Rocky Mountain lodgepole pine is moderately fire resistant in open stands due to light fuel characteristics and an open canopy [57,113].
Non-drought stressed Rocky Mountain lodgepole pine can transport substantial amounts of water to heated, foliated branches. This mechanism slows the rate of drying for branches subject to intense heat, therefore influencing crown ignition susceptibility and fire behavior [102].
Tree characteristics: Rocky Mountain lodgepole pine grows 45 to 150 feet (13-45 m) tall [17,140,180,200,217,219], with diameters exceeding 30 inches (76 cm) [140,180,219]. Rocky Mountain lodgepole pine often grows tall without reaching large diameters [309]; in Utah, trees only 5 inches (13 cm) in diameter at base are often 50 feet (15 m) tall [180]. Rocky Mountain lodgepole pine grows rapidly where competition is limited, reaching 79 feet (24 m) tall and 16 inches (41 cm) in diameter in 50 to 60 years [17]. The average lifespan of Rocky Mountain lodgepole pine is 150 to 200 years [37,170], though some Rocky Mountain lodgepole pine trees live more than 400 years [51,123,170,219,299].
Rocky Mountain lodgepole pine trees develop thin, narrow crowns [37,113,180,217] with a moderately low and open branch habit [4]. Lower branches self-prune in dense stands [113,217]; however, dead branches may persist on trees for several years [217]. Rocky Mountain lodgepole pine has 2 needles per fascicle (or rarely, 3) [180,217,305], with 2-inch (5 cm) long, moderately wide needles [37,180,309]. Rocky Mountain lodgepole pine bark is generally described as thin, scaly, and approximately 0.25 inch (0.6 cm) thick [4,37,113,217,309]. However, data collected on bark thickness at 7 locations in the Northern Rocky Moutnains show a range of approximately 0.05 to 1.2 inches (0.1-3.0 cm). Data are means [231].
Elevation Bark thickness Maximum bark thickness Minimum bark thickness 2,500-3,600 ft. (800-2,000 m) 0.61 in. (1.55 cm) 1.17 in. (2.98 cm) 0.20 in. (0.52 cm) 3,800-5,000 ft. (1,200-1,500 m) 0.29 in. (0.74 cm) 0.61 in. (1.56 cm) 0.06 in. (0.16 cm) 5,000-7,000 ft. (1,200-2,100 m) 0.19 in. (0.47 cm) 0.46 in. (1.16 cm) 0.04 in. (0.11 cm) >7,000 ft. (2,100 m) 0.13 in. (0.32 cm) 0.31 in. (0.79 cm) 0.04 in. (0.10 cm)The generally deep [4] root system of Rocky Mountain lodgepole pine is variable in form, depending primarily on soil type. A taproot is common, but so is profuse development of vertical sinkers from lateral roots [195,216,217]. The taproot is dominant during seedling and sapling development, but gradually becomes less important as trees mature and develop lateral root systems. Sinker roots develop near the base of the laterals and provide the major support thereafter [195,245]. Rooting depth of Rocky Mountain lodgepole pine is approximately 11 feet (3.3 m) [94]. Rocky Mountain lodgepole pine may develop adventitious roots in response partial stem burial from flooding or other disturbance [3]. Rocky Mountain lodgepole pine produces relatively few fine roots and relies heavily on mycorrhizal association for nutrient uptake [309]. Ectomycorrhizae enhance survivability of Rocky Mountain lodgepole pine seedlings, increasing primary needles and root:shoot ratios [223].
Rocky Mountain lodgepole pine cones are hard and heavy, and may be reflexed, projecting, or semi-erect on branches. Semi-erect cones are most common in regions removed from the present zones of natural hybridization with jack pine, and may indicate intergrading with jack pine in the past [115,309]. Rocky Mountain lodgepole pine staminate cones are 0.3 to 0.4 inch (8-10 mm) long and ovulate cones are 1.2 to 2.4 inch (3-6 cm) long, ovoid, and slightly lopsided [117]. Cone size, shape, and serotiny are variable within and among Rocky Mountain lodgepole pine populations [309]. Rocky Mountain lodgepole pine seeds are 0.15 to 0.2 inch (4-5 mm) long with wings 0.3 to 0.6 inch (8-16 mm) long [117].
Stand characteristics and variation: Rocky Mountain lodgepole pine occurs as an even-aged, single-storied and sometimes overly dense forest where favorable fire, seed, and climatic conditions once combined to produce a large number of seedlings at one time. Elsewhere it grows as multiaged, multistoried stands [12,14]. Spacing of multiaged stands ranges from dense to open [14,46,122]. Multistoried stands generally originate from either scattered trees that produced seed for subsequent stand development, or the gradual deterioration of old-growth stands resulting from wind, insects, and diseases [14]. Fire is also responsible for stand structure; Muir [228] found that within-stand age variability in tree ages was greatest after nonfire disturbances and lowest after stand-replacing fires. In extremely dense stands, Rocky Mountain lodgepole pine develops a whiplike form with little stem taper and only a sparse tuft of foliage in the upper crown. Rocky Mountain lodgepole pine in moderately dense stands also has little taper, but relatively longer, narrow crowns. Open-grown trees have considerable taper, large branches and fully foliaged, conical crowns [245]. Densely stocked stands exhibit less branch development and greater height growth relative to diameter than open stands [190]. Rocky Mountain lodgepole pine stand characteristics by density from 70-year-old stands in Alberta are presented below [190]:
Number of stems per acre Basal area per acre (ft 2) Crown closure (%) Stand Density Plot # Live stems Standing snags Total stems Live stems Snags Total Sparse 1 250 20 270 68 5 73 34 2 310 0 310 60 0 60 33 3 230 20 250 52 9 61 40 4 350 50 400 75 9 84 43 5 240 0 240 79 0 79 54 Moderate 6 490 50 540 93 6 99 45 7 870 160 1030 151 12 163 58 8 470 90 560 91 9 100 42 9 490 90 580 106 11 117 43 10 680 60 740 137 5 142 56 Dense 11 750 260 1010 129 20 149 51 12 1240 240 1480 163 16 179 63 13 940 440 1380 136 30 166 49 14 790 260 1050 140 21 161 65 15 880 540 1420 143 31 174 50Due to the widespread distribution of Rocky Mountain lodgepole pine, developmental differences may exist according to geographic areas. Local variations in Rocky Mountain lodgepole pine characteristics include 1) a high frequency of 3-needled fascicles in the Yukon Territory, and 2) a variable occurrence of thick bark, repeated stem forking, unusually fast juvenile growth, low incidence of serotinous cones, and high incidence of semi-erect cones in southern British Columbia [115,216,309]. On planting sites in Montana, Cole [105] found differences in height, diameter, and crown width of 12-year-old trees from British Columbia, Idaho, Montana, Utah, and Washington. Rocky Mountain lodgepole pine from Idaho exhibited greater growth in all 3 parameters, while individuals from Utah had the least growth. However, few differences between Rocky Mountain lodgepole pine origins were statistically significant [105]. A provenance study conducted in British Columbia found increased winter hardiness and tolerance of snow damage was associated with decreased growth potential from south to north and east to west, and from low to high elevation [314].
Botanical characteristics of Rocky Mountain lodgepole pine may also vary based on different successional populations. In a study of seedlings grown under the same field conditions from seral, persistent, and climax source populations, seral population seedlings had the smallest total leaf area, photosynthetic potential, degree of root system subdivision, and total root length. Seedlings from the climax population had the greatest total leaf area, photosynthetic potential, root density, and root length. Seedlings from the persistent population reached the greatest heights but had reduced lateral root densities and total root lengths [81]. For further information on successional roles of Rocky Mountain lodgepole pine, see Successional Status.
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 locationsFire 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. Find further fire regime information for the plant communities in which this taxon may occur by entering "Rocky Mountain lodgepole pine" in the FEIS home page under "Find FIRE REGIMES".
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 summaryIndividual fire killed or injured Rocky Mountain lodgepole pine are susceptible to insect attack [23,275]. Two years after the Yellowstone fires of 1988, 44% of Rocky Mountain lodgepole pine in 1 study was infested by pine engraver beetles; 95% of the infested trees had been scorched by fire. The rate of infestation increased with the percent of basal circumference girdled by fire [23]. Antiaggregative pheromones may help protect these heat injured trees by reducing attack and gallery densities, rendering attacks "unsuccessful" [24]. Though mountain pine beetles are not especially attracted to fire-injured trees until the trees are weakened by decay [275], fire exclusion renders old-growth Rocky Mountain lodgepole pine stands more susceptible to attack due to the predominance of older, larger trees [14].
Fire exclusion also encourages dwarf-mistletoe infestation, which in turn decreases stand vigor and increases fuel generation rates, increasing stand vulnerability to severe fire damage [32,191]. Prescribed fire may eliminate infected residual trees in harvested areas and remove heavily infected stands on unproductive sites so they can be replaced by young, healthy stands [79,80,232,316]. However, if infected trees do remain on the site they can quickly spread the parasite to Rocky Mountain lodgepole pines in the developing understory [79,80]. If prescribed fire is used to reduce dwarf-mistletoe in Rocky Mountain lodgepole pine forests, stand-replacing fires are required in order to remove the infected trees [191,316]. Survival of infected trees results in increased dwarf mistletoe infection rates in the postfire stands [191]. Fire Case Study 3 provides an example of using prescribed fire to treat lodgepole pine dwarf-mistletoe infestation.
