Montane Warm Dry Coniferous Douglas fir/white spirea-common snowberry/pinegrass

Description

The overstory is dominated by Douglas-fir, with minor amounts of western larch (Larix occidentalis), or at lower elevations, it is of ponderosa pine (Pinus ponderosa). Douglas-fir and ponderosa pine are well adapted to fire, having thick bark at maturity which protects the cambium layer from overheating. The understory has patchy white spirea, Rocky Mountain maple, and common snowberry with abundant rhizomatous grass species of pinegrass and/or Geyer’s sedge. The overstory can be multi-storied Douglas-fir or an open, park-like single story. Douglas-fir is moderately shade-tolerant compared to associates ponderosa pine, western larch, and lodgepole pine (Pinus contorta), which are all intolerant of shade. Frequent, non-lethal wildfires had historically maintained open, park-like stands. All four species are adapted to the historic fire regime as they regenerate well following disturbance, especially when mineral soils were exposed, which is a key factor in regeneration of ponderosa pine and western larch (and, to a lesser degree, lodgepole pine). Ponderosa pine and western larch are long-living (300-400 years), while lodgepole pine survives only 150-200 years. In the absence of naturally occurring wildfire, Douglas-fir is the only species that continues to regenerate in any abundance and thus gradually becomes dominant in those undisturbed stands. In this ecological site, Douglas-fir is present in all seral stages with lodgepole pine and western larch, and ponderosa pine is present in the lower-elevation sites. The understory has an abundance of rhizomatous grasses, pinegrass, and Geyer’s sedge, and the medium-sized shrubs common snowberry (Symphoricarpos albus), Oregon boxleaf (Paxistima myrsinites), Saskatoon serviceberry (Amelanchier alnifolia), creeping barberry (Mahonia repens), white spirea (Spiraea betulifolia), snowbush ceanothus (Ceanothus velutinus), kinnikinnick (Arctostaphylos uva-ursi), and fireweed (Chamerion angustifolium). These shrubs are adapted to this fire regime of a frequent, low-severity type by having the ability to resprout from root crowns or rhizomes after the low-intensity fire removes the aboveground portion of the plants. Specifically, Saskatoon serviceberry, Rocky Mountain maple (Acer glabrum), resprout from root crowns. Common snowberry, white spirea, thimbleberry (Rubus parviflorus), and thinleaf huckleberry (Vaccinium membranaceum) sprout from rhizomes. McLean (1970) describes the response to fire for common snowberry, white spirea, Oregon boxleaf as “resistant,” with taproots or a fibrous root system with rhizomes 5-13 cm deep. Pinegrass (Calamagrostis rubescens), creeping barberry, and heartleaf arnica (Arnica cordifolia) are considered “intermediate,” with shallower rhizomes. The “susceptible” category included the western rattlesnake plantain (Goodyera oblongifolia) and the Pyrola species, although these species are rarely found at this site. Twinflower (Linnea borealis) has rhizomes in duff, kinnikinnick has fibrous roots and stolons, and white hawkweed (Hieracium albiflorum) resprout with fibrous roots only. Snowbush ceanothus germinates from fire-stimulated seed, and fireweed produces many windborne seeds that will recolonize sites from unburned areas. Specifically, at the reference phase the understory has an abundance of rhizomatous grasses, pinegrass and Geyer’s sedge and the medium sized shrub, common snowberry. While primary data was collected in Glacier National Park, this site extends west onto the Flathead and Kootenai National Forests.

Submodel

Description

Another disease affecting this ecological site is root rot. Armillaria root disease is the most common root disease fungus in this region, and 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 most susceptible tree species first, leaving less susceptible tree species that mask the presence of disease. 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 involves entire stands and drainages, and often is severe by age 40. 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 correctly identify the type of root disease(s) on the management unit, and manage species such as late seral pine and larch. Pre-commercial thinning will improve growth and vigor of the residual stand. Thinning and harvest operations should remove susceptible species (Douglas-fir or true firs) to the degree practical, retaining late seral species such as western larch and pine (Hagle, 2010). Tree planting can be used to facilitate a shift in species composition to those conifers which have greater tolerance to root diseases. There has been a link determined between parent material and susceptibility to root disease.

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 forest stand could cross a threshold and become a shrubland, once all trees are gone (Kimsey et al., 2012). Persistent shrub fields may take a century or longer for the infected root mass to decline, which will return the root disease potential to background levels, and allow the reintroduction of resistant conifer species.

Submodel