442

Journal of the Torrey Botanical Society 132(3), 2005, pp. 442–457

Fire and persistence of montane chaparral in mixed coniferforest landscapes in the northern Sierra Nevada,

Lake Tahoe Basin, California, USA1

Thomas A. Nagel and Alan H. Taylor2,3

Department of Geography, The Pennsylvania State University,302 Walker Building, University Park, PA 16802

NAGEL, T. A. AND A. H. TAYLOR (Department of Geography, The Pennsylvania State University, 302 WalkerBuilding, University Park, PA 16802). Fire and persistence of montane chaparral in mixed conifer forest land-scapes in the northern Sierra Nevada, Lake Tahoe Basin, California J. Torrey Bot. Soc. 132: 442–457. 2005.—Tree cover in the mixed conifer zone in the Sierra Nevada is often interrupted by large shrub fields, or standsof montane chaparral. Chaparral stands are thought to be associated with either poor site conditions, or locationsthat have experienced severe fire. Fires have been excluded from mixed conifer forests for nearly a centurybecause of a management policy of suppressing fire. This study quantifies the intervals between fires, and theresponse of chaparral shrubs and trees to fire and fire exclusion in six montane chaparral stands. Quercusvaccinifolia and Arctostaphylos patula were the dominant shrubs on all sites and the last fires burned in the sixsites between 1861 and 1882. The mean point fire return interval before fire suppression was 28 yr (range 16–40 yr), and fire frequency in chaparral was lower than in nearby forest. The age structure of shrubs and trees inthe stands indicate that shrubs and trees regenerated immediately post-fire. Shrub and tree regeneration, however,were not confined to a brief post fire period, regeneration continued for at least another five decades. On oursites, exclusion of fire due to fire suppression has caused the average area of a chaparral stand to shrink by62.4%. Chaparral has been replaced by forest and this vegetation change has reduced the heterogeneity of themixed conifer forest landscapes in the Sierra Nevada.

Key words: forest dynamics, landscape ecology, mixed conifer forests, fire history, fire effects, restorationecology, fire exclusion, heterogeneity

Species abundance patterns in forested land-scapes are influenced both by site conditions(i.e., soil characteristics, temperature, moisture)and the type, severity, and extent of disturbances(Whittaker 1956, Romme and Knight 1981, Har-mon et al. 1983). In forested landscapes, highseverity disturbances such as fires (Romme1982), debris flows (Hupp et al. 1987), wind-storms (Forest and Boose 1982), and logging(Bormann and Likens 1979) have all been doc-umented to affect landscape vegetation patterns.For example, in California, tree cover in themontane zone is often interrupted by large shrubfields, or stands of montane chaparral (hereafter

1 This research was supported by a cost-share agree-ment between The Pennsylvania State University andthe USDA Forest Service Lake Tahoe Basin Manage-ment Unite (PA-05-98-19-030).

2 This work was completed with the help of manyindividuals. J. Swanson and M. Johnson provided im-portant administrative and logistic support, J. Sakulich,L. DeMais, T. Saladyga, and S. Heffelfinger assistedin field, and R.M. Beaty, and S.P. Norman providedlaboratory assistance. C.N. Skinner. R.M. Beaty, andA.G. Guarin provided comments on an earlier draft ofthis paper.

3 Address for correspondence: E-mail: aht1@psu.edu

Received for publication June 8, 2004, and in re-vised form May 26, 2005.

referred as chaparral). The location and extentof these chaparral stands are associated withboth harsh site conditions that inhibit treegrowth, and areas that have experienced severe,stand-replacing forest fire(s) (Show and Kotok1924, Rundel et al. 1977, Biswell 1974, Bolsin-ger 1989). Chaparral shrubs are fire-adapted andestablish rapidly after fire, either by sprouting orby germinating from seed stored in the soil(Weatherspoon 1985, 1988; Kauffman 1990,Keeley 1991, 2000). The structure of surfaceand aerial fuels, and the low rate of fuel pro-duction, predisposes chaparral to crown fire, andrecurring fires in chaparral have been observedto perpetuate shrub cover on sites otherwiseedaphically suited for trees (Wilken 1967, Bis-well 1974, Bock and Bock 1977).

Despite the widespread occurrence of chap-arral in mixed conifer forest landscapes in theSierra Nevada, little is known about their fireregimes. Fire frequency is thought to be lowerand more variable, and fire severity is thoughtto be higher, than in surrounding mixed coniferforests (Skinner and Chang 1996). In mixed co-nifer forests, surface fuel structure and high ratesof fuel production historically supported a re-gime of frequent (i.e., every 3–20 years) lowand moderate severity surface fires (Kilgore andTaylor 1979, Parsons and DeBenedetti 1979, Ca-

2005] 443NAGEL AND TAYLOR: FIRE AND MONTANE CHAPARRAL DYNAMICS

prio and Swetnam 1995, Taylor 2000a, Beatyand Taylor 2001, Bekker and Taylor 2001, Tay-lor and Skinner 2003). Yet, in the southern Cas-cade Range and Klamath Mountains, there is ev-idence that mixed conifer forests burned at highseverity and that high severity burns were im-portant for maintaining chaparral and even-agedforest patches in the landscape mosaic (Taylorand Skinner 1998, Beaty and Taylor 2001, Bek-ker and Taylor 2001). Chaparral and even-agedforest stands in these landscapes are proportion-ately more abundant on upper slope positions(Skinner and Taylor 1998, 2003; Beaty and Tay-lor 2001) where topographic controls on fire be-havior favor higher fire line intensities and se-vere fire (Rothermel 1983, Weatherspoon andSkinner 1995). Where topography strongly influ-ences the spatial pattern of severe fire, the lo-cation of chaparral stands in the mixed coniferforest matrix may be relatively fixed. In othertypes of terrain, however, the location of chap-arral may shift in the landscape as a high sever-ity burn generates chaparral from long livedseed buried in the soil and it is then replaced byforest (Conard and Radosevich 1982b, Weath-erspoon 1988). In either case, the highly com-petitive shrub cover appears to greatly reducethe rate at which forest may replace chaparral.In the Sierra Nevada, the role of recurring highseverity fire in the establishment and mainte-nance of chaparral, and in mixed conifer forestsdynamics is not well documented or understood,particularly during the period before logging andother human caused disturbances altered the pre-EuroAmerican forest landscape in the mid to late19th century. In many parts of the Sierra Nevada,contemporary shrub fields are thought to havedeveloped after heavy 19th century logging andslash fires removed the forest cover, and nearbyseed sources, leading to long term persistence ofchaparral shrubs on many sites (Sudworth 1900,Leiberg 1902, Biswell 1974).

