Ecological Succession and Keystone Species

Primary Succession: Pioneer species (moss, lichen) colonize bare rock.
- They secrete acids, releasing nutrients via chemical weathering.
- Death and regrowth lead to shallow, rocky soil formation.
- Grasses, wildflowers, and shrubs colonize.
- Organic matter increases, enabling intermediate species (shade-intolerant trees).
- Slow-growing, shade-tolerant trees (oak, maple) replace intermediate species, forming a climax community with high biomass and species richness.
Secondary Succession: Similar to primary succession, but occurs where soil is already present.
- Pioneer species (grass, wildflowers) colonize disturbed soil after events like forest fires or abandoned fields.

A keystone species is vital for ecosystem function; its removal can cause ecosystem collapse.
Example: Wolves control deer and elk populations; without them, overgrazing can occur.
Ecosystem engineers (beavers, mangrove trees) dramatically shape landscapes, creating habitats.
- Mangrove trees' stilt roots create mangrove swamps.
- Beaver dams create beaver ponds.