State 1
Reference State

Community 1.1
Black cottonwood-western hemlock/Cascade Oregon grape/western rattlesnake plantain

Structure: Mature deciduous forest with a mix of shrubs and conifer regeneration in the understory Black cottonwood is the dominant overstory species. Red alder commonly makes up a higher percentage of the species composition, but the black cottonwood trees typically are 20 to 50 feet taller than the red alder trees. Black cottonwood trees live longer (as long as 200 years) than red alder trees, which start to actively decline after 60 to 80 years. Western hemlock typically is just outside the active flood plain, and it becomes widely established in the forest canopy (Villarin, 2009). The reference community represents a lack of major flooding for at least 100 years, which allows the pioneering deciduous species to form a mature canopy and the secondary coniferous species, such as western redcedar and western hemlock, to seed underneath. The lack of flooding also allows for vigorous growth of understory shrubs, including vine maple, Cascade Oregon grape, and baldhip rose. Common disturbances include small gap dynamics (openings of 1/2 acre or smaller) following the decline of red alder and minor scouring from flooding. Community Phase Pathway 1.1A - This pathway is represents minor disturbances that maintain the overall structure of the reference community. The mortality of some trees creates gaps in the understory, allowing sunlight to reach the forest floor. This promotes growth of forbs and shrubs and regeneration of overstory species. Soil deposition following minor scouring from flooding temporarily affects the understory vegetation, but it does not alter the composition of the overstory vegetation.

Forest overstory. Western redcedar is dominant in the forest canopy cover, and Douglas-fir, red alder, and black cottonwood are subcomponents. The forest has multiple layers. The upper canopy ranges from 100 to 175 feet in height, and the average is 105 feet. Black cottonwood is the tallest tree in the reference community. The diameter of the trees varies depending on species, but the average diameter at breast height is 21 inches. Deciduous trees are dominant, and they make up the highest basal area along the flood plains. The basal area of conifers is higher on terraces and hillslopes (Villarian, 2009).

Forest understory. The understory composition varies depending on the overstory and the competition for moisture. Overall cover of shrubs such as vine maple and Cascade Oregon grape is 10 to 15 percent in the reference community. Overall cover of forbs such as vanillaleaf, western rattlesnake plantain, and Oregon oxalis is as much as 40 percent. Overall cover of western swordfern is as much as 55 percent in some areas.

Community 1.2
Black cottonwood-red alder/vine maple/common ladyfern

Structure: Single story/shrub Community phase 1.2 represents a riparian forest that is undergoing regeneration or stand initiation. Scattered remnant mature trees are in some areas. Successful regeneration is dependent on a local seed source, an adequate seedbed, and sufficient light and water (Nierenberg, 2000). Black cottonwood, red alder, and vine maple are the pioneering early seral species that become established first after a major disturbance. These deciduous species establish quicker than do conifers. Red alder fixes nitrogen in the soil on flood plains, which provides an early competitive advantage (Villarin, 2009). Seeds of deciduous species are light and can be transported long distances by wind and water, allowing for rapid recolonization. Most of the common shrubs, such as vine maple and baldhip rose, can readily regenerate by sprouting from the root crown that has been buried by flood deposits. The shrubs compete with seedlings and saplings until the tree species overtop them. A major disturbance allows seral forb species, such as western swordfern and Oregon oxalis, to become established.

Community 1.3
Black cottonwood-western redcedar/vine maple/common ladyfern-western rattlesnake plantain

Structure: Dense single story with diminished understory Community phase 1.3 is a forest in the competitive exclusion stage. Scattered remnant mature trees are in some areas. Individual trees compete for available water and nutrients. Red alder trees begin to die 40 to 70 years after a disturbance, which allows more light to penetrate the nitrogen-rich soils (Naiman, 2009). As a result, conifer species become more dominant in this community phase. Downed logs are important for conifer establishment (Villarian, 2009). Canopy closure is nearly 100 percent, which leads to diminished understory. Some understory species that are better adapted to shade, such as vine maple, remain in the community. The shrub community decreases in areas farther from the flood plain, leading to a closed canopy forest (Villarian, 2009). If red alder is present, it can be inferred that frequent minor flooding has influenced the dynamics of the site (Nierenberg, 2000). Over time, the forest thins as a result of competition and a decrease in species that are not tolerant of shade.

Pathway 1.1B
Community 1.1 to 1.2

Black cottonwood-western hemlock/Cascade Oregon grape/western rattlesnake plantain

Black cottonwood-red alder/vine maple/common ladyfern

This pathway represents a major 100- or 500-year flood that scours the stream channel, removes understory and overstory vegetation, and may alter the streamflow. This disturbance may completely reconfigure the sediment and reduce or eliminate the forest overstory.

Pathway 1.2A
Community 1.2 to 1.3

Black cottonwood-red alder/vine maple/common ladyfern

Black cottonwood-western redcedar/vine maple/common ladyfern-western rattlesnake plantain

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 1.3B
Community 1.3 to 1.1

Black cottonwood-western redcedar/vine maple/common ladyfern-western rattlesnake plantain

Black cottonwood-western hemlock/Cascade Oregon grape/western rattlesnake plantain

This pathway represents an area 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. It has small pockets of regeneration (both deciduous and coniferous) and a more diversified understory.

Pathway 1.3A
Community 1.3 to 1.2

Black cottonwood-western redcedar/vine maple/common ladyfern-western rattlesnake plantain

Black cottonwood-red alder/vine maple/common ladyfern

This pathway represents a major 100- or 500-year flood that scours the stream channel, removes understory and overstory vegetation, and may alter the streamflow. This disturbance may completely reconfigure the sediment and dramatically reduce or eliminate the forest overstory.

State 2
Undisturbed State

Community 2.1
Western hemlock–Douglas-fir/salal–Cascade Oregon grape

Structure: Multistory with small gap dynamics Transition State 2 represents a mature old-growth forest that has been undisturbed by major flooding. Western hemlock is the most common overstory species. It is shade tolerant and has the ability to release quickly following extended periods of suppression (Packee, 1990). Douglas-fir and western redcedar are present, but Douglas-fir regeneration is minimal because of the closed canopy. Red alder and Pacific yew are minor components of the overstory, but they commonly become established in areas that have been disturbed and receive more sunlight. The dense canopy created by multiple age groups of hemlock may block most of the sunlight from the forest floor, leading to sparse understory in some areas. Dense clumps of vine maple also block the sunlight. Most of the understory is in areas that have gaps in the mid-canopy and overstory that allow sunlight to reach the ground. The understory is continuous in areas that do not have a mid-canopy. The most common natural disturbance on this site is the small gap dynamics following the mortality of one or two trees.

Transition T1A
State 1 to 2

This pathway represents long-term growth uninhibited by natural disturbances, such as a 100-year flood. Deciduous overstory species are nearly absent, and the plant community shifts to an old-growth conifer forest.

Transition T2A
State 2 to 1

This pathway represents an area affected by major flooding, leading to the stand initiation phase of development.