More info for the terms: climax, competition, cover, crown fire, density, duff, extreme fire behavior, fire frequency, fire interval, fire regime, fire severity, forbs, frequency, fuel, fuel loading, fuel moisture, high-severity fire, ladder fuels, lichen, litter, low-severity fire, mean fire interval, mixed-severity fire, mixed-severity fire regime, natural, presence, serotinous, severity, shrub, shrubs, stand-replacement fire, stand-replacement fire regime, stand-replacing fire, succession, surface fire, tree
Fire adaptations: Rocky Mountain lodgepole pine thrives under the influence of fire [1], and on many sites fire is essential to Rocky Mountain lodgepole pine dominance [118,139,275]. In a Colorado study comparing subalpine forest stands of similar age (250 to 320 years), Rocky Mountain lodgepole pine regeneration was significantly greater (p<0.05) in areas that experienced surface fire than in areas where fire had not occurred. Rocky Mountain lodgepole pine comprised 41% of total species composition where surface fire was a factor, compared to 15% without fire [142].
Serotinous cones are an adaptation to stand-replacing fire [37,79,80], and the seed supply is nearly always available on the tree. No matter what season the fire occurs the seeds will reach the ground soon after, unless the cones burn [1]. Most Rocky Mountain lodgepole pine stands are composed of trees containing both serotinous and nonserotinous cones. The ratio of serotinous to nonserotinous cones seems to be related to the fire history of the site; for a full discussion of this topic, see Cone serotiny. Other characteristics that contribute to Rocky Mountain lodgepole pine success and site dominance following fire are early seed production, prolific seed production, high seed viability, high seedling survival, and rapid growth [79,80,118,139,275].
Fuels: The fuel accumulation in Rocky Mountain lodgepole pine stands varies, resulting in variable fire severity. Rocky Mountain lodgepole pine has short needles and does not produce a highly combustible litter layer [34,38], and changes in fuel loading over time are affected by decomposition of material killed but not consumed by the previous fire, the fall and decay of snags, stand development, and the effects of insects and diseases [118,275,301]. Insect infestations and disease, particularly lodgepole pine dwarf-mistletoe (Arceuthobium americanum), alter the quantity and spatial distribution of fuels in Rocky Mountain lodgepole pine stands [17,33,67,95,113,118,179,275], setting the stage for mixed-severity [95] or stand-replacing fires [17,33,79,80,113,118,179,275]. Fuel loads and fire hazard changes also vary according to the function of Rocky Mountain lodgepole pine in the stand: whether seral, persistent, or climax.
Seral and persistent: The propensity of Rocky Mountain lodgepole pine to exhibit high seedling density, initial rapid growth that slows with age, and high susceptibility to snow breakage, windthrow, lodgepole pine dwarf-mistletoe, and mountain pine beetles result in large fuel buildups [17,25,55,79,80]. Stand development, vegetation mortality, and fuel accumulation interact dynamically with fire in Rocky Mountain lodgepole pine forests. The type and degree of vegetation mortality affect the fuel buildup, which in turn determines the severity of later fires and subsequent stand regeneration. Historically, much of the surface fuel in Rocky Mountain lodgepole pine stands was probably generated following fire. Fuels increase when dense stands of seedlings occur and fire-killed trees eventually fall [79,80,118,275,301]. Dense stands of Rocky Mountain lodgepole pine result in competition for nutrients, water, and light, potentially killing weaker trees, naturally thinning the stand and reducing the presence of forbs and shrubs. This competition can result in further fuel buildup [79,80]. Density is also related to the distribution of fuel; in more open stands a higher proportion of fuel in larger size classes can be expected [190]. Dead stems fall within 20 years resulting in a dense network of woody fuels, while associated shade-tolerant trees often develop into significant ladder fuels [38,275]. Heavy loading of woody fuels increases the potential for severe fire behavior, although it may not directly affect ignition probability or fire spread [34,38,118,275]. In dense (5,600-10,400 stems/acre (14,000-26,000 stems/ha)) 47-year-old Rocky Mountain lodgepole pine stands of British Columbia, surface fuels were measured at 5-7 pounds/feet2 (24-34 kg/m2) of biomass, with 42 to 58% fallen dead woody material and 18 to 26% living lodgepole [73]. Moderately dense immature and mature stands of Rocky Mountain lodgepole pine have the lowest fire hazard [118,275], often due to the lack of understory vegetation and the self-pruning habit of Rocky Mountain lodgepole pine [275,292]. In an assessment of fires occurring in Yellowstone National Park from 1972 to 1988, Renkin and Despain [255] found that once a fuel moisture threshold is reached (13% fuel moisture in dead and down woody fuels >3 inches (7.6 cm) diameter), stand-replacing fire occurs more readily in later successional stages of mixed Rocky Mountain lodgepole pine, Engelmann spruce, and subalpine fir than in pure successional Rocky Mountain lodgepole pine and multiaged Rocky Mountain lodgepole pine types. Strong winds, however, are able to buffer or supersede the fuel moisture/forest type influence for short durations.
