Submitted by Burt Stalter, Dave Smith and Anne Lombardo
SIERRA NATIONAL FOREST — Forest thinnings, also known as fuel treatments, are done in our National Forests to reduce vegetation that can feed wildfires. Fuel treatments involve the thinning of trees, mastication of brush, branches and little trees or ladder fuels that can carry the fire into the crowns of the trees, and an occasional prescribed burning. Since 2013, four wildfires have burned into areas where fuel treatments have previously taken place on the Bass Lake Ranger District: the Sky, Willow, French, and Carstens Fires (2013).
The Old Grandad fuelbreak, located north of Oakhurst off Highway 41 along Sky Ranch Road leading to Nelder Grove, assisted in stopping the western progression of the Sky Fire which burned 500 acres into this area in June 2015.
The Whiskey fuelbreak, which runs from north to south along the top of the South Fork Bluffs east of North Fork towards the San Joaquin River, has been challenged by four large wildfires in the past 15 years: the 5,702 acre Willow Fire (2015), the 277 acre Cascadel Fire (2008), the 385 acre Source Fire (2003), and the 4,130 acre North Fork Fire. All four fires burned during the summer months of July, August, September or October under hot, dry conditions.
The Nehouse fuelbreak is located in the upper portion of the district east of Minarets Work Center. This fuelbreak was burned into by the French Fire in August of 2014, which burned over 13,832 acres, and the Nehouse Fire in 2004, which burned 285 acres.
All of these fires were human caused and are the largest fires on the Bass Lake Ranger District in the last 15 yrs.
The fire behavior for each of these fires prior to encountering these fuel treatments were fuels-driven fires with high intensity surface fire and passive tree crown fire. In each instance when the fire encountered areas with treatments, the fire behavior moderated significantly — enough that aerial delivered fire retardant alone checked the fire spread long enough for suppression crews to safely access and construct control lines around the fire.
These fuel treatments performed as planned, and allowed safe access for fire suppression forces to engage the fire and make use of the fire retardant that was dropped from aircraft. Treated areas substantially reduced the resistance to control, providing the ability to construct fire lines more closely to the fire’s edge with increased speed, resulting in more rapid containment of the fire. They also help to reduce the wildfire by keeping it closer to the forest floor as a surface fire and out of the trees’ crowns, which would allow the fire to move farther, faster.
The Big Creek Fire on the High Sierra Ranger District did not encounter any fuel treatment areas and burned a total of 5,250 acres over a ten-day period in late July of 1994. This fire, like the others, started at the base of the slope and burned uphill at a fast rate of spread in surface and ladder fuels. The area in front of the fire had no fuel treatments done, so the fire behavior was never modified enough for aerial delivered fire retardant to be effective at slowing the fire spread and allowing suppression forces to safely engage the fire along access roads.
Personal eyewitness accounts reported the fire burned very aggressively until a change in slope and topography moderated fire behavior enough to allow resources to effectively suppress the fire.
Our experience indicates that treatments on the district have resulted in a substantial reductions of fire suppression costs, time spent fighting the fire and resource damage.
Burt Stalter is a Fuels Officer and Dave Smith is a District Silviculturist, both for the U.S. Forest Service. Anne Lombardo is the Southern Site Representative for the Sierra Nevada Adaptive Management Project, SNAMP.