Forest Fire History of Desolation Peak, Washington
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350 Forest fire history of Desolation Peak, Washington Jnnps K. Acn,E.Ma.nx FINNEy.IAND Ror-RNooE GouvEruarN2 Collegeof Forest Resources,University of Woshington,Seattle, WA 98195,U.S.A. ReceivedApril 17, 1989 Accepted September 26, 1989 Ac;ee,J. K., FIttNtv, M., and on GouvuNatN,R. 1990.Forest fire historyof DesolationPeak, Washington.Can. J. For. Res.20: 350-356. Forestsin the vicinity of DesolationPeak, Washington,are of specialecological interest because of their transitional nature betweencoastal and interior foresttypes. The area is westof the CascadeMountain crestbut in the rainshadow ofmountains farther to the west. Fire return intervalswere hypothesizedto be shorter than typical for coastalforest types, such as those dominated by westernhemlock and Pacific silver fir, and longer than typical for interior forest types,such as ponderosapine, owing to the closejuxtaposition of thesetypes at DesolationPeak. Sevenforest comntu- nity typeswere defined, and a 400-yearl'ire history was developedfor this 3500-haarea. The averagenatural fire rota- tion was 100 years;this varied by a factor of two by century and by topographicaspect. Forest types typical of coastal regions,such as Douglas-fir,- westernhemlock and mountain hemlock- Pacificsilver fir, had mean fire return intervals (108-137years) much lower than in other westernWashington areas.The most interior forest type, ponderosapine - Douglas-fir, had a higher mean fire return interval (52 years)than reported for similar forest typeseast of the Cascades. Historically, fire has createdstructural and landscapediversity on DesolationPeak and may be an important process in the maintenanceof such diversitv into the future. AcEE, J. K., Ftt'tNtv,M., et DEC-iouverntN, R. 1990.Forest fire historyof DesolationPeak, Washington. Can. J. For. Res.20 : 350-356. L,esior€ts de la r6gion de DesolationPeak, Washington,sont d'un inter€t ecologiqueparticulier de par leur nature de transition entre les types forestiersde la cOteet ceux de I'int6rieur. Ce territoire se situe d I'ouest de la cr€te des Cascadesmais est une rdgion sous le vent abriteede la pluie des montagnesplus a I'oucst. A causede I'etroitejuxta- position dcs types forestiersd Desolation Peak, on a 6mis I'hypothdseque les cyclesdes incendiesforestiers y sont plus courts que la normale pour les types forestierstypiques de la c6te comme ceux domindspar la Pruchede I'ouest et le Sapingracieux, et plus longsque la normale pour lestypes forestiers de I'int€rieurtels lespinddes d Pin ponderosa. Sept communaut6sforestidres ont 6tc identifieeset un historiquedes incendiesforestiers des 400 dernidresanndes a 6tedresse pour ce tcrritoire de 1500 ha. La pdriodemoyenne de rotation desincendie-s forestiers naturels est dc 100ans, valeurvariant d'un factL'urde deuxselon lc sidcleet I'expositionde la pente.Les typesforestiers typiques de la c6te, comme les associationsSapin de Douglas - Pruchc de I'ouest et Pruche subalpine- Sapin gracieux,ont des cycles desincendies foresticrs beaucoup plus courts (108-137 ans) que ceuxdes autres regions de I'ouestdu Washington.Le type forestierle plus d I'int6rieur, I'associationPin ponderosa- Sapin de Douglas a un cycle des incendiesforestiers plus long (52 ans) que celui rapporte pour des types forestierssemblables d I'est des Cascades.Dans le pass6,les incendies ont crdeune diversitdde la structureet du paysageforestiers de DesolationPeak. lls pourraientconstituer un el6ment important du maintiend'une tellediversit6 dans I'avenir. [Traduitpar la revue] Inlroduclion The North Cascadesin Washington(Fig. I ) includelow- The fire history of lorestson the westside ol the Cascade Iand forestson the moistwest side of the Cascades,subalpine Mountains in Washington is usually characterizedby forestsalong the crest, and interior forestson the dry east infrequent (200-to 500-yearinterval) fires that kill all the side. A typical zonal forest-typesequence up the coastalwest trees in the stand (Morris 1934; Hemstrom and Franklin side of the Cascadesis westernhemlock (Tsuga heterophylla 1982). Fire has been an important disturbance process (Raf.) Sarg.), Pacific silver fir (Abies amabilis (Dougl.) in this maritime climate area for millennia (Sugita and Forbes),and mountain hemlock (Tsuga mertensians(Bong.) Tsukada 1982;Cwynar 1987).Tree regenerationafter fire Carr). A typical zonal forest-typesequencc up the eastside is often prompt, but may extend in some instancesover of the Cascadesis ponderosapine (Pinus ponderosa Dougl.), decades(Franklin and Hemstrom 198l). At high elevation Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), often (> 1500m), the tree re-establishmentprocess may take a rvith grand fir (Abies grandis(Dougl.) Forbes)or lodgepole