Postfire succession in Rocky Mountain lodgepole pine forests is accompanied by important changes in the flammability of the forest. The initial successional stages generally do not carry crown fire as readily as older stages [79,80]. In later stages, flammability increases due to the accumulation of surface fuels and fuel ladders resulting from downfall and the growth of small trees into the forest canopy [79,80,118,275,301]. In the early stages of Rocky Mountain lodgepole pine succession (1st 40 years), fuels consist mainly of forbs, grasses, and rotten logs. As time goes on, the number of rotten logs, tree seedlings, and saplings increases. Fires are moderately common at this stage [79,80]. On sites in northern Utah, Engelmann spruce and subalpine fir established under Rocky Mountain lodgepole pine within 20 years of stand-replacing fire; during this period the fuels configuration and arrangement were conducive to low-severity surface fire that would kill the young shade-tolerant tree species while causing little damage to the Rocky Mountain lodgepole pine overstory. A study in British Columbia found that though surface fire in Rocky Mountain lodgepole pine-dominated stands reduces surface fuels, new surface fuel complexes begin developing within the 1st year due to needle shed and understory development [208]. In the absence of surface fires, Engelmann spruce and subalpine fir provide vertical continuity into the Rocky Mountain lodgepole pine canopy after 40 years. Newly germinated seedlings provide the vertical fuel needed for crown fire in about 125 years [179]. Fuels at middle stages of stand development (40-150 years) are nearly all in the crowns of the dense Rocky Mountain lodgepole pine stand because the compact needle litter is difficult to burn, and fires are relatively rare. Mature Rocky Mountain lodgepole pine stands (150-300 years) retain the closed canopy but are usually less dense than the previous stage. Most of the dead trees have decomposed, understory species are more abundant, and shade tolerant tree saplings become more prominent. Fuels in this stage largely consist of herbaceous vegetation and low shrubs, though trees killed by bark beetles commonly fall and contribute to understory and ladder fuels. Old-growth Rocky Mountain lodgepole pine stands (300+ years) reflect the development of the climax forest as the pioneer Rocky Mountain lodgepole pine die. Fuels at this stage are conducive to burning, with young trees contributing to understory and ladder fuels. Lichen accumulations on older trees may contribute to fuel loading and flammability of the trees. The bulk of extreme fire behavior takes place at this stage of succession; these stands burn under normal moisture conditions, with torching common. If winds are present, crowning and spotting are nearly inevitable. Under dry conditions, local crowning and spotting is possible without wind; under wet conditions, fires smolder and persist for up to several weeks. Most fires occur during this stage [79,80].
Seral Rocky Mountain lodgepole pine occurs in a variety of forest types, and may indicate a recent history of severe or repeated burning [79,80]. In mixed conifer forests, Rocky Mountain lodgepole pine may be the only successful conifer regeneration in the early years following severe fire [112]. Generally, a fire return interval between 20 and 125 years yields a closed-successional sequence dominated by Rocky Mountain lodgepole pine. If the fire return interval exceeds 125 years, Rocky Mountain lodgepole pine is eventually replaced by climax species [31]. In grand fir forests, Rocky Mountain lodgepole pine is favored by severe fire at intervals less than 200 years, though if a 2nd fire occurs within 20 years of a stand-replacement fire, the Rocky Mountain lodgepole pine seed source may be eliminated [5]. Climax species in subalpine forests are not fire-tolerant, so stand-replacing fires are typical [7]. In subalpine forests, Rocky Mountain lodgepole pine may be the exclusive dominant 50 years after stand-replacing fire and replacement of this seral forest with climax species (subalpine fir, Engelmann spruce, mountain hemlock) may take up to 200 years [5,119]. Rocky Mountain lodgepole pine is likely to be the postfire dominant if it dominates prefire vegetation [57] and/or a seed source is present, indicating a previous fire in the last 2 centuries. If more than 200 years have passed since previous fire, short-lived Rocky Mountain lodgepole pine is likely to be gone from the site and not a constituent of seral vegetation [7].
