulse impact from wildfires.”
Lee MacDonald, senior researcher at Colorado State University, and Isaac Larsen, associate professor at the University of Massachusetts – Amherst, authored “Runoff and Erosion from Wildfires and Roads: Effects and Mitigation.” Over the long term, they say, “the amount of sediment delivered to streams from unpaved forest roads is equal to or greater than the amount of sediment that is delivered from high-severity wildfires. The chronic delivery of sediment from roads may be of greater significance to aquatic ecosystems than the pulsed delivery of sediment from high-severity wildfire.”
As is common for government agencies, the Forest Service plays the climate card, emphasizing that the “expected” and “anticipated” effects of climate change will increase fire frequency and severity. They focus on the past 20-30 years of data to show that wildfires are worsening, but forest lifespans are measured in centuries, and multi-century time scales reveal that current climatic conditions are not unprecedented. A recent report coauthored by MacDonald, Forests and Water: A State-of-the-Art Review for Colorado, cites long-time Colorado meteorologist Nolan Doesken’s statements on climate change: “The problem is that current models do not consistently indicate whether precipitation in Colorado might increase or decrease, and historic precipitation data do not show a clear trend over time.” Therefore, MacDonald concludes, “In the absence of a reliable prediction or documented trend in precipitation, it is not possible to predict how global climate change might affect fire frequency and fire severity, and thus how a change in climate might affect water quality.”
As the 2010 report concludes, “Additional research is needed to understand the cumulative effects of fuel treatments at the watershed scale.” More recent studies have reached similar conclusions; furthermore, mechanically thinning trees produces more greenhouse gas emissions than if the trees were to burn. While the Forest Service pushes funding into fuel treatments that most people would consider to be logging, the available science suggests that the treatments and associated forest roads cause just as much water-resource damage as severe wildfire.
For protecting water resources, a much less costly alternative to mechanical fuel treatments is process-based restoration (PBR), which Dr. Timothy Beechie et al. first defined in a 2010 report. PBR incorporates strategies that seek to restore the “physical, chemical, and biological processes that sustain river and floodplain ecosystems” — e.g., sediment transport, water storage, water routing, and nutrient cycling. The Beachie paper points to the Bridge Creek Project, designed to restore 20 miles of Bridge Creek in eastern Oregon. The creek had carved an incised channel deep enough to drain its alluvial aquifer, which once stored water that created wetlands and supported more consistent stream flows.
Researchers determined the river incision had been caused by a combination of beaver removal and channel straightening. “The primary restoration actions include riparian revegetation to increase habitat capacity for local beaver populations, and the use of small wood posts to support beaver dams during high flows and encourage beaver population expansion.” This low-cost project proved highly successful and gave rise to the terms low-tech process-based restoration (LTPBR) and beaver dam analogs (BDAs). BDAs are in-stream structures built with natural materials to promote effects that mimic beaver activity. As BDAs trap sediment, stream levels gradually rise, floodplains reconnect, and aquifers rehydrate. As incised streams begin to reconnect with their historic floodplains, they become habitable by beaver, which can maintain and expand upon these temporary structures to create beaver complexes like those that were common across the landscape prior to European influence.
As Jackie Corday notes in her 2022 review of LTPBR projects and studies, LTPBR utilizes native, locally sourced materials and minimal equipment; therefore, “it is gentler on the land” than the types of heavy equipment employed for mechanical fuel treatments. As LTPBR treatments allow beaver reintroduction, the improvements to ecosystem health and resilience become increasingly apparent. Corday cites numerous studies affirming these benefits, demonstrating that “restoring headwater floodplains and wetlands has been shown to reduce the risk of natural disasters, including drought, wildfires, and floods.”
In a 2022 article in Scientific American, Isobel Whitcomb reports that lush post-fire beaver-complex refuges have been documented “from Colorado to California, Idaho to Wyoming. Now, scientists are discovering that these green sanctuaries are part of a larger story of how beaver dams contribute to fire resilience. Along with deterring the flames themselves, beaver dams and ponds also function as filters for ash and other fire-produced pollutants that enter waterways — thus maintaining water quality for fish, other aquatic animals, and humans.”
Beaver complexes also mitigate post-fire flooding. A research group that included Cheri Westbrook with Colorado State University monitored the largest recorded flood in the Canadian Rocky Mountains, which occurred west of Calgary, Alberta. The researchers determined that 68% of beaver dams fully or partially survived the flood, and “the beaver dams (even failed ones) delayed downstream flood peaks.”
As Corday observes, “Research is showing the path forward moves away from using costly and unscalable restoration approaches that rely on diesel power and heavy equipment toward approaches that restore natural processes.”
Pre-planning for post-fire impacts on the Santa Fe National Forest includes building beaver dam analogs (BDAs). BDAs decrease stream velocity, reduce channelization and sedimentation, and improve cold-water habitat by reconnecting the stream with its floodplain and increasing groundwater recharge (Forest Service photo by Preston Keres).
