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Differences in wildfires among ecoregions and land managementagencies in the Sierra Nevada region, California, USA
JAY D. MILLER,1, BRANDON M. COLLINS,2 JAMES A. LUTZ,3 SCOTT L. STEPHENS,4
JAN W. VAN WAGTENDONK,5 AND DONALD A. YASUDA6
1USDA Forest Service, Pacific Southwest Region, Fire and Aviation Management, McClellan, California 95652 USA2USDA Forest Service, Pacific Southwest Research Station, Davis, California 95618 USA3College of the Environment, University of Washington, Seattle, Washington 98195 USA
4Ecosystem Sciences Division, Department of Environmental Science, Policy, and Management,University of California, Berkeley, California 94720 USA
5U.S. Geological Survey, Western Ecological Research Center, Yosemite Field Station, El Portal, California 95318 USA6USDA Forest Service, Pacific Southwest Region, McClellan, California 95652 USA
Citation:Miller, J. D., B. M. Collins, J. A. Lutz, S. L. Stephens, J. W. van Wagtendonk, and D. A. Yasuda. 2012. Differences
in wildfires among ecoregions and land management agencies in the Sierra Nevada region, California, USA. Ecosphere
Abstract. Recent research has indicated that in most of the western United States, fire size is increasing,large fires are becoming more frequent, and in at least some locations percentage of high-severity fire is
also increasing. These changes in the contemporary fire regime are largely attributed to both changing
climate and land management practices, including suppression of fires and past timber harvesting, over the
last century. Fire management, including suppression and using wildfire for resource benefits, varies
among federal land management agencies, yet no published studies have directly compared fire statistics
between federal land management agencies in our study area. The primary response to wildfire on Forest
Service areas is immediate suppression, while the National Park Service is more likely to use wildfire for
resource benefits. We use fire perimeters and satellite-derived estimates of fire severity to compare fire
statistics for wildfires (fire size, percentage of high-severity fire and high-severity patch size) among
ecoregions, forest types, and land management agencies 19842009 in the Sierra Nevada, Southern
Cascades, and Modoc Plateau of California, USA. High-severity patch size and percentage of high-severity
fire, regardless of forest type, were less (P , 0.05) in Yosemite National Park than on Forest Service lands.
Yosemite fires were smaller on average than fires on Forest Service lands on the east side of the Sierra
Nevada, southern Cascades and Modoc Plateau. Depending upon whether fires that crossed boundaries
were included or not, mean size of Yosemite fires was either smaller or not significantly different from
Forest Service fires on the west side of the Sierra Nevada. Even under current conditions, it appears that
fire management practices that emulate those used in Yosemite could moderate effects of past land
management, restoring and helping to maintain old forest conditions within the greater Sierra Nevada
region, including the southern Cascades and Modoc Plateau.
Key words: fire effects; fire severity; fire suppression policy; Forest Service; National Park Service; RdNBR; Sierra
Nevada, USA; wildfire.
Received 1 June 2012; revised 14 August 2012; accepted 24 August 2012; published 24 September 2012. Corresponding
Editor: J. Thompson.
Copyright: 2012 Miller et al. This is an open-access article distributed under the terms of the Creative CommonsAttribution License, which permits restricted use, distribution, and reproduction in any medium, provided the original
author and sources are credited.
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In dry forest types throughout the westernUnited States fire is the dominant process drivingacute change in forest structure and speciescomposition (Pyne et al. 1996). However, not allfire is equal; fire-caused change, or fire severity,can vary considerably. Species associated withdry forest types evolved largely with low tomoderate-severity fire, and in those forest typespost-fire landscapes are characterized by survivalof fire-tolerant, large-diameter individuals (Agee1993, Stephens et al. 2008, Larson and Churchill2012). Because large-diameter trees provide aseed source and ameliorate environmental stress,these forests can withstand or recover rapidlyfollowing low to moderate-severity fire. Further-more, dry forest tree species generally havelimited capacity to recover naturally followingextensive high-severity fire (Allen et al. 2002,Savage and Mast 2005).
Increases in tree density, especially of fireintolerant species, and decreases in the area ofpatchy forest cover resulting from past andcurrent land management practices (e.g., wide-spread grazing, extensive timber harvesting, firesuppression) have rendered large tracts of dryforests susceptible to extensive and uncharacter-istic high-severity fire (Fule et al. 2004, Hessburget al. 2005, Naficy et al. 2010, Collins et al. 2011).This increased susceptibility, combined with thelimited capacity to recover naturally from high-severity fire, has created great concern for federalland management agencies responsible for man-aging areas with these forest types (HFRA 2003,USDA 2011).
