No. 6. Lodgepole Pine Forest and Woodlands

Rex C. Crawford

Geographic Distribution. This habitat is found along the eastside of the Cascade Range, in the Blue Mountains, the Okanogan Highlands and ranges north into British Columbia and south to Colorado and California. 

With grassy undergrowth, this habitat appears primarily along the eastern slope of the Cascade Range and occasionally in the Blue Mountains and Okanogan Highlands. Subalpine lodgepole pine habitat occurs on the broad plateau areas along the crest of the Cascade Range and the Blue Mountains, and in the higher elevations in the Okanogan Highlands. On pumice soils this habitat is confined to the eastern slope of the Cascade Range from near Mt. Jefferson south to the vicinity of Crater Lake.

Physical Setting. This habitat is located mostly at mid- to higher elevations (3,000-9,000 ft [914-2,743 m]). These environments can be cold and relatively dry, usually with persistent winter snowpack. A few of these forests occur in low-lying frost pockets, wet areas, or under edaphic control (usually pumice) and are relatively long-lasting features of the landscape. Lodgepole pine is maintained as a dominant by the well-drained, deep Mazama pumice in eastern Oregon.

Landscape Setting. This habitat appears within Montane Mixed Conifer Forest east of the Cascade crest and the cooler Eastside Mixed Conifer Forest habitats. Most pumice soil lodgepole pine habitat is intermixed with Ponderosa Pine Forest and Woodland habitats and is located between Eastside Mixed Conifer Forest habitat and either Western Juniper Woodland or Shrub-steppe habitat.

Structure. The lodgepole pine habitat is composed of open to closed evergreen conifer tree canopies. Vertical structure is typically a single tree layer. Reproduction of other more shade-tolerant conifers can be abundant in the undergrowth. Several distinct undergrowth types develop under the tree layer: evergreen or deciduous medium-tall shrubs, evergreen low shrub, or graminoids with few shrubs. On pumice soils, a sparsely developed shrub and graminoid undergrowth appears with open to closed tree canopies.

Composition. The tree layer of this habitat is dominated by lodgepole pine (Pinus contorta var. latifolia and P. c. var. murrayana), but it is usually associated with other montane conifers (Abies concolor, A. grandis, A. magnifici var. shastensi, Larix occidentalis, Calocedrus decurrens, Pinus lambertiana, P. monticola, P. ponderosa, Pseudotsuga menziesii). Subalpine fir (Abies lasiocarpa), mountain hemlock (Tsuga mertensiana), Engelmann spruce (Picea engelmannii), and whitebark pine (Pinus albicaulis), indicators of subalpine environments, are present in colder or higher sites. Quaking aspen (Populus tremuloides) sometimes occur in small numbers.

Shrubs can dominate the undergrowth. Tall deciduous shrubs include Rocky Mountain maple (Acer glabrum), serviceberry (Amelanchier alnifolia), oceanspray (Holodiscus discolor), or Scouler’s willow (Salix scouleriana). These tall shrubs often occur over a layer of mid-height deciduous shrubs such as baldhip rose (Rosa gymnocarpa), russet buffaloberry (Shepherdia canadensis), shiny-leaf spirea (Spiraea betulifolia), and snowberry (Symphoricarpos albus and/or S. mollis). At higher elevations, big huckleberry (Vaccinium membranaceum) can be locally important, particularly following fire. Mid-tall evergreen shrubs can be abundant in some stands, for example, creeping Oregongrape (Mahonia repens), tobacco brush (Ceanothus velutinus), and Oregon boxwood (Paxistima myrsinites). Colder and drier sites support low- growing evergreen shrubs, such as kinnikinnick (Arctostaphylos uva-ursi) or pinemat manzanita (A. nevadensis). Grouseberry (V. scoparium) and beargrass (Xerophyllum tenax) are consistent evergreen low shrub dominants in the subalpine part of this habitat. Manzanita (Arctostaphylos patula), kinnikinnick, tobacco brush, antelope bitterbrush (Purshia tridentata), and wax current (Ribes cereum) are part of this habitat on pumice soil.

Some undergrowth is dominated by graminoids with few shrubs. Pinegrass (Calamagrostis rubescens) and/or Geyer’s sedge (Carex geyeri) can appear with grouseberry in the subalpine zone. Pumice soils support grassy undergrowth of long-stolon sedge (C. inops), Idaho fescue (Festuca idahoensis) or western needlegrass (Stipa occidentalis). The latter 2 species may occur with bitterbrush or big sagebrush and other bunchgrass steppe species. Other nondominant indicator graminoids frequently encountered in this habitat are California oatgrass (Danthonia californica), blue wildrye (Elymus glaucus), Columbia brome (Bromus vulgaris) and oniongrass (Melica bulbosa). Kentucky bluegrass (Poa pratensis), and bottlebrush squirreltail (Elymus elymoides) can be locally abundant where livestock grazing has persisted.

