Succession

Succession is the orderly process of one plant community gradually or rapidly replacing another. It is a result of the developmental changes in the ecosystem itself or from disturbances such as wind, fire, volcanic activity, insects and disease, or harvesting.

Classic Forest Succession

• Grass-forb - Forbs, grasses and shrubs dominate the site
• Shrub-seedling - Trees tend to share and then begin to dominate the site. The shade intolerant species grow rapidly and dominate over shade tolerant species
• Sapling-pole - Trees eventually overtop and out-compete the forb and shrubs. The intolerant trees continue rapid height growth while the shade-tolerant trees occupy their respective niche
• Young - Growth is still rapid. Tree-to-tree competition may be severe resulting in competition-caused mortality. Any intolerant individuals that drop behind may die and their growing space may be occupied by the tolerant trees.
• Mature - Competition-caused mortality continues. Both intolerant and tolerant trees may share the main canopy. In mixed conifer stands, there may be distinct layering of intolerants and tolerants.
• Climax - Shade-tolerant trees dominate the site and the climax species will reproduce. Shade-intolerant trees cannot replace themselves. Most climax stands (old growth) are set back to the early seral grass-forb or shrub-seedling stage by fire in the Northern Rockies.

Some stages of the characteristic sequence may be skipped.

Disturbance plays an important role in succession. Disturbance moves the community to a different, usually earlier, successional stage.

Primary succession Initiated by disturbances that expose substrates and are left with essentially no plant growth at the beginning Examples: glacial retreat; volcanic ash deposition

Secondary succession Established plant community has been destroyed but without severe disturbance of the soil Example: forest succession following wildfire - pioneer forest re-establishes and is eventually replaced with climax forest

Seral communities: The various “temporary” communities in the succession Seral species are those that will ultimately be replaced examples: annual plants, shrubs, intolerant trees

Climax community: The “final” stage of the succession - consists of those plants that can reproduce successfully beneath their own shade and therefore maintain the community indefinitely under the prevailing conditions Climax species: Those species that will occupy the site at the climax stage of succession Examples: tolerant tree species such as cedar and hemlock

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