State 1
Reference State

Community 1.1
Mountain hemlock-Alaska cedar/Cascade azalea/dwarf bramble

Structure: Multistory with small gap dynamics Mountain hemlock is the dominant overstory species in the reference community, and it is the most shade tolerant-species. Alaska cedar, subalpine fir, Pacific silver fir, and noble fir are subspecies. Reproduction of these species is restricted under a closed canopy of mountain hemlock (Means, 1990). The dense canopy created by multiple age groups of hemlock may block most of the sunlight from the forest floor, which leads to sparse understory in some areas. Gaps in the mid-canopy and overstory allow sunlight to reach the ground. The majority of the understory plants become established in these areas. The understory is more continuous in areas where there is no mid-canopy. Common understory species include rusty menziesia, black mountain huckleberry, dwarf bramble, Cascade azalea, and Sitka valerian. The most common natural disturbance is small gap dynamics following the death of some trees. From recorded plot data, the average diameter at breast height of mountain hemlock is 19 inches and the average age is 270 years. The growing conditions of this ecological site limit timber production. Community phase pathway 1.1A This pathway represents minor disturbances, such as small pockets of root disease, individual tree mortality, and windthrow, that maintain the overall structure of the reference community. Mortality of individual trees or clusters of trees creates openings that allow sunlight to reach the forest floor. This promotes the growth of forbs and shrubs and regeneration of overstory species and maintains the multi-storied, uneven-aged forest.

Forest overstory. The forest has multiple canopy layers. The upper canopy is 90 to 135 feet in height, and the average is 80 feet. The diameter of the trees varies depending on the species, but the average diameter at breast height is 19 inches.

Forest understory. The composition of the understory varies depending on the overstory cover and competition for sunlight and moisture. As the overstory community matures toward the reference state, the understory vegetation is less prevalent. At the higher elevations, the density of the understory species is higher because the trees are less mature and the canopy is not closed. Overall cover of shrubs such as Cascade azalea and black mountain huckleberry is 30 to 50 percent. Dense pockets of shrubs are in some areas. Overall cover of forbs such as common beargrass, Sitka valerian, five-leaved bramble, and dwarf bramble is 5 to 30 percent.

Community 1.2
Mountain hemlock-Alaska cedar/Cascade azalea/dwarf bramble

Structure: Mosaic of mature overstory and regenerating openings Community phase 1.2 resembles community phase 1.1 in some areas, but it also has moderate-sized openings (2 to 4 acres). Many of the shrubs respond well to increased sunlight and may delay or prevent reforestation of the openings.

Community 1.3
American bistort-common beargrass

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, large-scale windstorm, mass movement, or major insect infestation. Mountain hemlock is susceptible to damage from fire because of its low-hanging branches. It is not expected to survive moderate- or high-intensity fires; therefore, the fires are dominantly stand replacing (Tesky, 1992). Most of the trees are destroyed, but some fire-resistant trees may survive in the overstory. Standing, decaying snags are prevalent. The understory is dominantly shrubs and forbs such as American bistort, fireweed, common beargrass, and arctic lupine. Some grasses will establish, but they will be replaced by shrubs over time. Tree seedlings and saplings begin to establish within 3 to 10 years, depending on the severity of the disturbance.

Community 1.4
Western white pine-subalpine fir/Sitka mountain ash/American bistort-arctic lupine

Structure: Single story Community phase 1.4 is an early seral forest in regeneration. Scattered remnant mature trees that are fire resilient may be present. The species composition depends on the natural seed sources present and the intensity of the disturbance. Western white pine and subalpine fir are suited to reproduction after a disturbance (Means, 1990). After a moderate or severe fire, shrubs and forbs may outcompete tree seedlings. American bistort, artic lupine, and partridgefoot, which may have been moderate in abundance previously, rapidly recover and spread when top-killed. This slows the regeneration of the overstory species. Tree species, including early successional species such as western white pine, commonly regenerate from an existing seed source. The stand is mixed and may include western white pine, Douglas-fir, mountain hemlock, and subalpine fir.

Community 1.5
Subalpine fir-mountain hemlock/black mountain huckleberry/arctic lupine

Structure: Dense single story with diminished understory Community phase 1.5 is a forest in the competitive exclusion stage. Scattered remnant mature trees may be present. Competition among individual trees for available water and nutrients increases. The canopy closure is nearly 100 percent, which leads to a diminished understory. Some understory species better adapted to at least partial shade, such as Sitka valerian, increase in abundance. Over time, the forest will begin to self-thin due to competition. The species composition depends on the original seed sources available. The forest may be composed of a single species or mixed species, including subalpine fir, mountain hemlock, Pacific silver fir, Alaska cedar, and Engelmann spruce.

Community 1.6
Mountain hemlock-Pacific silver fir/rusty menziesia/dwarf bramble

Structure: Single story with few small openings Community phase 1.6 is a maturing forest that is beginning to become differentiated vertically. Individual trees are dying from competition, disease, insects, or windthrow, which allows some sunlight to reach the forest floor. The understory increases in abundance, and some pockets of overstory regeneration develop.

Pathway 1.1B
Community 1.1 to 1.2

Mountain hemlock-Alaska cedar/Cascade azalea/dwarf bramble

Mountain hemlock-Alaska cedar/Cascade azalea/dwarf bramble

This pathway represents a larger disturbance, such as a windstorm, insect infestation, or root rot pocket. Areas of regeneration are 2 to 4 acres in size. Historically, this spatial pattern was caused by pockets of disease, such as annosum root rot (Heterobasidion annosum) or laminated root rot (Phellinus weirii), minor insect infestations, or low- or moderate-intensity fires. Because mountain hemlock is shallow rooted, it is susceptible to laminated root rot and windthrow (Tesky, 1992).

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 large mass movement. The frequency of fire on this ecological site is 400 to 800 years. Volcanic activity has the potential to disrupt the landscape ecology beyond the boundaries of the ecological site and the purpose of this site description.

Pathway 1.2A
Community 1.2 to 1.1

Mountain hemlock-Alaska cedar/Cascade azalea/dwarf bramble

Mountain hemlock-Alaska cedar/Cascade azalea/dwarf bramble

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 large mass movement. This leads to the initiation phase of forest development.

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, large-scale windstorm, major insect infestation, or large mass movement. This leads to the 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, large-scale windstorm, major insect infestation, or large mass movement. This leads to the 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 over time and ongoing mortality lead to increased 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, large-scale windstorm, major insect infestation, or large mass movement. This leads to the initiation phase of forest development.