Species distribution and abundance patterns inmixed conifer forests have also been influencedby fire exclusion. Nearly a century of fire sup-pression has caused an increase in forest density,a compositional shift to more fire-sensitive spe-cies, and a shift from coarser to finer scale forestmosaics (Vankat and Major 1978, Parsons andDeBenedetti 1979, Skinner 1995, Taylor 2000a).Fire exclusion may also have affected chaparralstands. Repeat photographs of 19th centuryscenes of forested landscapes that were neverlogged or heavily disturbed by Euro-Americansoften show an expansion of trees and forest into

shrub fields (Vankat and Major 1978, Gruell2001). Forest encroachment into chaparral mayhave occurred gradually during the fire suppres-sion period, as infilling of trees has in mixedconifer forest (Parsons and DeBenedetti 1979,Taylor 2000a), or trees may have established im-mediately post-fire, having only recentlyemerged from beneath the shrub canopy. Lowsoil moisture and low light levels beneath theshrub canopy greatly inhibits the establishmentand growth of tree seedlings (Conard and Ra-dosevich 1982a, Conard and Sparks 1993).Moreover, little is known about shrub regener-ation except that chaparral species sprout or seedin prolifically immediately after severe fire(Bock and Bock 1977, Biswell 1974). Chaparralshrubs do regenerate episodically, after fire, butthey may also regenerate more continuously pro-moting long term site occupation by shrubs.

The goal of this study is to better understandthe role of fire and fire suppression in the dy-namics of vegetation patterns in mixed coniferforest landscapes in the Sierra Nevada. We hy-pothesize that naturally recurring severe firesmaintained chaparral and that replacement ofshrub fields by forest is associated with fire re-gime changes caused by fire suppression. Ourspecific objectives were to: 1) determine if firefrequency in chaparral stands was lower than insurrounding mixed-conifer forests; 2) determineif shrub stems were of similar age, reflecting ep-isodic establishment only after fire, or multi-aged suggesting a pattern of more continuousregeneration; 3) determine if the ages of treesgrowing in shrub fields were similar reflectingsimultaneous establishment with shrubs afterfire, or variable and multiple-aged, suggestingcontinuous establishment during a period withshrub dominance; and 4) determine the extent towhich chaparral has been replaced by forest andwhether forest expansion is associated with firesuppression.

Study area. Chaparral in the Sierra Nevadaoccurs within the mixed conifer forest zone,where any of six conifer species (Pinus ponde-rosa Laws.; Calocedrus decurrens (Torrey) Flo-rin; Pinus lambertiana Douglas; Pinus jeffreyiGrev. & Balf.; Abies concolor (Gord. & Glend.)Lindley; and Pseudotsuga menziesii var. menzie-sii (Mirb.) Franco may co-occur and share dom-inance in a stand depending on site conditions,latitude, and stand history (Barbour 1988). Inour study area, chaparral was dominated byQuercus vaccinifolia Kellogg and Arctostaphy-

444 [VOL. 132JOURNAL OF THE TORREY BOTANICAL SOCIETY

FIG. 1. Location of the six montane chaparralstands studied in the northern Sierra Nevada, Lake Ta-hoe Basin, California.

los patula E. Greene, but several other shrubspecies, including Ceanothus velutinus Hook.,C. cordulatus Kellogg, Castanopsis sempervi-rens (Kellogg) Hjelmq., Prunus emarginata(Hook) Walp., and Amelanchier alnifolia (Nutt)Nutt were present. These shrub species are pre-sent in chaparral throughout the Sierra Nevada(Vankat and Major 1978, Conard and Radosev-ich 1982, Bolsinger 1989, Skinner and Chang1996).

We studied chaparral stands in the northernSierra Nevada on the west side of the Lake Ta-hoe Basin, California (Fig. 1). Elevations rangefrom 1930 m to 2220 m and the terrain is steepand complex. Forest and chaparral grow on shal-

low (� 1m), excessively drained, medium acid-ity soils derived from Mesozoic aged granite de-veloped in glacial till (Rogers 1974, Hill 1975).The climate is characterized by warm, dry sum-mers and cold, wet winters. Mean annual pre-cipitation at Tahoe City (1890m) is 98.4 cm,86% of which falls as snow between Novemberand April. Mean monthly temperatures rangefrom 1 �C in January to 21.8 �C in July.

People have influenced vegetation in the LakeTahoe Basin for at least 9,000 years (Lindstrom2000). The Lake Tahoe Basin was used by Na-tive Americans (Washoe) seasonally, and theiruse may have modified local vegetation patterns.Washoe people burned forests to drive game andto increase production of certain plants for foodand fiber (Lindstrom 2000). Euro-Americansfirst arrived in the basin in 1844 but settlementwas limited until the 1860s. Forests in largeparts of the basin were cut heavily between 1873and 1900 to meet demand for wood in mines inVirginia City, Nevada (Lindstrom 2000, Taylor2004).

Although logging was extensive, there aretracts of uncut forest on the west shore of theLake and intermixed in these forests are largepatches of chaparral. Examination of 19th cen-tury historical documents (i.e., written and pho-tographic records; Lindstrom 2000), early aerialphotographs (1939), and field reconnaissance in-dicate that these shrub fields did not establishafter logging and that they had been present onthe landscape for � 100 years. We selected alllarge (� 40 ha) shrub fields (N � 6) on the westshore of the lake that were surrounded by uncutforest for intensive study.

Methods. COMMUNITY STRUCTURE AND COMP-OSITION. The structure and floristic compositionof each chaparral stand was determined by esti-mating species canopy cover in six to nine sys-tematically placed 5 � 50 m belt transects (Fig.2). Transects were placed in the middle, rightedge, and left edge, at the top, middle, and bot-tom of each stand. This plot placement was usedto detect any spatial differences in tree estab-lishment dates within the shrub fields that mightbe related to seed dispersal distance from theforest edge (Greene and Johnson 2000). The el-evation, slope aspect, slope pitch, and location(UTM) of each transect in each stand was alsorecorded (Table 1). Canopy cover of trees (�5cm dbh; diameter at breast height) and shrubsin each belt transect was estimated, by species,in contiguous 5 m x 5 m quadrats in one of six

2005] 445NAGEL AND TAYLOR: FIRE AND MONTANE CHAPARRAL DYNAMICS

FIG. 2. Location of plots, fire scar samples, and area of forest encroachment between 1939 and 2000 in sixmontane chaparral stands in the northern Sierra Nevada, Lake Tahoe Basin, California.

cover classes (�1%, 1–5%, 5–25%, 25–50%,50–75%, 75–100%). We also counted all seed-lings (0.5 m-1.4m tall) and saplings (�1.4 m tall� 5.0 cm dbh), and measured the diameter ofeach live and dead tree, and height of the tallestshrub, in each quadrat.

