Montana Field Guide

This ecological system is widespread but patchy in distribution in upper montane to subalpine zones of the Montana Rocky Mountains, and east into mountain island ranges of central Montana. These are upper montane to subalpine forests where the dominance of lodgepole pine (Pinus contorta)is related to fire history, topo-edaphic conditions and nutrient-poor soils. Presence of this system is determined more by substrate than by other factors. The most notable occurrence of this system is in the West Yellowstone Basin and surrounding Yellowstone Highlands, such as the Madison Plateau. In this region of Montana, cold-air ponding and coarse, rhyolitic outwash obsidian sands are the major factors contributing to the extensive development of this system in southwestern Montana. Fire is infrequent in this system, averaging every 150-400 years in subalpine forests. Following stand-replacing fires, lodgepole pine will colonize rapidly on sites that are too extreme for the establishment of other coniferous species, developing into dense, persistent, even-aged stands. Mature stands are primarily open, and develop past their initial even-aged structure to become a multi-aged structure. These stands last for longer intervals between disturbances than do conventional lodgepole pine-dominated stands.

Forest and woodland, acidic, very shallow ustic soils, organic A horizon less than 10 cm, Pinus contorta

These forests are dominated by lodgepole pine (Pinus contorta) withsparse undergrowth. At the closed canopy stage of stand development, undergrowth may be totally lacking. Some open stands with very sparse understories can experience a form of mixed-severity burning along downed logs when there are insufficient fuels between logs to carry fire. Depending on the arrangement and loading of logs to living trees, either mortality or fire-scarring may occur.

The shrub layer may be conspicuous to absent. Common species include bearberry (Arctostaphylos uva-ursi), snowbrush ceanothus (Ceanothus velutinus), twinflower (Linnaea borealis), creeping Oregon grape (Mahonia repens), antelope bitterbrush(Purshia tridentata), birch leaf spiraea (Spiraea betulifolia), Canadian buffaloberry (Shepherdia canadensis), dwarf huckleberry (Vaccinium caespitosum), grouse whortleberry (Vaccinium scoparium), snowberry (Symphoricarpos species) and currant (Ribesspecies).

Herbaceous layers are generally sparse, but can be moderately dense, and are typically dominated by perennial graminoids such as Columbia needlegrass (Achnatherum nelsonii), pinegrass (Calamagrostis rubescens), Geyer’s sedge (Carex geyeri), Ross’ sedge (Carex rossii), bottlebrush squirrel tail (Elymus elymoides), California oatgrass (Danthonia californica), blue wildrye (Elymus glaucus), and Idaho fescue (Festuca idahoensis). Common forbs include yarrow (Achillea millefolium), arnica (Arnica spp.), silky lupine (Lupinus sericeus), phlox (Phlox spp.), buckwheat (Eriogonum spp.), and beargrass (Xerophyllum tenax).

Establishment of lodgepole pine in this system is episodic and linked to stand-replacing fire. Lodgepole pine forests with very sparse understories experience longer fire return intervals ranging from 120 to over 300 years in comparison to stands with more productive understories (U.S. Department of Agriculture, 2012). This ecosystem also experiences a greater percentage of fires of mixed severity, with fewer stand-replacing fires than more productive lodgepole forests (USDA, 2012). Longer fire return intervals and decreased fire severity is largely attributable to the absence of significant ladder fuels in this system (Anderson, 2003). Fuel loading in this system is primarily a result of downed woody debris from past disturbances (e.g. mountain pine beetle, windfall), and sparse understory is not effective at sustaining high-intensity fires (Agee, 1996; Smith and Fischer, 1997). Fire severity is therefore only great as a result of long-term fuel accumulation, or severe climate conditions (Agee, 1996; Smith and Fischer, 1997).

Dense, even-aged stands resulting from stand-replacing fires are increasingly susceptible to windthrow and snow damage as they mature (Smith and Fischer, 1997). Individual trees that have matured in dense stands obtain a degree of protection from neighboring trees, such that the development of deep roots and other physical mechanisms to withstand wind exposure are unnecessary. Additionally, the shallow soils typical of this system contribute to the development of shallow rooting systems. As a result, increased wind exposure resulting from natural or mechanical thinning amplifies susceptibility to windfall (Anderson, 2003).

Trees with closed, serotinous cones appear to be strongly favored by stand-replacing fire, and allow rapid colonization of fire-cleared substrates (Burns and Honkala, 1990). These forests often exhibit a multi-aged population structure, with non-fire regeneration, and often exhibit a higher proportion of trees bearing non-serotinous cones. Additionally, the mixed-severity fires and generally longer fire return intervals characteristic of this system favor regeneration from non-serotinous cones (Anderson, 2003; Schoenagel et al., 2003). If serotiny is expressed in these stands, cone polymorphism exists and allows regeneration after non-fire disturbance.