Fire exclusion encourages the establishment of shade-tolerant species in Rocky Mountain lodgepole pine forests, which may increase the risk of severe fires due to the low branches and thin bark [301]. Prescribed burning may be used to regenerate Rocky Mountain lodgepole pine in stagnating stands, opening the stand and encouraging seedlings [275]. Opportunities to use understory burning in climax Rocky Mountain lodgepole pine stands are limited because Rocky Mountain lodgepole pine is susceptible to fire-kill; when fuels are moist enough to protect mature trees, surface fires burn patchily or are difficult to sustain unless conducted in late fall after a killing frost has dried fine fuels [118,189,275]. Keane and Arno [189] provide details for using late-season prescribed fire favoring Rocky Mountain lodgepole pine and whitebark pine. In addition, climax Rocky Mountain lodgepole pine forests often contain little surface fuel, so fires move slowly and consume little but logs [4].
The primary use of prescribed fire in Rocky Mountain lodgepole pine has been hazard reduction and site preparation in conjunction with tree harvesting and subsequent regeneration. Broadcast burning and pile and windrow burning have been the most often used methods of accomplishing these tasks [79,80,118,275]. Where broadcast burning has been used in slash treatment, postfire regeneration of Rocky Mountain lodgepole pine depends on seed remaining on site or on the proximity of seed sources [156]. On sites in central Montana, broadcast burning slash following clearcutting resulted in the destruction of seed present on site (in cones and litter) and a reduction in seedling establishment relative to mechanical treatment of logging slash [76]. Burning of the seedbed following harvest resulted in uniformly low Rocky Mountain lodgepole pine stocking [77]. On sites in central Idaho where Rocky Mountain lodgepole pine is largely nonserotinous, more seedlings established on sites subject to light scarification than on sites that were broadcast burned [144]. However, broadcast burning or piling and burning logging residue following clearcut harvest in Rocky Mountain lodgepole pine stands reduces fuel loads and fire potential [85], and releases nutrients more rapidly for use by tree seedlings [121]. On sites in British Columbia, Haeussler and others [149] found Rocky Mountain lodgepole pine growth was enhanced by site preparation treatment severity. Even low-severity mechanical treatment resulted in greater stem volume than no treatment, and Rocky Mountain lodgepole pine on sites where slash was windrowed and burned experienced the highest growth rates [149]. Two years after harvest in Wyoming, growth and survival of Rocky Mountain lodgepole pine seedlings was greater on sites where harvest residue was piled and burned or broadcast burned than on sites where residue was spread or removed [213]. Another study in Wyoming found Rocky Mountain lodgepole pine planted after clearcutting exhibited greater height growth and survival (90% compared to 50-60%) on scarified and broadcast burned sites than on sites where residue was chipped and spread or removed [266]. An evaluation of harvest residue treatments in Washington found that 5 years after treatment, height growth of Rocky Mountain lodgepole pine on sites broadcast burned in the spring substantially exceeded height growth for other treatments. Treatments also included piling and burning, pulling unmerchantable material, chopping residue, fall broadcast burning, clearing, and no treatment. No treatment of residue resulted in higher survival and growth of seedlings than mechanical treatments [315]. Lopushinsky and others [212] found that height growth of Rocky Mountain lodgepole pine seedlings 2 years after planting was greater on sites where harvest residue was piled and burned or broadcast burned than on sites where residue was left in place or removed. In contrast, a study conducted in northwest Montana found that Rocky Mountain lodgepole pine regeneration density was 89% less on sites where slash was piled and burned than on unburned sites. Growth of trees on burned sites was approximately 20% of growth on unburned sites [298].
Muir [228] found that relative density of Rocky Mountain lodgepole pine was higher following fire than following clearcutting, reflecting the abundant release of seeds from serotinous cones. Some seed is released from serotinous cones when harvest slash is piled and burned; however, many seeds are destroyed in the intense heat and are not well scattered across the area [228]. Habitat type may be important in Rocky Mountain lodgepole pine establishment after prescribed fire or mechanical treatment, based on competition and the relative presence of Rocky Mountain lodgepole pine in the pretreatment stand [79,80]. The following table offers estimates of Rocky Mountain lodgepole pine seed:seedling ratios for different site conditions in southwestern Montana [217]:
Representative habitat site conditions Site preparation None or slight Broadcast burning Bulldozer scarification Cool, moist, low to moderate competition 1,000:1 1,000:1 300:1 Moderate moisture and temperature, heavy competition 10,000:1 3,000:1 300:1 Cool and droughty 10,000:1 3,000:1 1,000:1 Hot and droughty w/out excessive competition 2,500:1 3,000:1 10,000:1 Hot and droughty w/ heavy competition 15,000:1 4,000:1 10,000:1Elevation and topography: Rocky Mountain lodgepole pine grows in a wide range of ecological conditions; from low to high elevations, dry to wet conditions, warm to cold temperatures, and on nearly every soil condition found in western North America [13,264]. Rocky Mountain lodgepole pine grows from 1,500 to 11,500 feet (450-3,500 m) in elevation. Rocky Mountain lodgepole pine stands are found throughout most of the northern Rockies at middle elevations (4,400-7,800 feet or 1,350-2,399 m) and are especially well developed on the broad ridges and high valleys near and east of the Continental Divide [33,86]. The elevational occurrence of Rocky Mountain lodgepole pine in the Rocky Mountains increases from north to south [285,288]. Rocky Mountain lodgepole pine is limited by a lack of water at lower elevations and short growing seasons at higher elevations [57,285]. The following table presents elevation ranges for Rocky Mountain lodgepole pine in different parts of its geographic distribution:
Rocky Mountain lodgepole pine grows well on gentle slopes and in basins [42,79,216], but good stands are also found on rough and rocky terrain and on steep slopes and ridges, including bare gravel [49,86,216]. Rocky Mountain lodgepole pine is found on all aspects [49,54,57,86,216,304], though it may be more abundant and robust on south and west aspects in the northern Rockies [12]. In a British Columbia field experiment evaluating planting position in a berm/trench system, Rocky Mountain lodgepole pine seedlings had the greatest increase in stem volume when planted on the east, south, or west berm position. However, seedlings in these positions also suffered the highest mortality, while seedlings planted on cool, north-facing microsites experienced reduced growth rates [92]. In Washington and Oregon, Rocky Mountain lodgepole pine is found primarily on dry eastern slopes [309].
Climate: Rocky Mountain lodgepole pine is found on dry to intermediate sites with a wide seasonal range of temperatures and occasionally long precipitation-free periods in summer [54,57]. Snowfall is heavy and supplies the major portion of soil water used for growth in early summer; winter temperatures are cold; summer has relatively low rainfall; and in many areas there is no true frost-free season, with summer temperatures falling below freezing at regular intervals [12,217]. Rocky Mountain lodgepole pine can withstand temperatures as low as 15 degrees Fahrenheit (-9 oC) when shoots are actively growing [37]. Rocky Mountain lodgepole pine can survive in areas receiving only 10 inches (250 mm) of precipitation, but generally grows where precipitation is 18+ inches (460 mm) [216,219]. Vigorous stands occur where the precipitation exceeds 21 inches (530 mm) [12,219]. The following table gives approximate total and growing season precipitation and July mean temperatures for some areas in the range of Rocky Mountain lodgepole pine [217]:
Total precipitation June, July, August precipitation Average July low Average July high Elevation inches (mm) oFahrenheit (oC) feet (m) n ID & ne WA 39 (1,000) 5 (13) 39 (4) 70 (21) 5,000 (1,500) sw MT 24 (600) 7 (19) 39 (4) 75 (24) 7,000 (2,100) e-c ID 20 (500) 4 (11) 39 (4) 81 (27) 6,000 (1,800) w-c ID 33 (850) 3 (8) 39 (4) 81 (27) 6,000 (1,800) w WY 26 (650) 5 (13) 30 (-1) 65 (18) 9,000 (2,700) w CO 30 (750) 8 (20) 39 (4) 70 (21) 10,000 (3,000) e CO 20 (500) 8 (20) 39 (4) 65 (18) 10,500 (3,200)Soils: Soils where Rocky Mountain lodgepole pine grows are often young with a poorly developed or shallow profile [12,57,113], though Rocky Mountain lodgepole pine grows best on deep, well developed soils [180]. Rocky Mountain lodgepole pine is found on coarse alluvial soils [2,12,79] derived from rhyolite, sandstone, shale, or granite [79,122,217,285,304]. A central Montana study found Rocky Mountain lodgepole pine occurrence much greater on granitic soils than on limestone soils [145]. Soils ranging from moist to well drained will support Rocky Mountain lodgepole pine stands [2,57,113,168,216,217,285], as well as sites where other conifers may be inhibited by water or nutrient stress [79]. The development of Rocky Mountain lodgepole pine root systems varies with soil and stand conditions. On deep, well-drained soils, trees have a better root system and are more stable than on shallow, fine-textured or poorly-drained soils [9,14]. Shallow, poorly-drained soils result in the development of a shallow rooting system [37,216]. Where trees develop a shallow root system, Rocky Mountain lodgepole pine is susceptible to windfall. Windfirmness varies with stand density, soil conditions, and topography [216]. Soil conditions being equal, individual stems in dense stands are less windfirm, because trees that have developed together in dense stands over long periods of time mutually protect and support each other and do not have the roots, boles, and crowns to withstand exposure to the wind when opened up drastically [14,132]. Rocky Mountain lodgepole pine is tolerant of flooding and shallow water tables [60,101,199,217,299]; however, productivity is restricted in some soils by barriers to root proliferation, such as restrictive layers or high water tables [101]. Flood tolerance is likely due to the production of large, gas-filled cavities in inundated roots and the ability to actively transport oxygen to submerged root tips in these cavities [60].