FIRE HISTORY. Since stands of chaparral es-tablish after high severity fire, it is difficult todetermine how often fires burn in them becauseevidence of earlier burns (i.e., fire scars, agestructure) is usually consumed by the fire. Yet,older trees scattered in or along the edges of

brush fields that survived the last fire are some-times present and their tree rings may containrecords of earlier fires (Skinner and Chang1996). We used trees with external fire scars thatwere growing in or on the edges of shrub fieldsto estimate the history of fire in each chaparralstand. Partial wood cross-sections from the firescarred trees were removed with a chainsaw(Arno and Sneck 1977) and sample locationswere then determined with a GPS, and recordedon a topographic map (Fig. 2). Fire years re-corded in each sample were determined by first

446 [VOL. 132JOURNAL OF THE TORREY BOTANICAL SOCIETYT

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sanding each specimen to a high polish and thencross-dating the sample’s annual growth ringsusing standard dendrochronological techniques(Stokes and Smiley 1968). The year of each treering with a fire scar lesion in it was then record-ed as the fire date.

To determine if fire was less frequent and in-tervals between fires were more variable inchaparral than forest, we compared fire frequen-cy and fire return intervals from samples inchaparral and forest in several ways. First, wecalculated mean point fire return intervals (FRI)for all fire scar samples in each chaparral standand compared them to mean point FRI for sam-ples (n � 45) from adjacent or nearby mixedconifer forest (Taylor 2000b). We chose to com-pare point FRIs, rather than composite FRIs, be-cause point FRI estimates are less affected byvariation in sample size than composites of mul-tiple samples (Arno and Petersen 1983). Next,we compared the fire frequency for all chaparralsamples (n � 17) to an estimate of fire frequencyfor 17 of the 45 forest samples. This was doneusing program SSIZ (Holmes 1995) which com-putes an estimate of fire frequency for differentsized, randomly selected subsets of sampledtrees using Monte Carlo techniques (Swetnamand Baisan 2002). Finally, we compared the fireinterval distribution of FRI for fires recorded inall point samples from chaparral and forest.

CHAPARRAL AGE STRUCTURE. We sampled thelargest diameter stems of Q. vaccinifolia and A.patula in each transect by removing at least twostem cross-sections of each species as close tothe ground as possible with a chainsaw. We as-sumed that the largest stems (basal diameter)were the oldest stems in the stand, an assump-tion that holds for other chaparral species (Kee-ley 1992). Quercus vaccinifolia and A. patulawere chosen for the age sampling because theywere dominant species on all sites. Stem crosssections were prepared in the laboratory bymaking a radial cut to the pith and shaving thecut edge with a razor blade. White chalk wasthen applied to the cut to accentuate ring bound-aries and the rings were counted beneath a bin-ocular microscope to estimate stem age. Stemages were then grouped into 10-year age-classesto infer temporal variation in patterns of shrubestablishment in each stand. Annual growthrings of Q. vaccinifolia could not be consistentlydistinguished even on full stem cross sections sothese samples were not included in the age struc-ture analysis.

TREE ENCROACHMENT. The ages of treesgrowing in each chaparral stand were estimatedby coring all trees to the pith 30 cm above theground surface in each transect. Cores weresanded to a high polish, their annual growthrings were cross-dated (Stokes and Smiley1968), and a tree age was assigned based on thecalendar year of the inner most ring. The dateof establishment of each tree was then estimatedby adding a correction factor to each core toaccount for the number of years a stem needs togrow to a height of 30 cm. The correction factorfor A. concolor (N � 131), and P. jeffreyi (N �49) was determined by removing two stem crosssections from seedlings and saplings, one at thesoil surface and the other at 30 cm. The crosssections were sanded to a high polish and theaverage difference between the stem age at thesoil surface and at 30 cm was then subtractedfrom the core date to estimate the tree establish-ment date. The average (� S.D.) difference forA. concolor was 29.2 � 12.6 yr and for P. jef-freyi it was 19.2 � 9.7 yr.

To identify the conditions of initial tree estab-lishment in chaparral stands we measured vari-ation in the temporal pattern of radial growth bycounting the number of rings/cm along thelength of each tree core. Presumably, trees withfast initial growth established immediately afterfire along with shrubs while those with slow ini-tial growth established in the low resource en-vironment beneath the shrub canopy.

After established trees overtop the shrub can-opy they may begin to reduce shrub vigor. Toassess this effect, we examined the relationshipbetween total tree cover (%) and live and deadshrub cover (%) for all transects in all sites usingcorrelation analysis.

Tree encroachment into chaparral was alsoquantified at the landscape scale using repeat ae-rial photography. First, the forest-chaparralboundary in the year 1939 was identified anddelineated for each study site by using variationin the tone and texture of the vegetation coverevident on 1939 aerial photographs, and it wasthen transferred to a topographic map (Scale 1:24,000). Second, forest-chaparral boundarieswere identified again for the year 2000 on aerialphotographs taken in 2000, and these boundarieswere also transferred to topographic maps.Third, the change in the area of forest and chap-arral was identified for each site by measuringforest and chaparral cover on each date using adot-grid overlay. Additionally, change in thearea of forest and chaparral at one site (Fallen

448 [VOL. 132JOURNAL OF THE TORREY BOTANICAL SOCIETY

Leaf) was qualitatively assessed by rephoto-graphing an early landscape photograph that in-cluded the chaparral stand. The initial photo-graph was taken in 1915 and the repeat photo-graph was taken in 2001.