The forb component of this habitat is diverse and varies with environmental conditions. A partial forb list includes goldthread (Coptis occidentalis), false solomonseal (Maianthemum stellata), heartleaf arnica (Arnica cordifolia), several lupines (Lupinus caudatus, L. latifolius, L. argenteus ssp. argenteus var. laxiflorus), meadowrue (Thalictrum occidentale), queen’s cup (Clintonia uniflora), rattlesnake plantain (Goodyera oblongifolia), skunkleaf polemonium (Polemonium pulcherrimum), trailplant (Adenocaulon bicolor), twinflower (Linnaea borealis), Sitka valerian (Valeriana sitchensis), western starflower (Trientalis latifolia), and several wintergreens (Pyrola asarifolia, P. picta, Orthilia secunda).

Other Classifications and Key References. The Lodgepole Pine Forest and Woodland habitat includes the Pinus contorta zone of eastern Oregon and Washington ⁸⁸. The Oregon Gap II Project ¹²⁶ and Oregon Vegetation Landscape-Level Cover Type ¹²⁷ that would represent this type is lodgepole pine forest and woodlands. Quigley and Arbelbide ¹⁸¹ referred to this habitat as Lodgepole pine cover type and as a part of the Dry Forest potential vegetation group. Other references detail forest associations with this habitat ^{117, 118, 122, 123, 144, 212, 221}.

Natural Disturbance Regime. This habitat typically reflects early successional forest vegetation that originated with fires. Inland Pacific Northwest lodgepole pine has a mean fire interval of 112 years ²². Summer drought areas generally have low to medium-intensity ground fires occurring at intervals of 25-50 years, whereas areas with more moisture have a sparse undergrowth and slow fuel build-up that results in less frequent, more intense fire. With time, lodgepole pine stands increase in fuel loads. Woody fuels accumulate on the forest floor from insect (mountain pine beetle) and disease outbreaks and residual wood from past fires. Mountain pine beetle outbreaks thin stands that add fuel and create a drier environment for fire or open canopies and create gaps for other conifer regeneration. High-severity crown fires are likely in young stands, when the tree crowns are near deadwood on the ground. After the stand opens up, shade-tolerant trees increase in number.

Succession and Stand Dynamics. Most Lodgepole Pine Forest and Woodlands are early- to mid seral stages initiated by fire. Typically, lodgepole pine establishes within 10-20 years after fire. This can be a gap phase process where seed sources are scarce. Lodgepole stands break up after 100-200 years. Without fires and insects, stands become more closed-canopy forest with sparse undergrowth. Because lodgepole pine cannot reproduce under its own canopy, old unburned stands are replaced by shade-tolerant conifers. Lodgepole pine on pumice soils is not seral to other tree species; these extensive stands, if not burned, thin naturally, with lodgepole pine regenerating in patches. On poorly drained pumice soils, quaking aspen sometimes plays a mid-seral role and is displaced by lodgepole when aspen clones die. Serotinous cones (cones releasing seeds after fire) are uncommon in eastern Oregon lodgepole pine (P. c. var. murrayana). On the Colville National Forest in Washington, only 10% of lodgepole pine (P. c. var. latifolia) trees in low-elevation Douglas-fir habitats had serotinous cones, whereas 82% of cones in high-elevation subalpine fir habitats were serotinous ⁴.

Effects of Management and Anthropogenic Impacts. Fire suppression has left many single- canopy lodgepole pine habitats unburned to develop into more multilayered stands. Thinning of serotinous lodgepole pine forests with fire intervals <20 years can reduce their importance over time. In pumice-soil lodgepole stands, lack of natural regeneration in harvest units has lead to creation of "pumice deserts" within otherwise forested habitats ⁴⁷.

Status and Trends. Quigley and Arbelbide ¹⁸¹ concluded that the extent of the lodgepole pine cover type in Oregon and Washington is the same as before 1900 and in regions may exceed its historical extent. Five percent of Pacific Northwest lodgepole pine associations listed in the National Vegetation Classification are considered imperiled ¹⁰. At a finer scale, these forests have been fragmented by roads, timber harvest, and influenced by periodic livestock grazing and altered fire regimes.