Ecological dynamics

Ecological Dynamics of the Site
This site is found west of the Continental Divide in moderately cool and moist mid-elevations sites. Within Glacier National Park (NP), this ecological site has its greatest expression on the eastern side of Lake McDonald. While primary data was collected in Glacier NP, this habitat type also spans into the adjacent US Forest Service (USFS) land Flathead National Forest (NF), and in the Kootenai NF.

Management
Various management strategies 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, then 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.

The USFS Habitat Type Guide (1973) states that the basal area on the western side of the Continental Divide for western hemlock/queencup beadlily is 267+/-55 ft2 per acre. The fifty-year site index for western white pine is 62, western larch is 80, spruce is 77, and grand fir is 50. Basal area for western redcedar/queencup beadlily is 305+/-96 ft2 per acre and the site index for Douglas-fir is 66, western larch is 63, PICEA is 72+/-14, grand fir is 61, and subalpine fir is 74.

Timber production on these sites is very high, particularly in the seral phases of this ecological site.

Each national forest has a specific management plan. The management plan for the Flathead N.F. also has an Appendix B that gives specific management guidelines for habitat types (which relate to our forested ecological sites) found on the forest in relation to current and historic data on forest conditions (Flathead N.F. Plan, 2001 and Appendix B). Another 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. While 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), it does not mean that other types were not common or not important. This could apply to some of the areas of this ecological site.
State 1.0
Western White Pine (Pinus monticola)(Western redcedar (Thuja plicata)-Western hemlock (Tsuga heterophylla))/pipsissewa (Chimaphila umbellata)-queencup beadlily (Clintonia uniflora).

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.

Prior to the 20th century, western white pine was a major component in forested ecosystems of the inland northwest U.S. It has been greatly reduced in distribution and abundance by white pine blister rust, mountain pine beetles, and anthropogenic fire exclusion (Tomback and Achuff, 2010). Western white pine has been replaced by Douglas-fir, grand fir, and western hemlock. Douglas-fir and grand fir are susceptible to a greater variety of insect and disease problems and hemlock is more sensitive to drought and decay. More stands have also progressed to the climax species-dominated phase, which previously were rarely achieved due to the fire rotations and susceptibility of these species to disease and forest pests. In a study of pathogens and insects effects on forests within the Inland Empire found that, excluding fire, there were more than 90% of sample stands changed to a different cover type, structure stage, or both during a 40-year period that was coincident with the blister rust epidemic and fire suppression policy. Root pathogens, white pine blister rust, and bark beetle were the cause of most changes, and this accelerated succession of western white pine, ponderosa pine, and lodgepole pine to later successional, more shade-tolerant species. Structure was reduced in stand density or prevented canopy closure. Grand fir, Douglas-fir, and subalpine fir were the predominant cover types at the end of the period, and were highly susceptible to root diseases, bark beetles, fire, and drought. It is estimated that there will be continuation of this trend occurring in low-density mature stands and younger pole-sized stands that result from root disease and bark beetle-caused mortality (Byler and Hagel, 2000). These stands also are less productive in terms of timber. They are dominated by species with high nutrient demands, and therefore nutrient storage and cycling rates are increasingly depressed. This will likely lead to ever-increasing stress and destabilization by pests and diseases. Drought can further exacerbate the situation by stressing trees.

The Inland Empire Tree Improvement Cooperative and the USFS have a breeding program for blister-resistant western white pine. Approximately 5 percent of the original acre range was re-planted with rust-resistant stock. Currently, the modified stock shows about 60 percent resistance to blister rust. A study modeling the effects of climate change found that warming temperatures would favor increased abundance of western white pine over existing climax and shade-tolerant species in Glacier NP, mainly because warmer conditions potentiate fire dynamics, including increased wildfire frequency and extent, which facilitates regeneration (Loehman, et al., 2011).



State 2.0
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.

