Ecological dynamics

ECOLOGICAL DYNAMICS OF THE SITE
STATE 1
The 43A Alpine Krummholtz Coniferous Ecological site is found along the Continental Divide in cold, high elevation sites in the upper subalpine and timberline zones. These sites are above the cold limits of Douglas fir, western white pine, western larch, and lodgepole pine with common species including whitebark pine, subalpine fir and Engelmann spruce and alpine larch. Trees are stunted, generally far less than 50 feet tall, and growing in clumps with the understory growing in mosaics. The stands are composed of whitebark pine and subalpine fir, with Engelmann spruce and alpine larch in a minor extent. The understory is not overly diverse: it is composed of only a few important species. Shrubs can include grouse whortleberry, pink mountainheath, and yellow mountainheath. There may be high cover of grouse whortleberry and/or Hitchcock’s smooth woodrush, which are indicative of cold climate conditions. Common forbs that may occur on these sites are broadleaf arnica, beargrass, Ross’ sedge, Idaho fescue, Parry’s rush, and Hitchcock’s smooth woodrush. Primary data was collected in Glacier National Park (NP) in Montana.

This ecological site is described as having cold and severe site conditions, with a fire return interval of 35 to over 300 years, with fire typically of low severity due to discontinuous fuels. Stand replacement fires occur after intervals of more than 200 years, typically during drought conditions and generally brought upslope from severe wind-driven crown fires burning in lower elevation forests. Forest fuels typically are relatively sparse fine fuels and moderate to heavy loads of widely scattered large diameter fuels. These larger fuels are from wind and snow breakage, windthrow, and mortality caused by insects and disease. The normally cool and moist site factors, short fire season, and the sparse, discontinuous, fine surface fuels layer lead to low fire severity. If dry conditions prevail, such as extended drought, then stand-replacing fire can occur. Vegetation succession afterwards is slow due to the extremely short growing season. Climatic site factors tend to control the production of these sites: the high rock and snow cover with low, discontinuous surface fuels and generally low vegetation production are more important to forest development than fire. Lightning fires do occur, but the rain that accompanies thunderstorms and the discontinuous fuels limit fire occurrence, spread, and severity. Fire is important in perpetuating an abundance of whitebark pine.

The general post-disturbance successional phases include the stand initiation phase dominated by herbaceous and shrub species and conifer seedlings, the young stand of pole-sized mixed conifers, the maturing forest of overstory mixed conifer trees, and the Reference Phase with small gap dynamics. A stand-replacing fire in the mature forest or Reference Phase would result in the stand initiation phase with species composition of seedlings varying with site conditions. The stand initiation phase will dominate for an extended period, up to 100 years, maintained by site conditions that allow physical disruption of the stand including snow load, windthrow, rock slides, and talus slippage. Whitebark pine, Engelmann spruce, subalpine fir, and alpine larch seedlings can occupy this site and will progress to the young stand with no major disturbance. Fire is unlikely in these earlier successional phases, but can occur as surface fires or severe fires of limited extent, which create vegetative mosaics. The stand progresses to the mature phase, during which heavier fuels from breakage or mortality may accumulate and allow stand-replacing fires in periods of extended drought. Without disturbance, the mature stand progresses to the Reference Phase, which is rarely affected by fires of low to moderate severity because of the open structure of the forest and discontinuous fire woody fuels. Stand-replacing fires that do occur can 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 include: Kootenai in 1998 that burned 8,041 acres, Trapper in 2003 (18, 453 acres), rampage Complex in 2003 (23,237 acres) and the Wedge in 2003 (53,570 acres). These fires burned areas primarily below this ecological site, but did effect this ecological site to a smaller extent.
Significant fires that have occurred on the east side of the Continental Divide that have affected this ecological site include the Red Eagle fire in 1998 that burned 45,559 acres. This fire burned areas primarily below this ecological site, but did affect this ecological site to a smaller extent.

