Montana Field Guide

This forest type is widespread in the upper montane and subalpine zones across the mountainous areas of the state, including the island ranges of north-central Montana and the Bighorn and Beartooth ranges of south-central Montana. Lodgepole pine (Pinus contorta) is the dominant tree in these communities, though other coniferous species such as Subalpine fir, Douglas-fir, Engelmann Spruce and Whitebark pine are often present in many of the forests depending on location, site characteristics and successional status. These stands may be relatively open or occur as dense canopies, especially in young, even-aged, “doghair” stands. The understory is usually open and may be composed of short shrubs, graminoids or forbs. In Montana, elevations range from 3,200-9000 feet though they primarily occur between 5,000 and 7,500ft in elevation (Pfister etal 1977). These forests occur on flats to slopes on all aspects. They generally occur on dry to intermediate sites. Conifer succession proceeds at different rates, moving relatively quickly on low-elevation, mesic sites and particularly slowly in high-elevation forests such as those along the Continental Divide in Montana. Fire is frequent, and stand-replacing fires are common in these habitats. Following stand-replacing fires, lodgepole pine will rapidly colonize and develop into dense, even-aged stands. Most forests in this ecological system occur as early- to mid-successional forests persisting for 50-200 years on warmer, lower elevation forests, and 150-400 years in subalpine forests.

This Group encompasses the Rocky Mountain Lodgepole Pine Forest and the Rocky Mountain Poor Site Lodgepole Pine Forest Ecological Systems.

Lodgepole Pine (Pinus contorta) Conifer Forest and Woodland; Rocky Mountains; Montane and Subalpine Zones; Stand Replacing Fire Regimes.

Widespread in the upper montane and subalpine zones across the mountainous areas of the state on both sides of the Continental Divide. It extends east to all of the island ranges including the Sweetgrass Hills, Little Rockies, the Snowy Mtns, and the Pryor and Bighorn Mtns.

In MT, G220 occurs within these Level III Ecoregions: 15 (Northern Rockies), 16 (Idaho Batholith), 17 (Middle Rockies) and 41 (Canadian Rockies).

In Montana, G220 occurs within these Major Land Resource Areas: 43A-Northern Rocky Mountains, 43B - Central Rocky Mountains, 44A - Northern Rocky Mountain Valleys, and 46 - Northern and Central Rocky Mountain Foothills.

Matrix

This group generally occurs on dry to intermediate sites at moderate to high elevations. In Montana, elevation ranges from 3,200-9000 feet. East of the Continental Divide, stands primarily occur between 5,000 and 7,500ft in elevation (Pfister etal 1977). Snowfall is heavy and supplies the major source of soil water used for growth in early summer. Lodgepole forests are typically associated with rock types weathering to acidic substrates, such as granite and rhyolite though in west-central Montana ranges such as the Big Belts and the Rocky Mountain Front, these forests are found on limestone substrates. These forests are especially well developed on the broad ridges and high valleys near and east of the Continental Divide. Succession proceeds at different rates, moving relatively quickly on low-elevation, mesic sites and particularly slowly in high-elevation forests such as those along the Continental Divide in Montana.

These forests are dominated by Lodgepole Pine (Pinus contorta) with shrub, grass, or barren understories. They may be relatively open to dense-canopied. Other conifers may be present, especially in later successional stands, especially Douglas-fir (Pseudotsuga menziesii), Engelmann spruce (Picea engelmannii), and subalpine fir (Abies lasiocarpa). Numerous other conifers may be present depending on location, site characteristics and successional status. In western Montana, other commonly occurring tree species in later seral stages, include western larch (Larix occidentalis), western white pine (Pinus monticola), grand fir (Abies grandis) and western hemlock (Tsuga heterophylla). In the subalpine zone, mountain hemlock (Tsuga mertensiana) may be present. In the productive habitats of western Montana, lodgepole pine stands often decline in a wave of mortality, usually before they are 120 years old. At montane elevations east of the Continental Divide, lodgepole pine stands succeed to Douglas-fir (Pseudotsuga menziesii) forests. At subalpine elevations, these sites usually transition to Spruce-fir forests.

The shrub stratum in Lodgepole Pine stands may be conspicuous to absent. Common shrub and subshrub species include Kinnikinnick (Arctostaphylos uva-ursi), snowbrush ceanothus (Ceanothus velutinus), twinflower (Linnaea borealis), Oregon grape (Mahonia repens), birch leaf spiraea (Spiraea betulifolia), Canadian buffaloberry (Shepherdia canadensis), dwarf huckleberry (Vaccinium caespitosum), grouse whortleberry (Vaccinium scoparium), mountain huckleberry (Vaccinium membranaceum), and currants or gooseberries (Ribes species).

Herbaceous layers are generally sparse, but can be moderately dense, and are typically dominated by perennial graminoids such as pinegrass (Calamagrostis rubescens), Geyer’s sedge (Carex geyeri) and Ross’ sedge (Carex rossii). Common forbs include yarrow (Achillea millefolium), Mountain arnica (Arnica latifolia), Lupine (Lupinus argenteus) and beargrass (Xerophyllum tenax). Mycoheterotrophic species such as coralroot orchid (Corallorhiza spp.), Indian pipe (Moneses uniflora), pinesap (Monotropa hypopithys), and pinedrops (Pterospora andromedea) are often associated with lodgepole pine forests. Non-native species are often absent or incidental in these forests though in western Montana, hawkeeds (Orange or Meadow) may invade some sites.

In Montana, this group encompasses 27 Associations grouped into 4 Alliances within the National Vegetation Classification. Associations within this group are generally well-documented and it is unlikely that additional types are warranted for Montana.

