Volume 19 • Number 1 2002 19

Jan W. van WagtendonkKent A. van Wagtendonk

Joseph B. MeyerKara J. Paintner

The Use of Geographic Informationfor Fire Management Planning in

Yosemite National Parkire has played a critical role in the ecosystems of YosemiteNational Park for millennia. Before the advent of Euro-Americans,lightning fires and fires set by Native Americans burned freelyacross the landscape. These fires burned periodically, with theinterval between fires dependent on the availability of ignition

sources, adequate fuels, and weather conducive to burning. As a result, differ-ent vegetation types burned at different intervals.

Designation of Yosemite Valleyand the Mariposa Grove as a statereserve in 1864, and of the remainingarea surrounding the valley as a na-tional park in 1890, led to an era offire suppression. Landscape-scalechanges resulted from decades of amanagement philosophy that ex-cluded naturally occurring fires.These landscape-scale changes arecharacterized by departures from thenatural fire-return interval—thenumber of years between successivenaturally occurring fires for a givenvegetation type. Prior to the exclu-sion of fire, intervals between firesranged from a few years in the lowermontane forests to centuries in thesubalpine forests.

Interruption of the natural regime,reflected in the fire return-intervaldeparture, is a major thrust in the

development and analysis of the Yo-semite fire management plan and en-vironmental impact analysis. Areasthat have missed multiple return in-tervals are more susceptible to stand-replacing wildland fires, which areuncommon in natural surface-burn-ing fire regimes. The plan strives torestore and maintain the naturalrange of variability by focusingtreatment of areas based on the firereturn-interval departures.

Geographic information systems(GIS) have been used in YosemiteNational Park for fire research andmanagement applications since theearly 1980s (van Wagtendonk 1991).A GIS model was used for the firereturn-interval departure analysis inthe new fire management plan for the

F

20 The George Wright FORUM

park. The analysis was originally de-veloped in Sequoia and Kings Can-yon National Parks (Caprio et al.1997). It combines information onfire history and fire ecology to assessthe ecological condition of all vege-tation communities, using departuresfrom the natural fire return intervalsas an indicator of change. The analy-sis consists of four steps: (1) vegeta-tion types are defined based onsimilar fuels and fire behavior, (2)fire return intervals are assigned toeach type, (3) the number of yearssince an area last burned is deter-mined from fire history maps, and(4) departures from the natural fireinterval are calculated using the re-turn interval. The results from thisanalysis are then applied to the firemanagement planning process.

Although the park is currently de-veloping a new vegetation map, themost recent map dates from the1930s and was compiled from fieldsurveys and sample plots (vanWagtendonk 1986). This map wasdigitized and entered into a GIS in1981. Over 6,500 polygons wereassigned species names from over1,200 unique combinations of spe-cies. These polygons were reclassi-fied into 33 types as part of the park’svegetation management plan. Firehistory maps and data have beencollected in the park since 1930 andwere also entered into a GIS in 1981.This GIS coverage has been updatedafter each fire season and includesthe name, year, management type,

and ignition source of each fire. Boththe vegetation map and the fire his-tory map were converted intoArcInfo raster data sets. The ArcInfoGRID module and the Spatial Ana-lyst extension of ArcView were usedto perform the fire return-intervaldeparture analyses (ESRI 1996).These modules allowed multipleraster data sets to be analyzed simul-taneously.

The vegetation zones across thepark follow general elevation bandsacross the Sierra Nevada from chap-arral oak woodlands, through lowermontane forests, upper montane for-ests, and subalpine forests, to alpinemeadows. At the lowest elevations inthe park (about 2,000 feet abovemean sea level), the vegetation ischaparral and oak woodland. Lowermontane mixed-conifer forests occurfrom about 3,000 to 6,700 feet. Up-per montane conifer forests occurfrom about 6,000 to 10,000 feet.Subalpine conifer forests occur from8,000 to 11,000 feet. Alpine com-munities dominate above 10,000feet.

Fire professionals examined eachof the 33 vegetation managementplan types and reclassified thembased on similar vegetation, fire be-havior, and fuel loads. In most cases,the reclassification was a simple reas-signment, but in a few cases vegeta-tion types were lumped based on thecharacteristics of neighboring types.

Volume 19 • Number 1 2002 21

For example, if a subalpine meadowadjoins a lodgepole pine forest, itwould be lumped with the forestsince the meadow would be likely toburn if the forest was ignited. If,however, the meadow was sur-rounded by barren rock, it would belumped with the rock since it wouldbe unlikely to be ignited. Theseneighborhood analyses were per-formed for meadows, riparian vege-tation types, and western juniper.

