Ecological Effects of Large Fires on US Landscapes: Benefit Or Catastrophe?
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#617 Review CSIRO PUBLISHING International Journal of Wildland Fire 2008, 17, 696–712 www.publish.csiro.au/journals/ijwf Ecological effects of large fires on US landscapes: benefit or catastrophe?A Robert E. KeaneA,I, James K. AgeeB, Peter FuléC, Jon E. KeeleyD, Carl KeyE, Stanley G. KitchenF, Richard MillerG and Lisa A. SchulteH AUSDA Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, 5775 Highway 10 West, Missoula, MT 59808, USA. BCollege of Forest Resources, Box 352100, University of Washington, Seattle, WA 98195, USA. Email: [email protected] CSchool of Forestry and Ecological Restoration Institute, Northern Arizona University, PO Box 15018, Flagstaff, AZ 86011-5018, USA. Email: [email protected] DUS Geological Survey, Western Ecological Research Center, Sequoia-Kings Canyon Field Station, 47050 Generals Highway, Three Rivers, CA 93271, USA. Email: [email protected] EUS Geological Survey, Northern Rocky Mountain Science Center, c/o Glacier National Park, West Glacier, MT 59936-0128, USA. Email: [email protected] FUSDA Forest Service, Rocky Mountain Research Station, Forestry Sciences Laboratory, Provo, UT 84606-1856, USA. Email: [email protected] GOregon State University, Department of Rangeland Ecology and Management, Corvallis, OR 97331-2218, USA. Email: [email protected] HNatural Resource Ecology and Management, Iowa State University, Ames, IA 50011-3221, USA. Email: [email protected] ICorresponding author. Email: [email protected] Abstract. The perception is that today’s large fires are an ecological catastrophe because they burn vast areas with high intensities and severities. However, little is known of the ecological impacts of large fires on both historical and contemporary landscapes. The present paper presents a review of the current knowledge of the effects of large fires in the United States by important ecosystems written by regional experts. The ecosystems are (1) ponderosa pine–Douglas-fir, (2) sagebrush–grasslands, (3) piñon–juniper, (4) chaparral, (5) mixed-conifer, and (6) spruce–fir. This review found that large fires were common on most historical western US landscapes and they will continue to be common today with exceptions. Sagebrush ecosystems are currently experiencing larger, more severe, and more frequent large fires compared to historical conditions due to exotic cheatgrass invasions. Historical large fires in south-west ponderosa pine forest created a mixed severity mosaic dominated by non-lethal surface fires while today’s large fires are mostly high severity crown fires. While large fires play an important role in landscape ecology for most regions, their importance is much less in the dry piñon–juniper forests and sagebrush–grasslands. Fire management must address the role of large fires in maintaining the health of many US fire-dominated ecosystems. Additional keywords: fire effects, fire regimes, megafires. Introduction same fires can return fire to deteriorating ecosystems where Large wildland fires pose an interesting dilemma for fire man- fires have been excluded for over 70 years, thereby improving agement in North America. Many politicians, members of the ecosystem health and reducing fire hazard (Agee 1998). Little is public, and government agency land managers have come to known of the ecological impacts, both short- and long-term, of believe that large wildfires (fires >10 000 ha) are an ecologi- large fires on historical and contemporary landscapes (Moreno cal disaster because they are perceived to burn vast areas with 1998). This uncertainty fuels the debate that surrounds both the high fire intensities and burn severities (Brown 1985; Mutch causes and ecological consequences of large fires, which con- et al. 1993; GAO 2002; Daniel et al. 2007). However, these fuses the fire management community and the general public AThe use of trade or firm names in the present paper is for reader information and does not imply endorsement by the US Department of Agriculture of any product or service. The current paper was partly written and prepared by US Government employees on official time, and therefore is in the public domain and not subject to copyright. © IAWF 2008 10.1071/WF07148 1049-8001/08/060696 Ecological effects of large fires on US landscapes Int. J. Wildland Fire 697 (Daniel et al. 2007). Just because a fire is large doesn’t neces- complex landscapes where, in normal climate years, subalpine sarily mean that it is unnatural or undesirable, unless, of course, to alpine ecosystems may stay moist throughout the year and it burns homes and threatens human life and property. Large fires thereby retard fire spread (Wadleigh and Jenkins 1996). Most may provide a unique opportunity for