Whitebark pine is considered a keystone species of this ecosystem. It is a slow-growing, long-lived tree that is well adapted to the severe, exposed conditions of the timberline zone. It is vital to wildlife through its nutritious seeds (large, wingless, less perishable than others with high fat and protein content) which are collected and buried by Clark’s nutcrackers, and collected and stored in middens by pine and red squirrels, which can be raided by grizzly and black bears for winter food. There are many plants, animals, and insects that depend on whitebark pine. Clark’s nutcrackers are the obligate seed dispersal source for whitebark pine. The structure and physical location of whitebark pine control snowmelt via the broad crowns that collect snow and shade it during spring, which melts out gradually, helping to slow spring runoff and allow for a more continuous water supply throughout the dry summer months (Asebrook, 2012). White bark pine is particularly susceptible to mountain pine beetles, white pine blister rust, red belt fungus, pini rot, needlecast, pine cone beetles, and western conifer seed bugs. Whitebark pine may be replaced by means of succession by more shade-tolerant species, such as subalpine fir, due to fire suppression coupled with damage from mountain pine beetles and white pine blister rust (Arno, 1986).

During the past several decades, whitebark pine has had considerable decline in numbers throughout its range. In 2011, the U.S. Fish and Wildlife Service placed whitebark pine as a high priority on the candidate species list of Endangered or Threatened species (U.S. Fish and Wildlife Service, 2011). Whitebark pine is imperiled mainly by white pine blister rust, but also by mountain pine beetles and fire suppression. A comparison study of whitebark pine in two major ecosystems found that for the Northern Divide Ecosystem (including Glacier NP) and the Greater Yellowstone Ecosystem (including Yellowstone NP), the overall stand densities were similar; however, the northern had only 79 live whitebark pine trees per hectare compared to 274 in the southern. White pine blister rust, crown die-off and mortality were all significantly greater in the northern forests. Nearly 75 percent of all whitebark pine were dead and approximately 90 percent of the remaining whitebark pine were infected with rust (Fiedler and McKinney, 2014). Whitebark pine habitat in Glacier NP was once extensive, with a study in 1996 finding 87,500 acres as potential seral whitebark pine habitat, with the majority of this on the east side of Glacier NP(Peterson, 1999). White pine blister rust is a fungus introduced to North America in the early 1900s from Europe via Asia, which causes branch and stem cankers that eventually lead to top-kill or death. Since cone-producing branches die first, there are less cones for wildlife, which could have cascading effects throughout the ecosystem. Rust affects five-needle pines, including western white, limber, and whitebark pines; Ribes species are the most common alternate hosts. Other hosts do exist, including louseworts and Indian paintbrush. A study of white pine blister rust in treeline whitebark pine in Glacier NP found rates of infection varied considerably, and that factors contributing to higher rates included sites exhibiting high flow accumulation rates, greater distances to wetlands, slopes facing southwest, higher curvature, greater wind speeds, and close proximity to Ribes and perennial streams (Smith, E., et al 2011). Mountain pine beetles feed on the phloem layer of the inner bark of most species of pine. This feeding girdles the tree and the tree is inoculated with blue stain fungi, which disrupts the water transport system and the tree is killed. There can be large outbreaks of this beetle to epidemic proportions in lower elevation lodgepole pine stands, and the beetles can move upward into whitebark pine stands. This can be very detrimental if trees are already stressed by drought or blister rust, or by overcrowding by subalpine fir or Engelmann spruce. Lack of fire can increase subalpine fir or Engelmann spruce, which could stress pines. Fire is needed by whitebark pine for seedlings to thrive, as well, Clark’s nutcrackers prefer burns for seed caches. Restoration of whitebark pine includes harvesting cones from rust-resistant trees, then growing and planting rust-resistant seedlings, allowing fire-created openings where nutcrackers can cache seeds and seedlings can grow, and the use of beetle-repelling pheromone on trees to prevent beetle attacks on sites. In 1997, the National Park Service (NPS) began collecting seed from whitebark pine and limber pine trees that showed phenotypic rust resistance, growing in a nursery, and monitoring growth. From 2000-2007 they planted 6,400 whitebark pine and 4,700 limber pine seedlings, and found in 2010 that 41 percent of whitebark pine had survived, while only 6 percent of the limber pine survived (Asebrook et al., 2001). Unfortunately, another study modelling the effects of climate change and fire frequency and severity on whitebark pine stands concluded that the presence of whitebark pine would likely reduce, suggesting that conservation and restoration efforts must target multiple threats of interacting disturbance agents (Keane and Loehman, 2010).