The resulting 15 vegetationgroups and the barren and water

categories are shown in Figure 1 andlisted in Table 1 for the 747,955acres in Yosemite National Park andthe 1,137 acres in the El Portal Ad-ministrative Site. The types are listedby zone, generally from higher tolower elevation. Table 2 includesinformation on fuel loads, firelineintensities, and typical fire behaviorin each of the vegetation types. Adescription of each of the vegetationzones follows.

Subalpine forests. The subalpinezone includes whitebark pine and

Vegetation zone Vegetation type AcresWhitebark pine–mountain hemlock forest 87,582Subalpine forestsLodgepole pine forest 175,516Red fir forest 68,125Western white pine–Jeffrey pine forest 132,708

Upper-montaneforests

Montane chaparral 15,137Giant sequoia–mixed conifer forest 218White fir–mixed-conifer forest 46,871Ponderosa pine–mixed-conifer forest 34,370Ponderosa pine–bear clover forest 33,846California black oak woodland 3,156Canyon live oak forest 21,473

Lower-montaneforests

Dry montane meadow 1,530Foothill pine–live oak–chaparral

woodland7,130

Foothill woodlands

Foothill chaparral 1,785Blue oak woodland 473

Subtotal,Vegetation

629,920

Barren Bare rock 112,022Water 7,150

Total 749,092

22 The George Wright FORUM

Volume 19 • Number 1 2002 23

Mountain hemlock forests andlodgepole pine forests, whichtogether occupy about 35% of thepark. Characteristic trees includelodge-pole pine (Pinus contorta),mountain hemlock (Tsuga mertensi-ana), and whitebark pine (Pinus al-bicaulis), with smaller amounts ofred fir (Abies magnifica), westernwhite pine (Pinus monticola) andwestern juniper (Juniperus occiden-talis). Although this zone receivesapproximately 35% of the lightningstrikes in the park, fires are infre-quent and do not become large (vanWagtendonk 1994). These fires usu-ally smolder or spread as low-inten-sity surface fires.Upper montane forests. The upper

montane zone includes red fir forest,western white pine/Jeffrey pine for-est, and montane chaparral, andmakes up about 30% of park vegeta-tion. Characteristic trees include redfir, western white pine, Jeffrey pine(Pinus jeffreyi), western juniper, andaspen (Populus tremuloides). Domi-nant shrub species in- clude green-leaf manzanita (Arctostphylos patula),pinemat manzanita (Arctostaphylosnevadensis), mountain white thorn(Ceanothus cordulatus), huckleberryoak (Quercus vacinifolia) and, atlower elevations, bitter cherry(Prunus emarginatus) and chinqua-pin (Castanopsis sempervirens). Thiszone receives 23% of the lightningstrikes in the park, and fires are nu-merous, generally remain small, andare of low intensity (van Wagtendonk

1994). However, under extremelydry and windy conditions, largestand-replacing fires can occur.

Lower montane forests. Thelower montane zone, which includesgiant sequoia, white fir, and ponder-osa pine mixed-conifer forests andponderosa pine–bear clover forest,covers about 15% of the park. Thiszone also contains California blackoak woodlands, canyon live oak for-ests, and dry montane meadows.Dominant tree species include pon-derosa pine (Pinus ponderosa), sugarpine (Pinus lambertiana), incense-cedar (Calocedrus decurrens), whitefir (Abies concolor), giant sequoia (Se-quoiadendron giganteum), Californiablack oak (Quercus kelloggii), andcanyon live oak (Quercus chrysolep-sis). The most common understoryshrubs are bear clover (Chamaebatiafoliolosa), whiteleaf manzanita (Arc-tostaphylos viscida), and deerbrush(Ceanothus intergerimus). Althoughthe lower montane forests receiveonly 17% of the lightning strikes inthe park, the mixed-conifer commu-nity experiences frequent, low-inten-sity fires (van Wagtendonk 1994).Many of these fire were suppressed,however, resulting in a change fromopen forest to dense thickets ofshade-tolerant tree species, particu-larly incense-cedar and white fir inthe upper part of the zone, and anincrease in shrubs in the lower part.Under natural conditions, the me-dian fire return interval is estimatedat 8 to 12 years. Existing conditions,

