The national fire and fire surrogate study: Ecological consequences of alternative fuel reduction methods in seasonally dry forests

The national fire and fire surrogate study (FFS) is a multi-site interdisciplinary research project that evaluates the ecological consequences of prescribed fire and its mechanical surrogates (Weatherspoon, 2000), treatments that are intended to reduce fire risk in seasonally dry forests of the USA (Agee and Skinner, 2005). The need for a comprehensive national FFS study stems from concern that forest management practices over the past 150 years have resulted in conditions in dry forests that are undesirable and unsustainable. In particular, structure and composition of forests that once experienced frequent, low intensity fires have been altered by fire suppression, overgrazing, and preferential harvest of large diameter trees (Parsons and DeBennedetti, 1979; Agee, 1993). Increased stand density, decreased overall tree size, increases in shade tolerant species, and increases in fuel loads are well documented for forests of this type (Leopold et al., 1963; Kilgore, 1974; Parker, 1984; Covington and Moore, 1994; Skinner, 1995; Hessburg and Agee, 2003). Currently, over 10 million hectares of forests in the United States of America (USA) are in moderate or high fire hazard condition classes (Stephens and Ruth, 2005), and much of this land area is widely thought to need some form of restoration, such as prescribed fire, mechanical treatments, or both (Agee and Skinner, 2005). Retrospective work has indicated that some fuel reduction treatments can be effective in reducing fire severity when wildfires occur (Omi and Joyce, 2003; Pollett and Omi, 2002), and yet little comparative experimental information exists that would give forest managers confidence to choose between alternative fuel reduction treatments. The primary goal of the FFS is to measure the effectiveness and ecological consequences of commonly used treatments intended to reduce potential fire risk at each of 12 sites, 5 sites in the eastern USA, and 7 sites in the west (Fig. 1). All treatments were designed to produce stands such that 80% of the dominant and co-dominant trees would survive a wildfire under 80th percentile fire weather conditions (Stephens and Moghaddas, 2005). Repeated use of prescribed fire and its mechanical surrogates would be expected to modify stand structure, and could result in stand conditions reflective of pre-European settlement. Yet, the FFS was designed to measure the effects of a single entry of each treatment, and to focus on how this entry would influence the resistance of stands to wildfire. Site-level treatments included no treatment (control), prescribed fire only, mechanical treatment only, and a mechanical plus fire treatment. Each of the 12 sites implemented treatments with the help of local experts, including fire management personnel, fuel specialists, and silviculturists. At each site, treatments were assigned randomly to at least three replicate units, each measuring at least 15 ha in size. Treatment effects were evaluated for a wide variety of variables at the 12 sites, including trees and other vegetation, the fuel bed, soils (both chemical and physical), bark beetles (pine sites only), and wildlife (small mammals, birds). Analyses were conducted on single disciplines at single sites, but multivariate and multi-site analyses were also performed (Waldrop and McIver, 2006). The seven western sites vary widely in many attributes, including elevation, tree species composition and productivity (Fig. 1). All sites however, are located in the seasonally dry interior and are dominated by conifer species, mostly firs and pines. The Northeastern Cascades site is located between 650 and 1150 m elevation in north-central Washington, about 15 km west of Wenatchee (Dodson et al., 2008). Annual precipitation averages 75 cm, falling mostly as snow in the winter. Estimated mean pre-settlement fire-free interval was 17 years. Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) are the principle tree species, and pretreatment stands averaged 32 m/ha basal area. Logging in the 1930s and pre-commercial thinning in 1970s has resulted in the current dense stands of small diameter trees. Bitterbrush (Purshia tridentata), birch-leaf spirea (Spiraea betulifolia), and perennial grasses dominate the understory. Experimental units are dispersed widely over a 100 km area in the Wenatchee National Forest. Trees were felled by hand and yarded by helicopter between January and June 2001. Prescribed fire was applied with the strip head-fire technique in the spring of 2004, and again in the spring of 2006. The Blue Mountains site is located in northeastern Oregon near Enterprise. Elevation is between 1040 and 1480 m, and precipitation falls primarily as snow, averaging about 50 cm annually (Youngblood et al., 2006). Pre-settlement fire return interval is estimated to have been 3–22 years. Ponderosa pine and Douglas-fir are the dominant tree species, with www.elsevier.com/locate/foreco Available online at www.sciencedirect.com