In recent years, unusually large stand-replacing wildfires have heightened public concern and increased recognition of the need for fuel treatments to mitigate fire hazard. Prescription burning and the use of wildland fires have been advocated as management tools for restoring forest structure and reducing fuels. In areas with limited opportunities for prescribed fire, mechanical thinning treatments are being used as a surrogate for the stand-thinning actions of fire, sometimes termed “emulation silviculture.” Changes in vegetation and fuels were evaluated from measurements taken before and after fuel reduction treatments (prescribed fire, mechanical treatments, and the combination of the two) at 12 Fire and Fire Surrogate (FFS) sites located in forests with a surface fire regime across the conterminous U.S. To test the relative effectiveness of fuel reduction treatments and their effect on ecological parameters, Drs. Dylan Schwilk and Jon Keeley of the USGS, and USFS, University of California, and University of Montana colleagues have used an information-theoretic approach on a suite of 12 variables representing the overstory (basal area, and live tree, sapling, and snag density), the understory (seedling density, shrub cover, and native and alien herbaceous species richness), and the most relevant fuel parameters for wildfire damage (height to live crown, total fuel bed mass, forest floor mass, and woody fuel mass). Their study was published recently in Ecological Applications.

In the short term (one year after treatment), mechanical treatments were more effective at reducing overstory tree density and basal area, and increasing quadratic mean tree diameter. Prescribed fire treatments were more effective at creating snags, killing seedlings, elevating height to live crown, and reducing surface woody fuels. Overall, the response to fuel reduction treatments of the ecological variables presented in this paper was generally maximized by the combined mechanical plus burning treatment. If the management goal is to quickly produce stands with fewer and larger-diameter trees, less surface fuel mass, and greater herbaceous species richness, the combined treatment gave the most desirable results. However, because mechanical plus burning treatments also favored alien species invasion at some sites, monitoring and control needs to be part of the prescription when using this treatment.

Management Implications

• In forests where fire has been excluded for more than a century, mechanical treatments produced stand densities more in line with historical stand conditions.
• Reduction in surface fuel and height to live canopy were most strongly associated with burning.
• Burning alone generally requires more than a single treatment in these forests.
• Mechanical treatments alone did not generally emulate fire’s effects on understory vegetation.

Schwilk, D.W., J.E. Keeley, E.E. Knapp, J. McIver, J.D. Bailey, C.J. Fettig, C.E. Fiedler, R.J. Harrod, J.J. Moghaddas, K.W. Outcalt, C.N. Skinner, S.L. Stephens, T.A. Waldrop, D.A. Yaussy, and A. Youngblood. 2009. The national Fire and Fire Surrogate study: effects of fuel reduction methods on forest vegetation structure and fuels. Ecological Applications 19:285–304.

[Complete article can be downloaded from web site above.]

Download this publication brief in pdf format