Ecological dynamics

Ecological Dynamics of the Site
This ecological site is found west, and to a smaller extent east, of the Continental Divide in open growing stands of Douglas-fir (Pseudotsuga menziesii) at lower elevations, but also is found at higher elevations on southerly and westerly aspects. This ecological site is above the warmest coniferous zone dominated by ponderosa pine and below the cooler and moister zone dominated by subalpine fir and Engelmann spruce.

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 PSME/SYAL. The USFS Habitat Type guide states that the basal area on the WEST side of the Continental Divide for is 172+/-23 ft2 per acre and site index at 50 years for Ponderosa pine=54, Douglas fir=52. The USFS Habitat Type guide states that the basal area on the east side of the Continental Divide is 196+/-26 ft2 per acre, and the site index is at 50 years for PIPO=43, PSME=41.

Timber production ranges from low to high and site preparation must take into account the abundance of rhizomatous grasses.

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).

In Personal communication with sivicultural forester on the Flathead N.F.:
PSME/SYAL Habitat Type
This habitat type is a minority type on the Flathead N.F. and is found mainly in the WUI zone (wildland urban interface). It is managed so that disturbance such as fire do not cross ownership boundaries and impact private lands nearby. In order to achieve this, it is managed for open forest structure and to promote ponderosa pine (Pinus ponderosa) when possible. Fire suppression will increase Douglas fir density on this habitat type and Douglas fir is particularly prone to root disease. Root disease is very prevalent on the Flathead N.F. with pockets of effected stands throughout the area. This is a forest health issue. As well, lower density of Douglas fir allows for a fire regime conducive to maintaining ponderosa pine (frequent and lower intensity). If there were a severe stand replacement fire in this habitat type that destroyed mature ponderosa pine, it would be difficult to recover ponderosa pine since its seed dispersal radius is small due to heavy seed. In stands with good ponderosa pine presence, forest health concerns may require thinning of Douglas fir to reduce ladder fuels and increase resiliency of ponderosa pine, use of shelter wood harvests for seedling establishment and no uneven age management strategies (due to the shade tolerant nature of Douglas fir). Prescribed burning is also important to create and maintain resilient mature ponderosa pine (Pinus ponderosa) stands, but could be issue with WUI zone. Western larch is managed for the mesic phases of this habitat type. The forest does treat in old growth stands on this habitat type to maintain single story stand conditions that were traditionally maintained by frequent low intensity fire.

State 1.0
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.


Fire Regime Description
This ecological site occurs on moderately warm and dry sites. The open, park-like stands of this ecological site were historically maintained by fires of low to moderate severity that had a return interval of approximately 36 (28-52) years and stand replacing fire frequency of 141 years (Barrett, 1991). This relates to Fire Group Six: moist Douglas fir habitat types with mean fire intervals of 16-42 years (Fischer, 1987). Douglas fir habitat type forests on the Bitterroot, Lolo and Flathead National Forests had historic mean fire intervals ranging 25-49 years (USFS, FEIS, PSEMENG page). This fire regime has been coined mixed severity, ranging from low to moderate severity surface fires at relatively frequent intervals (7-20 years) to severe crown fires at long intervals (50-400 years). Frequent fires of moderate intensity favor lodgepole pine and western larch survival and regeneration over Douglas-fir. In the absence of short-interval understory burns, severe stand-replacement fires can occur on this ecological site if a closed canopy configuration develops along with the development of dense understories, resulting in a build-up of hazardous fuels at all levels, especially in periods of severe drought. Stand-replacement fires can favor lodgepole pine, especially if there is a serotinous cone seedbank. The average fuel loading is 12 tons per acre, but can be much heavier. Fire as an agent for seedbed preparation is less important for this ecological site, since Douglas-fir can grow in multiple types of seedbeds.

