Ecological dynamics
This ecological site is on the warm, moist, lower slopes of Mount Rainier. Elevation ranges to 4,600 feet, depending on aspect. The site is on north- and east-facing slopes at the lower elevations and on south- and west-facing slopes at the higher elevations. Western hemlock (Tsuga heterophylla) and Douglas-fir (Pseudotsuga menziesii) are the most common overstory species. Western redcedar (Thuja plicata) is a minor component in the overstory. Red alder (Alnus rubra) and Pacific yew (Taxus brevifolia) may be present.
The more open the forest canopy, the more dense and diverse the understory. Cascade Oregon grape (Mahonia nervosa), vine maple (Acer circinatum), red huckleberry (Vaccinium parvifolium), salal (Gaultheria shallon), baldhip rose (Rosa gymnocarpa), little prince’s pine (Chimaphila menziesii), and prince’s pine (Chimaphila umbellata) are the main shrub species in areas where the overstory canopy is open. Western rattlesnake plantain (Goodyera oblongifolia), deerfoot vanillaleaf (Achlys triphylla), twinflower (Linnaea borealis), pioneer violet (Viola glabella), and western swordfern (Polystichum munitum) are common forbs. The understory species included in the Canopy Cover Summary Table had at least a 40 percent rate of constancy in the 20 inventory plots.
The most common disturbance is the patchy, small pockets of windthrown overstory trees, which commonly occurs in conjunction with root-, butt- or stem-rot. Western hemlock is highly susceptible to rot diseases such as Armillaria ostoyae, Heterobasidion annosum, Phellinus weirii, and Echinodontium tinctorium (Tesky, 1992). The resulting openings in the canopy allow sunlight to reach the forest floor, which benefits the understory. The historic fire regime consists of low frequency (150 to 300 years or more), moderate- to high-intensity fires. The fires are stand-replacing although individual trees or patches of trees survive, providing a seed source for re-establishment.
Community 1.1
Western hemlock–Douglas-fir/salal–Cascade Oregon grape
Structure: Multistory with small gap dynamics
Western hemlock is the most common overstory species. It is shade tolerant and releases quickly after extended periods of suppression (Packee, 1990). Douglas-fir and western redcedar are present, but regeneration of Douglas-fir is minimal in the absence of canopy openings. Red alder and Pacific yew are minor components of the overstory; they commonly become established in areas that are disturbed and receive more sunlight. The dense canopy created by multiple age groups of hemlocks may block most of the sunlight from the forest floor, leading to sparse understory in some areas. Thick clumps of vine maple have the same effect. Most of the understory vegetation is in areas where there are gaps in the mid-canopy, which allow sunlight to reach the ground. The understory is more continuous in areas where there is no mid-canopy. The most common natural disturbance on this site is small gap dynamics following the mortality of one or two trees.
Community phase pathway 1.1A
This pathway represents minor disturbances, such as small pockets of root disease, individual tree mortality, or windthrow, that maintain the overall structure of the reference community. Mortality of individual trees or clusters of trees creates gaps in the overstory, allowing more sunlight to reach the forest floor. This promotes growth of forbs and shrubs and regeneration of overstory species, perpetuating the multi-storied, uneven-aged forest.
Forest overstory. Western hemlock and Douglas-fir make up 50 to 95 percent of the forest canopy cover. The forest has multiple layers. The upper canopy is 90 to 170 feet in height, and it averages 133 feet. The diameter of the trees varies depending on the species, but the average diameter at breast height 23 inches. Alder and western redcedar trees typically are smaller than western hemlock and Douglas-fir trees.
Forest understory. The composition of the understory varies depending on the overstory cover and competition for moisture. Overall cover of shrubs such as Cascade Oregon grape, vine maple, and red huckleberry is 1 to 40 percent, and overall cover of salal is as much as 80 percent in some areas. Overall cover of forbs such as western rattlesnake plantain, deerfoot vanillaleaf, and twinflower is 1 to 25 percent, and overall cover of western swordfern is as much as 45 percent in some areas. Grass species were not recorded for this ecological site.
