Communities for Healthy Forests support the use of prescribed fire for fuel reduction, but site conditions must be exacting.
By Mark Buckbee | Communities for Healthy Forests | August 25th, 2022
Communities for Healthy Forests supports the use of thinning and prescribed fire as tools for fuels reduction in western forests. The buildup of woody fuel is among the principal reasons that wildland fires have become more common, more difficult to control and more severe. The distribution and loading of fuels are both important factors. Trees can be killed if the fire is able to reach the crown via “ladder fuels”, which are smaller trees and shrubs which form a bridge between the ground and the tree crowns. Trees can also be killed if heavy fuels burn around the base of a tree. Mortality can occur even if the dominant tree species is a so-called fire adapted species. Witness the mortality of Sequoia trees in California from wildfire in the past several years.
There are several ways to reduce the incidence and impact of wildfire upon forests. The first is to reduce human caused ignitions. The second is to reduce fuel loading using thinning, or prescribed fire (planned/controlled burning) or a combination of both. Each of these fuel reduction options has advantages and disadvantages depending on multiple factors including existing ground and ladder fuel loads, topography, and forest type (eg. mixed conifer vs. Douglas-fir/hemlock vs. Ponderosa Pine). If ladder fuel loads are heavy, then removal of the fuel via thinning is the best course. Whole-tree harvesting is optimal in these circumstances since much of the tree will be yarded to a landing, where limbs and tops can be chipped or piled, then burned during wet periods. Otherwise, limbs and tops can be left in the forest where they will eventually decay, but remain as ground fuel until then. Foresters often prefer thinning for fuel reduction because some of the trees removed will have commercial value and help defray the cost of the operation. This allows the fuel treatment budget to be stretched farther.
If a stand already has heavy ground fuel loading, then piling, away from “leave trees”, which are trees slated to be retained, may be appropriate. This has been done in some of the groves of Sequoia in California. If topography allows, ground fuels can be crushed close to the ground using a masticator or some type of track machinery. This is sometimes used in some Ponderosa and Lodgepole pine stands in central/eastern Oregon and other western states.
Communities for Healthy Forests support the use of prescribed fire for fuel reduction, but site conditions must be exacting. Prescribed fire should only be used where there is little ladder fuel, and ground fuel loading is sufficiently light that few of the leave trees will be killed by the fire. This tool is not appropriate in stands of thin bark species such as true firs (Abies species), spruces, western redcedar and young Douglas-fir. It can work well in pole size and older stands of Ponderosa pine, western larch, Incense-cedar, Sequoia and other thick bark species. But prescribed fire has inherent risks. It is riskier in steeper topography, and in areas having a matrix of variable aged stands. Fuel moistures must be exacting. Changing weather conditions such as wind are problematic. The proximity of man-made structures are a concern. Thinning followed by prescribed fire can be very effective, but the slash left by thinning cannot be too heavy lest the prescribed burning kill the leave trees.
Stands which have been thinned and/or prescribed burned can serve as control areas against wildfire. Because the fuel loads are light in these stands, fires that enter these stands will typically burn less hot, with lower flame length, and are easier to control using fire line, water and other control measures. This has been demonstrated numerous times in the past several years with wildfires in Oregon and California. In this era of longer, hotter and drier fire seasons with larger and more severe wildfires, active management of our forests using thinning and prescribed fire is imperative. We need to greatly increase our pace of treatments. The USFS estimates that in the west, there are 60 million acres of forestland with high or very high risk of wildfire. This number will increase annually as untreated forests continue to produce biomass.
Mark Buckbee is a retired Federal forester who had a 34 year career with the Bureau of Land Management in western Oregon. He holds a Bachelors degree in Forest Resources Management from SUNY-Syracuse and a Masters degree in Forest Science from Utah State University.