Forest succession after disturbance follows the stand initiation phase of herbs, shrubs, and seedlings to the competitive exclusion phase of dense pole-sized seral tree species, to the maturing forest stage, and with no further disturbance, the Reference phase. Douglas-fir can be present in all seral stages along with lodgepole pine, western larch, and ponderosa pine, especially at lower elevations. Quaking aspen (Populus tremuloides) also has been found in seral succession on certain sites. After a stand-replacement fire, grass, forb, and shrub species dominate the site with seedlings of tree species, usually Douglas-fir, western larch, and lodgepole pine depending upon patch size and adjacent and soil-banked conifer seed sources. If another fire occurs, then this phase would be maintained for longer. Without disturbance, the seedlings grow into saplings. Fire in the sapling stage would thin stands if ponderosa pine or western larch are dominant or eliminate Douglas-fir and lodgepole pine where these are dominant. Pole-sized Douglas-fir, western larch, and ponderosa pine would survive low to moderate fires, whereas severe fires would kill all trees and return the site to the stand initiation phase. In the mature phase, low to moderate severity fires would thin the overstory and understory, while severe fire would return the site to the stand initiation phase. The Reference phase is rare, because of the presence of seral species whose longevity is greater than the usual fire return interval, except where Douglas-fir is also the dominant seral species. Frequent low to moderate severity fires create the open, park-like stands of the reference phase, but severe fire would return the site to the stand initiation phase. Significant fires that have occurred on the WEST side of the continental Divide that have effected this ecological site are: Wedge (2003, 53,570 acres), Red Bench (1988, 34,051 acres), Adair (1994, 9,753 acres), Anaconda (1999, 9,657 acres), Moose (2001, 66,688 acres), Robert (2003, 54,191 acres), Middle Fork Complex (2003, 11,996 acres), Crystal Creek (1984, 2,886 acres) and Rampage Complex (2003, 23,237 acres). One significant fire that occurred on the east side of the Continental Divide and has affected this ecological site is the Red Eagle fire in 2006 that burned 32,461 acres.

Pest/Disease Description
Douglas-fir is subjected to a variety of diseases and insect pests including Armillaria and Annosus root diseases, Schweinitzii root and butt rot, laminated root rot, pouch and red belt fungus, pini rot, metallic wood borers, roundheaded borers, Douglas-fir beetle, blue-stain of sapwood, spruce canker, fir canker, Douglas-fir dwarf mistletoe, western spruce budworm, Douglas-fir needle midge, and Swiss and Rhabdocline needlecast.

Aerial photography is a good tool to use to discern the levels of insect and disease, the damage patterns, and whether these are at endemic or epidemic levels. 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. For the northern region, the major impact is from defoliation by western spruce budworm, occurs mostly on subalpine fir-Engelmann spruce forests, and to a lesser degree on Douglas-fir-dominated stands. As the name implies, the Douglas-fir beetle attacks Douglas-fir, with the greatest mortality occurring in stressed stands or on stressed individuals. Larch casebearer, a defoliator of western larch, and generalized needlecast of western larch was also found to a much lesser degree. Scattered smaller polygons were also found throughout the region, including mortality from mountain pine beetle on lodgepole pine.

Community Phase 1.1
Structure: Multistory with small gap dynamics

The overstory is dominated by Douglas fir with other seral tree species with small gap dynamics in which small numbers of trees are dead and regeneration is infilling. Overstory canopy cover can range from 25-75%. The understory has the most frequently occurring species including pinegrass, white spirea and common snowberry. Other common species include Oregon boxleaf, serviceberry, creeping barberry, snowbush ceanothus, kinnickinnik and fireweed. Infrequently, thimbleberry can have high cover. Foliar cover dataset of four sites indicates that the ground cover is predominantly duff (95%), and very low cover of moss and lichen. The vegetation structure is that of tall trees with average height of 20-31 m (67-100 feet) (Western larch and Douglas fir) and a multistoried understory. The top layer is 51-102 cm (20-40 inches) tall and includes russet buffaloberry (Shepherdia canadensis), common snowberry (Symphoricarpos albus) and blue wildrye (Elymus glaucus). There are two lower layers that include diverse shrubs, forb and grass species. One layer is at an average height of 25-40 cm (10-16 inches) tall and can include white spirea (Spirea betulafolia), fireweed (Chamerian angustifolia), western meadowrue (Thalictrum occidentalis) and the lower layer up to 20 cm or 8 inches tall that can include lupine species, heartleaf arnica, erigeron species and fragaria species. The presence of root rot pockets can shift the composition of this community away from its host species, although the threat is low. The understory of this community is low storied with the medium shrub white spirea and common snowberry in clumps and the herbaceous layer varied but low growing with pinegrass that can have high cover. This community is prone to Armillaria root rot and defoliation by Western Spruce budworm on fir.

Community Phase Pathway 1.1A
This pathway represents a larger disturbance, such as an insect infestation, wind storm, or rot pocket to create this forest structure. Areas of regeneration range from approximately 2 to 5 acres.

Community Phase Pathway 1.1B
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
Forest canopy cover ranges from 25-75 percent and is dominated by Douglas-fir with western larch in minor amounts.
Site index for Douglas fir averages 40 feet at a base age of 50 years, and the Cumulative Mean Annual Index is 44 cubic feet per acre per year @ 60 years.

