Upper Subalpine Cold Coniferous subalpine fir (Engelmann spruce) /thinleaf huckleberry-rusty menziesia/ Hitchcock’s smooth woodrush-beargrass/yellow avalanche lily.

Description

Subalpine fir dominates the Reference State with the long-lived seral species whitebark pine and Engelmann spruce. Subalpine fir is tall, usually growing more than 15.24 m (50 feet) tall at maturity and is not stunted in the krummholtz form. The understory has the indicator species Hitchcock’s smooth woodrush, which is indicative of cold conditions, and is generally multi-storied with numerous shrub, forb and grass species. Shrubs include rusty menziesia (Menziesia ferruginea) and thinleaf huckleberry (Vaccinium membranaceum). Common forbs and grasses are Hitchcock’s smooth woodrush (Luzula glabrata var. hitchcockii), carex species, blue wildrye (Elymus glaucus), Rocky Mountain groundsel (Packera streptanthifolia), broadleaf arnica (Arnica latifolia), heartleaf arnica (Arnica cordifolia), fireweed (Chamerion angustifolium), lanceleaf springbeauty (Claytonia lanceolata), cow parsnip (Heracleum maximum), beargrass (Xerophyllum tenax), bracted lousewort (Pedicularis bracteosa), arrowleaf ragwort (Senecio triangularis), alpine leafybract aster (Symphyotrichum foliaceum), threeleaf foamflower (Tiarella trifoliata), green false hellebore (Veratrum viride), western meadowrue (Thalictrum occidentale), yellow avalanche lily (Erythronium grandiflorum) and viola species. Primary data was collected in Glacier National Park.

This ecological site is described as having cold and moist to moderately dry site conditions, with a variable, and hard to define, fire return interval, with fire typically of low severity due to discontinuous fuels. Stand-replacement fires can occur after intervals of more than 200 years, typically during drought conditions, and brought up from severe wind-driven crown fires from lower elevations forests (Fischer, 1987). Forest fuels typically are relatively sparse fine fuels and moderate to heavy loads of widely scattered large diameter fuels. These larger fuels are from wind and snow breakage, windthrow, and mortality caused by insects and disease. The normally cool and moist site factors, short fire season, and the sparse, discontinuous, fine surface fuels layer generally leads to low fire severity. If dry conditions exist, such as extended drought, then stand-replacement fire can occur. Vegetation succession afterwards is slow due to the extremely short growing season and cold climate. Site factors such as the cold and moist climate, the high rock and snow cover with low discontinuous surface fuels, and generally low vegetation production are more important to forest development than fire. Lightening fires do occur, but the rain that accompanies thunderstorms and discontinuous fuels limit fire occurrence, spread, and severity.

The general post-disturbance successional phases include the stand initiation phase dominated by herbaceous and shrub species and conifer seedlings, the young stand of pole-sized mixed conifers, the maturing forest of overstory mixed conifer trees, and the Reference Phase dominated by subalpine fir with small gap dynamics. A stand-replacement fire in the mature forest or reference phase would result in the stand initiation phase with species composition of seedlings varying with site conditions. The stand initiation phase will dominate for an extended period, up to 100 years, maintained by site conditions that allow physical disruption of the stand including snow load, windthrow, rock slides, and talus slippage. Whitebark pine, Engelmann spruce, subalpine fir, and subalpine larch seedlings can occupy this site and will progress to the young stand with no major disturbance. Fire is unlikely in these earlier successional phases, but can occur as surface fires or limited extent severe fires, which create vegetative mosaics. The stand progresses to the mature phase, which can sustain stand replacement fires in extended drought due to heavier fuels from breakage or mortality. Without disturbance, the mature stand progresses to the Reference Phase, which is rarely affected by low to moderate severity fires because of the open structure of the forest and discontinuous fire woody fuels. Stand-replacement fires that do occur can return the site to the stand initiation phase.

The significant fire that has occurred in the vicinity of the Continental Divide that affected this ecological site are the Kootenai (burned 8041 acres in 1998) Trapper (burned 18,453 acres in 2003), Rampage Complex (burned 23,237 acres in 2003) and the Red Eagle fire (burned 32,461 acres in 2006).

While subalpine fir can be subjected to a variety of diseases and insect pests, the US Forest Service (USFS) Stand Health map shows that for this specific ecological site, there has not been significant damage to the extent seen in lower elevation ecological sites dominated by subalpine fir and Engelmann spruce. Diseases and insect pests that can affect subalpine fir include root rot, stem decay, bark beetles, and wood borers and defoliators. These can weaken and or kill trees, which results in small openings scattered throughout the forest, or major mortality during an outbreak such as western spruce budworm (Choristoneura occidentalis). Windthrow is a common disturbance after either type of disturbance. Subalpine fir is most commonly susceptible to Armillaria and Annosus root disease, pouch, Indian paint, and red belt fungi which cause stem decay, metallic, roundheaded, and Western balsam bark beetles, fir canker, and defoliators such as Delphinella shoot blight, black mildew, brown felt blight, fir needlecast, snow blight, and fir-blueberry rust.

Submodel

Description

Another disease affecting the 43A UPPER SUBALPINE COLD CONIFEROUS ecological site is root rot. Armillaria root disease is the most common root disease fungus in this region, especially prevalent west of the Continental Divide. It may be difficult to detect until it has killed enough trees to create large root disease pockets or centers, ranging in size from a fraction of an acre to hundreds of acres. The root disease spreads from an affected tree to its surrounding neighbors through root contact. The root disease affects the most susceptible tree species first, leaving less susceptible tree species that mask its presence. When root rot is severe, the pocket has abundant regeneration or dense brush growth in the center. In western Montana and northern Idaho, Armillaria is present in most stands with diffuse mortality and large and small root disease centers. The disease pattern is one of multiple clones merging to form essentially continuous coverage of sites. Grouped as well as dispersed mortality can occur throughout the stand. A mosaic of brushy openings, patches of dying trees, and apparently unaffected trees may cover large areas. There can be highly significant losses, usually requiring species conversion in the active management approach. Management tactics include to identify the type of Armillaria root disease present and manage for pines and larch. Pre-commercial thinning may improve the growth and survival of pines and larch. Avoid harvests that leave susceptible species (usually Douglas-fir or true firs) as crop trees (Hagle, 2010). There has been a link determined between parent material and susceptibility to root disease, and metasedimentary parent material is thought to increase the risk of root disease. Glacier National Park is dominated by metasedimentary parent material, and may be more at risk than other areas to root disease (Kimsey et al., 2012). If a stand sustains very high levels of roots disease mortality, then a coniferous stand could cross a threshold and become a shrubland, once all conifers are gone (Kimsey et al., 2012).

Submodel