The general fire succession process is that after stand replacement fires, the community reverts to an herbaceous one, then to shrubland. If fire is reoccurring in this phase, then the phase is maintained for a long time. The herbaceous community can be dominated by the disturbance-loving fireweed, beargrass, or numerous other species, depending upon the seedbank at the site and beyond. Duration of the herbaceous or shrubland phase is also dependent upon the availability of tree seed. If serotinous lodgepole pine seeds are available, then the site will become dominated by it and a lodgepole pine stand will develop for about 10-25 years (Habeck, 1968). After that time, other species become established including western larch and other conifers. If serotinous lodgepole pine seeds are not present, then the seedlings are a very diverse mixture of conifers. These seedlings form a thick carpet on the site shared with shrub species such as Scouler’s willow, white spirea, thinleaf huckleberry, thimbleberry, and Oregon boxwood. Forbs present include ferns, beargrass and fireweed. Moss cover can be variable. If fire does not occur, the seedlings will grow to saplings and then pole-sized trees of diverse seral species. Low to moderate fires in this stage would favor fire-tolerant seral species over western redcedar, grand fir, or western hemlock, which are less fire-resistant. Severe fires will return these to the herbaceous or shrubland phase. In the pole-sized phase, seral species are abundant and western redcedar and western hemlock are just becoming established and usually have low cover (3-15 percent of the stand).Without further disturbance, this phase will continue to the maturing forest in which western redcedar and western hemlock become more evident in the stand and eventually have higher cover than the seral tree species. Western larch may survive severe fires in the maturing or mature phases. These trees would then provide seed for the stand initiation phase after a fire. As well, after frequent low to moderate fires in the mature phase, a relict western larch stand could occur. Reference stands in which only western redcedar and western hemlock occur can be rare, as seral species are long-lived and fire occurs frequently enough that stands seldom develop beyond the mature phase. Along the shores of Lake McDonald in Glacier NP, there were abundant stands that were in the Reference phase. The Robert fire in 2003 heavily impacted some areas on the west side of Lake McDonald, but other areas close to the shore were not affected. Reference stands may withstand low fires that thin the stand, but moderate or severe fires would return the site to the herbaceous or shrubland phase. Significant fires that have occurred on the west side of the Continental Divide that have affected this ecological site are the Robert Fire in 2003 that burned 54,191 acres, the Moose Fire in 2001 that burned 66,688 acres, and the Middle Fork Complex Fire in 2003 that burned 11,996 acres. There were historic fires within the area of this ecological site that burned significant portions in 1735 and another portion in 1926 (NPS Stand Age spatial layer).

Both western hemlock and western redcedar are subjected to a variety of diseases and insect pests including Armillaria root disease, Annosus root disease, pouch fungus, red belt fungus, pini rot, metallic wood borers, and roundheaded borers. Western redcedar also is susceptible to cedar laminated butt rot, cedar brown pocket rot, and cedar bark beetles. Western hemlock is also susceptible to Indian paint fungus.

A good tool to use to discern the levels of insects and diseases, the damage patterns, and whether these are at endemic or epidemic levels is aerial photography. These maps capture only moments in time, and infestations grow and move from location to location following their preferred habitat, so repeated photography can be necessary. Specifically for the northern region, the USFS Stand Health map shows, via many very large polygons throughout the area, that the major impact is defoliation by western spruce budworm. The defoliation was categorized as mostly of low severity (equal to or less than 50% defoliation) and some of high severity (with greater than 50% defoliation) on Abies species, and the damage is contiguous or nearly continuous. The forest type was categorized as W. Fir-Spruce. There also was defoliation by western spruce budworm on Douglas-fir, but to a much lesser degree. Larch casebearer, a defoliator of western larch, and generalized needlecast disease of western larch also was found, to a much lesser degree. Scattered small polygons showing damage were found throughout the region, including mortality from mountain pine beetle on lodgepole pines, Douglas-fir beetle on Douglas-fir, spruce beetle on Engelmann spruce, fir engravers and woolly adelgid on Abies species, and general Abies species mortality. These would affect the seral tree species of this ecological site and field notes corroborate these findings.