Rocky Mountain lodgepole pine grows well on nutrient-poor soils [307], though increased nutrient availability can increase productivity [101]. Rocky Mountain lodgepole pine is often found on sites low in available nitrogen [159,249], and nitrogen deficiencies arise in Rocky Mountain lodgepole pine ecosystems due to slow litter decay rates coupled with high nitrogen immobilization [159]. Rocky Mountain lodgepole pine may not grow well on soils high in calcium or magnesium [199,216], though extensive stands are found on calcareous soils in Canada [216]. Rocky Mountain lodgepole pine tolerates a wide range of pH in soils, though pH exceeding 8.0 may exclude Rocky Mountain lodgepole pine [195]. Some physical and chemical characteristics of soils in 6 Wyoming Rocky Mountain lodgepole pine stands are presented below [135]:
Depth % by volume Bulk density (g/cm2) pH mg/g dry mass Stones Gravel Clay (<2 mm) Ca Mg K Na Fe Mn Stand 1 root zone 19.7 31.7 15.4 1.40 5.56 0.91 0.100 0.130 0.008 0.06 0.08 subsoil 18.0 47.1 15.9 1.70 5.59 0.73 0.150 0.040 0.006 0.01 0.01 Stand 2 root zone 18.8 19.0 23.9 1.22 5.20 1.53 0.240 0.100 0.009 0.02 0.16 subsoil 18.1 54.0 21.1 1.44 4.88 1.20 0.260 0.035 0.003 0.01 0.01 Stand 3 root zone 0.3 55.6 12.6 1.33 5.40 0.82 0.098 0.070 0.006 0.023 0.017 subsoil 0 72.4 8.4 2.40 5.61 1.15 0.183 0.056 0.005 0.006 0.009 Stand 4 root zone 5.5 63.0 12.0 1.43 5.55 1.33 0.145 0.126 0.010 0.030 0.047 subsoil 6.6 41.0 11.5 1.74 5.65 2.75 0.431 0.089 0.010 0.012 0.003 Stand 5 root zone -- -- -- -- 5.67 0.72 0.110 0.124 0.010 0.054 0.058 subsoil -- -- -- -- 6.06 1.25 0.202 0.021 0.008 0.008 0.005 Stand 6 root zone 4.4 1.9 39.3 0.91 -- -- -- -- -- -- -- subsoil 19.3 24.1 27.7 1.35 -- -- -- -- -- -- --Tolerances: Rocky Mountain lodgepole pine grows best on noncalcareous soil [2,113] and is intolerant of saline soils [303]. It is also adversely affected by high concentrations of zinc, copper, cadmium, and mercury [177]. Rocky Mountain lodgepole pine is shade intolerant [14,17,26,93,97,115,140,199,216,217,264,309], and though some seedlings may establish under a forest canopy, they seldom grow to maturity unless released [217,264]. In a study of Washington sites following fire, Rocky Mountain lodgepole pine regeneration was greater than Douglas-fir regeneration where residual density of the stand was lowest and where high proportions of Rocky Mountain lodgepole pine existed in the prefire stand. In high residual-density stands, the proportion of Douglas-fir regeneration increased. Occurrence and growth of Rocky Mountain lodgepole pine regeneration increased with fire intensity (decreased residual density) and distance from residual tree cover, while Douglas-fir regeneration on the same sites was more tolerant of residual tree cover [137].
Rocky Mountain lodgepole pine has moderate drought tolerance [93] and moderate to high frost tolerance [199,216]. Low air temperatures and cold air ponding also influence distribution of Rocky Mountain lodgepole pine; its relative tolerance of lower night temperatures during seedling emergence allows establishment in frost pocket areas where other species (e.g. ponderosa pine, Douglas-fir) may be eliminated [216,299]. Rocky Mountain lodgepole pine is, however, susceptible to winter drying damage with foliage damage ranging from light to severe, potentially resulting in tree mortality. Reductions in height growth and terminal bud length are proportional to the amount of damage, which may reach 80% of foliage in young trees [64]. Winter burn, or "red belt", is caused by the alternate chilling and warming of needles in air of low moisture content when warm air results in transpiration before trees are able to translocate water from the roots to the needles, resulting in needle desiccation [263].
Mule deer, moose, and elk may browse Rocky Mountain lodgepole pine, generally when other food is scarce [14,202,256]. Small mammals including snowshoe hares, pocket gophers, voles, and squirrels feed on the cambium of Rocky Mountain lodgepole pine [9,50,62,75,195,282,283], as do porcupines and black bears [14,37,75,283].
Rocky Mountain lodgepole pine seeds are an important food source for red crossbills year-round [65]. Blue grouse and spruce grouse also eat seeds as well as needles of Rocky Mountain lodgepole pine [114,241]. In late summer and fall, seeds are important for small mammals [1,195,217], especially red squirrels, which are Rocky Mountain lodgepole pine's most significant seed predator [65,206,216,217]. Harvest of Rocky Mountain lodgepole pine seeds can prove difficult for red squirrels, however, due to cone density and overdeveloped scales on the exposed sides of the cones [206].
Rocky Mountain lodgepole pine forests provide summer range for big game animals [75] and habitat for a variety of nongame birds [42]. Downed Rocky Mountain lodgepole pine provides drumming sites for ruffed grouse [74].
In Washington, densely stocked Rocky Mountain lodgepole pine stands are preferred foraging habitat for Canada lynx due to abundant populations of snowshoe hares [90,196]. Mountain pine beetle larvae harbored by Rocky Mountain lodgepole pine are an important food source for woodpeckers [88].
Palatability/nutritional value: The palatability of Rocky Mountain lodgepole pine has been rated as poor [125].
The nutritional composition of Rocky Mountain lodgepole pine needles (% dry weight) from 2 sites in Canada is presented below:
Location Lignin Protein Ether extract N-free extract Crude fiber Total mineral Ca P Mg K Na Reference BC -- 6.90 8.47 57.23 24.98 2.42 -- -- -- -- -- [111] AB 26 8.2 -- -- 42 -- 0.14 0.12 0.11 0.52 0.22 [241]The following table presents Rocky Mountain lodgepole pine nutrient content from 2 experimental forests in Montana (data are in mean micrograms/gram - ovendried) [276]:
Ca Cu Fe K Mg Mn N Na P Zn Lubrecht Experimental Forest green needles 3,220 6.2 126 4,442 1,015 757 9,195 42 1,363 37.2 twigs (0-0.64 cm) 4,082 7.2 248 2,238 997 252 4,151 39 790 28.6 twigs (0.64-2.5 cm) 3,670 5.3 148 1,004 642 222 1,969 33 321 22.9 Coram Experimental Forest green needles 3,259 7.8 105 4,123 1,067 768 10,773 103 343 52 twigs (0-0.64 cm) 3,828 6.7 315 2,756 970 423 4,066 108 178 49 twigs (0.64-2.5 cm) 3,762 4.1 181 1,220 652 275 2,408 90 93 29 branches (1.3-1.9 cm) 4,264 6.1 141 889 514 429 1,988 164 79 46 branches (1.9-2.5 cm) 3,398 5.3 76 920 528 273 1,680 87 73 27.6 branches (2.5-5 cm) 2,758 3.4 37 702 476 135 1,414 72 146 16.5 branches (5-7.6 cm) 2,460 5.3 22 456 439 105 1,288 71 128 10.9Cover value: Rocky Mountain lodgepole pine stands provide cover for big game animals, upland game birds, small nongame birds, and small mammals [125,173,275]. Cover value for big game animals changes over time, reflecting the growth and structural development of Rocky Mountain lodgepole pine stands [217]. Rocky Mountain lodgepole pine is used for roosting cover by ruffed grouse [172] and provides nesting sites for a variety of birds including the northern goshawk [237].
Rocky Mountain lodgepole pine occurs in 3 different ecological roles: 1) as a seral species to
more shade tolerant tree species; 2) as a relatively stable codominant with 1
or more other species (persistent); and 3) as the only tree layer dominant
(persistent or climax) [299].
For more information on succession in Rocky Mountain lodgepole pine communities,
see Successional Status.
Rocky Mountain lodgepole pine grows with nearly all of the other mountain conifers
in its range and often forms dense, nearly pure stands [26,37]. Pure Rocky Mountain lodgepole pine stands frequently
result after repeated fires and where there is no seed source for other species [2,14,54]. In pure stands of
Rocky Mountain lodgepole pine, there
is seldom an understory of reproduction, though in low-density stands there may
be younger trees in the understory [14]. Mixed stands of Rocky Mountain
lodgepole pine and other species are also common,
especially stands of Rocky Mountain lodgepole pine, Engelmann spruce (Picea engelmannii), and subalpine fir
(Abies lasiocarpa) at higher elevations [2,14,54], and stands of Rocky
Mountain lodgepole pine and Rocky Mountain Douglas-fir
(Pseudotsuga menziesii var. glauca) at lower elevations. In mixed stands the overstory may be either pure
Rocky Mountain lodgepole pine or may
contain a mix of the above mentioned conifer species,
with the more shade-tolerant climax species in the understory [14].
