Ecological dynamics

This ecological site group relates to numerous USFS Habitat Types in the Engelmann spruce series (Pfister, 1977), which is in Fire Group 9 and in the updated USFS Region 1 Montana Potential Vegetation Type Group PICEA (9 cool and wet) and in the old Habitat Type Group 8. It was in the Vegetation Response Unit 8.


►OVERVIEW◄
The Montane Wet Cool Coniferous ecological site group spans the zone between the lower, warmer and drier Douglas fir zone and the higher and cooler subalpine fir zone. This ecological site includes a range of wet to moist site conditions and is typified by an overstory of Engelmann spruce with various understories and seral communities. The wet site conditions are less common than the moist site conditions within this LRU. The moist to wet site conditions, location on drainageways or swales, occurrence of mesic plants and dominance by Engelmann spruce in the overstory define the modal concept, though the water table depth and degree of flooding and ponding vary slightly between these site conditions. The wettest sites will have only Engelmann spruce in all seral stages and have an understory dominated by field horsetail in the reference community. The moist site conditions will have Engelmann spruce and seral tree species including Douglas fir, western larch, and lodgepole pine as well as a diverse understory.
The wettest site conditions will be found on flat areas with poor drainage on broad alluvial valley bottoms with soils that are usually wet throughout the year and often have standing water (ponding). This relates to the USFS Habitat Type Engelmann spruce/field horsetail (Pfister, 1977). The water tables are usually less than 50 cm deep. These wettest sites are usually located near drainages, ponds or fens. Engelmann spruce is present in all seral stages and dominates the overstory in the reference stage, though other species, usually subalpine fir, may be present in trace amounts on dry hummock microsites (composed of root crown and windthrow mounds) (Pfister, 1977). The understory is dominated by field horsetail (Equisetum arvense) and to a lesser extent mesic species including redosier dogwood (Cornus sericea), twinberry honeysuckle (Lonicera involucrata), sedges (Carex species), fragrant bedstraw (Galium triflorum), arrowleaf ragwort (Senecio triangularis), largeleaf avens (Geum macrophyllum), claspleaf twistedstalk (Streptopus amplexifolius), common ladyfern (Athyrium filix-femina), dwarf red blackberry (Rubus pubescens), bunchberry dogwood (Cornus canadensis), Canadian white violet (Viola canadensis), and rarely American skunkcabbage (Lysichiton americanus). Post-disturbance community is dominated by Engelmann spruce, water birch (Betula occidentalis), thinleaf alder (Alnus incaca ssp. tenuifolia), Bebb willow (Salix bebbiana), and field horsetail (Equisetum arvense) (Pfister, 1977). This ecological site group has limited use for cattle but moderate use by wildlife (Hansen, 1995). It can be important as shading areas for livestock, but the soils are sensitive to disturbance due to wet conditions, and cattle can easily churn the wet soil and destroy plant cover. Due to high water tables, the trees are extremely susceptible to windthrow and soil loss may follow all forms of timber harvesting- therefore limiting potential use (Hansen, 1995). Deer, elk, moose have moderate use; field horsetail (Equisetum arvense) is important food for grizzly bears, black bear use it for wallows, big game for rutting, and small mammals and avian species make high use due to structural diversity (Gautreaux, Russ. 1999).
This ecological site also includes moist site condition areas which have less flooding and ponding and a deeper seasonal water table than the wet sites. It is found on undulating or flat alluvial benches and gentle north slopes (Hansen, 1995). The reference community has an overstory dominated by Engelmann spruce but has a variety of tree species in the seral communities including Douglas fir, western larch and lodgepole pine. The understory is diverse with multi-layered shrubs, forbs and grasses including: bride’s bonnet (Clintonia uniflora), wild sarsaparilla (Aralia nudicaulis), bunchberry dogwood (Cornus canadensis), redosier dogwood (Cornus sericea), dwarf red blackberry (Rubus pubescens), twinflower (Linnaea borealis), American trailplant (Adenocaulon bicolor), and fragrant bedstraw (Galium triflorum). The warmest, driest sites will not have bride’s bonnet (Clintonia uniflora), but will have bunchberry dogwood (Cornus canadensis), fragrant bedstraw (Galium triflorum), dwarf bilberry (Vaccinium cespitosum). This relates to the USFS Habitat Type Engelmann spruce/bride’s bonnet (Pfister, 1977). The drier site conditions, compared to the wet sites, will have more livestock and wildlife use, but this use is still low. Herbage production is low to moderate due to dense overstory and therefore limits use by livestock (Gautreaux, Russ. 1999). Redosier dogwood is very desirable to livestock and wildlife such as deer and elk, and browsing can be very high (Hansen, 1995). Deer and elk use these sites as winter range and moose will use them year-long in flat mountain valleys. Timber production ranges moderate to high but is complicated or restricted by high water tables (Hansen, 1995). Two other habitat types associated with this ecological site are found in moist conditions including Englemann spruce/fragrant bedstraw and Englemann spruce/starry false lily of the valley. The former is found in cool, moist locations usually bordering streams with an understory of various wet site forbs including fragrant bedstraw, red baneberry, claspleaf twistedstalk, thimbleberry, prickly currant and common snowberry (Pfister, 1977). The latter is found on warm, moist benches and lower slopes with an understory of forbs including starry and feathery false lily of the valley, western meadowrue, roughfruit fairybells, Richardson’s geranium (Pfister, 1977).
The driest site conditions within the spectrum for this ecological site has an overstory dominated by Engelmann spruce in the reference community but has various tree species in seral communities and a diverse understory. Understory species include pinegrass, dwarf bilberry (Vaccinium cespitosum), twinflower (Linnaea borealis), white spirea (Spiraea betulifolia), common snowberry (Symphoricarpos albus). The post-disturbance community includes: Saskatoon serviceberry (Amelanchier alnifolia), starry false lily of the valley (Maianthemum stellatum), Virginia strawberry (Fragaria virginiana), sweetcicely (Osmorhiza berteroi), western meadow-rue (Thalictrum occidentale), Rocky Mountain maple (Acer glabrum), creeping barberry (Mahonia repens), redosier dogwood, alderleaf buckthorn (Rhamnus alnifolia). This relates to the USFS Habitat Type Engelmann spruce/dwarf bilberry (Pfister, 1977). Engelmann spruce reestablishes quickly after disturbance but assumes dominance slowly and shrub cover is moderate (Hansen, 1995). Another habitat type found in drier sites is Englemann spruce/twinflower which resides on cool, well drained benches and gentle northeast slopes with an understory of thinleaf huckleberry, VASC, ALVIS, pinegrass and common snowberry (Pfister, 1977).