Lodgepole pine is a colonizing species and shade-intolerant conifer that occurs in the upper montane to lower subalpine forests throughout the major mountain ranges of Montana. Establishment is episodic and linked to stand-replacing disturbances, primarily fire. Historically, fire frequency varied between 50 and 300 years, depending on local climate and elevation, with fire frequency declining with increasing elevation (Schoenagel et al. 2003). In the Northern Rockies, severe fires have created large expanses of even-aged stands of lodgepole pine, although more frequent low- to mixed-severity burns may also occur in the intervals between stand-replacing fires, generating a matrix of mixed-age stands (Hardy et al. 2000; Arno et al. 1993). Occasionally, fire severity may be such that cones are destroyed and regeneration will rely on wind-dispersed seeds from nearby stands, resulting in slower regrowth (Anderson 2003). Repeated fires allow lodgepole pine to persist as the climax species in this system by eliminating the potential for succession by more shade-tolerant species (Pfister et al. 1977).

Trees with closed, serotinous cones where seed release is a response to an environmental trigger, require high temperatures to release seeds and appear to be strongly favored by fire, allowing rapid colonization of fire-cleared substrates (Burns and Honkala 1990). The incidence of serotinous cones varies within and between varieties of lodgepole pine, but within Rocky Mountain populations, serotiny varies both across regions and with stand age (Schoenagel et al. 2003). Stands that occur at lower elevations where fire return intervals are shorter exhibit greater serotiny, whereas higher elevation stands with greater fire return intervals favor non-serotinous cones which are more advantageous for successful regeneration (Schoenagel et al. 2003). Lodgepole pine stands exhibiting a multi-aged population structure also exhibit a higher proportion of trees bearing non-serotinous cones. Even-aged stands that establish after stand-replacing fires exhibit greater serotiny than those that establish after wind or insect disturbances (Anderson 2003).

In fire-generated stands of similar age, trees become increasingly susceptible to both mountain pine beetle (Dendroctonus ponderosae) and lodgepole pine dwarf mistletoe (Arceuthobium americanum) infestations as they mature, often resulting in large-scale mortality from the former. In general, pine beetles preferentially attack large individuals with greater nutritional resources (Cole and Amman 1969). In these communities, large scale, stand-replacing fires have occurred frequently throughout Montana during the past 20 years, increasing stand homogeneity favorable to beetle attack. Elevated temperatures and increasing drought severity additionally combine to favor beetle population growth and weaken lodgepole pine defense mechanisms, thereby increasing susceptibility to mountain pine beetle attack (Raffa et al. 2008). Interactions between biotic and abiotic disturbance agents in lodgepole pine systems are complex, and the widespread mortality associated with these disturbances alters ecosystem processes. Ecosystem-level effects of mountain pine beetle outbreaks include changes to carbon cycling (Kurz et al. 2008), hydrology (Bearup et al. 2014; Mikkelson et al. 2013), and fuel structure and flammability (Hicke et al. 2012; Jolly et al. 2012). However, at broad spatial scales it does not appear that pine beetle caused mortality increases stand susceptibility to fire (Hart et al. 2015; Simard et al. 2011). Alternatively, dwarf mistletoe increases host susceptibility to fire by altering fuel dynamics, and intensifies host vulnerability to insect attack (Hawksworth et al. 2002).

Effects of fire, fire suppression, fuel accumulation, stand development, insects, and disease in these forests interact to control the establishment and maintenance of stands. Because they are often initiated by stand-replacing fire, Rocky Mountain lodgepole pine stands are frequently even-aged. However, stands of similar age frequently differ in density, ranging from open stands of large trees to very dense, stunted "doghair" stands. In the absence of natural fire, periodic prescribed burns and selective thinning can be used to maintain these communities. Thinning may, however, increase long-term stand susceptibility to mountain pine beetle attack (Fettig et al. 2006), and dense, even-aged stands may be vulnerable to windthrow as a result of thinning (Anderson 2003). Low intensity prescribed burning may increase long-term resistance to mountain pine beetle attack (Hood and Sala 2013), although stands may be more vulnerable to attack in the short term (Kulakowski and Jarvis 2013). Prescribed burning may also encourage dwarf mistletoe success if infected individuals are not eliminated, as dwarf mistletoe germination rates are enhanced by smoke exposure (Kipfmueller and Baker 1997).

Non-native species are often absent or incidental in these forests though in western Montana, hawkeeds (Orange or Meadow) may invade some sites.

Low-frequency stand-replacing fires are characteristic of this system (Stephens et al. 2013), with higher frequency low- to mixed-severity burns occurring in the intervals between high-severity fires (Hardy et al. 2000). Restoration strategies will depend largely on management goals. Low intensity prescribed burning and selective thinning may be utilized as restoration strategies to restore historic fire regimes and increase long term resistance to mountain pine beetle attack (Hood and Sala 2013; Fettig et al. 2006). Under favorable moisture conditions, seeds released from serotinous cones during fire germinate on exposed mineral soil and disturbed duff the following spring. Fire creates a favorable seedbed by removing loose organic matter and exposing mineral soil or decomposed organic matter, which encourages germination. Therefore, in most scenarios, additional post-fire restoration practices are not required. However, regeneration success may be marginal when stand-replacing fires are followed by years of severe drought (Stephens et al. 2013) and may require supplemental restoration efforts. When supplemental planting is necessary, germination rates for seeds from serotinous cones may be enhanced by short exposure to flame (Anderson 2003). Early successional stages following fire in lodgepole pine forests are dominated by an understory of forbs and to a lesser extent, graminoids such as fireweed (Chamerion angustifolium), aster (Aster species), nettleleaf giant hyssop (Agastache urticifolia), and pinegrass (Calamagrostis rubescens).

M.E. Hall 2013

S. Mincemoyer, L. Vance, T. Luna, S.V. Cooper

12/4/2024