Understory in
Rocky Mountain lodgepole pine varies with location, time since last disturbance, and site
characteristics. In dense or climax Rocky Mountain lodgepole pine stands the understory cover
is sparse with moderate diversity of species [58,79,275]. On a lakeside Rocky
Mountain lodgepole pine-black spruce (Picea mariana)/Schreber's moss (Pleurozium
schreberi) series near Peace River, central British Columbia, Haeussler and others [149] found a significant negative
correlation (p<0.01, r<-0.50) between Rocky Mountain lodgepole pine stem volume
((π -3)(basal diameter -2)2(tree
height)) and species
richness and diversity. Understory production also decreases as
Rocky Mountain lodgepole pine canopy cover increases [58,122].
Dominant understory tree and shrub associates in Rocky Mountain lodgepole
pine stands include American green alder (Alnus viridis ssp. crispa) [109,110,204],
greenleaf manzanita (A. patula) [300], bearberry (A. uva-ursi) [13,45,107,164,198,204,247,300],
big sagebrush (Artemisia tridentata), snowbrush (Ceanothus velutinus) [300], bunchberry
(Cornus canadensis) [109], common juniper (Juniperus communis) [13,13,45,107,160,197,220,247,257,277],
bog Labrador tea (Ledum groenlandicum) [109,110,204], twinflower (Linnaea borealis) [13,107,204,246,257,277],
Oregon-grape (Mahonia repens) [220], menziesia (Menziesia ferruginea) [109,110,204], quaking aspen (Populus
tremuloides) [247], Oregon boxwood (Paxistima
myrsinites) [45], bitterbrush (Purshia tridentata) [107,141,246,300], Cascade azalea (Rhododendron albiflorum)
[109,110], wax currant (Ribes cereum) [141,300], strawberryleaf raspberry
(Rubus pedatus) [109,110], dwarf red blackberry (R. pubescens) [109], russet buffaloberry
(Shepherdia canadensis) [13,13,45,141,160,161,204,247,311],
white spirea (Spiraea betulifolia) [13,107,109,277], Douglas' spirea (S. douglasii)
[198], dwarf huckleberry (Vaccinium caespitosum) [107,108,220,246,278], big huckleberry (V. membranaceum) [13,103,107,109,110,150,277],
velvetleaf blueberry (V. myrtilloides) [45,109,197], grouse whortleberry (V. scoparium)
[13,13,45,103,107,108,150,160,164,165,197,204,218,220,246,252,277,278,300], bog blueberry (V. uliginosum)
[141,198,300], and highbush cranberry (Viburnum edule) [109].
Dominant understory grass and forb associates in Rocky Mountain lodgepole
pine include Columbia needlegrass (Achnatherum nelsonii) [141,300], heartleaf
arnica (Arnica cordifolia) [13,107,252,277],
bluejoint (Calamagrostis canadensis) [220,252], pinegrass (C. rubescens) [13,103,107,150,246,277],
elk sedge (Carex geyeri) [13,13,45,107,160,161,197,277,278], long-stolon sedge
(C. inops) [300], Ross' sedge (C. rossii)
[13,13,107,277], California oatgrass (Danthonia
californica) [120,141], blue wildrye (E. glaucus) [141], Idaho fescue (Festuca idahoensis) [120,262,278,300],
boreal wildrye (Leymus innovatus) [110,204], Kentucky bluegrass (Poa pratensis) [107,198],
and beargrass (Xerophyllum tenax) [107,108,300].
Classifications listing Rocky Mountain lodgepole pine as a plant community dominant include
the following:
Native Americans boiled the inner bark of Rocky Mountain lodgepole pine for food [169].
Wood Products: Native Americans used Rocky Mountain lodgepole pine for tipi poles [151]. Rocky Mountain lodgepole pine is harvested for sawtimber, paneling, floor joists, poles, pulpwood, firewood, fenceposts, and fence rails [25,37,68,195,216]. It is also important in plywood, fiberboard, and composite/laminate products [195]. Rocky Mountain lodgepole pine contributed greatly to the early economic development of the northern and central Rocky Mountain regions. Between 1975 and 1985, annual lumber production from lodgepole averaged between 500 and 700 million board feet. In Montana, Rocky Mountain lodgepole pine provided 25% of the timber processed in 1981 [294]. Utilization potential of Rocky Mountain lodgepole pine stands in Montana is addressed by Benson and Strong [68], and Koch [195] provides discussion regarding Rocky Mountain lodgepole pine growth characteristics relative to merchantable material. An example of relationships between stand age, stocking level, tree development and typical yield in natural stands of Rocky Mountain lodgepole pine (in Montana and Idaho) is presented below [216]:
Age Stocking Avg. height of dominants Avg. stand diameter Total cubic volume Merchantable volume years trees/acre trees/ha feet meters inches cm ft3/acre m3/ha ft3/acre m3/ha 20 500 1,240 18 5.5 3.4 8.6 230 16.1 -- -- 8,000 19,770 10 3.0 1.6 4.1 400 28.0 -- -- 50 479 1,180 41 12.5 6.5 16.5 2,070 144.9 1,860 130.2 6,150 15,200 30 9.1 2.7 6.9 2,370 165.9 -- -- 80 418 1,030 59 18.0 8.1 20.6 4,080 285.6 3,800 266.0 3,034 7,500 48 14.6 3.6 9.1 4,000 280.0 -- -- 110 344 850 73 22.3 9.3 23.6 5,510 385.7 5,190 363.3 1,861 4,600 62 18.9 4.5 11.4 5,100 357.0 3,900 273.0 140 275 680 83 25.3 10.5 26.7 6,410 448.7 6,090 426.3 1,243 3,070 73 22.3 5.5 14.0 5,950 416.5 4,300 301.0Ninety percent of Rocky Mountain lodgepole pine seed germinates by early July [57]. Bud burst occurs in late May and shoot growth generally ends by August, when winter buds are formed [267].
Pollen of Rocky Mountain lodgepole pine is shed in spring and early summer, with specific dates varying both geographically and seasonally [115,217,267]. Pollen shedding may occur from mid-May to late June in the northern part of the range (central Montana north to British Columbia) and as late as mid July further south (northern Utah) [216,245]. The time at which pollen matures appears related to elevation and climate [216].
Fertilization occurs approximately 13 months after pollination [216,217]. Once fertilized, cones and seeds mature rapidly. By late summer or early fall of the 2nd growing season following pollination, they are fully mature [195,217,245,267]. Nonserotinous cones open shortly after they ripen, usually the latter part of September. Though most seedfall occurs in September and October, seed release may extend over several months [200,217,285].Growth response: Individual Rocky Mountain lodgepole pine may exhibit accelerated ring growth after fire due to improved site conditions (nutrient release and increased sunlight) and attempts to "heal over" fire wounds [10]. Peterson and others [244] found, however, that 70% of surviving Rocky Mountain lodgepole pine on sites in eastern Idaho experienced a decline in radial growth following fire. Percent of basal scorch and crown scorch had the greatest negative correlation with postfire growth.
Regeneration: Though it has thin bark, serotinous Rocky Mountain lodgepole pine is a fire evader due to the production of serotinous cones [4,5]. This adaptation ensures reestablishment following fire [5,59,79,80,139]. Serotinous cones are retained on trees for many years, which results in the release of large numbers of seeds when heat from a fire causes the cones to open [27]. While most Rocky Mountain lodgepole pines are killed by fire, they still provide an abundant seed supply [1]. However, severe crown fire may consume or kill most of the seed stored in the canopy, regardless of serotinous cones [27,215]. For more information on the relationship between Rocky Mountain lodgepole pine regeneration and fire, see Regeneration Processes.
Rocky Mountain lodgepole pine also exhibits an invader response to fire, pioneering plant succession following disturbance [4]. In one study, recovery of Rocky Mountain lodgepole pine in grand fir habitat types of northeastern Oregon ranged from 15 to 20% cover by postfire year 5 and 50% cover by postfire year 10, with higher rates of cover corresponding to increased fire severity. In subalpine fir habitat types, postfire year 5 Rocky Mountain lodgepole pine cover ranged from 10 to 80% [181].
Rocky Mountain lodgepole pine reproduces from seed [12], which may be borne in serotinous or nonserotinous cones. Individuals will have predominately open or closed cones [26,113,229], and both cone types occur in single stands [26,113,230]. Rocky Mountain lodgepole pine is likely to exhibit a higher degree of cone serotiny than the other varieties of lodgepole pine [6,26], but nonserotinous or open cones may predominate in persistent or climax Rocky Mountain lodgepole pine forests [6,113]. If serotiny is expressed in these stands, cone polymorphism exists and allows Rocky Mountain lodgepole pine regeneration after nonfire disturbance [6].
The degree of serotiny can affect the age distribution in the Rocky Mountain lodgepole pine stands. Seed from open-coned trees produces uneven-aged stands where seedlings establish over a period of years. Closed-cone trees generally produce even-aged stands, developing from the flush of seedlings that follows fire-induced seed release [79,80]. The success of Rocky Mountain lodgepole pine regeneration following disturbance is strongly controlled by the persistence of a seed source and the size of the area disturbed [299].
Breeding system: Rocky Mountain lodgepole pine is monoecious [180,216,217]. Seed cones are most often borne in the upper crown, but may also occur on leaders of secondary branches. Pollen cones occur most frequently on older, less dominant branches in the lower crown, although they may also be found on the smaller laterals of branches bearing seed cones [216,217]. It is not uncommon to find a predominance of male or female cones on individual trees [216]. Separation of male and female cones within the crown is one important mechanism for preventing a high degree of self-fertilization in Rocky Mountain lodgepole pine. Also discouraging self-fertilization is a disjunction in the time of pollen release and receptivity on the same tree [217].