Developments in acquiring and analyzingspatial data to capture not only fire extents, butfire effects as well, have led to robust character-izations of contemporary fire patterns (e.g.,Morgan et al. 2001, Key and Benson 2006b, Millerand Thode 2007). These characterizations haveallowed for a number of analyses investigatingfactors influencing fire severity both withinindividual fires (Finney et al. 2005, Collins et al.2007, Roman-Cuesta et al. 2009, Collins andStephens 2010, Prichard et al. 2010) and amongnumerous fires within particular regions (Holdenet al. 2007, Miller et al. 2009b, Miller et al. 2012,van Wagtendonk et al. 2012, Kolden et al. Inpress). Additionally, fire extent and severity data
have been used to compare fire patterns amongregions (Dillon et al. 2011) and forest types(Miller et al. 2009b, Miller et al. 2012). Suchcomparisons are useful for identifying potentialdifferences in the processes driving fire (e.g.,climate, forest structure, topography). To datehowever, no previous studies have examinedwhether differences in land management prac-tices between land management agencies withina given region could be contributing to differ-ences in the fire regime (but see van Wagtendonkand Lutz  for a comparison of fires used forresource benefit and prescribed fires with wild-fires).
Characterizing contemporary fire patterns (fireextent and effects) often involves an assessmentof whether or not current patterns are within thehistorical or natural range of variability (Landreset al. 1999, Schoennagel et al. 2004). However,issues associated with those types of assessmentscan lead to considerable uncertainty: (1) datafrom historical forest and fire reconstructionstudies can never achieve the level of detail orspatial coverage that contemporary characteriza-tions can, (2) historical reconstructions areinherently incomplete because they are basedon extant data (i.e., some data are lost from fireand decomposition; Heinselman 1973), and (3)due to a fairly ubiquitous and long-establishedpolicy of fire exclusion, there are very fewcontemporary reference sites with historic andintact fire regimes (Stephens et al. 2008, Scholland Taylor 2010), and the few that there are havebeen impacted by early fire suppression efforts(see Rollins et al. 2002, Collins and Stephens2007, Holden et al. 2007).
Because of these challenges, there is no perfectmethod for assessing current fire effects onforests relative to pre-settlement forestfire dy-namics. However, some comparisons can pro-vide insight into the potential alteration ofcontemporary fire patterns. One such compari-son is between lands managed by the ForestService (FS) and National Park Service (NPS) inthe Sierra Nevada. Comparing fire patternsbetween the two agencies within the same regionallows for partial identification of past andcurrent management impacts on contemporaryfire patterns. Although both NPS and FS policieshave allowed the use of wildland fire for resourcebenefit since the late 1960s and early 1970s,
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respectively, implementation has varied betweenthe two agencies (van Wagtendonk 2007). Whileimmediate suppression is the most commonresponse on all FS lands in our study area,managing fire for resource benefit has occurredto some extent since 1999, primarily in wilder-ness areas. In 2009, the US Department ofAgriculture and the US Department of theInterior issued updated guidance for implement-ing federal wildland fire policy (USDA-USDI2009). The guidance provides for the use ofwildland fire for resource benefits specified inland or resource management plans. Nationalparks in the Sierra Nevada, which were subjectedto fire exclusion policies similar to FS lands priorto the early 1970s, use both prescribed fire andmanaged wildfire on most NPS lands. Inaddition to the increased use of wildfire forresource benefit starting in the 1970s, NPS landshave not experienced extensive timber harvestingor recent livestock grazing since the current parkboundaries were established (Collins et al. 2011),making NPS lands at least partially capable ofserving as contemporary reference forests.
Our objectives with this study were to: (1)characterize fire patterns (effects, extents) for allfires . 80 ha that occurred between 1984 and2009 in the Sierra Nevada, southern Cascadesand Modoc Plateau; (2) summarize and comparefire patterns among ecoregions and land man-agement agencies, particularly FS and NPS lands;and (3) summarize and compare fire patterns byforest type within ecoregions, wilderness vs. non-wilderness, and agencies. Specifically, we wantedto examine the similarities or differences in high-severity fire among ecoregions, forest types, andfire management strategies.