Although subalpine fir can be subjected to a variety of diseases and insect pests, the effects of these disturbance factors within this near-timberline ecological site have not resulted in significant damage to subalpine fir and Engelmann spruce to the extent seen in lower elevation ecological sites dominated by subalpine fir or Engelmann spruce (USDA USFS ADSM 2014). Diseases and insect pests that can affect subalpine fir include root rot, stem decay, bark beetles, and wood borers and defoliators. These can weaken and or kill trees and result in small openings scattered throughout the forest, or major mortality during an outbreak such as western spruce budworm (Choristoneura occidentalis). Windthrow is a common disturbance after weakening of root systems. Subalpine fir is most commonly susceptible to Armillaria and Annosus root disease, and the pouch, Indian paint, and red belt fungi, which cause stem decay. Subalpine fir also is susceptible to metallic, roundheaded, and Western balsam bark beetles, fir canker, and defoliators such as Delphinella shoot blight, black mildew, brown felt blight, fir needle cast, snow blight, and fir-blueberry rust.

The alpine krummholtz coniferous ecological site can be associated with slopes dominated by the forb species beargrass (Xerophyllum tenax) particularly on southerly facing aspects of steep sloping (20-40%) backslope positions on mountain slope and cirque wall landforms. Harsh site conditions, frequent avalanches, frequent spotty and low intensity fires and soil conditions can contribute to the dominance of beargrass. Beargrass is particularly suited to withstanding the harsh site conditions and avalanches by its mat-forming physiology. The frequent spotty and low intensity fires keep tree encroachment to a minimum while not eliminating the growing points of beargrass. The soils tend to not hold water and are therefore more prone to droughty conditions, which beargrass can withstand. As well, slope processes and erosion from avalanches lead to less developed soils in which beargrass can thrive. These slopes are dominated and stabilized by the mat-forming and long lived member of the lily family, beargrass (Laursen, 1984). When whitebark pine or subalpine fir occur on these slopes, they are stunted and form small islands within the beargrass dominated slope. This community is dominated by beargrass, but also has significant cover of the shrubs thinleaf huckleberry and grouse whortleberry. The herbaceous layer is diverse and includes false green hellebore, sitka valerian, and western meadow-rue. The total annual production for the beargrass slopes average 7,216 pounds per acre, predominantly from beargrass (6,405 pounds per acre). The foliar cover is very high (84% total foliar cover) for the beargrass slopes.

