Ecology
Ecological Succession
Predictable changes in community over time after disturbance
Ecological succession is the process of change in species composition of a biological community over time. Two main types: (1) Primary succession — starts with bare rock or new substrate (e.g., after volcanic eruption, glacier retreat). (2) Secondary succession — after disturbance to existing community (e.g., fire, abandonment of farm). Stages: pioneer species (lichens, hardy plants) → intermediate species → climax community (mature, stable). Time scale: decades to centuries. Studied by Frederic Clements (early 20th century). Modern view: more dynamic; multiple climax states possible.
- Primary successionFrom bare substrate (volcanic, glacial)
- Secondary successionAfter disturbance to existing community
- Pioneer speciesFirst colonizers (lichens, hardy plants)
- Climax communityMature, relatively stable end state
- Time scaleDecades to centuries
- StudiedFrederic Clements (early 1900s)
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Why succession matters
- Restoration. Restoring damaged ecosystems.
- Conservation. Understanding habitat needs.
- Wildfire management. Disturbance vs suppression.
- Climate change. Predicting community changes.
- Agriculture. Crop rotation, succession in farming.
- Forestry. Sustainable harvesting.
- Education. Foundational ecology.
Common misconceptions
- Succession deterministic. Stochastic factors important.
- Climax always reached. Often not; disturbance keeps systems from climax.
- Single climax type. Multiple stable states possible.
- Succession always slow. Some types fast.
- One pioneer species. Multiple usually.
- Succession good or bad. Just process; outcomes vary.
Frequently asked questions
What's primary succession?
Begins on substrate without soil. Examples: volcanic lava flows, glacial moraines, sand dunes, exposed rock. Steps. (1) Pioneer species (lichens, mosses): tolerate harsh conditions; break down rock; produce organic matter. (2) Soil develops gradually. (3) Small plants (grasses, shrubs) colonize. (4) Larger plants follow. (5) Trees eventually. (6) Climax community. Slow: 100s-1000s of years for forest from bare rock.
What's secondary succession?
After disturbance damages or removes existing community but soil remains. Examples: forest fire, abandoned farm, hurricane damage. Faster than primary because soil already present. Steps. (1) Annual plants colonize quickly. (2) Perennial plants follow. (3) Shrubs, small trees. (4) Larger trees. (5) Eventually return to climax (or different state). Decades typically.
What's a climax community?
Stable end state of succession. Self-sustaining; stays relatively constant over long time. Each climate/region has typical climax. Examples: oak-hickory forest in US East, beech-maple in cooler regions, prairie grassland. Concept: simplified — modern view recognizes multiple stable states possible. Disturbance can prevent reaching climax.
How does succession work?
Pioneer species modify environment for next species. (1) Facilitation: pioneers prepare habitat for next species (provide soil, shade, microbes). (2) Tolerance: later species tolerate conditions; earlier ones decline. (3) Inhibition: existing species prevent newcomers; succession only after they die. Different mechanisms for different ecosystems.
What was the Mt St Helens example?
1980 volcanic eruption: massive devastation. Studied since: primary succession on bare lava, ash. Pioneer species: lupines (legumes; nitrogen fixers — improved soil), fireweed, alders. Decades later: forest beginning. Demonstrates: how much time succession takes; importance of N-fixers for soil development.
What's the modern view?
Less linear, less predictable than Clements thought. Random factors matter. Different climaxes possible (alternative stable states). Some communities never reach climax due to frequent disturbance. Disturbance regimes (fire, flood, etc.) integral to many ecosystems. Many ecosystems: not single stable climax; mosaic of patches at different stages.
How does succession affect biodiversity?
Different stages support different species. Early successional: pioneer species, generalists, invaders. Mid-successional: maximum diversity often. Late: specialists adapted to mature conditions. Disturbance (creating early stages) often increases regional biodiversity by maintaining patches at all stages. Conservation: maintaining heterogeneous landscape with disturbance.