Dominant plant species
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Douglas-fir (Pseudotsuga menziesii), tree
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western hemlock (Tsuga heterophylla), tree
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western redcedar (Thuja plicata), tree
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red alder (Alnus rubra), tree
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Pacific yew (Taxus brevifolia), tree
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Cascade barberry (Mahonia nervosa), shrub
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salal (Gaultheria shallon), shrub
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vine maple (Acer circinatum), shrub
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red huckleberry (Vaccinium parvifolium), shrub
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dwarf rose (Rosa gymnocarpa), shrub
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pipsissewa (Chimaphila umbellata), shrub
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little prince's pine (Chimaphila menziesii), shrub
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western rattlesnake plantain (Goodyera oblongifolia), other herbaceous
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sweet after death (Achlys triphylla), other herbaceous
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twinflower (Linnaea borealis), other herbaceous
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pioneer violet (Viola glabella), other herbaceous
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western swordfern (Polystichum munitum), other herbaceous
Community 1.2
Western hemlock–Douglas-fir/salal–Cascade Oregon grape
Structure: Mosaic of mature overstory and regenerating openings
Community phase 1.2 has some areas that resemble community phase 1.1, but it also has moderate-sized openings (2 to 4 acres). Depending on the seed sources present, the overstory species of community phase 1.1 as well as bigleaf maple and grand fir may be in the openings. Many of the shrub species, including vine maple, red huckleberry, Cascade Oregon grape, and baldhip rose, also respond well to increased sunlight. The shrubs may delay or prevent reforestation of the openings.
Community 1.3
Red alder/red huckleberry-vine maple/fireweed
Structure: Open meadow with snags
Community phase 1.3 is an early seral plant community that has been impacted by a stand-replacing disturbance such as a wildfire, a large-scale windstorm, a major insect infestation, or mass movement. Only some fire-resistant trees may survive in the understory. The species composition depends on the natural seed sources present and the intensity of the disturbance. Standing and decaying snags are prevalent. After a disturbance, red alder quickly establishes in areas where soil moisture and sunlight are available. Tree seedlings and saplings will begin to establish within 3 to 10 years, depending on severity of the disturbance.
Douglas-fir can survive moderately intense fires because of its thick, corky bark. Depending on the severity of the fire and the extent of the damage to the cambium, mature Douglas-fir trees may remain dominant in the overstory. Western redcedar and western hemlock may be at a stage of full stand replacement post fire (Tesky, 1992).
After a moderate or severe fire, shrubs commonly outcompete tree seedlings. Vine maple, red huckleberry, salal, baldhip rose, and Cascade Oregon grape, which may have been only moderately abundant previously, recover and spread rapidly when top-killed, slowing successful regeneration of the overstory. Seed sources for tree species are from the surrounding, undisturbed forests and any trees that survived the disturbance. This results in a mixed stand that can include Douglas-fir, western hemlock, red alder, bigleaf maple, western redcedar, and grand fir.
Community 1.4
Douglas-fir–western hemlock/vine maple–red huckleberry/western swordfern–deerfoot vanillaleaf
Structure: Single story
Community phase 1.4 is an early seral forest in regeneration. Scattered remnant mature trees may be present. Red alder begins to be replaced by more shade-tolerant species. Douglas-fir and western hemlock regenerate rapidly and increase in dominance, creating thick patches of saplings. Vine maple and bigleaf maple remain prevalent in the forest openings, and western swordfern begins to re-establish on the forest floor.