Results. COMMUNITY STRUCTURE AND COMP-OSITION. Mean shrub cover on the study sites ex-ceeded 60% except at Angora (mean�30%) (Ta-ble 1). Quercus vaccinifolia had the highest cov-er of all shrubs on each site, followed by A. pa-tula (Table 1). Ceanothus cordulatus was alsopresent on all sites, but it had low mean cover(0.5—to 3 %). The shrubs C. velutinus, Prunusemarginata, Amelanchier alnifolia, and Chry-solepsis sempervirens each occurred on two orthree sites but they always had low mean cover(�5%). Mean maximum shrub height was sim-ilar among sites (P� 0.05, Kruskal-Wallis H-test) and ranged from 0.3 m to 1.7 m (Table 1).Trees were growing among chaparral shrubs oneach site and A. concolor had the highest meancover followed by P. jeffreyi, A. magnifica, C.decurrens and P. lambertiana (Table 1). Meantree cover ranged from 26 to 55%, and in someindividual transects tree cover exceeded 75%.

Density and basal area of trees growing in thechaparral varied by species and among sites (Ta-ble 2). The mean tree density was 784 trees ha�1

(range, 516–1139 trees ha�1) and most treeswere A. concolor and P. jeffreyi. Abies concolor,on average, was more abundant than P. jeffreyibut P. jeffreyi was more abundant than A. con-color at Cascade and Meeks. Average basal areawas 40.1 m2 ha�1 (range 27.7–66.4 m2 ha�1) andA. concolor basal area, on average, was muchhigher than that of P. jeffreyi. However, P. jef-freyi basal area was higher than that of A. con-color’s at Cascade and they were similar atMeeks and Fallen Leaf.

Tree seedlings and saplings were also present,and they had average densities of 121.2 (range57–173 stems ha�1) and 107.3 stems ha�1 (55–301 stems ha�1), respectively (Table 2). Seed-lings and saplings of A. concolor were moreabundant than those of P. jeffreyi and other spe-cies, except at Cascade and Meeks. At Cascadeand Meeks, A. concolor and P. jeffreyi saplingswere present in about equal proportions.

FIRE HISTORY. Thirty-two fires were recordedin the fire scar samples (N � 17) between 1714and 1882 (Table 3). The last fire in each of thechaparral stands occurred between 1861 and1882. The grand mean point FRI was 28 yr and

the mean site FRI ranged from 16 to 40 yr (Ta-ble 3). There was a wide range in the minimum(6–40 yr) and maximum (20–77 yr) interval be-tween fires among the fire scar samples. For for-est, in contrast, the grand mean point FRI was14 yr, the range of minimum FRI was narrower(1–12 yr), but the range of maximum FRI waswider (16–81 yr). The mean point FRI was lon-ger in chaparral than forest (P � 0.05, MannWhitney U-test). The FRI distributions for chap-arral and forest were also different. There weremore short than long fire intervals in forest thanchaparral (P � 0.05, Kolmorgorov-Smirnov twosample test), the chaparral distribution was moreskewed (1.52 vs. 1.09) to the right, and moredispersed (kurtosis) (3.04 vs. 0.98). Finally, thecomposite fire frequency for chaparral (10.1fires per century) (N � 17) was lower than theestimate (99% CI) for forest (16.5 � 4.4 firesper century) for the same number of samples (N� 17).

CHAPARRAL AGE STRUCTURE. The age struc-ture of A. patula stems in the six stands wasquite variable but they had certain commoncharacteristics (Figure 3). First, a pulse of re-cruitment was associated with the date of the lastfire on most sites. Second, A. patula stems werepresent in a wide range of younger age-classessuggesting that recruitment was not limited tothe immediate post-fire period. Moreover, onthree of the sites, the ages of some A. patulastems pre-dated the last fire. Finally, the lack ofrecruitment in the last 50 yr may be, in part, asampling artifact. Small diameter stems in thetransects were not aged and these stems mayhave established during the last 50 yr.

TREE ENCROACHMENT. There were similaritiesin the temporal patterns of tree establishmentamong sites (Fig. 4). Most trees growing in thechaparral stands established after the last fire andthe age-class distributions for both A. concolorand P. jeffreyi were broadly unimodal. Tree re-cruitment into the chaparral stands was highestduring the first two or three decades after thefire, but tree establishment continued for at leastfive decades after the last fire in all of the stands.The apparent lack of recent recruitment is a sam-pling artifact since seedlings and saplings werenot aged and they represent trees that probablyestablished during the last 50–75 yr. Finally, inthree of the study sites (Meeks, Cascade, Tallac)establishment dates for some trees pre-date theyear of the last fire.

The timing of tree establishment within the

2005] 449NAGEL AND TAYLOR: FIRE AND MONTANE CHAPARRAL DYNAMICS

Tab

le2.

Den

sity

(Den

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ems

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sal

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931 81 121 6 0

35.8 2.4

4.6

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359 7 0

10.2 0 16.5 1.03

0

321 0

184 11 0

34.3 0 30.7 1.4

0

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14.9 0 12 0 2.

2

421 0

331 0 0

25.9

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625 39 99 0 0

24.4 2.7

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1139

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727

.73

516

66.4

944

29.1

752

39.7

763

34.8

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conc

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Cal

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rus

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rren

s

122 27 24 0 0

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57 0 0 0 0

57 0 81 0 22

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155 9 5 0 0

Tot

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369

5716

099

169

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7378

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301

450 [VOL. 132JOURNAL OF THE TORREY BOTANICAL SOCIETY

Table 3. Fire return interval (FRI) statistics for six montane chaparral stands in the northern Sierra Nevada,Lake Tahoe, California.

Parameter Angora Cascade Fallen Leaf Meeks Sugar Pine Tallac All sites

Number of samplesTotal number of firesMean point FRI (yr)Minimum sample FRI (yr)Maximum sample FRI (yr)Year of last fire

36

301048

1882

28

246

771872

48

291346

1861

45

161220

1872

33

271632

1861

12

404040

1881

173228

677

FIG. 3. Dates of establishment of A. patula in six montane chaparral stands in the northern Sierra Nevada,Lake Tahoe, California. The year of the last fire in the stand is indicated by an *.

2005] 451NAGEL AND TAYLOR: FIRE AND MONTANE CHAPARRAL DYNAMICS

FIG. 4. Dates of establishment of Abies concolor (Abco), Abies magnifica (Abma), Calocedrus decurrens(Cade), and Pinus jeffreyi (Pije), trees (� 5 cm dbh) in six montane chaparral stands in the northern SierraNevada, Lake Tahoe Basin, California. The year of the last fire in the stand is indicated by an *.

chaparral stands at each site was not clearly re-lated to distance of transects from the forestedge. The average difference in the median ageof trees in the transects within each site was only27 yr (range 13–47 yr). In some stands (e.g.,Tallac), median tree ages near the forest edgewere older than in the center of the shrub field(edge � 112 yr, range 107–116 yr; center � 90yr, range 87–92 yr). Yet in other stands (e.g.,Angora), median tree ages near the forest edge

were not older than in the center of the shrubfield (edge � 108 yr, range 106–112 yr; Angoracenter � 99.5 yr, range 90–106 yr).

