Ecological dynamics
These sites are found within the rainshadow of the Olympic Mountains in the Puget Trough on moist soils and are not restricted to San Juan county. Red alder is a pioneer species – it produces a consistent seed crop, prefers mineral soil in full sun for a seed bed and has rapid height growth. Because Sitka spruce is moderately shade tolerant and prefers light shade for early growth, it will often seed in after red alder when there is a major disturbance. Sitka spruce is much longer lived than red alder; it would be common to find very few alders in stands over 100 years old without a large disturbance. Both overstory species are at least somewhat susceptible to pathogens that cause root rot and pockets of wind-thrown trees due to either rot or shallow root structures are the most common natural disturbance on these sites. Competition of regeneration in these pockets would be strong; smaller pockets would favor Sitka spruce, while larger pockets would favor red alder. These sites also support several species of shrubs, such as salmonberry and red elderberry, which can out-compete red alder in some instances. The resulting shrub-dominated areas may persist for years.
Community 1.1
Sitka spruce - red alder/salmonberry/field horsetail
Structure: multistory with small gap dynamics.
Sitka spruce is the dominant tree species in the historic climax plant community. Red alder will appear sporadically in the plant community, most frequently as mature trees resulting from old, large disturbances. In the small openings most common in this plant community, spruce seedlings and horsetails will be the most common species. Depending on light levels and seed availability, salmonberry patches may be present in the understory. Communities on the wettest end of the range will often have an understory of slough sedge.
Community 1.2
Sitka spruce – red alder/salmonberry – cluster rose/field horsetail
Structure: mosaic of mature overstory and regenerating openings. PC 1.2 retains some areas that resemble the HCPC but also contains moderate sized (2-5 acres) areas of regeneration. Pockets of disease or insect infestations, multiple tree tip-ups or uneven-aged management create these openings, allowing sunlight to reach the forest floor. Red alder, lodgepole pine, black cottonwood and Sitka spruce seedlings can be found in these gaps. Salmonberry, red elderberry and other understory species that require more sunlight than is found in the HCPC, such as cluster rose and trailing blackberry, will become more prevalent given these conditions. Without management some openings may be dominated by shrubs for many years until their coverage gradually diminishes due to overstory shading.
Community 1.3
Red alder – Sitka spruce/salmonberry – cluster rose/stinging nettle – field horsetail
Structure: regenerating single story/shrub. PC 1.3 is forestland in regeneration; species composition depends on the natural seed sources present and the intensity of management. If the seedlings are planted, red alder would most likely be selected because spruce prefers more shade than is found early in PC 1.3. The major disturbance which led to this community exposes mineral soil and all four of the common tree species germinate well given these conditions. Increased sunlight will also benefit many understory species, including cluster rose and stinging nettle. Control of the shrub community may be necessary to allow trees to become successfully established.
Community 1.4
Pasture grasses/red alder/salmonberry
Structure: abandoned pasture with regeneration. PC 1.4 is abandoned crop or pasture land. It will typically include both native and non-native grass species, with shrubs and trees gradually encroaching from the edges. Because Sitka spruce prefers some shade for regeneration, it would likely be a secondary colonizer after red alder and/or lodgepole pine. Over time shade-intolerant understory species will diminish as the overstory canopy closes.
Community 1.5
Red alder – Sitka spruce/salmonberry – cluster rose/stinging nettle – field horsetail
Structure: single story with somewhat diminished understory. PC 1.5 is the ‘competitive exclusion’ phase of stand development. The overstory canopy has closed, leading to competition for sunlight and a somewhat diminished understory. These stands are typically dense with minimal vertical differentiation. Alder stands at this stage could be commercially thinned for pulpwood; if not, mortality due to self-thinning will occur. In the later stages of this plant community alder could be commercially harvested for saw logs.
Community 1.6
Sitka spruce – red alder/salmonberry/field horsetail
Structure: single story with scattered openings. PC 1.6 is a transitional community with alder losing any remaining co-dominance to the spruce. Alder trees in this age range are susceptible to various fungi and any management at this stage would likely be to salvage remaining alders and to maintain the health of spruce trees. If not harvested, the majority of alders will succumb to age and the stand will be primarily spruce. The community is starting to differentiate vertically, with the death of individual alders allowing more sunlight to reach the forest floor.
Pathway 1.1a
Community 1.1 to 1.2
This pathway represents a larger disturbance – major windstorms or spreading disease pockets would be the main natural disruptive force while a group selection or shelterwood (with reserves) harvest would represent the human-initiated community. Areas of regeneration would generally range from 2 to 5 acres.
Pathway 1.1b
Community 1.1 to 1.3
This is the pathway of major disturbance. Because this plant community is found on moist to very moist soils, major fires are rare (150-350+ year return interval). When fires do occur, they would result in almost 100% mortality, as represented by this pathway. A clear-cut or block harvest would simulate this disturbance.
Pathway 1.1c
Community 1.1 to 1.4
This pathway signifies the conversion of forested land to either cropland or pasture.
Pathway 1.2a
Community 1.2 to 1.1
This pathway indicates growth over time with no further major disturbances. The areas of regeneration pass through the typical stand phases – competitive exclusion, maturation, understory re-initiation – until they resemble the old-growth structure of the HCPC.
Pathway 1.2b
Community 1.2 to 1.3
This pathway represents intensive management or large-scale disturbance, most likely either a major wind storm or a block harvest. The mature forest is cleared; regeneration would be either planted red alder or a mix of species that naturally seed in.
Pathway 1.3a
Community 1.3 to 1.5
This pathway represents growth overtime with or without active management. In alder stands, a pulpwood thinning in the later stage or PC 1.3 would lower stand density and prevent mortality due to competition. If not managed, the stand will start to self-thin because only dominant or co-dominant trees receive sufficient sunlight to survive.
Pathway 1.4a
Community 1.4 to 1.3
This pathway represents either the gradual shift from open field to forest or the active management of restoring forestland.
Pathway 1.5b
Community 1.5 to 1.3
This pathway indicates intensive management focusing on wood products. Block harvest with subsequent site preparation will create a suitable seedbed for either natural seeding or tree planting.
Pathway 1.5a
Community 1.5 to 1.6
This pathway represents growth over time, with or without management. Trees released by prior thinnings will continue to grow although some individuals may start to develop various rots at this stage.
Pathway 1.6a
Community 1.6 to 1.1
This pathway represents growth over time with no further management or major disturbance. Vertical differentiation continues as small openings allow for regeneration of tolerant tree species. The diversity of understory species increases as the stand regains the characteristics of the HCPC.