24 The George Wright FORUM

Fuel LoadVegetationType Duff Woody

FirelineIntensity

Typical FireBehavior

-----Tons/ac----- --Btu/ft/s--Whitebarkpine–mountainhemlock forest

50.2 3.7 1-40mean=10

Smoldering or lowintensity, surfacefire

Lodgepole pineforest

27.7 2.0 1-40mean=10

Smoldering or lowintensity, surfacefire

Red fir forest 39.8 8.9 1-120mean=25

Surface fire, flames<1 ft, flare-ups inheavy fuel

Western whitepine– Jeffreypine forest

41.7 1.5 1-60mean=30

Moderate intensityfire, flames 1-4 ft,torching may occur

Montanechaparral

— 3.5 50-6,330mean=3,000

Fast spreadinvolving entirebiomass, flames20-30 ft

Giant sequoia–mixed-coniferforest

68.6 10.4 20-1,000mean=100

Erratic spread,flames <2 ft,intense burning inheavy fuels

White fir–mixed-coniferforest

36.1 4.6 20-1,000mean=100

Slow spread,flames <2 ft,intense burning inheavy fuels

Ponderosapine–mixed-conifer forest

55.5 4.4 20-1,000mean=100

Low intensity,surface fire, flames2 ft

Ponderosapine–bearclover forest

48.0 4.4 20-1,000mean=100

Surface fire inshrub layer, flames2 ft

Volume 19 • Number 1 2002 25

CaliforniaBlack oakforest

10.0 2.0 1-120mean=25

Low intensity,surface fire, flames<1 ft

Canyon liveoak forest

— 25.0 50-6,330mean=3,000

Torching of largetrees, frequentcrown fire

Dry montanemeadow

3.0 (grass) 4-125mean=100

Fast spread withwind, flames 2-10ft

Foothillpine–live oak–chaparral

20.7 21.7 50-6,330mean=3,000

Fast spread,torching andcrowning in treesand shrubs

Foothillchaparral

— 14.0 50-6,330mean=3,000

Fast spreadinvolving entirebiomass, flames20-30 ft

Blue oakwoodland

0.75 (grass) 4-125mean=100

Fast spread in grasswith wind, flames2-10 ft

however, often generate fires of muchgreater intensity than would occurunder a natural fire regime.

Foothill woodland. The foothillwoodland zone includes foothillpine–live oak–chaparral woodland,blue oak woodland, and foothillchaparral. This zone covers about5% of the park ranging from 1,700 to6,000 feet. Dominant tree speciesinclude California black oak, foothillpine (Pinus sabiniana), canyon liveoak, interior live oak (Quercus wis-lizenii), and blue oak (Quercusdouglasii). Many of the types arebetter recognized by the dominantshrubs, including mountain mahog-any (Cercocarpus betuloides), poison

oak (Toxicodendron diversiloba),whiteleaf manzanita, deerbrush, andbuckbrush (Ceanothus cuneatus).Lightning is not frequent in the foot-hill zone, receiving only 2% of therecorded strikes in the park (vanWagtendonk 1994). Even whenmade proportional to the size of thezone, only 8% of the strikes occurthere. Consequently, lightning firesare not very frequent, but when theydo occur, they spread quickly andare very intense.

Fire plays a varying role in thevegetation types, characterized bythe fire return interval. A fire return

26 The George Wright FORUM

interval for a given vegetation type isdefined as the number of years be-tween fires at a specific location thatis representative of that type. Forexample, a fire scar analysis of asample of trees in a stand of ponder-osa pines might show that fire hasoccurred in that stand from as fre-quently as every two years (minimumvalue) or as infrequently as every sixyears (maximum value). The averagefire return interval is the arithmetricmean of all the intervals (mean inter-val); due to sampling techniques, it isusually closer to the minimum inter-val than the maximum. If fire returnintervals for all trees are arrangedfrom shortest to longest, the tree inthe middle would have the medianinterval, which might be every fouryears (median value).

Table 3 lists the minimum, me-dian, and maximum fire return inter-vals for each of the vegetation typesand the sources for that information.In some cases, only the mean valuewas available; it is listed in table 3 inthe median column. Skinner andChang (1996) give a thorough dis-cussion on return intervals and werethe primary or secondary source formost of the entries. Caprio and Line-back (1997) provided additionalsources. In cases where no specificstudies existed for a species, theclosest ecologically similar specieswas selected. The information fromTable 3 was used to reclassify thepark vegetation map into maximumand median fire return-interval maps.

Maximum fire return intervalsranged from five years for drymontane meadows to 508 years forwhitebark pine and western hemlockforests. These same types had theshortest (1 year) and longest (187years) median intervals.