Trees that established in chaparral had slowinitial growth (Fig. 5). Initial growth rates for A.concolor and P. jeffreyi trees were 10–20 rings/cm. The period of slow initial growth lasts for30–50 yr and then radial growth doubles as treesreach a diameter of 8–10 cm (at 30 cm) andemerge from the shrub canopy (Fig. 5).

452 [VOL. 132JOURNAL OF THE TORREY BOTANICAL SOCIETY

FIG. 5. Mean number of annual growth rings forAbies concolor (Abco), Abies magnifica (Abma), andPinus jeffreyi (Pije) per cm of tree core counted fromthe pith for trees (�5 cm dbh) growing in six montanechaparral stands in the northern Sierra Nevada, LakeTahoe Basin, California.

Once trees emerge from the chaparral canopythey compete with shrubs for light which mayreduce shrub vigor and growth (Conard and Ra-dosevich 1982a,b). There was a negative asso-ciation between tree cover and shrub cover(Spearman’s rs � �0.61, P � 0.01) in the chap-arral stands (Fig. 6). In transects with no treecover, the average shrub cover was 89 %, whilein transects with � 75% tree cover mean shrubcover was only 28%. Moreover, the shrub re-sponse to high tree cover seemed to vary by spe-cies. Arctostaphlos patula cover declined contin-uously as tree cover increased, whereas Q. vac-cinifolia appears to be only affected by high treecover (Fig. 6).

Replacement of chaparral by forest was evi-dent on the 1939 and 2000 aerial photographs(Table 4). On average, the area of chaparral ineach stand decreased by 55.9 ha (range 30.3–80.8 ha) which represents an average decreaseof 62.4% (range, 41.8–89.3%) in chaparral oneach site. The replacement of chaparral by forestwas also evident in the repeat photo pair of theFallen Leaf landscape. Since 1915, forest has re-placed much of the chaparral stand at FallenLeaf (Fig. 7).

Discussion. The species composition ofchaparral stands on the west shore of Lake Ta-hoe was similar to chaparral stands elsewhere inthe Sierra Nevada (Vankat and Major 1978,Conard and Radosevich 1982, Bolsinger 1989,

Skinner and Chang 1996). On our sites, chap-arral was dominated by Q. vaccinifolia and A.patula, which both have life history traits thatpromote rapid establishment and site dominanceafter high severity fire. Quercus vaccinifolia re-sprouts vigorously from a root crown whenaboveground parts of the plant are damaged andA. patula sprouts from underground lignotubers(Biswell 1974, Keeley 1988). Arctostaphylospatula also establishes from fire-triggered ger-mination of dormant seeds stored in a soil seedbank (Keeley 1988). Species of Ceanothus werealso present in our stands and their long-lived(�200 yr) seeds also germinate after heat scar-ification by high severity fire. Great seed lon-gevity may be particularly important for the per-sistence of Ceanothus sp. during long fire freeperiods (Geier-Hayes 1989, Conard et al. 1985,Weatherspoon 1985, 1988) because they may beshorter lived than other chaparral species andchaparral shrubs such as Q. vaccinifolia mayovertop them during chaparral canopy develop-ment (Keeley 1992).

Determining how often fires burn in chaparralis difficult because of the stand replacing natureof chaparral fires and this explains, in part, thescant fire-scar evidence found in or on the edgesof our chaparral stands, a scarcity also noted forArizona chaparral (Dietrich and Hibbert 1990)Yet, our limited sample does support the ideathat fire frequency is likely to be lower, morevariable, and more severe than in surroundingmixed conifer forests (Skinner and Chang 1996).The mean point FRI for chaparral was twice aslong as that for nearby mixed-conifer stands(Taylor 2000b) and the FRI distribution forchaparral was more dispersed and skewed to theright than for forest. Our mean FRI estimate forchaparral from the point samples is probably anunderestimate because fires recorded by some ofthe scarred trees on the edges of chaparral standsmay have burned in the forest and not in thechaparral. A longer FRI for chaparral than ad-jacent forest is consistent with differences inhow the structure and composition of fuels inthese two vegetation types affect flammability,and the spread and behavior of fire. For exam-ple, low intensity fires burning in surface fuelsin mixed conifer forests under average weatherconditions have been observed to stop spreadingwhen they reach chaparral because of changesin the structure and abundance of surface fuels,and the high live fuel moisture in chaparralshrubs (Weatherspoon and Skinner 1995). Therate of fuel recovery after fire in chaparral is also

2005] 453NAGEL AND TAYLOR: FIRE AND MONTANE CHAPARRAL DYNAMICS

FIG. 6. Mean (� SE) shrub cover (%) by abundance class of conifer canopy cover for all transects at allsites (N � 50).

Table 4. Area of montane chaparral at sample sitesin 1939 and 2000 in the northern Sierra Nevada, LakeTahoe, California. The reduction in chaparral at eachsite was caused by forest encroachment.

Study site

Year/area (ha)

1939 2000Area

changePercentchange

AngoraFallen LeafMeeksSugar PineTallacCascade

90.568.394.849.1

161.2100.1

9.738.029.612.193.845.2

�80.8�30.3�65.2�37.0�67.4�54.9

89.344.468.875.441.854.8

slower than in mixed conifer forest (Skinner andChang 1996).