Beargrass is a perennial, evergreen plant that forms thick tussocks (Hitchcock, 1969). It has linear leaves that are scabrous and wiry. Beargrass blooms cyclically and may go many years without blooming: colonies of beargrass bloom in 5-7 year cycles (Stickney, 1981). Beargrass slopes can be exceptionally beautiful during flowering. It reproduces both by seed, which needs cold stratification for germination, and vegetatively by offshoots of the rhizome. After disturbance, vegetative resprouting from rhizomes allows for recovery (Antos, 1980). Beargrass is a survivor species that will resprout and regrow in place after fire. The meristematic region, or growing point, of beargrass is at or above the interface between organic material and mineral soil. Therefore, duff-consuming or severe fires that damage the meristematic region can kill beargrass (Arno, 1985). It has been found in Waterton Park, to the north of Glacier National Park, on moderate to steep south-facing slopes on colluvial and moraine landforms with Engelmann spruce, subalpine fir and whitebark pine (Achuff, 1989). The fire regime of these beargrass dominated slopes is similiar to the general vegetation community of the alpine timberline krummholtz coniferous ecological site, which has a fire-return interval of 35 to over 300 years; the fire typically is of low severity due to discontinuous fuels. Stand replacement fires occur after intervals of more than 200 years; these occur typically during drought conditions and are brought up by severe wind-driven crown fires from forests at lower elevations. Beargrass can be very sensitive to competition by shrubs after disturbance by severe fire with resident fire-tolerant shrubs (Stickney, 1981). It is moderately shade tolerant, growing best in full sun. Nimlos (1981) found that beargrass was associated with soils that had an ash layer. We found that to hold true for most of our sites.
Site conditions can be harsh with steep slopes, high elevation, and therefore cold conditions and shorter growing seasons. Beargrass is uniquely adapted to thrive in these site conditions. The slopes are stabilized by the dense mat-forming nature of beargrass roots (Halverson, 1986). As well, the leaves of beargrass are adapted to forces from snow load and frequent snow avalanches occurring from site conditions. Site conditions also give beargrass a competitive advantage over conifer species, which generally are stunted in the krummholtz form when they occur on this site. Conifer regeneration also is difficult due to cold subsurface soil temperatures, high surface temperatures after snowmelt, rapid soil drying, beargrass-sedge mats, pocket gophers, and a short growing season with prolonged frosts (Smart, 1977). The stabilization of the slope is from fine root fibers that extend down into the soil 12-15 cm (Damm, 2001). This extensive fibrous root system and the prostrate growing basal shoots are extremely resistant against soil creep and erosion: they stabilize the slopes and therefore the whole vegetation community. Very little bare ground exists at this site. Site conditions, such as steepness which provides good drainage and southerly aspects leading to dry conditions in late summer and fall, are perfect for the xerophilic beargrass. The ridged, sedge-like leaves of beargrass are adapted to drought, wind desiccation, and snow load (Damm, 2001). Snow loads can be high, but slopes melt out early in comparison to other slope aspects which can lead to summer drying. Also, beargrass is evergreen, which provides a much quicker start to springtime assimilation. Beargrass and grouse whortleberry are adapted to snow avalanches as well by their morphological attributes: beargrass has long, slender leaves and grouse whortleberry has broom-like flexible branches (Daubenmire, 1968). Beargrass is very hardy: it’s very frost tolerant and, because of its tough, wiry leaves and tufted growth form, beargrass is tolerant of human trampling (Cole, 1987).



STATE 2
Another disease affecting this ecological site is root rot, although to a lesser extent than adjoining ecological sites at lower altitudes. 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 affects the most susceptible tree species first, leaving less susceptible tree species that mask its presence. When root rot is severe, the pocket has abundant regeneration of dense brush, and seedlings and saplings of susceptible tree species may be present that will eventually succumb to the root rot as they grow, usually at less than thirty years of age. The growth is in the center of the root rot. Armillaria is present in most stands in western Montana and northern Idaho, 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 can occur throughout the stand. 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 identify the type of Armillaria root disease is present, 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, USFS July 2010). A link has been postulated between parent material and susceptibility to root disease: metasedimentary parent material is thought to increase the risk of root disease. Glacier NP 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
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 for ecological services like water quality and quantity, old growth, or endangered species.