Pollination: Rocky Mountain lodgepole pine is wind pollinated [227].
Seed production: Rocky Mountain lodgepole pine begins producing seed within 5 to 15 years of establishment [1,26,37,97,200,245,309]. Trees with the serotinous genotype produce only open cones for up to 60 years, followed by a gradual transition to serotinous cones [26]. Cones bearing viable seed are produced by trees as young as 5 years in open stands and by trees 15 to 20 years old in more dense stands. This feature not only allows relatively young stands to regenerate following fire, but also allows the seed from open cones of recently regenerated Rocky Mountain lodgepole pine to fill voids left by serotinous cones [26,79,80]. However, when Rocky Mountain lodgepole pine is suppressed a tree may reach 50 years before producing seed. Cone production is related to the amount of water and light available. Due to their large crowns, trees growing in open stands tend to produce larger numbers of cones than those in dense stands. The number of cones produced in a single growing season by mature Rocky Mountain lodgepole pines in Colorado ranges from none in a suppressed individual to 9,000 in a 99-year-old tree in an open stand [97]. Rocky Mountain lodgepole pine is generally described as a prolific seed producer with good crops at 1- to 3- year intervals [12,57,79,80,245] with light crops in intervening years [79,80]. Hellum [157] argues, however, that Rocky Mountain lodgepole pine is in fact a light cone producer, with 30 cones/tree/year being common. Often, trees bear an abundance of seeds that remain unopened in serotinous cones [12,57,59]. The average serotinous cone remains on the tree for about 15 years, with few remaining on a tree for more than 30 years. It is the accrual of cones on the tree over time that results in large numbers of seed available for regeneration following disturbance, rather than high seed production [157]. Most of the viable seeds are borne on scales nearest the tip of the cone (except for the 1st few scales) [97,217]. The number of seeds in a cone depends on the age of the tree or branch, number of cone scales, and number of seeds per cone scale [97,217]. Nonserotinous trees may have more seeds per cone than serotinous trees, perhaps indicating that serotinous trees invest relatively heavily in cone materials to protect seeds (which are retained in cones for many years), while nonserotinous trees (which shed seed every year) invest relatively heavily in seeds [227,230]. Annual seed production in nonserotinous stands may exceed 600,000 seeds per acre (1.5 million seeds/ha) with high levels of viability [6].
Cone serotiny: Serotinous cones require high temperatures to open and release seed [1,17,275], and they are well insulated to survive brief periods in flames [1]. Individual trees predominantly bear either open or closed (serotinous) cones [115], and most mature Rocky Mountain lodgepole pine stands contain trees that have both closed and open cones [217,275]. Wind pollination encourages heterogeneity of cone habit [229].
Level of serotiny varies over time and space, and is a legacy of past fire [26,59,113,116,156] and possibly also geographic location [116], tree age, and elevation [26,115]. In Yellowstone National Park, the proportion of serotinous trees across the landscape was most variable at intermediate scales (1-10 km) and least variable at fine scales (<1 km) and at very broad scales (tens of km) [289].
Rocky Mountain lodgepole pine stands originating from stand-replacing fire generally have a high percentage of trees with serotinous cones, while stands originating after other disturbance are likely to have a greater proportion of nonserotinous cones [26]. Lotan [214] found that an even-aged stand of Rocky Mountain lodgepole pine in Montana (generated from seed in closed cones made available by stand-replacing fire) was composed of 58% predominantly serotinous trees, compared with 38% in an uneven-aged stand (established primarily by open-coned trees over time) [214]. Predominant cone type in a stand may shift over time, depending on the nature of the last major disturbance. Muir [227] found that the level of serotiny in Rocky Mountain lodgepole pine stands was more closely related to the type of stand-initiating disturbance than to fire frequency. In a study in western Montana, between-stand variation in serotiny indicated a predominance of serotinous trees in stands that originated after stand-replacing fire, and of nonserotinous trees in stands that originated after nonfire-related disturbance [227,229].
Nonserotinous trees may be favored at both ends of the fire frequency gradient. The absence of fire over a long period may result in stands dominated by trees with nonserotinous cones as regeneration from open cones replaces the original trees [275]. Long intervals between fires often allow large fuel accumulations, resulting in intense burns which may destroy many seeds in serotinous cones. With frequent fires, fuel accumulation may be low and the resulting fire intensity may be too low to open closed cones [229]. In addition, disturbance may occur before the serotinous cone habit is expressed. Though Rocky Mountain lodgepole pine may start bearing cones at less than 10 years of age, serotiny is not expressed until trees are 30 to 60 years old [217].
Seed dispersal: The seeds of Rocky Mountain lodgepole pine are small and disperse easily with wind [115,309]. Rocky Mountain lodgepole pine has 2 modes of seed dispersal, based on cone serotiny [264]. In Rocky Mountain lodgepole pine stands with predominantly serotinous cones, releasing and scattering seed on the forest floor after fire opens cones is the most important method of dispersal [12]. Serotinous cones require temperatures of 113 to 120 degrees Fahrenheit (45-50 oC) to melt the resin that binds the scales of the cone [57,79,80,97,113,275], temperatures that generally accompany moderate to severe fire [79,80,113]. Crown fires in Rocky Mountain lodgepole pine usually cause maximum release of stored seed [215]. In stands with primarily nonserotinous cones, the small, winged seeds are dispersed at maturity from standing trees largely by wind. Seedfall drops off rapidly as distance from source increases, with most seeds falling within about 200 feet (60 m) of the parent tree [12,57,97,245,268,286]. Other dispersal agents include runoff and small mammals [97].
Seed banking: Rocky Mountain lodgepole pine seeds are stored in serotinous cones on standing trees [5,12,26,217,309]. Seeds are protected in these cones until exposure to heat (generally from fire) melts the resin seal [5,25]. Very severe fires, however, may destroy much of the seed supply [275]. Not all Rocky Mountain lodgepole pine stands exhibit a high degree of cone serotiny, and this variability in cone habit affects regeneration patterns [12]. Seeds in canopy-stored, serotinous cones are viable for up to 80 years [1,37,57,79,97,116,309].
Germination: When tested under standard laboratory conditions, the germinative capacity of Rocky Mountain lodgepole pine seeds ranges from 65 to 90% [97,195,217]. Viability is highly variable from year to year, but does not seem to decrease as a function of age of the cones attached to trees [195,217].
Germination of Rocky Mountain lodgepole pine seeds requires light but not stratification [115,116,209,216,309]. After dispersal, viable seeds of Rocky Mountain lodgepole pine that survive over winter normally germinate in the spring or early summer following snowmelt. Under favorable moisture conditions, Rocky Mountain lodgepole pine germinates on exposed mineral soil and disturbed duff [12,245]. Fire creates a favorable seedbed by removing loose organic matter and exposing mineral soil or decomposed organic matter, which encourage germination [1]. Fire may also reduce competing vegetation, improving opportunities for seedling establishment [1,57,216]. The decrease in canopy cover following fire provides high light intensity necessary for vigorous Rocky Mountain lodgepole pine seedling growth [1,79]. Moderate to heavy shade reduces germination 20% [217]. Germination rates are best in full sunlight, though on some sites radiation intensities under full exposure can create temperature and moisture conditions unfavorable to germination. High temperatures and rapid drying of the seedbed can prevent seeds from imbibing sufficient water to germinate [12,216]. Temperatures fluctuating between 47 and 78 degrees Fahrenheit (8-26 oC) favor germination [216,245]. Rocky Mountain lodgepole pine seeds do not germinate well on surface soils that are dry and cold in the spring [101].
Despain and others [124] found that exposure for 10 to 60 seconds in a flame front designed to simulate a crown fire enhanced germination of Rocky Mountain lodgepole pine seeds from serotinous cones, but not seeds from nonserotinous cones. Maximum germination rates for serotinous cone seeds ranged from 37 to 64% and occurred after 10 to 20 seconds of exposure to flames. Germination after 60 seconds averaged 0.3 to 14%. Maximum germination of seeds from nonserotinous cones was approximately 80%, occurring with no exposure to flame and after 10 seconds exposure to flame [124]. Knapp and Anderson [194] found that Rocky Mountain lodgepole pine seeds from serotinous cones heated to 149 degrees Fahrenheit (65 oC) showed no difference in germination than those from a serotinous control group maintained at 68 to 77 degrees Fahrenheit (20-25 oC). Seeds heated to 169 degrees Fahrenheit (76 oC) and higher, however, exhibited a significant decrease (p<0.01) in germination. These results suggest the existence of a threshold temperature (149-167 oF or 65-75 oC) above which germination is reduced, coinciding with the upper temperatures required to open serotinous cones (140-156 oF or 60-69 oC). The maximum germination rate for the control group was 38% [194]. In another study evaluating the effects of drying and scorching on Rocky Mountain lodgepole pine seeds (from serotinous cones), seeds subjected to drying in a rotating kiln for 23 hours were more "vigorous" than seeds dried in a conventional kiln for 16 hours, perhaps because seeds could drop free of the kiln environment once released from the cones. Seeds with the greatest vigor, however, were those extracted from cones subjected to up to 1.5 minutes of scorching at 428 degrees Fahrenheit (220 oC) followed by 23 hours drying in the rotating kiln. Seeds subjected to 2.0 minutes scorching exhibited a substantial reduction in germinability and vigor, as well as loss of membrane integrity [302].