Community Phase 2.1: Reference
Western redcedar-western hemlock/prince’s plume-queencup beadlily-western rattlesnake plantain-twinflower/moss
Structure: Multistory with small gap dynamics

The Reference Community is dominated by western cedar and western hemlock, with seral tree species constrained to less than 3% of the overstory canopy. The ground cover consists predominantly of duff with fairly high cover of moss and trace cover of embedded litter and stones. The vegetation structure is that of very tall trees from 500-1,100 inches tall of western larch, western redcedar and western hemlock. The understory is multistoried though fairly sparse. Species occurring with the highest frequency of occurrence include thinleaf huckleberry, darkwoods violet, twinflower, western rattlesnake plantain, queencup beadlily and prince’s plume ( 15 sites of canopy cover data). Foliar cover at six sites indicate that the foliar cover is fairly high (50.8%) and the ground cover is primarily litter, which includes woody litter, litter or duff (total is 74%, duff is 63%) and moss (30%). The tallest understory layer is 20-40 inches tall and can include common ladyfern (Athyrium filix-femina), common snowberry (Symphoricarpos albus), white spirea (Spiraea betulifolia), and thinleaf huckleberry (Vaccinium membranaceum). The lowest layer is less than 10 inches tall and can include fireweed (Chamerion angustifolium), pipsissewa (Chimaphila umbellata), queencup beadlily (Clintonia uniflora), western rattlesnake plantain (Goodyera oblongifolia), twinflower (Linnaea borealis), threeleaf foamflower (Tiarella trifoliata), and Oregon boxleaf (Paxistima myrsinites). The most common seral tree species is western larch. The understory is depauperate of species and cover is very low. Species are shade-loving and include prince’s plume, queencup beadlily, western rattlesnake plantain, and twinflower with a thick cover of moss.

Community Phase Pathway 2.1A
This pathway represents a major stand-replacement fire disturbance such as a high-intensity fire, large scale wind event, or major insect infestation.

Forest overstory summarization table.

FOREST OVERSTORY
Forest canopy Canopy cover Average= 60%, Range= 45-90%
Average basal area Total 260-380 ft2/acre
Site Index at 100 yrs.: THPL (64-86); TSHE (65-91)

Community Phase 2.2: Stand Initiation. Regen: Lodgepole pine-western larch (mixed seral species)/
Scouler’s willow-white spirea-thinleaf huckleberry/thimbleberry-Oregon boxwood/fireweed-beargrass/moss.
Post- fire 1-5 years
Structure: Initially this post fire disturbance community is dominated by herbaceous and shrub species most commonly fireweed, species with a resident seedbank or disturbance loving species.
Structure: Continuous cover of regeneration-single story mixed tree species.
Post-fire 5-50 years

Structure: This is a forest in the stand initiation phase, possibly with scattered remnant mature trees; the composition of the seedlings depends on the natural seed sources available. Habeck found that in the vicinity of Lake Mcdonald in Glacier N.P., the dominant seral tree species is Lodgepole pine for 10-25 years post-fire. Afterwards, Western Larch will co-dominant from 25-50 years post-fire with other seral tree species at lower cover. Throughout the entire area of this ecological site, the regeneration will probably be a mixture. Overstory canopy cover is generally less than 10%, but the regeneration tree cover is very high forming a thick carpet. It is a mixture of species including: Lodgepole pine, Western larch, subalpine fir, Paper birch, Engelmann spruce, Western white pine, Black cottonwood, Quaking aspen, Douglas fir, Western redcedar and Western hemlock. The understory is a diverse mixture of herbaceous and shrub species including tall willow species, particularly Scouler’s willow, medium statured shrubs white spirea and thinleaf huckleberry, the low statured shrubs thimbleberry and Oregon boxwood. Herbaceous species include: fireweed, beargrass. Moss cover is variable.

Community Phase Pathway 2.2A
This pathway represents growth over time with no further significant disturbance. The areas of regeneration pass through the typical stand phases-competitive exclusion, maturation, understory reinitiating-until they resemble the old-growth structure of the reference community.