Climax: In old stands there can be large fuel buildup due to overstory mortality and slow decay rates. Litter and duff are shallow; downed woody fuel loadings depend on the quantity of small branches from self-pruning, level of dwarf-mistletoe infestation, and extent of overstory mortality [4,275]. Grass and shrub fuels are too scattered to be effective fire carriers, and crown fuels may also be limited [4]. The most continuous fire vector is logs. Partially decayed logs from earlier disturbances carry most fires, and fire behavior is more a function of coarse woody debris than of fine-fuel dynamics [4,6]. Where fuels are light or discontinuous, rapid fire spread and uniform burning only occur during severe climatic conditions [4,275]. Fire hazard may be high, however, when areas of dense Rocky Mountain lodgepole pine have intermingled crowns and low branches reaching surface fuels. Lodgepole pine dwarf-mistletoe infestation increases the potential for torching and crowning, and heavy fuel loading associated with mountain pine beetle attack increases potential for severe fire. Moderate rates of lodgepole pine dwarf-mistletoe infection occur in climax Rocky Mountain lodgepole pine stands, locally increasing surface fuels and vertical fuel continuity [275]. For more information on the successional status of Rocky Mountain lodgepole pine and the effects of disturbance, see Successional Status.
Older Rocky Mountain lodgepole pine stands (100+ years) are best represented by model G in the National Fire-Danger Rating System, which addresses a dense conifer stand that has a heavy accumulation of litter and downed woody material. These stands are typically comprised of mature trees influenced by insect, disease, wind, or ice damage that create a heavy buildup of dead material on the forest floor. Young Rocky Mountain lodgepole pine stands (<100 years) are best represented by model H in the rating system, characterized by healthy stands with sparse undergrowth and a thin layer of ground fuels [292].
The following tables present some surface fuel characteristics in Rocky Mountain lodgepole pine-dominated forests in the northern Rockies:
Litter (tons/acre) 0-0.25" fuels (tons/acre) 0.25-1.0" fuels (tons/acre) 1-3" fuels (tons/acre) Location* mean median mean median mean median mean median 1 0.38 0.18 0.16 0.12 0.59 0.33 3.13 1.60 2 0.59 0.33 0.21 0.15 0.68 0.32 0.61 0 3 0.99 0.69 0.21 0.138 0.69 0.31 1.42 0 4 0.29 0.16 0.13 0.098 0.72 0.62 2.59 1.53 [87] *data are from several mature Rocky Mountain lodgepole pine stands in 4 different locations
Stand Age (yrs) Tons/acre (mean) 0-0.25" fuels 0.25-1.0" fuels 1-3" fuels 3-6" fuels 6-10" fuels 10-20" fuels 20+ " fuels Total 1 80 0.55 0.90 3.80 1.42 0.40 0 0 7.07 2 125 0.32 1.20 5.10 4.27 1.09 0 0 11.98 3 165 0.32 1.40 8.10 11.82 1.02 0 0 22.66 4 50 0.26 0.80 2.40 2.82 6.31 22.14 0 34.73 [118]
Fire behavior: Fires in Rocky Mountain lodgepole pine stands tend toward 1 of 2 extremes, with intensities ranging in excess of 5,000 kW/m to so low they cannot be measured with usual flame-length criteria [6]. Fires may be low-severity surface fire, consuming litter and duff, or high-severity, stand-replacing crown fires [5,6,118]. Low- to moderate-severity surface fire thins the understory and prepares a mineral seedbed [118]. Low-intensity fires occur due to sparse undergrowth and stand growth habit; cool, moist conditions prevail under a dense closed canopy, and fires usually remain on the surface [79,80]. If fuel and weather conditions are right, surface fires may torch some trees [208]. These frequent, low-severity fires may thin Rocky Mountain lodgepole pine stands without doing serious damage, though they may induce fungi or beetle activity [215]. Frequent fire may prevent successional establishment of more shade-tolerant species [118].