Seedling establishment/growth: Soil temperature, air temperature, water availability, and light level are the primary factors controlling seedling performance of Rocky Mountain lodgepole pine [97,98,100]. Rocky Mountain lodgepole pine is noted for its ability to establish on burned surfaces, though early seedling success may be greater on exposed, unburned mineral soil with more stable moisture conditions [12,26,79,80]. Thick organic seedbeds may dry quickly and expose seedlings to drought, the primary cause of mortality the 1st year [26]. In an Alberta study of Rocky Mountain lodgepole pine reforestation efforts, better growth and survival of planted seedlings were observed on burned areas than on unburned, unscarified sites [132]. The highest seedling densities following harvest in Wyoming were found on naturally seeded sites (vs. planted sites) where residue had been either piled and burned or chipped and removed [213]. However, Rocky Mountain lodgepole pine does not require bare mineral soil or sites free from potential competitors for establishment. Anderson and Romme [27] found large numbers of Rocky Mountain lodgepole pine seedlings on sites where the effects of a surface fire had been minimal and the duff and understory plants were relatively disturbed. A central Idaho study was inconclusive, with a higher percentage of Rocky Mountain lodgepole pine seedlings establishing on bare soil than on litter-covered soil on some sites, while the reverse was observed on other sites [144]. Snags and logs may provide buffering of both high and low temperatures and higher soil moisture, resulting in high concentrations of regeneration on these microsites [6].
Growth of Rocky Mountain lodgepole pine is characterized as rapid in young trees and slow in old trees [17,115,217,264,309], and may be impacted by elevation. In a Colorado study, the average annual height growth at higher altitudes (approx. 10,000 feet/3,000 m) was 0.8 inch (2 cm); at slightly lower altitudes (9,000 feet/2,700 m) it was 3 inches (8 cm) [97]. Early seedling development is generally considered best in full sunlight [12,78,79,216,245], though full exposure may result in Rocky Mountain lodgepole pine seedling mortality due to heat injury [78,100]. On sites in Colorado at an elevation of 10,000 feet, full exposure resulted in 100% seedling mortality by the end of the 1st growing season [78]. In a central Idaho study, moderate shrub canopy cover (33-66%) resulted in greater Rocky Mountain lodgepole pine seedling establishment than light or heavy cover [144]. Unfavorable temperature and moisture conditions in full exposure may kill seedlings by stem girdle or drought [12,26,78,100,217]. Water stress can decrease Rocky Mountain lodgepole pine seedling establishment and survival [43,57,62,100,115,217,281,309]. Shading reduces losses to moisture stress, with large seedlings faring better due to well-developed root systems [43,281]. Growth of seedlings may also be limited by low fertility and compacted subsoil [62]. Following a wildfire in Colorado, Rocky Mountain lodgepole pine seedlings were more abundant on lower slope positions due to greater soil moisture and slightly deeper soils than on higher slope positions [57]. Though mature Rocky Mountain lodgepole pine prefers well-drained soil [97], seedlings are tolerant of high soil water levels, even with extended soil saturation [99]. Seedlings are susceptible to frost-heaving [115,309]. Frost heaving can kill new germinants and partially destroy roots of older seedlings, slowing their growth [101,217]. Newly germinated seedlings are susceptible to early fall frosts when they are still actively growing, but older seedlings are seldom damaged by frosts during the growing season [12,100,217]. Shade may reduce mortality from frost damage by reducing loss of radiant energy from soil and seedlings [12]. Cold hardiness and drought tolerance of seedlings vary between populations [60]. Newly germinated seedlings may also be killed by damping-off fungi early in the growing season when seedbeds are damp [12,217]. Seedlings are vulnerable to trampling, predation by small mammals, and competition from understory vegetation, particularly grasses [12,26,62,215,216,217,275]. One study in British Columbia found that Rocky Mountain lodgepole pine seedling diameter was 84% greater with the removal of competing vegetation than on undisturbed vegetation. Survival of seedlings may also be reduced by up to 20% due to competing vegetation [98]. Another British Columbia study found that seeding of clearcuts with grass and forb species reduced planted, 1-year-old Rocky Mountain lodgepole pine diameter by up to 38% (p<0.004) and heights by up to 30% (p<0.005) over 3 years; diameter, height, and survival decreased linearly with increased seeding rates [248]. A 3rd study found mean diameters of Rocky Mountain lodgepole pine seedlings growing free of competing vegetation were 21% greater than diameters of seedlings grown with competition. Removal of competing vegetation favors increased seedling growth by increasing soil temperature, air temperature, and light availability [272]. Removal of intraspecific competitors generally results in greater improved growth of Rocky Mountain lodgepole pine than removal of interspecific competitors [26].
Fire and regeneration: The effects of fire, fuel accumulation, stand development, insects, and disease in Rocky Mountain lodgepole pine forests interact to control the establishment and maintenance of stands [14,118]. Because they are often initiated by stand-replacing fire, Rocky Mountain lodgepole pine stands are frequently even-aged [27,54]. However, stands of similar age frequently differ in density, ranging from open stands of large trees to very dense, stunted "doghair" stands [26,27]. Patterns of Rocky Mountain lodgepole pine regeneration following the 1988 Yellowstone fires included 1) a dense, uniformly distributed cohort developing as a single-storied stand; 2) Rocky Mountain lodgepole pine islands or clusters that form, over several decades, around isolated seedlings that mature and produce seed; 3) a moderate- to low-density cohort that will gradually fill with multiple age classes over time; and 4) a cohort of only widely scattered single seedlings that initially form as small nearby tree islands, and will eventually converge into a more continuous stand [235]. Low-density stands resulting from severe fires are generally more robust with more aboveground biomass, reflecting lower levels of competition and possibly more favorable abiotic factors (e.g. light availability, earlier snowmelt, and favorable growth temperatures earlier in the season) [26]. Dense stands of Rocky Mountain lodgepole pine are susceptible to stagnation, snow breakage, and windthrow as they mature [275]. A study of fire-initiated Rocky Mountain lodgepole pine stands in Colorado found 2 distinct structures in stands originating from crown fires at approximately the same time. Several stands had high tree densities (cover >70%) with few saplings or large seedlings, numerous standing dead trees, and even-aged diameter distributions. Other stands had more open canopies (cover <65%) with lower tree densities, more saplings and seedlings, and a range of diameter classes. The open stands suggest low stocking density following stand-replacing fire and/or repetitive surface fires that have allowed somewhat continuous recruitment over time [236]. Similar relationships between density and diameter distribution were found in an Alberta study, with higher density stands containing a smaller range of diameters [190].
If seed sources are close and abundant, Rocky Mountain lodgepole pine often reproduces abundantly following fire or harvest, developing dense stands of seedlings in which diameter and height growth are substantially reduced [12,57,72,79,80,97,115,168,190,216,218,245]. Following the stand-replacing Sleeping Child fire in western Montana, Rocky Mountain lodgepole pine densities were as high as 159,000 seedlings per acre (393,000/ha), though the average over 11 transects was 34,000 per acre (84,000/ha). Survival of these seedlings was 52% in the 1st 12 years [218]. In Rocky Mountain lodgepole pine-dominated successional forest of the central Rockies, 80-year-old trees may be 0.8 to 1.2 inches (2-3 cm) in diameter, less than 10 feet (3 m) tall, and spaced at 2 trees/ft2 (20 trees/m2) [72]. Following a severe fire in Colorado, Rocky Mountain lodgepole pine seedling density ranged from 0 to 4,800 seedlings per acre (0-12,000/ha) by the 3rd postfire growing season, with most seedlings establishing in the 1st year [57]. However, seeding often occurs over several years with wider seedling spacing; after 80 years Rocky Mountain lodgepole pines in this regeneration pattern range from 4 to 12 inches (10-30 cm) in diameter, 49 to 66 feet (15-20 m) in height, and have 6.6- to 10-foot (2-3 m) spacing [72]. Variations in seedling density following fire reflect severity of fire, soil type, elevation, patch size, and levels of serotiny [26,59,215]. Levels of serotiny combined with fire severity determine seed availability after fire [59]. Seed from open-coned trees establishes less dense stands that are somewhat uneven-aged [275]. Seedling densities increase exponentially with the proportion of serotinous trees in prefire stands [26,59]. The range of seedling density at different sites subject to similar fire severity are likely due to the availability of seeds at the time of fire, a function of the proportion of serotinous trees in the stand [27,131,215]. Seventeen years after a severe mixed surface and crown fire in Wyoming, Engelmann spruce density was greater than that of Rocky Mountain lodgepole pine due to a low percentage of serotiny in the burned stand and low density of Rocky Mountain lodgepole pine in the unburned forest near the burned area [128].
The effect of fire on the structure and composition of a Rocky Mountain lodgepole pine stand depends greatly on its severity. Fires in Rocky Mountain lodgepole pine vary from surface fires of low severity to crown fires of high severity. Stand-replacing fires generally result in heavy seeding from serotinous cones, producing a dense, even-aged young stand [14]. In a northern Cascades study of regeneration after low-severity fire, Finney [137] found that Rocky Mountain lodgepole pine regeneration increased as fire intensity increased and postfire residual density decreased. Occasionally, fires may be intense enough to destroy cones, resulting in a thinly stocked stand. Low-severity surface fires may leave some residual Rocky Mountain lodgepole pine, resulting in an uneven-aged stand [14]. With low-severity fires, moisture content of duff is an important factor in determining stand density. When duff is dry a low-intensity fire exposes mineral soil, resulting in dense stocking. When duff is moist, fire exposes less mineral soil. This often results in poor seedbed conditions and low seedling density. Widely spaced stands may result; in time, multi-aged stands can develop. In surface fires with considerable patches of crowning, mineral soil is exposed, serotinous cones open, and if seed is abundant, a dense stand results [215]. Mixed-severity burns are sufficiently intense to kill some trees and allow for establishment of a new age class of the shade intolerant Rocky Mountain lodgepole pine [38].