Community Phase 1.2
Douglas fir (western larch-ponderosa pine)/Serviceberry/white spirea-common snowberry/Creeping barberry/pinegrass
Structure: Mosaic of mature overstory and regenerating openings
Community Phase 1.2 retains some areas that resemble CP1.1 but also contains moderate sized (2-5 acres) openings. Canopy cover can range 30-50%. The overstory is a mixture of Douglas fir, western larch, Engelmann spruce, and ponderosa pine at low elevation sites and can have minor amounts of black cottonwood, paper birch and quaking aspen. The understory can have clumps of the tall shrub Saskatoon serviceberry, the medium statured shrubs white spirea and common snowberry, with a carpet of diverse herbaceous layer sometimes dominated by the rhizomatous grass pinegrass (Calamagrostis rubescens) and or Geyer’s sedge (Carex geyeri). Douglas fir is susceptible to mortality from the Douglas fir beetle and is a host to organisms causing root rot and heart rot and with windthrow can cause large pockets of overstory mortality. These areas may take decades to become reforested, resulting in either patches of shrubs or seral species (western larch, lodgepole pine). As the organisms slowly die off due to a lack of host trees, Douglas fir will re-colonize these areas. This community is prone to Armillaria root rot and defoliation by Western Spruce budworm on fir.

Community Phase Pathway 1.2A
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 reinitiation—until they resemble the old-growth structure of the Reference Community.



Community Phase Pathway 1.2B
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 1.3
(Douglas fir-Lodgepole pine-Aspen-Western larch)/white spirea-common snowberry/geyer’s sedge
Structure: Thick carpet of regeneration, single story canopy.
Community Phase 1.3 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. Canopy cover is generally less than 10% as a mixture of conifers including Douglas fir, lodgepole pine, western larch, and resprouting aspen. If serotinous lodgepole seedbank is present, then this species will dominate the area. The understory is a mixture of shrubs and herbaceous species including: fireweed, common snowberry, pinegrass, Geyer’s sedge and Scouler’s woollyweed. Pinegrass and Geyer’s sedge can have very high canopy cover.
Community Phase Pathway 1.3A
This pathway represents continued growth over time with no further major disturbance.

Community Phase 1.4: Lodgepole pine/common snowberry/pinegrass
Structure: Dense, single story canopy.
Community Phase 1.4 is a forest in the competitive exclusion phase, possibly with scattered remnant mature trees; there is increasing competition among individual trees for the available water and nutrients. The canopy cover can range from 60-100 percent. The overstory is dominated by lodgepole pine, with minor amounts of Douglas-fir, western larch, and ponderosa pine; and the understory can have clumps of common snowberry and pinegrass. Canopy closure is very high within the areas successfully reforested, leading eventually to a diminished graminoid community but also providing protection for those species which do well in the shade. The majority of Douglas-fir and ponderosa pine that reach this stage have increased resistance to fire kill with their thickening bark. This community is tolerant of Armillaria root rot due to the forest stand composition. Understory at the three sites in which canopy cover data was collected had high cover. The most frequently occurring species were serviceberry, heartleaf arnica, pinegrass, strawberry species, white spirea and common snowberry. Only common snowberry and pinegrass had moderate to high canopy cover.
Community Phase Pathway 1.4A
This pathway represents continued growth over time with no further major disturbance.

Community Phase Pathway 1.4B
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 1.5
Douglas fir (western larch-Ponderosa pine)/Serviceberry/white spirea-common snowberry/creeping barberry/pinegrass
Structure: Single story canopy with few small openings
Community Phase 1.5 is a maturing forest which is starting to differentiate vertically. Canopy cover ranges 30-60%. The overstory is a mixture of Douglas fir, western larch, Engelmann spruce, and ponderosa pine at low elevation sites and can have minor amounts of black cottonwood, paper birch and quaking aspen. The understory can have clumps of the tall shrub Saskatoon serviceberry, the medium statured shrubs white spirea and common snowberry, with a carpet of diverse herbaceous layer sometimes dominated by the rhizomatous grass pinegrass and or geyer’s sedge. Individual trees are dying (whether due to insects, disease, competition or windthrow) allowing some sunlight to reach the forest floor. This allows for an increase in the understory as well as some pockets of overstory tree species regeneration. This community is prone to Armillaria root rot and defoliation by Western Spruce budworm on fir.
Community Phase Pathway 1.5A
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 1.5B
This pathway represents a major stand-replacement fire disturbance leading to the stand initiation phase of forest development.

State 2.0
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.