The coincidence of fire dates in fire scarredtrees with the onset of establishment of mostshrubs and trees is a strong indicator that highseverity fires initiated the chaparral stands in ourstudy in the mid to late 19th century. In thenorthern Sierra Nevada and southern Cascades,there are many chaparral stands that establishedin this period after heavy early-day logging(Sudworth 1900, Leiberg 1902, Biswell 1974,McKelvey and Johnson 1992). Chaparral shrubsrespond vigorously to removal of the forest can-

454 [VOL. 132JOURNAL OF THE TORREY BOTANICAL SOCIETY

FIG. 7. Photo pair showing conversion of chaparral to forest at the Fallen Leaf site between the period 1915(top) and 2000 (bottom).

opy by heavy logging and if subsequent wild-fires remove surviving trees, return of trees tothese sites can be very slow (Biswell 1974, Wal-stad et al. 1987). In fact, there are large chap-arral stands elsewhere in the Lake Tahoe Basinthat were initiated by 19th century logging (Lind-strom 2000). However, there was no logging onour sites and chaparral dominance is not restrict-ed to sites that have experienced logging. High

severity fires in the late 19th and early 20th cen-tury in old growth forest landscapes in thesouthern Cascades (Bekker and Taylor 2001,Beaty and Taylor 2001), Klamath Mountains(Taylor and Skinner 1998, 1993) and Sierra Ne-vada (Gruell 2001) generated large chaparralstands. Moreover, in deeply incised terrain (Tay-lor and Skinner 1998, 2003; Beaty and Taylor2001) chaparrals stands appear to be relatively

2005] 455NAGEL AND TAYLOR: FIRE AND MONTANE CHAPARRAL DYNAMICS

fixed in place due to feedbacks between terraincharacteristics and fire behavior (Rothermel1983). Our chaparral stands were predominantlyon more xeric south and southeast facing slopesand conditions on these slopes may have predis-posed them to recurring high severity fire ratherthan the low severity surface fires typical of sur-rounding forest. Thus, our chaparral stands mayhave been relatively fixed in the landscape dueto recurring high severity fire on the same sites.Yet, data to support an interpretation of chap-arral as being fixed in position in our landscapesis scarce because stand replacing fires erase theevidence of earlier fires.

Recurring fire in the same chaparral stand,however, has been observed to maintain shrubdominance and prevent replacement of chaparralshrubs by trees elsewhere in the Sierra Nevada,since at least the mid 19th century. An analysisof historical records (i.e., GLO survey notes,newspaper articles, USDA Forest Service fire re-cords) has documented repeated fires in a large(�800 ha) chaparral stand that established some-time before 1866 (Wilken 1967). Since 1911,burns �40 ha occurred six times and burns tend-ed to be patchy, but there were some areas ofrepeat burning during the1911–1963 analysisperiod. In three of our chaparral stands, therewere some trees and shrub stems that had estab-lishment dates well before the last fire. The areasoccupied by these older trees and shrubs wereprobably not affected by the last fire and sug-gests that the burns were patchy, a finding sim-ilar to Wilken’s (1967).

Fires in the chaparral stands we studied ini-tiated new cohorts of shrubs and trees and thislarge post-fire pulse of regeneration was a con-spicuous feature of shrub and tree age structuresin the chaparral stands. Yet, shrub and tree es-tablishment was not confined to the immediatepost fire period. In each chaparral stand, on av-erage, shrub and tree recruitment occurred inseven different 10-yr age-classes. Thus, bothtree and shrub populations in the stands are noteven-aged but multi-aged. The multi-aged struc-ture of the A. patula populations indicates thatrecruitment of A. patula is not limited to the im-mediate post-fire period but that it continuesduring fire free periods. Similar, multi-aged pop-ulations of chaparral shrubs have been identifiedin lower elevation stands of foothills chaparralthat have not burned in over a century (Keeley1992). In foothills chaparral, the shrub canopyis rejuvenated continuously via sprout recruit-ment (Keeley 1992). Similarly, sprout recruit-

ment by A. patula and Q. vaccinifolia may bean important regeneration mechanism that con-tributes to shrub dominance in our chaparralstands.

Tree encroachment was conspicuous in ourchaparral stands. Abies concolor was the mostfrequent colonizer followed by P. jeffreyi andthe density and basal area of invading trees issimilar to reported values for other post-firemixed conifer stands with chaparral in the north-ern Sierra Nevada (Conard and Radosevich1982b). Abies concolor is highly shade tolerantand can establish and grow slowly for long pe-riods beneath a shrub canopy (Conard and Ra-dosevich 1982a). In our chaparral stands it tooknearly 30 yr, on average, for an A. concolorseedling to grow to a height of 30 cm. Oncetrees grow tall enough to emerge from the shrubcanopy they increase growth dramatically, castshade, and reduce the vigor of shrubs whichleads to replacement of chaparral by forest. Dur-ing the �120 yr fire free period in our standsthe area of a chaparral stand declined, on aver-age, by 62.4%.

Changes in the structure and composition ofmixed conifer forests since the late 19th centuryhave also been identified the Sierra Nevada(Vankat and Major 1978, Parsons and De-Benedetti 1979), the southern Cascades (Taylor2000a), and the Klamath Mountains (Skinner1995, Taylor and Skinner 2003). In general,nearly a century of fire exclusion has caused anincrease in forest density, a shift in compositionfrom more fire-resistant to more shade tolerantor fire-sensitive species, and a reduction in forestheterogeneity. In our chaparral stands, no fireshave occurred since the mid to late 19th century(i.e., 1861–1882). The �120 yr fire free periodin our chaparral stands exceeds the longest in-terval between fires identified in the chaparralfire scar samples by several decades. This un-usually long fire free period is probably the mostsignificant factor leading to replacement ofchaparral by forest in our study sites. Similarencroachment of trees into chaparral has beenobserved in mixed conifer forest landscapeselsewhere in the Sierra Nevada (Bock and Bock1977, Conard and Radosevich 1982b), the south-ern Cascades (Bekker and Taylor 2001, Beatyand Taylor 2001), and the Klamath Mountains(Skinner 1995). Our data suggest that the welldocumented effects of fire suppression on mixedconifer forest structure and composition also ap-ply to the forest-chaparral mosaic. Forests haveexpanded into chaparral and reduced the coarse

456 [VOL. 132JOURNAL OF THE TORREY BOTANICAL SOCIETY

grained structural heterogeneity of mixed coni-fer forest landscapes.

Our data indicate that stands of chaparral werea conspicuous feature of the mixed conifer forestlandscape in the northern Sierra Nevada at or nearthe time of Euro-American settlement and thatthey were maintained mainly by fire. However,the extent and spatial pattern of chaparral in thepre-EuroAmerican mixed conifer forest landscapeis uncertain because contemporary chaparralstands originated after both fire and early-daylogging. Historical records, either natural (i.e.,trees and shrubs) or documentary (i.e., written,photographic) are insufficient in most areas to as-sess, for example, what proportion of the land-scape in chaparral might have been. Nevertheless,after a century or more of fire exclusion treeshave established in chaparral stands and they areconverting to forest. In the Lake Tahoe Basin re-source managers and citizen stakeholders areseeking ways to restore forests to a conditionmore like those at the time of Euro-American set-tlement (Christopherson et al. 1996). Our studysuggests that maintenance of chaparral should bean integral part of ecosystem restoration plans formixed conifer forest landscapes in the Lake Ta-hoe basin and northern Sierra Nevada.