Fire history maps dating back to1930 for the park proper and to1958 for the El Portal administrativesite were used to develop informa-tion on ignition source, fire size,number of times a particular area hasburned, the decade in which eachburn occurred, and the last year inwhich a burn occurred within a par-ticular area. The fire history data areas complete as possible, but there area few historic fires that are incom-pletely documented, and it is sus-pected that there are a few historicfires that are totally undocumented.Table 4 shows the variation in thearea burned over the decades. Re-burns within a decade are not re-counted, but reburns occurring inmultiple decades are. During the1930s, fuel accumulations had notbecome critical and most fires didnot become large before they weresuppressed. A single human-causedfire in 1948 accounted for most ofthe acres burned during that decade.Increased suppression efforts in the1950s and 1960s, combined withnew equipment and technology, re-sulted in a reduction in the acreageburned.

Volume 19 • Number 1 2002 27

Return IntervalVegetation type

Min. Med. Max.Source

---------Years---------Whitebark pine–mountain

hemlock forest4 187 508 Caprio and

Lineback 1997Lodgepole pine forest 4 102 163 Kiefer 1991Red fir forest 9 30 92 Caprio and

Lineback 1997Western white pine–Jeffrey pine

forest4 12 96 Skinner and

Chang 1996Montane chaparral 10 30 75 Caprio and

Lineback 1997Giant sequoia–mixed-conifer

forest1 10 15 Swetnam et

al.1991White fir–mixed-conifer forest 3 8 35 Skinner and

Chang 1996Ponderosa pine–mixed-conifer

forest3 9 14 Kilgore and

Taylor 1979Ponderosa pine–bear clover

forest2 4 6 Caprio and

Swetnam 1993California black oak woodland 2 8 18 Stephens 1997Canyon live oak forest 7 13 39 Skinner and

Chang 1996Dry montane meadow 1 2 5 Anderson 1993Foothill pine–live oak–chaparral

woodland2 8 49 McClaran and

Bartolome 1989Foothill chaparral 10 30 60 Caprio and

Lineback 1997Blue oak woodland 2 8 49 McClaran and

Bartolome 1989

The prescribed burning andwildland fire use programs began in1970 and 1972, respectively, usher-ing in the era of fire management.The acreage burned increased dra-matically as these programs began to

allow fire to play its natural role inthe ecosystem. This growth contin-ued during the 1980s in spite of themoratorium on management fires in1989 as a result of the Yellowstonefires. During the 1990s, three large

28 The George Wright FORUM

lightning fires that were suppressedburned nearly 60,000 acres in thepark and the administrative site.Only 47 acres were burned in 2000,the year of another moratorium, thisone resulting from the Los Alamosfires.

Figure 2 shows the year of lastburn by vegetation type for all igni-tion sources combined. This map is

used in the calculation of fire return-interval departure as an indicator ofthe most recent fire to burn an area.Ecologically, it makes no differencewhether the fire was ignited by light-ning or by humans, on purpose or byaccident. The large burns on thewestern edge of the park were sup-pressed lightning fires that occurredin 1990 and 1996. The area in the

DecadeVegetation Type

1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000

-----------------------------------Acres--------------------------Whitebark pine-

–mtn. hemlock 16 0 0 2 23 31 3 0Lodgepole pine

forest 20 175 13 233 897 4,536 3,059 39Red fir forest 6 744 48 576 1,435 7,706 7,466 4W. white pine–

Jeffrey pine 66 4,962 249 390 6,720 18,928 20,296 6Montane chaparral 6 910 11 262 277 1,832 1,368 0Giant sequoia–

mixed-conifer 0 0 0 0 81 31 88 0White fir–mixed-

conifer 41 390 61 300 2,439 7,541 17,144 1Ponderosa pine–

mixed-conifer 6 381 468 817 4,796 4,641 14,956 3Ponderosa pine–

bear clover 11 481 832 794 4,604 4,602 18,055 0California black oak

forest 0 56 4 0 241 622 354 0Canyon live oak

forest 331 3,514 83 638 1,517 129 9,258 0Dry montane

meadow 0 36 5 30 197 125 434 0Foothill pine–oak–

chaparral 5 440 2,163 962 269 126 6,216 0Foothill chaparral 0 0 0 32 0 63 363 0Blue oak woodland 0 0 0 0 116 4 301 0Total 508 12,089 3,937 5,036 23,612 50,917 99,361 53

Volume 19 • Number 1 2002 29

30 The George Wright FORUM

south-central portion of the park in-cludes the Illilouette Creek basinwhere large lightning fires have beenallowed to run their course since1972 as part of the wildland fire -seprogram (van Wagtendonk 1994).Similar areas of large lightning firesoccur in the Frog Creek drainagenorth of Hetch Hetchy Reservoir.