Severe fires are most likely to occur where dead fuels have accumulated. With concentrations of dead fuels, individual trees or groups of trees may torch, and fire can continue through the crowns aided by high winds [79,80,215]. The open, self-pruning crowns of Rocky Mountain lodgepole pine are less prone to crowning than species such as Engelmann spruce and subalpine fir [215]. The chance of crown fire occurring in Rocky Mountain lodgepole pine stands is governed by the amount of heat released from surface fuel, the height of tree crowns above the ground, and fire weather conditions [79,80,215]. Severe fires in Rocky Mountain lodgepole pine may burn extensive areas, and severity in part determines the potential fire behavior of future fires by influencing stand density and fuels potential [215]. In Yellowstone National Park, "intense" fire behavior in Rocky Mountain lodgepole pine occurs during extended periods of little or no rainfall. Fuel moistures drop and fires are ignited by lightning. Fire spread is mainly through the understory and from log to log, occasionally torching out individual trees with some short-range spotting. Fires ignited under these conditions may burn for months, but most acreage burned is during short-duration crown fire runs. "Extreme" fire behavior in the Park occurs when 1) a significant understory of ladder fuels is present; 2) 1,000 hour fuel moisture values drop below 10% (drought conditions); and 3) there are sustained high winds. Resultant fire behavior is an independent crown fire driven by high winds, with short-duration sustained runs of 10 miles per hour and long-range spotting. Extreme behavior is sustained until significant precipitation occurs, winds decline, and/or the fire reaches an area with lower fuel levels [292]. In a study of Rocky Mountain lodgepole pine/subalpine fir/Engelmann spruce forests of Alberta, weather was found to be a stronger influence on fire behavior than variations in fuels associated with stand age. Based on fire models, the relative importance of fuels diminishes during extreme weather conditions because all stands achieve the threshold required to permit crown fire development [70].
Two biotic factors that have great impact on the fire dynamics of Rocky Mountain lodgepole pine are lodgepole pine dwarf-mistletoe and mountain pine beetle. Lodgepole pine dwarf-mistletoe reduces tree vigor and may increase mortality, while the type of fire affects the potential for lodgepole pine dwarf-mistletoe infection [79,80,215]. A stand thinned by fire may become more susceptible to lodgepole pine dwarf-mistletoe [79,80]. Large accumulations of dead material caused by periodic beetle infestations result in "very hot" fires when they do occur [17,19]. Mountain pine beetle preference for large diameter trees dramatically increases fuel loading, and within 5 to 20 years the biomass arrangement shifts from a vertical to a horizontal distribution, creating a fuel bed conducive to fire spread [31]. These "hot" fires eliminate even tree species generally more resistant to fire damage than Rocky Mountain lodgepole pine (Douglas-fir); the shade-tolerant species are eliminated, returning the stand to pure Rocky Mountain lodgepole pine [17,19]. When beetles attack a stand they generally remove large trees with sufficiently thick phloem to support a brood of larvae. The following few years have a greater probability of high-severity fire because of increased fine fuels in the crown or on the forest floor. Then fire potential declines until the beetle-killed trees fall. These logs may then sustain slow-moving, smoldering fires which can scar trees or kill roots, creating stress on adjacent live trees and encouraging further insect or disease attack [5,6]. Fires in persistent or climax Rocky Mountain lodgepole pine forests are not likely to be as severe as those in seral forest where large beetle epidemics have occurred. Smaller, more continuous fuel deposits are available on the forest floor, though lighter fuel accumulations predominate due to lighter infestation levels. Mountain pine beetle kills only the larger trees in these multi-storied stands, resulting in a smaller proportion of trees killed than in even-aged seral stands. Lighter fuel accumulations result in fires that eliminate some trees but are not likely to cause total regeneration of the stand [17,113]. Low- to moderate-severity fires that open the stand and expose mineral soil seedbeds are more likely [113]. In the absence of fire, cyclical infestations of mountain pine beetle may remove Rocky Mountain lodgepole pine from the stand [17,19]. For additional information on the effects of dwarf mistletoe and mountain pine beetle in Rocky Mountain lodgepole pine forests, see Other Management Considerations.
Fire behavior fuel models can be used to predict surface fire behavior in Rocky Mountain lodgepole pine forests. The most representative for predicting fire behavior in Rocky Mountain lodgepole pine is model 8, closed timber litter. Model 10, timber litter and understory, best represents stands where there is significant down and dead Rocky Mountain lodgepole pine logs. Fire behavior fuel model 12, medium logging slash, has been used successfully to predict surface fire behavior in stands of lodgepole with 30 tons or more per acre down and dead material [292].