Literature Cited

ARNO, S. F., AND K.M. SNECK. 1977. A method fordetermining fire history in coniferous forests of themountain west. Gen. Tech Rpt. INT-42. USDA For-est Service, Intermountain Forest and Range Ex-periment Station, Ogden, UT.

ARNO, S. F. AND T. D. PETERSEN 1983. Variation inestimates of fire intervals: a closer look at fire his-tory in the Bitterroot National Forest. Gen. Tech.Rpt. INT-30. USDA Forest Service, IntermountainForest and Range Experiment Station, Ogden, UT.

BARBOUR, M. G. 1988. California upland forests andwoodland, pp. 131–164. In M.G. Barbour and W.D.Billings (eds.), North American terrestrial vegeta-tion.Cambridge University Press, Cambridge, UK.

BEATY, R. M., AND A. H. TAYLOR. 2001. Spatial andtemporal variation of fire regimes in a mixed co-nifer forest landscape, Southern Cascades, Califor-nia, USA. J. Biogeog. 28: 955–966.

BEKKER, M. F., AND A. H. TAYLOR. 2001. Gradientanalysis of fire regimes in montane forests of thesouthern Cascade Range, Thousand Lakes Wilder-ness, California, USA. Plant Ecol. 155: 15–28.

BISWELL, H. H. 1974. Effects of fire on chaparral, pp.321–364. In T.T. Kozlowski, and C.E. Ahlgren(eds.), Fire and ecosystems, Academic Press, NewYork, NY.

BOCK, C. E., AND J. H. BOCK. 1977. Patterns of post-fire succession on the Donner Ridge burn, SierraNevada, pp. 464–469. In H. A. Mooney and C. E.Conrad (Tech. Coor.), Proceedings of the sympo-sium on the environmental consequences of fire

and fuel management in Mediterranean ecosystems.Gen. Tech. Rpt WO-3,USDA Forest Service,Washington, DC.

BOLSINGER, C. L. 1989. Shrubs of California’s chap-arral, timberland, and woodland: area ownershipand stand characteristics. Res. Bull. PNW-RB-160.USDA Forest Service, Pacific Northwest ResearchStation, Portland, OR.

BORMANN, F. H. AND G. E. LIKENS 1979. Pattern andprocess in a forested ecosystem. Springer-Verlag,New York, NY.

CHRISTOPHERSON, J., S. R. LEWIS, AND M. HAVERCAMP.1996. Lake Tahoe’s Forest Health ConsensusGroup. J. For. 94: 10–12.

CONARD, S. G., AND S. R. RADOSEVICH. 1982a. Growthresponses of white fir to decreased shading and rootcompetition by montane chaparral shrubs. For. Sci.28: 309–320.

CONARD, S. G. AND S. R. RADOSEVICH. 1982b. Post-fire succession in white fir (Abies concolor) vege-tation of the northern Sierra Nevada. Madrono 29:42–56.

CONARD, S. G. AND S. R. SPARKS. 1993. Abies concolorgrowth responses to vegetation changes followingshrub removal, northern Sierra Nevada, California.Res. Paper PSW-218. USDA Forest Service, Pacif-ic Southwest Research Station, Albany, CA.

DIETERICH, J. H., HIBBERT, A. R. 1990. Fire history ina small ponderosa pine stand surrounded by chap-arral, pp. 168–173. In J.S. Krammes (ed.), Effectsof fire management of southwestern natural re-sources. Gen. Tech. Rpt. RM 191. USDA ForestService,Rocky Mountain Forest and Range Exper-iment Station, Fort Collins, CO.

FOSTER, D. AND E. BOOSE. 1992. Patterns of forestdamage resulting from catastrophic wind in centralNew England, USA. J. Ecol. 80: 79–98.

GREENE, D. A. AND E. A. JOHNSON 2000. Tree recruit-ment from burn edges. Can. J. For. Res. 30: 1264–1274.

GRUELL, G. E. 2001. Fire in Sierra Nevada forests: aphotographic interpretation of ecological changesince 1849. Mountain Press, Missoula, MT.

HARMON, M. E., S. P. BRATTON, AND P. S. WHITE 1983.Disturbance and vegetation responses in relation toenvironmental gradients in the Great Smoky Moun-tains. Vegetatio 55: 129–139.

HILL, M. 1975. Geology of the Sierra Nevada. Uni-versity of California Press, Berkeley, CA.

HOLMES, R. L. 1995. Effect of sample size on fire fre-quency estimates: description of computer programSSIZ. Retrieved April 28, 2001 from Dendrochro-nology Program Library. �http://www.ltrr.arizona.edu/pun/dpl/�

HUPP, C., W. R. OSTERCAMP, AND J. L. THORNTON 1987.Dendrogeomorphic evidence and dating of recentdebris flows on Mount Shasta, Northern California.USGS Prof. Paper 1396-B. Dept. of the Interior,U.S. Geological Survey, Denver, CO.

KAUFFMAN, J. B. 1990. Ecological relationships of veg-etation and fire on the Pacific Northwest, pp. 39–52. In J.D. Walsted, S.R. Radosevich, and D.V.Sandberg (eds.), Natural and prescribed fire in Pa-cific Northwest forests. Oregon State UniversityPress, Corvallis, OR.

KEELEY, J. E. 1988. Bibliographies on chaparral andthe fire ecology of other Mediterranean systems.

2005] 457NAGEL AND TAYLOR: FIRE AND MONTANE CHAPARRAL DYNAMICS

2nd ed. University of California, California WaterResources Center Report No. 69. Riverside, CA.

KEELEY, J. E. 1991. Seed germination and life historysyndromes in the California Chaparral. Bot. Rev.57: 81–116.

KEELEY, J. E. l992. Demographic structure of Califor-nia chaparral in the long-term absence of fire. J.Veg. Sci. 3: 79–90.

KEELEY, J. E. 2000. Chaparral. Pages, 203–253. InNorth American terrestrial vegetation, M. G. Bar-bour and W. D. Billings (eds). 2nd edition. Cam-bridge University Press, Cambridge, UK.