Community Phase 2.3: Intermediate Aged Forest.
Lodgepole pine-Douglas fir-Engelmann spruce-western larch-paper birch-subalpine fir-western white pine (western redcedar-western hemlock)/white spirea-snowberry-thinleaf huckleberry/thimbleberry/prince’s plume-queencup beadlily-twinflower-beargrass/moss.
This community phase is dominated by seral tree species that have matured to pole size and are in the competitive exclusion phase of forest succession. Overstory tree canopy is dense and competition for resources is very high. Canopy cover averages 50%. This community is incredibly diverse in tree species including: Lodgepole pine, Douglas fir, Engelmann spruce, Western larch, Paper birch, subalpine fir, Western white pine, Western redcedar and Western hemlock. The overstory canopy of Western redcedar and Western hemlock is less than 3% as they are just beginning to become established. The understory can have high cover of the medium sized shrubs white spirea, snowberry, Oregon boxleaf, common snowberry and thinleaf huckleberry. The short statured thimbleberry can have high cover. The herbaceous layer is diverse, with medium statured beargrass occurring frequently and sometime in high cover. Other herbaceous species include the short statured prince’s plume, queencup beadlily, trailplant and twinflower.

Figure 7. Plant Community 2.3 Intermediate Aged Forest, Dense Thick Pole Sized Trees.

Community Phase Pathway 2.3A
This pathway represents continued growth over time with no further major disturbance.

Community Phase Pathway 2.3B
This pathway represents a major stand-replacement fire disturbance such as a high-intensity fire, large scale wind event or major insect infestation.
Community Phase 2.4: Maturing Forest.
Western redcedar-western hemlock-subalpine fir-lodgepole pine-Engelmann spruce-western white pine/thinleaf huckleberry-snowberry-white spirea/wild sarsaparilla-heartleaf arnica-queencup beadlily-twinflower-beargrass/moss.
Structure:
This community is a maturing forest with vertical differentiation in the overstory tree canopy. Canopy cover averages
60%. This community has diverse tree species with Western redcedar and Western hemlock ranging 3-15% each and other seral tree species about equally distributed. These species include: Subalpine fir, Lodgepole pine, Engelmann spruce, Western white pine. The understory has patchy medium sized shrubs including: thinleaf huckleberry, snowberry, white spirea. There is a diverse understory of herbaceous species including: wild sarsaparilla, heartleaf arnica, queencup beadlily, twinflower and beargrass. There can be high cover of moss.

Community Phase Pathway 2.4A
This pathway represents continued growth over time with no further major disturbance.

Community Phase Pathway 2.4B
This pathway represents a major stand-replacement fire disturbance, such as a major insect outbreak, or major fire event which leads to the stand initiation phase of forest development.

Community Phase 2.5: Mature Forest.
Western redcedar-western hemlock (remnant seral species)/thinleaf huckleberry/threeleaf foamflower-prince’s plume-queencup beadlily-western rattlesnake plantain/moss.
Structure: Mature forest with vertical differentiation in the stand. Overstory is dominated by Western redcedar and Western hemlock although seral tree species are present and can have up to 15% cover each. Overstory canopy cover ranges 50-80%. Western larch is the most common seral species but others include: Grand fir, subalpine fir, Paper birch,
Lodgepole pine, Western white pine, and Douglas fir. The understory is diverse but generally has low overall cover. Thinleaf huckleberry occurs in clumps and queencup beadlily and western rattlesnake plantain are common.

Figure 9. Plant Community 2.5 Mature forest with some small gap dynamics, remnant seral tree species and western redcedar and western hemlock dominant.

Community Phase Pathway 2.5A
This pathway represents no further major disturbance. Continued growth over time, as well as ongoing mortality, leads to continued vertical diversification. The community begins to resemble the structure of the reference community, with small pockets of regeneration and a more diversified understory.

Community Phase Pathway 2.5B
This pathway represents a major stand-replacement fire disturbance leading to the stand initiation phase of forest development.

State 3.0
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).