High-severity fires often result in fewer postfire seedlings than less severe burns, potentially reducing seedling density by 75-96% relative to moderately burned areas [26]. In a study of Rocky Mountain lodgepole pine stands 1 year after the 1988 Yellowstone fires, nearly 1/3rd of vascular plants were Rocky Mountain lodgepole pine seedlings. In comparing paired plots, moderate fire resulted in higher seedling density (0.14-2 seedlings/ft2 or 1.6-21.9 seedlings/m2) than severe canopy fire (0-0.28 seedlings/ft2 or 0.4-3.1 seedlings/m2) [27] due to the loss of viable seed in severe fires [26,27,131]. A severe crown fire may kill up to 80% of seeds stored in the Rocky Mountain lodgepole pine canopy relative to seed survival after a "hot" surface fire [26,215]. Following the Yellowstone fires of 1988, severe surface-burned areas and large burned patches had higher cover and density of Rocky Mountain lodgepole pine seedlings than small patches or areas experiencing crown fire. Fire intensities and spreads in severe surface-burned areas may have been optimal for the opening of serotinous cones and release of seed, but fire conditions in severe crown fires may have resulted in cone ignition and substantially reduced seed viability. Rocky Mountain lodgepole pine density was positively related to the number of prefire serotinous trees surrounding the sampling point [290]. At other sites evaluated after the Yellowstone fires, seedling densities were also consistently higher on moderately burned areas and lower on areas subject to severe canopy fire. Seedling densities on severely burned sites >328 feet (100 m) from the nearest moderately burned or unburned sites were 2- to 7-fold less than on severely burned areas adjacent to or within 197 feet (60 m) of a moderately burned or unburned area. Seedling densities were also higher on sites with a greater number of cones on the ground and with closer proximity to stands having a high proportion of serotinous cones. Greater stand serotiny and high postfire seedling densities were positively correlated (r=0.71, p=0.0031 for moderately burned transects, r=0.75, p=0.0023 for severely burned transects). Regardless of fire severity, seedling density far exceeded the density of the prefire forest [131].
Rocky Mountain lodgepole pine invades dry meadows and sites previously dominated by big sagebrush [120,238,262]. However, Rocky Mountain lodgepole pine is primarily an aggressive pioneer on disturbed sites, with its occurrence due largely to fire [6,12,14,26,238]. Postfire tree regeneration depends on the severity and uniformity of fire behavior, the relative availability of open and closed cones, and postfire moisture conditions. Regeneration from open cones is slower than when most seed is from closed cones, but it may be more dependable because seed is available most years. Regeneration patterns reflect burning patterns; regeneration is widely distributed if fire behavior was relatively uniform, but is sparse in severely burned patches and clumped in even-age patches where fire was of mixed severity. Following stand-replacing fire, Rocky Mountain lodgepole pine can establish in nearly pure stands or with other tree species that are suppressed under the fast-growing Rocky Mountain lodgepole pine. In either case, Rocky Mountain lodgepole pine generally dominates regeneration [275]. Rocky Mountain lodgepole pine may also co-dominate on these sites with other early successional, shade-intolerant species. For example, whitebark pine may also establish immediately following fire or other stand-replacing disturbance [176,211]. The success of Rocky Mountain lodgepole pine at dominating a site following fire is due to the high rate of seedling survival, rapid growth of young trees, early seed production, prolific seed production, and high seed viability [113].
The successional status of Rocky Mountain lodgepole pine depends on environmental conditions, disturbance history and pattern, and competition from associated species [14,299,310]. Succession proceeds at different rates, moving relatively fast on low-elevation mesic sites and particularly slow in high-elevation forests such as those along the Continental Divide in Montana [264]. Rocky Mountain lodgepole pine matures and gives way to shade-tolerant conifers at ages from 50 to 100 years in mesic habitats, 100 to 200 years in warmer, drier forests, and 150 to 400 years in subalpine forests [245]. Fire perpetuates or renews Rocky Mountain lodgepole pine stands. Where Rocky Mountain lodgepole pine is seral, shade-tolerant trees will replace Rocky Mountain lodgepole without fire or other disturbance because of its shade intolerance and mineral seedbed preference [79,80,118]. Absence of stand disturbance favors regeneration and eventual dominance of shade-tolerant species [137,217,240,299]. Rocky Mountain lodgepole pine is seral in stands that have either a mixed overstory or contain appreciable amounts of advance reproduction of other species [12]. Rocky Mountain lodgepole pine is especially important in postfire succession of subalpine forests, particularly on moderately to severely burned sites [49]. Successional development where Rocky Mountain lodgepole pine is either seral or persistent usually follows multiple pathways depending upon associated species and stand history [299]. Rocky Mountain lodgepole pine also occurs in climax stands, exhibiting size-class distribution and growth habits typical of climax species not dependent on fire for maintenance [123].
Seral Rocky Mountain lodgepole pine: Rocky Mountain lodgepole pine is a minor seral species in some mixed stands [4,14,17,72,118,138,245,264]. In mixed stands, Rocky Mountain lodgepole pine may establish with late-successional, shade-tolerant species [296]. Rapid growth rates enable Rocky Mountain lodgepole pine to maintain a competitive position in the canopy for several years. However, it does not regenerate under the mixed-species canopy and is eliminated from the stand as mortality occurs [245,296]. It is generally replaced in 50 to 100 years by more shade-tolerant associates [14,17,72,118,138,264].
Rocky Mountain lodgepole pine is a dominant seral where it is an overstory species with a vigorous understory of shade tolerant associates (Douglas-fir, subalpine fir, Engelmann spruce) [14,17,245]. For example, the largest, most continuous Rocky Mountain lodgepole pine forests occur on subalpine fir habitat types. Rocky Mountain lodgepole pine typically regenerates following stand-replacing or mixed-severity fire. It grows rapidly and dominates the site, but subalpine fir regenerates well under the canopy of lodgepole [95]. In a Utah study, Engelmann spruce and subalpine fir began to establish beneath Rocky Mountain lodgepole pine approximately 20 years after a stand-replacing fire [179]. Succession proceeds at variable rates and is particularly slow in some high elevation forests [217]. An Alberta study found that an even-aged stand of Rocky Mountain lodgepole pine was succeeded by an Engelmann spruce-subalpine fir forest within 150 to 200 years. As even-aged Rocky Mountain lodgepole pine ages, death of old trees permits an irregular to all-aged spruce-fir forest to emerge and dominate [119]. In a fire-initiated Engelmann spruce-subalpine fir forest of British Columbia, Rocky Mountain lodgepole pine accounted for only 3.4% of the canopy after 330 years, with no Rocky Mountain lodgepole pine in the subcanopy or sapling age class [29]. Stand conditions determine the fire potential, and the kind of fire that occurs determines postfire stand density and early composition (open stand may lead to earlier establishment of climax species) [79,80]. On sites where Rocky Mountain lodgepole pine is the sole or dominant seral species, an initial herb-shrub community develops after a stand-replacing fire. Fires of any severity maintain this state. Where Rocky Mountain lodgepole pine is serotinous (or nonserotinous with an adequate seed source), dense stands of even-aged seedlings and saplings establish quickly. Low- to moderate-severity fires provide seed release and openings for regeneration of Rocky Mountain lodgepole pine and shade-tolerant species. Due to heavy fuel loads, stands with a dying Rocky Mountain lodgepole pine overstory and Engelmann spruce-subalpine fir understory are susceptible to severe fire, which recycles the stand. Without recurrence of fire, a dense mature stand of lodgepole results, which will eventually be dominated by climax species as the lodgepole pine senesces [79,80,113,138,275]. If an open stand develops (e.g. where cones are nonserotinous or on exposed south slopes) following severe fire, seedling establishment will usually continue, leading to an uneven-aged stand with varying proportions of Rocky Mountain lodgepole pine. In these stands, a low-severity surface fire removes young trees and creates a seedbed for subsequent regeneration, with relatively frequent low-severity fires maintaining the open stand and mixed forest. In the absence of fire, seral Rocky Mountain lodgepole pine eventually dies out due to insects, disease, and old age, releasing shade-tolerant climax species [113].
Replacement of seral Rocky Mountain lodgepole pine in these types of communities usually requires 100 to 200 years [14,17,119,245]. In the event of mountain pine beetle removal of larger Rocky Mountain lodgepole pine, the time required for climax species to occupy the site is shortened [14,17]. In stands where Rocky Mountain lodgepole pine is seral, mountain pine beetles periodically remove the large, dominant pines, providing growing space for climax species and hastening succession [17,113,179,299]. A fire may interrupt the sere at any time, returning the stand to pure Rocky Mountain lodgepole pine or a combination of Rocky Mountain lodgepole pine and other early seral tree species (e.g. whitebark pine) [17,30,113,119,176,211].