KILGORE, B. M., AND TAYLOR, D. 1979. Fire history of aSequoia-mixed conifer forest. Ecology 60: 129–142.

LEIBERG, J. B. 1902. Forest conditions in the northernSierra Nevada, California. U.S. Geological SurveyProfessional Paper No. 8. Series H. Forestry, No. 5.U.S. Government Printing Office, Washington, DC.

LINDSTROM, S. 2000. A contextual overview of humanland use and environmental conditions, pp. 23–122.In D.D. Murphy, and C.M. Knopp (eds.), Lake Ta-hoe watershed assessment: Volume I. Gen. Tech.Rep. PSW-175. USDA Forest Service, PacificSouthwest Research Station, Albany, CA.

MCKELVEY, K. S. AND J. D. JOHNSTON. 1992. Historicalperspectives of forests of the Sierra Nevada and theTransverse Ranges of southern California: forestconditions at the turn of the century, pp. 225–246.In J. Verner, K.S. McKelvey, B. Noon, R.J. Gu-tierrez, C.I. Gould, and T.W. Beck (Tech. Coor.),The California spotted owl: a technical assessmentof its current condition. Gen. Tech. Rpt. PSW-133.USDA Forest Service, Pacific Southwest ResearchStation, Albany, CA.

PARSONS, D. J. AND S. H. DEBENEDETTI. 1979. Impactof fire suppression on a mixed-conifer forest. For.Ecol. Manag. 2: 21–33.

ROGERS, J. H. 1974. Soil survey Tahoe Basin Area:California and Nevada, USDA Soil ConservationService.

ROMME, W. H. AND D. H. KNIGHT. 1981. Fire frequencyand subalpine forest succession along a topographicgradient in Wyoming. Ecology 62: 319–326.

ROTHERMEL, R. C. 1983. How to predict the spread andintensity of wildfires. Gen. Tech. Rpt. INT-GTR-143. USDA Forest Service, Intermountain Forestand Range Experiment Station, Ogden, UT.

RUNDELL, P. W., D. J. PARSONS, AND D. T. GORDON.1977. Montane and subalpine vegetation of the Si-erra Nevada and Cascade Ranges, pp. 559–599. InM.G. Barbour and J. Major (eds.) Terrestrial veg-etation of California. John Wiley and Sons, NewYork, NY.

SHOW, S. B., AND E. I. KOTOK. 1924. The role of firein the California pine forests. USDA Bull. 1294.

SKINNER, C. N. 1995. Change in spatial characteristicsof forest openings in the Klamath Mountains ornorthwestern California USA. Landscape Ecol. 10:219–228.

SKINNER, C. N., AND C. R. CHANG. 1996. Fire regimes,past and present. Sierra Nevada Ecosystem Project:final report to Congress, Vol. II, pp. 1041–1069.Assessment and scientific basis for managementoptions. University of California Davis, Center forWildland Resources, Davis, CA.

STOKES, M. A., AND T. L. SMILEY. 1968. An introduc-

tion to tree-ring dating. University of ChicagoPress, Chicago, IL.

SWETNAM, T. W. AND C. H. BAISAN 2002. Tree-ringreconstructions of fire and climate history in theSierra Nevada and southwestern United States,Pages 158–195. In T. T. Veblen, W.L. Baker, G.Montenegro, and T.W. Swetnam (eds). Fire and cli-matic change in temperate ecosystems of the west-ern Americas. Springer-Verlag, New York, NY.

SUDWORTH, G. B. 1900. Stanislaus and Lake TahoeForest Reserves, California and adjacent territory.In Annual Reports of the Department of the Inte-rior, 21st Annual Report of the U.S. Geological Sur-vey, Part 5, pp. 505–561. U.S. Government PrintingOffice, Washington, DC.

TAYLOR, A. H. 2000a. Fire regimes and forest changesin mid and upper montane forests of the southernCascades, Lassen Volcanic National Park, Califor-nia, USA. J. Biogeog. 27: 87–104.

TAYLOR, A. H. 2000b. Reconstruction of pre-Euro-American forest structure and composition, and fireregimes of mixed conifer forests on the west shoreof Lake Tahoe. Final report for the USDA ForestService, Lake Tahoe Basin Management Unit-Pennsylvania State University Cost Share Agree-ment, 95 pp.

TAYLOR, A. H. 2004. Identifying reference conditionson early cut-over lands, Lake Tahoe Basin, USA.Ecol. Appl. 14: 1903–1920.

TAYLOR, A. H. AND C. N. SKINNER. 1998. Fire historyand landscape dynamics in a late-successional re-serve, Klamath Mountains, California, USA. For.Ecol. Manag. 111: 285–301.

TAYLOR, A. H. AND C. N. SKINNER. 2003. Spatial pat-terns and controls on historical fire regimes andforest structure in the Klamath Mountains. Ecol.Applic. 13: 704–719.

VANKAT, J. L. AND J. MAJOR. 1978. Vegetation changesin Sequoia National Park, California. J. Biogeog.5: 377–402.

WALSTAD, J., M. NEWTON, R. BOYD, AND J. RAYMOND

1987. Forest vegetation problems in the Northwest,pp. 15–53. In J.D. Walstad, and P.J. Kuch (eds.),Forest vegetation management for conifer produc-tion.John Wiley and Sons, New York, NY.

WEATHERSPOON, C. P. 1985. Preharvest burning forshrub control in a white fir stand: preliminary ob-servations, pp. 71–88. In S.L. Cooper (Compiler),Proceedings–6th Annual Forest Vegetation Manage-ment Conference, University of California, ShastaCounty Cooperative Extension, Redding, CA.

WEATHERSPOON, C. P. 1988. Preharvest prescribedburning for vegetation management: effects on Ce-anothus velutinus seeds in duff and soil, Pages125–141. In S.L. Cooper (Compiler), Proceedings–9th Annual Forest Vegetation Management Confer-ence, University of California, Shasta County Co-operative Extension, Redding, CA.

WEATHERSPOON, C. P., AND C. N. SKINNER. 1995. Anassessment of factors associated with damage totree crowns from the 1987 wildfires in northernCalifornia. For. Sci. 41: 430–451.

WHITTAKER, R. H. 1956. Vegetation of the GreatSmoky Mountains. Ecol. Monogr. 26: 1–80.

WILKEN, G. C. 1967. History and fire record of a tim-berland brush field in the Sierra Nevada of Cali-fornia. Ecology 48: 302–304.