The ignition source data areshown in Table 5. Acreage numbersdo not include areas that were re-burned by fires of the same ignitionsource; however, areas burned byfires from more than one ignitionsource are counted two or threetimes. Lightning accounts for over93% of the unplanned ignitions. Theresulting fires have burned over145,400 acres. Two hundred forty-five human-caused fires have burnednearly 18,600 acres; 12,000 acresburned in a single fire in 1948. Man-agers have ignited 399 prescribedfires between 1970 and 2000, andthose fires have burned over 41,000acres. Most of the prescribed burn-ing has been conducted in the whitefir and ponderosa pine types wherefuel conditions have been affected byfire exclusion in the past.

When reburned areas are not re-counted, a total of 160,511 acres(25%) of the vegetated areas of thepark and the administrative site haveburned during the past 71 years(Table 6). Over 469,400 acres havenot burned; most of these are in thewhitebark pine–mountain hemlockand lodgepole pine forest types in the

subalpine zone. Only 877 acres haveburned four or more times, while6,880 acres have burned three times;36,100 acres burned two times, and116,653 acres burned only once.Reburns have been most common inthe mixed-conifer types where pre-scribed burns have been set and inthe Illilouette Creek and Frog Creekbasins.

The largest number of acresburned by a single lightning fire ineach vegetation type and the year ofthat fire are shown in Table 7; how-ever, these data do not include the1990 A-Rock and Steamboat fires orthe 1996 Ackerson fire. Data col-lected in the field on the 1990 firesindicate that, in addition to unnatu-rally high fuel loads, atmosphericconditions combined with steepslope topography and local windscontributed to catastrophic fire be-havior. Fire suppression activities,particularly back-firing on the Acker-son fire, have also increased the areaburned beyond what might havedone so naturally for all three firesomitted from Table 7. The 1953 firewas the only one that did not occurunder the wildland fire-use programand indicates the maximum size thatmight be expected to burn in eachvegetation type under natural condi-tions. Landscape-scale changes inthe fire regime are characterized byan analysis of departures from the firereturn interval that would have pre-vailed had fires been allowed to burnnaturally.

Volume 19 • Number 1 2002 31

Ignition SourceVegetation Type Lightning Human Prescribed

No. Acres No. Acres No. AcresWhitebark pine–

mountainhemlock forest

56 121 0 0 0 0

Lodgepole pineforest

427 8,358 25 399 13 354

Red fir forest 591 16,767 18 1,004 5 307Western white

pine–Jeffreypine forest

893 41,982 47 6,385 24 5,584

Montanechaparral

126 2,651 11 1,175 22 755

Giant sequoia–mixed-coniferforest

0 0 0 0 17 241

White fir–mixed-conifer forest

427 20,436 25 625 13 7,387

Ponderosa pine–mixed-coniferforest

341 15,545 19 809 88 10,976

Ponderosa pine–bear cloverforest

247 19,160 59 1,494 121 11,619

California blackoak woodland

24 353 3 81 22 868

Canyon live oakforest

108 10,510 21 5,001 22 2,025

Dry montanemeadow

16 421 3 54 36 433

Foothill pine–liveoak–chaparralwoodland

34 8,555 8 1,424 3 302

Foothill chaparral 17 336 3 25 6 110Blue oak

woodland2 315 3 120 7 62

Total 3,309 145,462 245 18,596 399 41,023

32 The George Wright FORUM

Times BurnedVegetation type

0 1 2 3 4+Total

------------------------------Acres------------------------------Whitebark pine– mtn

hemlock87,461

1210

0 0 87,582

Lodgepole pine forest 166,903 7,467 989 157 0 175,516Red fir forest 50,483 16,084 1,476 81 1 68,125Western white– Jeffrey

pine88,668

34,4776,884

2,423 256 132,708

Montane chaparral 11,285 2,787 874 185 6 15,137Giant sequoia– mixed-

conifer36

8881

9 4 218

White fir–mixed-coniferforest

22,42620,000

3,979448 18 46,871

Ponderosa pine– mixedconifer

14,74412,609

6,178792 47 34,370

Ponderosa pine– bearclover

12,16812,411

7,2011,731 335 33,846

California black oakforest

2,012959

15827 0 3,156

Canyon live oak forest 10,250 4,871 5,596 661 95 21,473Dry montane meadow 911 402 154 38 25 1,530Foothill pine–oak–

chaparral705

3,6662,357

312 90 7,130

Foothill chaparral 1,243 503 39 0 0 1,785Blue oak woodland 114 208 135 16 0 473Total 469,409 116,653 36,101 6,880 877 629,920

In general, the further that vege-tation communities depart fromtheir natural fire regimes, the morethat unnatural conditions will pre-vail and the higher the risk of theoccurrence of a stand-replacingwildland fire that is not natural tosurface-burning fire regimes. Maxi-mum fire return-interval departurerepresents the most conservativeestimate of how severe the deviationfrom natural conditions might be interms of fuels and vegetation. Me-

dian fire return-interval departuregives a more moderate view, whilethe minimum presents the most ex-treme situation of how far the standis from its natural condition. Forexample, if fire suppression hasbeen successful in excluding firefrom the stand for sixty years, itwould have missed thirty fires basedon the minimum fire return intervalof two years, fifteen fires based onthe median interval of four years,and ten fires based on the maximuminterval of six years. These depar-

Volume 19 • Number 1 2002 33

tures from the normal fire regime areexpressed in terms of fire return-in-terval departures of 30, 15, and 10missed intervals, respectively.

