Colorado Front Range Fire Study Questions Conventional Wisdom about Fire Regimes

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1 Colorado Front Range Fire Study Questions Conventional Wisdom about Fire Regimes Nine large fires have occurred on the Colorado Front Range since the turn of the century, beginning with the 2002 Hayman Fire, which burned 138,000 acres and destroyed 138 homes southwest of Denver. Other destructive and dangerous fires followed, including the 2010 Fourmile Canyon Fire west of Boulder, the 2012 High Park Fire outside of Fort Collins, and the 2012 Waldo Canyon fire near Colorado Springs. Many of these fires were complex and dangerous interface fires that resulted in deaths of firefighters and local residents. In addition, the fires caused widespread destruction of homes and infrastructure and impacted watersheds critical for growing urban populations in the region. Consequently, there is a growing perception that wildfires are becoming increasingly severe along the Front Range. The most commonly cited culprit for this perceived increase in fire intensity is the belief that aggressive fire-suppression since 1920 has created overly dense forests prone to exceptionally severe fires. In response, federal agencies have focused efforts and funding on fuels management projects aimed at restoring forest health and mitigating the impacts of large fires. However, a new study finds that fires on the Front Range may not be increasing in intensity or severity when examined in historical context before 20 th century firefighting. The findings of the study could hold important implications for the design and implementation of fuels reduction projects. Fire researchers, led by University of Colorado fire ecologist and geography professor Tom Veblen and Tania Schoennagel, a research scientist with the University of Colorado Institute of Arctic and Alpine Research, worked across 1.3 million acres of ponderosa, Douglas fir and lodgepole pine forests from Teller County west of Colorado Springs to Larimer County west of Fort Collins. The group reconstructed the timing and severity of past fires using fire-scarred trees and tree-ring data going back to the 1600s. They concluded that severe fires have been an inherent part of Front Range ecosystems for centuries. The team published a paper on their work in the September,

2 The Fourmile Canyon Fire burning west of Boulder, Colorado in Credit: Glenn Asakawa, University of Colorado 2014 issue of the journal PLOS ONE. Other researchers involved in the project include associate professor Rosemary Sherriff of Humboldt State University, University of Colorado doctoral student Meredith Gartner, and Associate Professor Rutherford Platt of Gettysburg College. Tom Veblen says that modern fires in the Front Range forests are not radically different from the fire severity experienced in the region before the effects of fire suppression shaped the forests. It has long been a common assumption that in the relatively dry ponderosa pine forests of the West, fires were relatively frequent and of low severity. Fires in ponderosa burned through the understory, cleaning up the forest and were not lethal to most large trees. The researchers found that the high-frequency, low-severity fire model applies to Front Range ponderosa pine forests as well, but high-severity fires also burned through these systems regularly. These occurrences were often widespread across the region and directly associated with favorable climate conditions for fire growth and severity. The study found that about 70 percent of the forest study area experienced a combination of moderate and high-severity fires in which large percentages of the mature trees were killed. Tree regeneration increased after these high-severity fires, and often attained densities much greater than those reconstructed for Southwestern ponderosa pine,

3 Tom Veblen, shown here coring a Douglas fir tree, is part of a research team studying fire history on the Front Range of Colorado. Credit: University of Colorado where much of the work was done describing the high frequency, low severity fire regime for ponderosa pine. These results call into question some of the accepted conventional wisdom regarding Front Range forests. Widespread surface fires were not the primary fire type shaping forests in the pre-20 th century in the northern Colorado Front Range, except for some forests at the lowest elevations within the study region. The researchers say that over most of the ponderosa pine zone, forest structures were shaped primarily by infrequent severe fires that killed large percentages of canopy trees promoting dense post-fire patches of regeneration across the Front Range. Also, the researchers concluded that high tree densities at higher elevations are primarily a legacy of nineteenth century severe fires rather than a consequence of any suppression of low-severity fires during the 20 th century. For land and forest managers these findings have a number of important management implications. First, homeowners and fire managers along the Front Range should expect a regular occurrence of high-severity fires regardless of efforts to reduce fuels. The potential for extreme fire behavior may largely be explained by extreme weather conditions (for example, high winds and low humidity during periods of drought) rather than fuel conditions. Also, management attempts to restore historic forest structures and/or fire conditions must recognize that infrequent severe fires were an important component of the historic fire regime in this forest type on the Front Range.

4 Many of the current fuels management approaches in this landscape are based on the belief that thinning of stands throughout the ponderosa pine zone will both reduce fire hazard and restore the vegetation to an open structure formerly maintained by relatively frequent fires. However, management efforts designed to create large areas of open woodlands in the higher elevation areas of the ponderosa pine zone of the Front Range would not be consistent with historic fire regimes and stand structures. At low elevations in the study area the historic fire regime of more frequent and lowseverity fires implies that the goals of ecological restoration and wildland fire hazard mitigation converge. In contrast, in areas naturally characterized by low frequencies of mixed- to high-severity fires, the goals of ecological restoration and fire hazard mitigation often diverge. In other words, thinning forests around watersheds and communities may make sense; however, forest thinning with the goal of restoration to historic conditions may rest on questionable assumptions about what those conditions were, and is of questionable effectiveness in preventing severe wildfires. The researchers argue that the mixed conifer forests above 7,400 feet are not in need of restoration since they have not fundamentally changed. There are dense stands up there today, many established in the late 1800s, pre-suppression trees. It is dense because it is naturally dense. It is not dense because fires were suppressed and trees grew in," Tania Schoennagel says. "But do we have to thin large areas away from people and away from watersheds? That's more questionable, especially because it is so expensive." The Front Range study is important because it calls into question many of the assumptions that influenced not only our views of fire on the Front Range but also approaches to management. While the authors recognize that more research is needed to fully delineate the drivers of fire severity and frequency in the region s forest ecosystems, the information provided thus far should already be taken into consideration in preparing Front Range communities and ecosystems for the wildfire challenges of the 21 st century. Sources: Sherriff R.L., Platt R.V., Veblen T.T., Schoennagel T.L., Gartner M.H. (2014) Historical, observed, and modeled wildfire severity in montane forests of the Colorado Front Range. PLoS ONE 9(9): e Sherriff R.L. and Veblen, T.T. (2007) A spatially-explicit reconstruction of historical fire occurrence in the ponderosa pine zone of the Colorado Front Range. Ecosystems 10(2):

5 The Wildland Fire Lessons Learned Center actively promotes a learning culture for the purpose of enhancing safe and effective work practices in the entire U.S. wildland Fire community. It is located at the National Advanced Fire & Resource Institute in Tucson, Arizona.