century or more (Agee and Smith 1984). In the eastern pine (Pinus contorta Dougl. var. latifolia Engelm.), and Cascadesof Washington,with an interior climaticinfluence, subalpine fir (Abies lasioc'arpa(Hook.) Nutt.l (Agee and the subalpine fire regime is similar to that of west side Kertis 1987). forests,but the low-elevation( < 1000m) fire regimeis one Forestsin the vicinity of the upper Skagit River, Ross of more frequent(10- to 50-yearinterval) fires (Agee 198l), Lake area,are of a specialbotanical interest because of therr which may resultin forestswith multipleage-classes (Larson transitional nature betweenmoist coastaland dry interior l98l). forests(Franklin and Dyrness1973). The areais westof thc Cascadecrest but is in the rainshadowof mountainsfarther to the west,including Mount Baker,Mount Shuksan,and lPresent address:Department of Forestryand RangeManage- the Picket Range.The uniquenessof the arealies in the close me-nt,University of California, Berkeley,CA, U.S.A. juxtaposition 'Present of coastal and interior forest communities address:Bureau of Land Management,Palm Springs, rather than the presenceof unique community types (Agee CA, U.S.A. Pnnred in aanadi lnrpnrnrl au ( anada AGEE ET AL 351 for determinationof age; selectionwas basedon adequaterepre- sentation of speciesand sizecohorts in eachstand. Wedge samples were cut and removed from 50 trees in all locations where single or multiple fire scarswere present(Arno and Sneck 1977),except along trails. Multiple sampleswere taken in the same area only when there was an obvious differencein the number of scarson adjacent samples. Vegetation communit-v analysis Two-way speciesindicatory analysis(TwtNSpAN) was used to +-'). \, 'or,'ul classifythe vegetationdata (Hilt 1979;Gauch 1982).Species impor- tancevalues used as inputs to the programswere cover classesfor shrubs and herbs and an averageof relative basal area and relative cover (expressedon the same1-6 scale)for trees(Agee and Kertis 1987). Fire history analysis Incrementcores were mounted on boards,sanded, and counted under a binocular microscope.Total tree ageon a sarnplewas deter- mined by adding to the ageof eachcore an estimatedage lor core height. factors were on unpublished from WASHINGTON Correction based data similar sitesthroughout the region(J.K. Agee,unpublished data). At 30 cm height, for example,the correction factor was as fol- lows: Douglas-fir and grand fir, 3 years (mesic site) to 5 years Ftr;. L Locationof DesolationPeak study area (shownin (dry site);lodgepole pine, 3 years(low elevation)to 5 years(high black)within Ross Lake National Recreation Area (NRA) in the elevation).Pacific silver fir and subalpinefir correction factors NorthCascades of Washineton.Broken line is thecrest of the were basedon height and the .spacingof the innernroslrings on CascadeMountains. the sample:at 30 cm height, l0 rings/cm,the correctionfactor was 5 years,while at 30 cm height,50 rings/cm, the correctionfactor and Kertis 1987).Commonly, the west side zonal forest was 20 years. sequenceoccurs on mesicnorth and east aspects,whereas Fire dates were recorded from cores (Barrett and Arno 1988) the eastside zonal forest sequenceis found on drier south and wedges.USDA ForestService and the United StatesDepart- and west slopes. ment of the Interior National Park Servicerecords were reviewed The objectiveof this study was to definethe forestfire for additional 20th century fire occurrences.Age-class informa- tion rvas to determine dates. historyin the vicinityol'Desolation Peak jusl eastof Ross also used disturbance Distinct age- clas.sseparations between groups of treeson a plot were determined Lake. It was hypothesizedthat the fire frequenciesfor east from clustersof'tree agesfrom each plot. Each defined age-class sideand westside forest communities would reflectthe close was representedby the oldest tree age in the cluster for plotting proximity of thesequite different fire regimes:on the low on the site map. Recruitmentperiods after disturbancein multiaged end of the rangefor forest typescommon on the west side, standswere usually lessthan 30 years.Age-class coverage across and on the high end of the range for typescommon to the the study area was mapped using I : 12 000 aerial photography east side of the Cascades.To achievethis objective it was and the mapped age groups in the plots. necessaryto define the forest community typeson Desola- Although fireswere dated to specificyears (e.g., ca. 1648),there tion Peakand reconstructthe disturbancehistory over the wasa lack of correspondencebetween dates among wedgesamples study area. For thc purposesof this study, a low severity owing to unusualannual ring patternsin the vicinityof .scars(Arno and 1977); trees were fire is defined as one that kills primarily understorytrees. Sneck otdest in cohortsof age-classdata