The number of interval depar-tures for both the median and maxi-mum fire return interval departuresis calculated using the followingmap algebra:

Fire return-interval departure =[fire return interval – (current year– year last burned)] ÷ fire returninterval

The fire return-interval departuremap is the absolute value of the firereturn-interval map minus the valueof the current year less the year-last-burned map all divided by the fire

return-interval map. The return in-terval can be calculated for both themaximum and median interval. Forareas that have not burned since1930 in Yosemite National Park or1985 for the El Portal administrativesite, the year last burned was con-sidered to be 1930 and 1958, re-spectively.

Maximum and median fire re-turn-interval departures weregrouped into three categories: 0-2intervals missed, 3-4 intervalsmissed, and five or more intervalsmissed. These groupings are basedon the assumption that fire exclu-sion increases surface and ladderfuels, greatly increasing the potentialfor catastrophic fire.

Vegetation type Acres Year

Whitebark pine–mountain hemlock forest 20 1988Lodgepole pine forest 773 1987Red fir forest 1,265 1999Western white pine–Jeffrey pine forest 3,274 1974Montane chaparral 641 1999Giant sequoia–mixed-conifer forest 0 1976White fir–mixed-conifer forest 1,092 1988Ponderosa pine–mixed-conifer forest 960 1999Ponderosa pine–bear clover forest 1,247 1987California black oak woodland 91 1999Canyon live oak forest 3,517 1999Dry montane meadow 35 1988Foothill pine–live oak–chaparral woodland 1,909 1953Foothill chaparral 43 1987Blue oak woodland 5 1987

34 The George Wright FORUM

These high-intensity and severefires are outside the natural range ofvariability. The rationale for the 0-2departures-missed group is that, formost vegetation types, two medianintervals lie between the minimumand maximum return intervals. Forexample, California black oakwoodland has a median interval ofeight years, and twice that interval(16years) falls between the minimum(two years) and maximum (18 years)fire return intervals. Areas that havemissed two or fewer median fire re-turn intervals are considered to bewithin their natural range of variabil-ity. For most vegetation types, a de-parture of three or more median re-turn intervals was outside of themaximum fire return interval for thetype. For example, the median firereturn interval for lodgepole pineforest is 102 years. If a lodgepolepine stand has a departure value ofthree, it means that the area has notburned for at least 306 years. Thislength of time is much greater than163 years, the recorded maximumreturn interval for the type. But in afew vegetation types, a return intervaldeparture of three is still within themaximum fire return interval for thetype. The red fir forest median re-turn interval is 30 years, and 90 yearswill have passed before areas havemissed three fire cycles. This value isless than the maximum return inter-val of 92 years.

Results of the analysis using themaximum fire return-interval depar-ture indicate that 95% of the parkand the administrative site hadmissed no more than two return in-tervals (Table 8). The remaining 5%was all in short fire return-intervaltypes containing ponderosa pine ordry montane meadows. The medianfire return-interval departure analysisis depicted in Figure 3. The analysisshows that 74% of the vegetation hasmissed no more than two return in-tervals and is considered to be in anacceptable ecological condition (thatis, exhibiting little to no deviationfrom a natural fire regime) as of 2000(Table 9). These areas are expectedto remain in an acceptable ecologicalcondition as long as the natural fireregime is maintained. Another 1% ofthe vegetation shows significant de-viation from natural conditions, and25% is considered highly compro-mised by past fire suppression. Mostof the deviation from natural condi-tions occurs in the lower-to-mid-ele-vation conifer forests, including thegiant sequoia groves. Despite ongo-ing reintroduction of fire to thegroves over the past 30 years, pro-gress has been slow—17% of thegroves still contain unnaturally highlevels of fuel. The analysis does showpositive effects from fire managementactivities because many areas are inan acceptable condition, but also un-derscores the fact that large areas re-quire attention.