The effect of fire in seral Rocky Mountain lodgepole pine varies by habitat type. Low-severity surface fires are not necessarily adequate to kill Douglas-fir and return Rocky Mountain lodgepole pine to a dominant position in the stand [17]. In drier habitat types (e.g. Douglas-fir/pinegrass), recurrent low- to medium-severity surface fires reduce accumulated woody biomass resulting from beetle attack. In contrast, cooler, more mesic habitat types (e.g. subalpine fir/queencup beadlily) may experience stand-replacing fires rather than cyclic surface fires, allowing the continuous accumulation of woody residues until a severe fire consumes the surface fuels [30]. However, once succession is complete, Rocky Mountain lodgepole pine seed will no longer be available to seed the burned areas except along edges where the site joins persistent or climax Rocky Mountain lodgepole pine [17,113]. Succession occurs most rapidly where Rocky Mountain lodgepole pine and shade-tolerant associates establish simultaneously [17]. Rocky Mountain lodgepole pine gains dominance through rapid early growth, but shade-tolerant species persist and assume dominance as individual Rocky Mountain lodgepole pines die [17,118,168]. In a Colorado study reconstructing Rocky Mountain lodgepole pine and Engelmann spruce stands, the Rocky Mountain lodgepole pine cohort established in the 1st decade following fire, with initially high but decreasing mortality in the 1st 10 years. Mortality was low and constant until "self-thinning" began at year 25; mortality then increased for the next 200 years. Rocky Mountain lodgepole pine understory recruitment began around postfire year 15, with understory trees experiencing high mortality with a <0.5% chance of reaching the canopy. Engelmann spruce also experienced high mortality, though not as high as Rocky Mountain lodgepole pine, with sporadic recruitment over time [182].
Habitat types in which Rocky Mountain lodgepole pine occurs as a dominant seral species include ponderosa pine (Pinus ponderosa), subalpine fir, whitebark pine (Pinus albicaulis), Engelmann spruce, grand fir (Abies grandis), mountain hemlock (Tsuga mertensiana), western redcedar (Thuja plicata), western larch (Larix occidentalis), white fir (Abies concolor), and Douglas-fir [5,28,79,80,113,118,138,139,275,299].
Persistent Rocky Mountain lodgepole pine: Rocky Mountain lodgepole pine is a persistent seral or subclimax species where stands are the result of periodic, stand-replacing fires; some areas have burned so often and so extensively that large acreages are nearly all Rocky Mountain lodgepole pine [12,14,119]. On these sites, fire may be infrequent but recurs before the more shade tolerant climax species can replace lodgepole [245,299]. The proportion of Rocky Mountain lodgepole pine will increase with each successive fire, provided the interval between fires is neither too short nor too long [168,292]. Because Rocky Mountain lodgepole pine begins producing seed at 3 to 15 years of age, the amount of time that a new stand is seedless and subject to destruction by subsequent fire is relatively short [1]. In grand fir forests, Rocky Mountain lodgepole pine dies out 120 to 160 years following fire if not subsequently burned; repeated fires at <100 year intervals favor Rocky Mountain lodgepole pine while intervals >200 years eliminate Rocky Mountain lodgepole pine [28]. These seral stages persist indefinitely if subject to fire at intervals favoring the regeneration of Rocky Mountain lodgepole pine (fire-free intervals less than the life span of Rocky Mountain lodgepole pine) and preempting the establishment of climax forests [12,113,142,275]. Fires tend to eliminate competitive tree species such as Douglas-fir, the true firs (Abies spp.), and spruce (Picea spp.), while Rocky Mountain lodgepole pine seeds in abundantly following fire [17,113]. In these situations, Rocky Mountain lodgepole pine is maintained on the site, preventing succession to climax species [14,245]. Rocky Mountain lodgepole pine maintains its dominance because of inadequate seed sources for potential competitors, stand densities too great to allow regeneration of any other species, and low-severity surface fires that remove seedlings without killing overstory Rocky Mountain lodgepole pine [17,217].
Climax Rocky Mountain lodgepole pine: Climax Rocky Mountain lodgepole pine forests are primarily topoedaphic climaxes, occurring where other tree species have no seed source, competitive advantage, or capability of growing on particular sites, and where Rocky Mountain lodgepole pine is self-perpetuating [5,14,17,79,80,113,123,216,225,245,299]. Rocky Mountain lodgepole pine climax communities occur on marginal sites including frost pockets; sites subject to temperature extremes; well-drained or droughty, infertile soils; poorly-drained, highly organic soils; cold, dry sites; and many sites with soils that are saturated in the spring but very dry in late summer [113,275,299,309]. For example, extensive climax Rocky Mountain lodgepole pine forests are found on pumice sites in south-central Oregon [4,309] and on associated flats where extended frost pockets occur [4]. Climax Rocky Mountain lodgepole pine stands are found throughout its range [79,80,275,309], though they occur predominantly in south-central Oregon, Wyoming, and northern Colorado [4,113,123,225]. Though Rocky Mountain lodgepole pine is shade intolerant, the mature overstory in climax stands is often sparse enough that sufficient light reaches the forest floor to allow young Rocky Mountain lodgepole pine to persist and eventually replace overstory trees [123,275]. In other climax stands, Rocky Mountain lodgepole pine regeneration occurs by gap phase replacement [299]. Climax Rocky Mountain lodgepole pine stands produce primarily open cones, so seed is available to regenerate in openings created by lightning, fire, mountain pine beetle attack, snow breakage, and windthrow [275,299].
Mountain pine beetle and Rocky Mountain lodgepole pine: In fire-generated stands of similar age (seral stands), trees become susceptible to mountain pine beetle attack at approximately the same time, resulting in large-scale infestations [25,113]. Where Rocky Mountain lodgepole pine is persistent or climax, mountain pine beetle infests and kills most large Rocky Mountain lodgepole pine. The openings created by beetle kills are seeded by Rocky Mountain lodgepole pine, and the cycle is repeated as other trees reach the size and phloem thickness conducive to beetle populations [17,19]. Mountain pine beetle and other nonfire disturbances effectively thin the larger size classes. Combined with patchy fire spread [6], this complex disturbance regime results in multi-storied, mosaic stands consisting of different age and size classes [6,17,19]. The overall effect is chronic infestations of mountain pine beetle due to the constant food source [17].
The currently accepted scientific name of Rocky Mountain lodgepole pine is
Pinus contorta Dougl. var. latifolia Engelm. (Pinaceae) [126,162,163,169,188,205,297,308].
Pinus contorta includes 4 distinctly different varieties that are interfertile. In
addition to Rocky Mountain lodgepole pine, these are shore pine (P. contorta var. contorta),
Sierra lodgepole pine (P. contorta var. murrayana), and Bolander pine (P. contorta
var. bolanderi) [58,309]. These varieties differ in
tree longevity, dimensions, form, and branchiness; needle size and structure;
cone form, density, orientation, persistence, and serotiny; the timing of
reproductive events; seed size and germination behavior; resin composition; and
parasites and predators [116,309]. Bolander pine is found only in limited areas of California [116,188].
The above mentioned varieties are referred to in this species summary by their
full common names; "lodgepole pine" refers to the species as a whole.
Rocky Mountain lodgepole pine and jack pine (P. banksiana) are morphologically
similar and hybridize where their ranges overlap in western Canada [116,199].
Rocky Mountain lodgepole pine is frequently used in reforestation efforts, particularly in northern Europe [309]. It is successfully used to revegetate mine sites [84,146,303]. There are approximately 1,000 Rocky Mountain lodgepole pine seeds per pound [37,217], though seed amounts may vary geographically [115].
Though it grows well on nutrient poor soils, nitrogen fertilizer may enhance growth of Rocky Mountain lodgepole pine [83,249,250,307]. A field study in British Columbia found that nitrogen-fertilized Rocky Mountain lodgepole pine experienced 34% greater stem volume increase than unfertilized trees after 8 growing seasons [250]. However, low nitrogen may enhance cold-hardiness in containerized Rocky Mountain lodgepole pine seedlings [130], and added nitrogen may cause phosphorus deficiencies [307] and nitrogen-sulphur imbalances [83]. Thinning of Rocky Mountain lodgepole pine may increase nitrogen fixation by understory vegetation (e.g. russet buffaloberry), improving growth of remaining trees [159]. Height and diameter growth of Rocky Mountain lodgepole pine seedlings are higher following inoculation with ectomycorrhizae [146].
Fresh Rocky Mountain lodgepole pine seeds need no stratification; however, when seeds have been stored, stratification for 30 to 56 days may hasten germination and/or improve overall germination rates [158,200,209,217]. Soaking the seeds in cold water for 1 to 2 days then storing while damp in plastic bags at 33 to 41 degrees Fahrenheit (0.5-5.0 oC) is the most effective stratification procedure [209,217]. If seeds have not yet matured, they may be damaged by cold stratification [158]. Seed lot germinability of Rocky Mountain lodgepole pine may be improved using the IDS (incubation-desiccation-separation) technique [127,271], which can increase germinability as much as 38% [127]. Approximately 4 weeks of acclimation increases frost hardiness and root growth capacity of Rocky Mountain lodgepole pine seedlings, improving the success of containerized planting [273].
Based on laboratory and field experiments, growth potential, morphology, cold hardiness, and periodicity of shoot elongation may vary between populations of Rocky Mountain lodgepole pine, with a large proportion (up to 77% in Utah, 83% in Idaho and Wyoming) of the variation attributed to the elevation and geographic location of the seed source [253,254]. Lester and others [210] offer the following elevational constraints for seed transfer in British Columbia:
Maximum elevational transfer (ft/m) Latitudinal range Upward Downward 49 to 56o 984/300 328/100 56 to 60o 328/100 164/50
