Ecological Succession Notes

Communities and ecosystems change over time through ecological succession.
Primary succession occurs on newly exposed surfaces (e.g., fresh lava, glacier retreat).
Secondary succession occurs after disturbances in existing communities (e.g., abandoned farmland).

Initiated by events like glacier retreat, exposing bare rock.
Chronosequences reveal changes in species richness and community composition.
Plant communities transition from non-vascular plants (mosses, lichen) to herbaceous plants, then woody vegetation.
- Salix, Alnus, spruce. Salix and Alnus can block coloization by other species.
Early species like Dryas drumondii facilitate succession by building soil and fixing nitrogen.

Occurs after disturbances like fire or clearcutting.
In forests, abandoned farmland transitions from few woody species and grass dominance to shrubs, then pine, and finally oak and hickory.
Bird succession follows plant succession.

Different disturbances (clearcutting, wildfire, storms, insect infestations) create different conditions and structures.
Algal succession in streams occurs much faster than forest succession.
Succession in desert streams and rocky intertidal zones also exhibits community-specific timelines.

Facilitation: Pioneer species improve the environment for later species.
Species A facilitates species B by improving the environment (may degrade the environment for itself).
Climax community tolerates the conditions and does not improve the environment for other colonizers.
Inhibition: Early colonists inhibit the establishment of new species.
Colonists degrade the environment for others.
Later colonists establish only if disturbance removes earlier colonists.
Succession is an interplay of both inhibition and facilitation.