Volume 19 • Number 1 2002 35

Number of Maximum ReturnIntervals MissedVegetation type

0-2 3-4 5+Total

----------------------Acres----------------------Whitebark pine–mtn.

hemlock forest87,582 0 0

87,582

Lodgepole pine forest 175,516 0 0 175,516Red fir forest 68,125 0 0 68,125Western white

pine–Jeffrey pineforest

132,708 0 0132,708

Montane chaparral 15,137 0 0 15,137Giant sequoia–mixed-

conifer forest182 36 0

218

White fir–mixed-coniferforest

46,871 0 046,871

Ponderosa pine–mixed-conifer forest

19,414 557 14,39934,370

Ponderosa pine–bearclover forest

20,013 1,174 12,65933,846

California black oakwoodland

1,143 2,013 03,156

Canyon live oak forest 21,473 0 0 21,473Dry montane meadow 545 27 958 1,530Foothill pine–live

oak–chaparral7,130 0 0

7,130

Foothill chaparral 1,785 0 0 1,785Blue oak woodland 473 0 0 473Total 598,097 3,807 28,016 629,920

The fire return-interval departureanalysis was used extensively in thedevelopment of a new fire manage-ment plan. Although the nature and

extent of the unnatural build-up offuels had long been recognized, themaps depicting the results of theanalysis reinforced this recognitionand communicated the extent andseverity of the problem. The results

36 The George Wright FORUM

of the analysis were an important toolin the development of the alterna-tives, because they identified the ar-eas in greatest need of treatment. Ar-eas that had missed numerous returnintervals, and thus were in greatestdanger of an undesired fire, were afocal point for analysis of environ-mental consequences.

Fire return-interval departures

were used extensively to compareenvironmental consequences of dif-ferent alternatives in the plan. Theanalysis of potential impacts onvegetation, wildlife habitat, water-sheds, soils, and water quality usedreturn-interval departures as a basisfor determining if areas were withinthe natural range of variability.

The impacts on the ecosystem

Number of Median ReturnIntervals MissedVegetation type

0-2 3-4 5+Total

----------------------Acres----------------------Whitebark pine–mtn.

hemlock forest87,582 0 0 87,582

Lodgepole pine forest 175,516 0 0 175,516Red fir forest 68,125 0 0 68,125Western white

pine–Jeffrey pine forest40,970 3,035 88,703 132,708

Montane chaparral 15,137 0 0 15,137Giant sequoia–mixed-

conifer forest182 0 36 218

White fir–mixed-coniferforest

23,871 374 22,626 46,871

Ponderosa pine–mixed-conifer forest

18,414 1,354 14,602 34,370

Ponderosa pine–bearclover forest

18,311 1,766 13,769 33,846

California black oakwoodland

921 210 2,025 3,156

Canyon live oak forest 10,729 623 10,121 21,473Dry montane meadow 251 101 1,178 1,530Foothill pine–live

oak–chaparral6,272 1 857 7,130

Foothill chaparral 1,785 0 0 1,785Blue oak woodland 338 21 114 473Total 468,404 7,485 154,031 629,920

Volume 19 • Number 1 2002 37

38 The George Wright FORUM

were examined by looking at thenumber of departures. Similarly,analysis of cultural concerns useddepartures to determine the poten-tial for damage by fire based onchanges in fuel loading.

For prescribed burning opera-tions, the fire return-interval depar-ture analysis will be used to prioritizeareas for treatment; i.e., those withthe highest departure values wouldbe burned first. In the wildland fire-use unit, the analysis would highlightareas where intensive monitoringmight be necessary because of un-naturally high fuel accumulations ordense stands. Similarly, the analysiswould aid fire suppression opera-tions by indicating where wildlandfires might be expected to be moreintense than under natural condi-tions, and would help set priorities

for fuel treatments in the wild-land–urban interface.

An effective fire management pro-gram requires spatial and non-spatialscientific data. Therefore, an analysisof these data is essential for long-range fire management planning.The fire return-interval analysis is anexcellent example of how scientificdata and analyses were used in thefire management plan, resulting in ascience-based plan. The analysis willcontinue to improve and evolve asother factors, such as slope, aspect,and elevation, are incorporated intothe model. Additionally, the com-pletion of a modern vegetation mapfor the park will better reflect currentvegetative conditions, and the analy-sis will be updated annually based onfuture fires.

Anderson, M.K. 1993. Indian fire-based management in the sequoia–mixed conifer forests of the centraland southern Sierra Nevada. Ph.D. dissertation, University of California–Berkeley.

Botti, S.J. 1990. Fire Management Plan, Yosemite National Park. El Portal, Calif.: National ParkService, Yosemite National Park.