The US Forest Service (USFS) Habitat Type guide states that the basal area on the eastern side of the Continental Divide for PIAL-ABLA is 247+/-63 ft2 per acre and site index at 50 years for Abies is 25. The USFS Habitat Type guide states that the basal area on the West side of the Continental Divide for whitebark pine-subalpine fir (PIAL-ABLA) is 146+/-46 ft2 per acre and site index at 50 years for Abies =16. Timber production on these sites is very low, and rarely an important management objective. Watershed management is very important, as well as wildlife sanctuaries. Each national forest has a specific management plan. The management plan for the Flathead National Forest (NF) also has an Appendix B that gives specific management guidelines for habitat types (which relate to forested ecological sites) found on the forest in relation to current and historic data on forest conditions (Flathead NF 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.
The USFS Habitat Type PIAL-ABLA is common on the Flathead NF, located just west of GNP. The following is a personal communication with a sivicultural forester on management of PIAL-ABLA on the Flathead N.F.
These HTs are not typically managed since they are usually in areas that are unsuitable for timber production under our forest plan. The majority of management is taking advantage of recent wildland fires to plant whitebark pine. The fire kills subalpine fir and accomplishes site preparation for whitebark pine planting. Planting is typically done on a 15-foot spacing (200 TPA) and locating the seedlings next to shade is key. Micro-siting is so important in planting whitebark pine that we pay the planters by the hour instead of by the acre when planting whitebark pine. The thought is that paying by the hour will provide incentive to the planters to look for micro sites shaded from the afternoon sun. The Condon Mountain fire and the Spotted Bear fires recently provided new areas to plant whitebark pine. Before those fires we were starting to run low on acres suitable to plant whitebark pine. Some planning projects are now proposing slashing and prescribed burning to prepare conditions for whitebark pine planting. We cannot plant in Wilderness Areas which hold much of these habitat types. Subalpine fir encroachment will be a future problem in the areas planted with whitebark pine.

STRUCTURE: Multistory with small gap dynamics.
Community Phase 1.1
The overstory is dominated by whitebark pine and subalpine fir that is stunted with small gap dynamics in which small numbers of trees are dead and conifer regeneration is infilling. The canopy cover ranges from 10-20 percent. The ground cover consists predominantly of litter and duff with very low cover of embedded litter, moss, and soil. This community phase is multistoried with a lower tree layer of subalpine fir at 90 inches tall, with a shorter understory layer of forbs and
grasses less than 20 inches tall including beargrass, western meadow-rue, thinleaf huckleberry, and others. At these higher elevations, subalpine fir is slow growing and infill can take several decades, sustaining the multistory structure of this community. The presence of root rot pockets can shift the composition of this community away from its host specie, although the potential for this is very low. The understory of this community has the medium-statured thinleaf huckleberry and beargrass. At this phase, Armillaria root rot can have a low impact.
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.

Table 2. Forest overstory summarization of canopy cover, basal area and site index.
FOREST OVERSTORY.
Forest canopy Canopy cover range 10-40%
Basal Area ranges Site index at 100 years: ABLA=30-40 CMAI=26@150 years


COMMUNITY PHASE 1.2:
Structure: high cover of herbaceous and shrub species with patchy clumps of regeneration of seedlings and saplings.
Community Phase 1.2 is a forest in the stand initiation phase, possibly with scattered remnant mature trees. The composition of the seedlings depends upon the natural seed sources available, but generally include whitebark pine, Engelmann spruce, subalpine fir, and subalpine larch (Larix lyallii). The canopy cover is very low. This phase generally is tolerant to Armillaria root rot.

Community Phase Pathway 1.2a
This pathway represents continued growth over time with no further major disturbance.

COMMUNITY PHASE 1.3:
Structure: Clumps of single-story conifer species including whitebark pine, Engelmann spruce, subalpine fir, and subalpine larch. This phase generally is tolerant to Armillaria root rot.

Community Phase Pathway 1.3a
This pathway represents continued growth over time with no further major disturbance.

COMMUNITY PHASE 1.4:
Structure: Mature-sized trees of mixed conifers including whitebark pine, Engelmann spruce, subalpine fir, and subalpine larch. This phase generally is tolerant to Armillaria root rot.

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 major disturbance such as Armillaria root rot, stand-replacing fire, or pest outbreak.