FIRE REGIMES: Natural fire frequency in Rocky Mountain lodgepole pine stands ranges from a few years to 200 years [118]. Fire intervals of 100 to 250 years are characteristic of Rocky Mountain lodgepole pine in the northern Rockies [53,56]; however, mean fire intervals may be as short as 20 to 50 years in small stands [33]. The mean fire interval in subalpine forests (Rocky Mountain lodgepole pine/subalpine fir/Engelmann spruce) of Alberta has been estimated at 90 years [70]. In a study of fire history in the northern Rockies, Arno [33] found fire in Rocky Mountain lodgepole pine was more frequent and less intense in areas having dry summers. Surface fires of low to medium intensity were common, especially on gentle slopes. Minimum fire-free intervals in Jasper National Park, Alberta were 1 to 16 years; maximum fire-free intervals ranged from 31 to 88 years. Less frequent, large stand-replacing fires were prevalent in areas having moist summers [33,38]. Fire intervals in Rocky Mountain lodgepole pine have changed over time; in a northern Utah study of the Rocky Mountain lodgepole pine cover type, mean fire interval during the presettlement period (1700-1855) was 39 years, with a range of 12 to 122 years. During the settlement period (1856-1909), the mean fire interval was 6 years (range 1-12 years) while no evidence was found for fires occurring in the post-settlement suppression period (1910-1988) [301]. A study in Jasper National Park examined 5 Rocky Mountain lodgepole pine forests and found mean fire return intervals of 12, 23, 25, 29, and 45 years, respectively [287]. Rocky Mountain lodgepole pine in a mixed-severity fire regime generally experiences fire every 25 to 75 years, while fires at longer intervals (100 to 300 years) and patchy burn pattern are typical of Rocky Mountain lodgepole pine in a stand-replacement fire regime [34,35,38].
Seral and persistent: Many Rocky Mountain lodgepole pine communities are subject to a mixed-severity fire regime, where a combination of low, moderate, and high severity fires occurs over space and time [4]. Fire scars in some Rocky Mountain lodgepole pine communities attest to a sequence of low severity surface fires [34,38]. In areas where Rocky Mountain lodgepole pine functions in both early and late seral roles (Colorado, Yellowstone National Park, south-central Oregon), Rocky Mountain lodgepole pine forests exhibit a moderate severity fire regime, tied closely with disturbance by insects and disease. In large patches, the average fire return interval is 60 to 80 years, though individual trees may reach 300+ years. In small patches, fire return intervals mimic those of surrounding forest types [6]. Mixed-severity FIRE REGIMES consist of a combination of understory and stand-replacement fires, and any given location within a mixed-fire regime could experience some stand-replacement fires, some nonlethal fires, and a number of mixed-severity fires. Fuels are variable and complex in this regime, with patches of postfire regeneration and uneven accumulations of woody fuels due to irregular occurrence of mortality factors (fire, insects, disease). Rocky Mountain lodgepole pine is subject to a mixed severity fire regime where fine surface fuels and dry climate facilitate lower intensity fires. Where an accumulation of down woody, ladder, and crown fuels occur, Rocky Mountain lodgepole pine stands with sufficient fuel are more likely to support stand-replacing surface or crown fire. Fuel loading is indirectly related to stand age in stand replacement regimes. Young dense stands containing ladder fuels of associated spruce and fir, and accumulated downfall from a former beetle-killed or fire-killed overstory have high potential to support a stand-replacement fire. Pole-size stands of Rocky Mountain lodgepole pine (with sparse lower limbs) arising after a burn that removed most large fuels, have low potential to support fire. As trees age, susceptibility to bark beetle attack and lodgepole pine dwarf-mistletoe damage increases, resulting in an accumulation of woody fuel that adds to the potential of stand-replacement fire [35]. High elevation sites (8,000 feet in Wyoming) support slow-growing subalpine Rocky Mountain lodgepole pine forests with sparse understories and less mountain pine beetle-created fuels; these stands may require up to 300 years to accumulate enough fuel to sustain a spreading fire, though the fires will likely be stand-replacing when they do occur [30,33,38]. In cool, high-elevation Rocky Mountain lodgepole pine forests, dead material decays slowly, encouraging accumulation [30,67].
