Lower Subalpine Frigid Coniferous western redcedar (Thuja plicata)-western hemlock (Tsuga heterophylla)

Description

Historically western white pine would have been within Flathead County, which encompasses the Flathead N.F. and in lower elevations, west of the Continental Divide in Glacier NP. The historic extent of western white pine in Glacier National Park was primarily along the western border. Originally, western white pine covered five million acres in the Inland Northwest. Western white pine is incredibly productive for timber with a very high growth rate, tall and deep–rooted, and competes best on highly variable, high resource sites. As well, it is tolerant to the native root rot diseases and other native forest pests. Western white pine is susceptible to Armillaria root disease only when young, and to mountain pine beetle largely at advanced ages (over 140 years). It also has the capability to thrive in a wide variety of sites and environments, which means it has high ecological flexibility. It is a long-living seral species that tolerated intense timber harvesting practices and severe fire disturbance by its ability to regenerate heavily on mineral soil and full sunlight. Fire greatly influences the composition, structure, and function of vegetation across the landscape. Historically, it was mixed severity fire between severe stand replacement fires. Western larch and western white pine are long-lived, fire-adapted, shade-intolerant tree species that historically thrived. Also present in significant amounts particularly in young stands, but declined through time due to effects of insects and pathogens, were the shorter-lived, shade-intolerant, fire-adapted tree species such as Douglas-fir and lodgepole pine. Shade-tolerant, fire-intolerant tree species such as western cedar, western hemlock, grand fir, Engelmann spruce, and subalpine fir were present, but rarely survived long enough to dominate stands except in areas where the interval between fires was unusually long and where root disease was not severe.

Submodel

Description

Western redcedar (Thuja plicata)-Western hemlock (Tsuga heterophylla)/pipsissewa (Chimaphila umbellata)-queencup beadlily (Clintonia uniflora)-western rattlesnake plantain (Goodyera oblongifolia)-twinflower (Linnea borealis)/moss.

State 2 is different than State 1 in that western white pine no longer plays a significant role in the seral communities. It has been dramatically reduced in numbers and area by the epidemics of white pine blister rust and western spruce budworm, and by dramatic fire suppression. Therefore, climax species have been able to fill the seral role that western white pine once held. As well, more forests are progressing to the climax or Reference Phase than historically, when most forests were in the fire-maintained western white pine-dominated seral phase. State 2 forests are now dominated by the shade-tolerant climax species western redcedar and western hemlock. While there is a tremendous effort to bolster the numbers of western white pine, it currently covers only 5 percent of its historic range.

This ecological site is described as having moderately cool and moist site conditions. The Reference state is dominated by western redcedar and western hemlock, both of which are shade-tolerant climax conifers that grow in similar environments. Western redcedar has a larger geographic extent in Montana, but western hemlock usually is capable of attaining dominance over western redcedar and other species at climax because it is better able to reproduce under a dense forest canopy. Western redcedar is able to maintain itself indefinitely as a minor climax species because of its shade tolerance, longevity (often 600-1,000 years), and apparent ability to regenerate vegetatively (USFS H.T. Guide, 1973). Within Glacier NP, these species are co-dominant in nearly all of the sites visited. The seral successional stages have very diverse overstory tree composition and can be very productive in terms of basal area. Douglas-fir, western larch and, to a lesser extent, spruce are often dominants in seral stands with lodgepole, western white pine, and paper birch as minor components. Grand fir and subalpine fir can be either minor seral or climax components. Western redcedar and western hemlock will regenerate after disturbance along with seral species, and it will take centuries for these species to gain dominance in the overstory over the seral species. The early successional phase can be dominated by fireweed (Chamerion angustifolium). The understory in seral successional phases have moisture-loving forbs or shrubs including Scouler’s willow, thimbleberry, serviceberry, rocky mountain maple, thinleaf huckleberry, and snowbush ceanothus. The historic fire regime of these forests is one of low fire frequency, but fire severity can be highly variable. It can be low due to the most common moist conditions, but can be severe during times of drought. Fire return intervals range from 50 to greater than 200 years, but include mixed severity fires on 50-85 year intervals, as well as stand replacement fires on 150-250 year intervals. Western redcedar can thrive for centuries on this ecological site without disturbance. The Northern Rocky Mountain mesic montane mixed-conifer forest-cedar groves are in fire regime group 5 and had a fire interval of 334 years, with 87 percent of fires classified as of replacement severity and 13 percent of fires classed as mixed severity and none as low severity (USDA, USFS, FEIS, Fire Regime). Fuel loadings for this ecological site can be very high due to deadfall and natural thinning of small and medium-sized branches. In early and intermediate successional phases, the understory can have high cover adding to fuel loadings. Due to the generally moist conditions, fire return intervals can be long. In general, the variability in fire regime and the high diversity of tree species present in most stands, except the Reference, allow this ecological site to form a diverse mosaic landscape with varying dominance or mixes of seral species.

Submodel

Description

Another disease affecting this ecological site is root rot. While Douglas-fir, grand fir, and subalpine fir are most susceptible, western redcedar and western hemlock can be affected as well. Armillaria root disease is the most common root disease fungus in this region, and is 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 effects the tree species most susceptible 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. Western redcedar is moderately resistant to Armillaria root rot in Idaho and Montana. The common disease expression is some mortality in saplings, and residuals of partial harvests often develop severe infections but are very slow to die (Hagle, 2010). There has been a link determined between parent material and susceptibility to root disease (Kimsey et al., 2012). 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 root disease mortality, then a coniferous stand could cross a threshold and become a shrubland, once all conifers are gone (Kimsey et al., 2012). Management tactics include to identify the type of Armillaria root disease, and manage for pines and larch. Pre-commercial thinning may improve growth and survival of pines and larch. Avoid harvests that leave susceptible species (usually Douglas-fir or true firs) as crop trees (Hagel, 2010).

Submodel