►ECOLOGICAL DYNAMICS◄
The primary ecological processes are infrequent events such as severe flooding, windthrow, and wind-driven fire from adjacent drier sites. Specifically, fire is not a significant (in terms of frequency or common severity level) disturbance agent due to moist fuel beds, lush mesic undergrowth, and high humidity (Gautreaux, Russ. 1999). Engelmann spruce is easily killed by fire due to the dead, dry, flammable lower limbs, low growing canopy, thin bark and lichen growth in the branches which contribute to low fire resistance. Additionally, the shallow root system is readily subject to injury from fire burning through the duff (the deep accumulation of resinous needle litter) (Hansen, 1995). Large older trees may survive light severity fires. Redosier dogwood (Cornus sericea) and the associated shrub species can survive all but the most severe fires that remove duff and cause extended heating of the upper layer of soil. These resprout from surviving rhizomes or stolons. Seral and climax stages dominated by Engelmann spruce and other seral species occur on hummocks or drier areas within the site on wettest site conditions; while drier conditions have other tree species during seral phases including: Douglas fir, western larch and lodgepole pine. Stands have moderate or high density forest structure and these are periodically reduced by bark beetles, windthrow or fire from surrounding drier areas (Gautreaux, Russ. 1999). Mature stands in highly productive, moist settings are susceptible to high levels of heartrot, root disease, white pine blister rust, dwarf mistletoe (Hagle, 2003). In stands with root disease, fir engraver beetles may occur as well. Blowdown susceptibility is high due to the high water table, shallow-rooted species, and presence of root disease or other decay-causing pathogens. Scouler willow can dominate in sites where a rise in water table height follows a severe fire. Additionally, the effects of extensive tree mortality can increase the level of cold air at a site resulting in frost impacts on conifer regeneration. This delay would allow for shrubs, such as serviceberry, thinleaf alder, redosier dogwood, and Rocky Mountain maple, to dominated (Gautreaux, Russ. 1999).