ecosystem restoration and area burned in large fires occurs during short-term wind events fuel management treatments (van Wagtendonk 1995). and under very hot and dry (low relative humidity) conditions The present paper presents a review and summary of the cur- (Cohen and Miller 1978; Schoennagel et al. 2004). Some evi- rent knowledge of the ecological effects of large fires in some dence suggests that the amount and contagion of dead and live major ecosystems of the United States. It is organised by those vegetation (fuels) on landscapes can also contribute to large fires important biomes that typically experience large fires, with each (Gardner et al. 1997; Turner et al. 1998), but this may not be true section written by local experts. Regions include the Pacific in all ecosystems and geographical regions owing to the inter- North-west, southern California, Northern Rockies, the south- actions of high winds, spotting, and large fire behaviour (Bessie western United States, Great Basin, and Midwest with empha- and Johnson 1995; Schmoldt et al. 1999). Lightning starts most sis on the following ecosystems: ponderosa pine, Douglas-fir, of today’slarge fires, especially in the western US, while human- sagebrush–grasslands, piñon–juniper, chaparral, Great Lakes ignited fires are also important in the eastern and south-eastern conifer–hardwood forests, and spruce–fir. We attempt to address US, and California (Stephens 2005). Ignition dynamics (number, many important issues associated with large fires including location, and source) are critically important in climate–fuel–fire (1) the scale of fire heterogeneity; (2) climate, vegetation, and interactions because without ignitions, large fires are impossible, topographical factors that may precondition large fire events; even in extreme drought years (Ricotta et al. 1999). (3) departure of current large fire effects from those that occurred The effects of large fires on ecosystems can be distinctly dif- historically; (4) responses of key biota to large fires; and ferent from small fires. Large fires can create large burn patches (5) broad generalities between and across major biomes. We also (Agee 1998) that could slow wind and mammal dispersal of contrast effects of small fires and large fires in a spatial domain. seed from unburned edges, thereby delaying common vegetation development processes. Large fires may be more severe because more fuel may be consumed and the additional heat generated Background can kill more aboveground vegetation and the deeper heat pulse Conventional wisdom holds that 70 years of fire exclusion, cou- will kill more belowground biota (Ryan 2002). Large fires are pled with timber harvesting practices and livestock grazing, have more difficult and costly to fight, and the subsequent effects of tended to increase hazardous fuels that are now capable of foster- those fires may be economically more damaging than small fires ing larger and more severe fires (Brown 1985; Arno and Brown (Butry 2001; Calkin et al. 2005; Daniel et al. 2007). Last, large 1991; Mutch et al. 1993; Kolb et al. 1998; Keane et al. 2002; fires will tend to affect the most people and destroy the most Pinol et al. 2005). In the absence of fire, subsequent vegetation property because of their sheer size. However, severe large fires development will generally increase canopy and surface fuels, may be required on many landscapes to emulate historical fire and these fuels will be more connected and continuously dis- dynamics and sustain healthy ecosystems (Fulé et al. 2004). As tributed across landscapes (Baker 1992; Ferry et al. 1995). It large fires were common on most historical US landscapes, it fol- follows that increased fuels may burn in intense, large fires that lows that there are many plant and animal species that depend on could kill most plants, propagules, and animals (Agee 1998), the severity pattern created by large burns (Habeck and Mutch and alter many soil and biophysical site conditions (Ryan 2002). 1973; Agee 1993; Hutto 1995; Debano et al. 1998). Regeneration of diverse post-fire plant communities on severely burned areas may be delayed or prevented because of adverse Regional effects of large fires site conditions in the burned area, and this could increase the fre- Pacific North-west quency and severity of erosional events (McNabb and Swanson 1990). However, large fires were common on historical land- Large and severe fires are historically characteristic of Pacific scapes where the majority of burned area occurred during large North-west forests. This section focusses on the forests west fire events (Strauss et al. 1989; Malamud 2005; Cui and Perera of the Cascade Mountains called the Douglas-fir region, which 2006). In fact, the annual area burned by large fires during the are influenced by a maritime