Rocky Mountain lodgepole pine/subalpine fir sites in north-central Idaho average mixed severity underburns every 39 years. As these stands age, fire hazard decreases over time followed by an increase in stand flammability at later successional stages (150-300 years old) [51]. On sites in northern Idaho, Barrett and Arno [54] found stands of Rocky Mountain lodgepole pine and subalpine fir in a mixed-severity fire regime showed a mean return interval of 117 years for stand-replacing fire and a 43-year mean return interval for surface fire. In a broader study of sites in the northern Rockies, Rocky Mountain lodgepole pine/subalpine fir forests experienced stand replacing fires every 112 years (mean interval) and understory/mixed severity burns every 47 years (mean interval) [86]. A study in western larch-Rocky Mountain lodgepole pine forests of Glacier National Park showed sites with a relatively dry climate and gentle topography experienced a mixed-severity fire regime ranging from nonlethal underburns to stand-replacing fires at mean intervals ranging from 25 to 75 years, depending on the site. Steeper, wetter sites experienced a regime of infrequent stand-replacing fires at mean intervals ranging from 140 to 340 years, depending on the site [55]. Less frequent (100+ years) but more severe fires result in dense, even-aged stands of Rocky Mountain lodgepole pine, often in higher elevation forests. Where more frequent (25-50+ years), creeping surface fires predominate (lower elevations of the subalpine zone) Rocky Mountain lodgepole pine stands are often 2- or 3-aged [156]. Barrett [52] found that low elevation Rocky Mountain lodgepole pine sites (<5,900 feet (1,800 m)) in Yellowstone National Park experienced short to moderate fire-return intervals (25-150 years) with fires burning in a mixed severity pattern. Higher elevation (>6,900 feet (2,100 m)) sites were subject to stand-replacing fires at long fire intervals (300-400 years) [52]. On relatively moist north slopes of the Yellowstone Plateau (6,500-10,800 feet (2,000-3,300 m)), stand-replacing fires occur at mean intervals of 200 years [52,53]. Drier south slopes experience a shorter interval between stand-replacing fires (178-year mean interval), with evidence of some partial replacement fires that triggered new seral age classes 20 to 80 years after stand initiation [53].
Climax: Climax Rocky Mountain lodgepole pine forests also have a mixed-severity fire regime, which in combination with insects and disease create multi-aged stands [4,5]. Fire return intervals in this fire regime range from 40-60 years in south-central Oregon (the most concentrated area of climax Rocky Mountain lodgepole pine forest) [5]. Young stands of Rocky Mountain lodgepole pine in these communities are open with occasional dense patches [113]. Mature forest structure develops in relation to disturbance history and site conditions [275]. Low-severity fires maintain a mosaic of open canopy lodgepole in different size and age classes, though stand-replacement fires are possible during droughts with high winds. Patchy or low-severity fire thins the stand and exposes a seedbed for regeneration, favoring Rocky Mountain lodgepole pine regeneration from open cones [113,275]. Severe fires in climax stands reinitiate the Rocky Mountain lodgepole pine forest [113]. Climax Rocky Mountain lodgepole pine stands are generally small and isolated, and may be strongly affected by changes in the fire regime of neighboring stands [275].
FIRE REGIMES for plant communities and ecosystems in which Rocky Mountain lodgepole pine occurs are summarized below. For further information regarding FIRE REGIMES and fire ecology of communities and ecosystems where Rocky Mountain lodgepole pine is found, see the 'Fire Ecology and Adaptations' section of the FEIS species summary for the plant community or ecosystem dominants listed below.
Community or Ecosystem Dominant Species Fire Return Interval Range (years) grand fir Abies grandis 35-200 [35] sagebrush steppe Artemisia tridentata/Pseudoroegneria spicata 20-70 [239] basin big sagebrush A. tridentata var. tridentata 12-43 [261] mountain big sagebrush A. tridentata var. vaseyana 15-40 [36,91,222] western larch Larix occidentalis 25-100 Engelmann spruce-subalpine fir Picea engelmannii-Abies lasiocarpa 35 to > 200 [35] black spruce P. mariana 35-200 [129] blue spruce* P. pungens 35-200 [35] whitebark pine* Pinus albicaulis 50-200 [5,32] jack pine P. banksiana <35 to 200 [129] Rocky Mountain lodgepole pine* P. contorta var. latifolia 25-340 [33,35,51,53,55,86,259,287,301] western white pine* P. monticola 50-200 [35] interior ponderosa pine* P. ponderosa var. scopulorum 2-30 [35,44,207] quaking aspen (west of the Great Plains) Populus tremuloides 7-120 [35,147,221] mountain grasslands Pseudoroegneria spicata 3-40 (10**) [33,35] Rocky Mountain Douglas-fir* Pseudotsuga menziesii var. glauca 25-100 [35,36,39] western redcedar-western hemlock Thuja plicata-Tsuga heterophylla > 200 western hemlock-Sitka spruce T. heterophylla-Picea sitchensis > 200 mountain hemlock* T. mertensiana 35 to > 200 [35] *fire return interval varies widely; trends in variation are noted in the species summary
**mean