Community 1.5
Douglas-fir–western hemlock/vine maple–red huckleberry/twinflower–western swordfern
Structure: Dense single story with diminished understory
Community phase 1.5 is in the competitive exclusion stage of forest development. Scattered remnant mature trees may be present. Individual trees compete for available water and nutrients. The canopy closure is nearly 100 percent, which leads to diminished understory. Some understory species better adapted to partial shade, such as twinflower and red huckleberry, begin to increase in abundance. Over time, the forest begins to self-thin as a result of competition. The species composition depends on the original seed sources available. The forest may be composed of a single species or mixed species, including Douglas-fir, western hemlock, red alder, bigleaf maple, western redcedar, and grand fir.
Dominant plant species
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Douglas-fir (Pseudotsuga menziesii), tree
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western hemlock (Tsuga heterophylla), tree
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red alder (Alnus rubra), tree
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bigleaf maple (Acer macrophyllum), tree
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grand fir (Abies grandis), tree
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western redcedar (Thuja plicata), tree
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vine maple (Acer circinatum), shrub
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red huckleberry (Vaccinium parvifolium), shrub
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twinflower (Linnaea borealis), other herbaceous
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western swordfern (Polystichum munitum), other herbaceous
Community 1.6
Western hemlock–Douglas-fir/Cascade Oregon grape–vine maple/western rattlesnake plantain–deerfoot vanillaleaf
Structure: Single story with few small openings
Community phase 1.6 is a maturing forest that is beginning to differentiate vertically. Individual trees are dying due to competition, disease, insects, or windthrow, which allows some sunlight to reach the forest floor. The understory increases in abundance, and the overstory tree species regenerate in some pockets.
Pathway 1.1B
Community 1.1 to 1.2
This pathway represents disturbances such as a windstorm, an insect infestation, or a pocket of rot. Historically, these disturbances have included pockets of disease, such as annosum root rot (Heterobasidion annosum) or laminated root rot (Phellinus weirii), minor insect infestations, and low- or moderate-intensity fires. Areas of regeneration are 2 to 4 acres in size.
Pathway 1.1C
Community 1.1 to 1.3
This pathway represents a major stand-replacing disturbance such as a high-intensity fire, large-scale windstorm, major insect infestation, or mass movement. The frequency of fire is 150 to 300 years. Volcanic activity has the potential to disrupt the landscape ecology beyond the boundaries of the site and the purpose of this site description.
Pathway 1.2A
Community 1.2 to 1.1
This pathway represents growth over time with no further significant disturbance. The areas of regeneration go through the typical phases of stands, including competitive exclusion, maturation, and understory reinitiation, until they resemble the old-growth structure of the reference community.
Pathway 1.2B
Community 1.2 to 1.3
This pathway represents a major stand-replacing disturbance such as a high-intensity fire, large-scale windstorm, major insect infestation, or mass movement.
Pathway 1.3
Community 1.3 to 1.4
This pathway represents growth over time with no further major disturbance.
Pathway 1.4B
Community 1.4 to 1.3
This pathway represents a major stand-replacing disturbance such as a high-intensity fire, a large-scale windstorm, a major insect infestation, or mass movement. This leads to the stand initiation phase of forest development.
Pathway 1.4A
Community 1.4 to 1.5
This pathway represents growth over time with no further major disturbance.
Pathway 1.5B
Community 1.5 to 1.3
This pathway represents a major stand-replacing disturbance such as a high-intensity fire, a large-scale windstorm, a major insect infestation, or mass movement. This leads to the stand initiation phase of forest development.
Pathway 1.5A
Community 1.5 to 1.6
This pathway represents growth over time with no further major disturbance.
Pathway 1.6A
Community 1.6 to 1.1
This pathway represents growth over time with no further major disturbance. Continued growth and ongoing mortality result in more vertical diversification. The community begins to resemble the structure of the reference community, including small pockets of regeneration and a more diversified understory.
Pathway 1.6B
Community 1.6 to 1.3
This pathway represents a major stand-replacing disturbance such as a high-intensity fire, a large-scale windstorm, a major insect infestation, or mass movement.