►FIRE REGIME◄
Due to the moist or wet site conditions, fire is not the dominant disturbance process for this ecological site. Fires can occur on this site, usually as wind driven events from adjacent, drier terrain. The fire regimes of northern Rocky Mountain conifer swamp communities has a modeled fire interval using LAND FIRE that is 400 years and severity is replacement (FEIS, USDA, USFS). The fire regime group was Five, which indicates the frequency is over 200 years and with generally replacement severity fires, but can include fires of any severity (FEIS, USDA, USFS). The fire frequency during average moist and moderate summers is generally low. Burning of the understory by creeping fires is not a major impact because of the high fuel moisture and the long fire return interval typical of this ecological site. Non-uniform lethal fires have a 300 to 400 year fire return interval in spruce bottoms (Gautreaux, Russ. 1999). In the Kootenai National Forest, lethal fires historically occurred every 150 to 400 years in riparian areas with an average 220 year fire return interval (FRI) for VRU 8 (wet cool types)(Gautreaux, Russ. 1999). Wetter sites are a deterrent to ground fires, but fire can scar trees residing on the edges. Stand replacing events occur only during prolonged drought conditions that dry out the high levels of fuels. After severe fire, regeneration is dependent on site conditions. Shade tolerant species are favored in small openings where duff is still intact whereas shade intolerant species and hardwoods dominate early seral stages in large openings by overtopping the tolerant species (Gautreaux, Russ. 1999). Cold temperatures, wet soils, and lush undergrowth favor early dominance by spruce (Hansen, 1999). Fire exclusion has not produced measurable effects because most historic fire return intervals were longer than the period of effective fire suppression.

►PEST/DISEASE DESCRIPTIONS◄
Engelmann spruce is susceptible to a variety diseases and insect pest damage to the root, stem, and foliage. Armillaria and Annosus root disease and Schweinitzii root- and butt-rot can be a concern, although the primary hosts for these diseases are Douglas fir and subalpine fir (Hagle, 2003). Stem decays on Engelmann spruce include Red belt fungus and Pini rot. Bark beetles and wood borers that attack include Metallic and roundheaded wood borers and Spruce beetle. Blue stain of sap wood also damages the stem. Spruce broom rust and Spruce cankers harm the branches and terminals of Engelmann spruce, while the foliage is damaged by Brown felt blight.

►ARMILLARIA 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. Rock types of the Flathead Valleys area is dominated by metasedimentary parent material of the Belt Supergroup (Ravallii group) with some Tertiary sediments, eolian deposits and glacial lake deposits. Metasedimentary rocks 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.

►MANAGEMENT◄
There are various management strategies that can be employed for this ecological site, depending upon the ownership of the particular land and which value is prioritized. The management of the forest determines the composition of the stand and the amount of fuel loading. A stand will be managed differently and look differently if it is managed for timber or ecological services like water quality and quantity, old growth, or endangered species. If a stand is managed for timber, it may be missing certain attributes necessary for lynx habitat. If a stand is managed for lynx habitat, it may have increased fuels and therefore an increased risk of wildfires.
This ecological site relates to the USFS Habitat Type PICEA/CLUN2 (Pfister, 1987). The USFS Habitat Type guide states that the basal area on the WEST side of the Continental Divide is 241+/- 38 ft2 per acre and site index at 50 years for PSME= 60, PICO=60, PICEA=69 (Pfister, 1987). It also relates to the USFS Habitat Type PICEA/VACA which has site index for PICO=65, LAOC=74, PICEA=64 (Pfister, 1987).
Timber production ranges from moderate to high and feasibility must take into account the wet soils and management of redosier dogwood and other resprouting shrubs post-disturbance (Pfister, 1987).
A guiding USFS document is the Green et al. document (2005) which defines “Old Growth” forest for the northern Rocky Mountains. This document provides an ecologically-based classification of old growth based on forest stand attributes including numbers of large trees, snags, downed logs, structural canopy layers, canopy cover, age, and basal area. This document finds that the bulk of the pre-settlement upland old growth in the northern Rockies was in the lower elevation, ground fire-maintained ponderosa pine/western larch/Douglas-fir types (Losensky, 1992).