Study areaThe study area, which encompasses the extent
of the Sierra Nevada Forest Plan Amendment(SNFPA), is divided by three ecoregions asdefined by Bailey et al. (1994): the Sierra Nevadaproper, portions of the Modoc Plateau includingthe Warner Mountains, and the eastern portion ofthe southern Cascades (Bailey et al. 1994, Milesand Goudey 1997, USDA 2004). The ecoregionclassification system developed by Bailey et al.(1994), based upon climate, elevation and land-
form, has been used as a basis for examiningdifferences in fire regimes (e.g., Sugihara andBarbour 2006). The fire regime concept wasdeveloped to provide a framework for investi-gating differences in the way fire influencesecosystems (Heinselman 1981). Because climateand the distribution of forest types vary through-out our study area, we use the fire regimeconcept and Baileys ecoregions to define regionswithin our study area and examine differences infire statistics.
Climate throughout the study area is Mediter-ranean, characterized by warm, dry summersand cool, wet winters with almost all precipita-tion falling between October and April. Depend-ing upon elevation, much of the precipitation isin the form of snow. Variation in precipitationand vegetation is primarily due to elevation andrain shadow effects. The crest of the range, whichgenerally runs north-to-south, divides the SierraNevada ecoregion into two distinct precipitationsubregions usually denoted as the eastside andwestside (Major 1988). Precipitation on the west-side of the Sierra Nevada varies from about 500mm in the foothills to over 2000 mm at the crestin the northern end of the ecoregion. The ModocPlateau and most of the eastern portion of thesouthern Cascades ecoregions have precipitationamounts similar to the eastside of the SierraNevada, generally less than 1000 mm, due to rainshadow effects from Mt. Shasta and Mt. Lassen(Major 1988, Minnich 2006, Skinner and Taylor2006).
Vegetation on the westside of the SierraNevada crest is dominated by ponderosa pine(Pinus ponderosa) at lower elevations; white fir(Abies concolor), incense-cedar (Calocedrus decur-rens), sugar pine (P. lambertiana), ponderosa pine,and Douglas-fir (Pseudotsuga menziesii ) at inter-mediate elevations; and Jeffrey pine (P. jeffreyi )and red fir (A. magnifica) at higher elevations.Eastside forests are characteristically more openthan westside forests. Pinyon pine (P. monophylla)is common at lower elevations on the eastside ofthe Sierra Nevada, especially south of LakeTahoe. Jeffrey and ponderosa pine dominatemid-elevations, transitioning to mixed white firand pine forests at higher elevations. Douglas-fir,most common on the westside, reaches itssouthern extent within Yosemite National Park(NP) and only occurs in small amounts on the
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eastside (Lanner 1999, van Wagtendonk andFites-Kaufman 2006, Sawyer et al. 2008). Thecrest is higher in the southern portion of therange, reaching its maximum at Mt. Whitney, thehighest peak in the continental US. The westernslopes are therefore generally steeper in thesouthern portion of the range due to the higherelevation of the crest, leading to much shortertransitions between forest types.
Similar to the Sierra Nevada, in the southernCascades mixed conifer forests dominate mid-elevations west of the crest; and east of the crestJeffrey and ponderosa pine dominate. At higherelevations forests transition to mixed white fir,red fir and pine forests, but species dominancevaries widely, influenced by precipitation, topog-raphy, and substrate (Skinner and Taylor 2006).Further to the east, forests on the Modoc Plateauare dominated by ponderosa pine at lowerelevation and transition to mixed ponderosapine, Jeffrey pine and white fir as elevationincreases. At upper elevations white fir can occurin almost pure stands but also mixes withwestern white (P. monicola), ponderosa, Jeffrey,and Washoe (P. washoenis) pines. Red fir does notoccur within the ecoregion, and Douglas-fir andsugar pine only occur on the extreme westernedge (Riegel et al. 2006).
Conifer forests throughout the region histori-cally experienced low to moderate-severity fire,falling into either fire regime group I or III (Table1; Sugihara et al. 2006b, Hann et al. 2010). Yellowpine forests dominated by either ponderosa orJeffrey pine and mixed conifer forests historicallyexperienced low-severity fires with mean firereturn intervals of 11 to 16 years (fire regimegroup I; Perry et al. 2011). Red fir forestsexperienced low to moderate-severity fires withmean fire return intervals of 40 years (fire regimegroup III; van Wagtendonk and Fites-Kaufman2006, Stephens et al. 2007, Van de Water andSafford 2011).
Four national parks exist within the study area:Lassen, Yosemite, Sequoia an...