Caprio, A.C., C. Conover, M.B. Keifer, and P. Lineback. 1997. Fire management and GIS: aframework for identifying and prioritizing fire planning needs. Presented at the 1997 ESRIInternational User Conference, 8-11 July, San Diego, California. Web site:http://www.esri.com/library/userconf/proc97/home.htm.

Caprio, A.C., and P. Lineback. 1997. Pre-twentieth century fire history of Sequoia and Kings CanyonNational Parks: a review and evaluation of our knowledge. N.p.

Caprio, A.C., and T.W. Swetnam. 1993. Fire history and fire climatology in the southern and centralSierra Nevada: progress report 1992/1993 to the National Park Service, Global Change Program,Southern and Central Sierra Nevada Biogeographical Area. Tucson, Ariz.: Laboratory of Tree-Ring Research, University of Arizona.

———. 1995. Historic fire regimes along an elevational gradient on the west slope of the Sierra Nevada,California. Pp. 173-179 in Proceedings of the Symposium on Fire in Wilderness and ParkManagement. J. K. Brown, R. W. Mutch, C. W, Spoon, and R. H. Wakimoto, tech. eds. GeneralTechnical Report INT-GTR 320. Ogden, Utah: U.S. Department of Agricuture–Forest Service.

ESRI [Environmental Systems Research Institute]. 1996. ArcView GIS. Redlands, Calif.:Environmental Systems Research Institute.

Volume 19 • Number 1 2002 39

Kiefer, M.B. 1991. Age structure and fire disturbance in southern Sierra Nevada subalpine forests. M.S.thesis, University of Arizona, Tucson.

Kilgore, B.M., and D. Taylor. 1979. Fire history of a sequoia–mixed conifer forest. Ecology 60, 129-142.

McClaran, M.P., and J.W. Bartolome. 1989. Fire-related recruitment in stagnant Quercus douglasiipopulations. Canadian Journal of Forest Research 19, 580-585.

Skinner, C.N., and C. Chang. 1996. Fire regimes, past and present. In Volume II, Chapter 38: SierraNevada Ecosystem Project: Final Report to Congress. Davis: University of California–Davis,Wildland Resources Center.

Stephens, S.L. 1997. Fire history of a mixed conifer–oak–pine forest in the foothills of the SierraNevada, El Dorado County, California. Pp. 191-198 in Proceedings of a Symposium on OakWoodlands: Ecology, Management, and Urban Interface Issues. N.K. Pillsbury, J. Verner, and W.D.Tieje, tech. coords. General Technical Report GTR-PSW-160. Albany, Calif.: U.S. Department ofAgricuture–Forest Service.

Swetnam, T.W., R. Touchan, C.H. Basian, A.C. Caprio, and P.M. Brown. 1991. Giant sequoia firehistory in the Mariposa Grove, Yosemite National Park. Pp. 249-258 in Yosemite CentennialSymposium Proceedings, Natural Areas and Yosemite: Prospects for the Future. San Francisco: TheYosemite Fund.

Taylor A.H., and C.N. Skinner. 1998. Fire history and landscape dynamics in a late-successionalreserve, Klamath Mountains, California, USA. Forest Ecology and Management 111, 285-301.

van Wagtendonk, J.W. 1986. The role of fire in the Yosemite Wilderness. Pp. 2-9 in Proceedings of theNational Wilderness Research Conference: Current Research. R.C. Lucas, comp. General TechnicalReport INT-212. Fort Collins, Colo.: U.S. Department of Agricuture–Forest Service.

———. 1991. GIS applications in fire management and research. Pp. 212-214 in Fire and theEnvironment: Ecological and Cultural Perspectives. S.C. Nodvin and T.A. Waldrop, eds. GeneralTechnical Report SE-69. Knoxville, Tenn.: U.S. Department of Agricuture–Forest Service.

———. 1994. Spatial patterns of lightning strikes and fires in Yosemite National Park. Proceedings of the12th Conference on Fire and Forest Meteorology 12, 223-231.

van Wagtendonk, J. W., J. M. Benedict, and W. M. Sydoriak. 1998. Fuel bed characteristics of SierraNevada conifers. Western Journal of Applied Forestry 13:3, 73-84.

Jan W. van Wagtendonk, U.S. Geological Survey Western EcologicalResearch Center, Yosemite Field Station, El Portal, California 95318;jan_van_Wagtendonk@usgs.gov

Kent A. van Wagtendonk, Yosemite National Park, El Portal, California95318; kent_van_wagtendonk@nps.gov

Joseph B. Meyer, Yosemite National Park, El Portal, California 95318;joe_meyer@nps.gov

Kara J. Paintner, Yosemite National Park, El Portal, California 95318;kara_paintner@nps.gov

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