TIME →→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→ Centuries to Millennia
Year 0-50 Year 50-200 Year 200-500 Year 500-1000+ Year 1000+
│ │ │ │ │
▼ ▼ ▼ ▼ ▼
BARE ROCK CRUSTOSE MOSSES HERBACEOUS SHRUBS
(volcanic LICHENS colonize thin PLANTS (woody
lava, (pioneer soil created (grasses, plants,
glacial species) by lichens forbs) dense
retreat, Chemical cover)
bare weathering
granite) begins
Thin proto-
soil forms
│
▼
TREES →
CLIMAX
FOREST
(stable,
self-
perpetuating)
Key events at each stage:
| Stage | Key processes | Soil depth | Species richness |
|---|---|---|---|
| Bare rock | Abiotic weathering (rain, freeze-thaw) | 0 | 0 |
| Crustose lichens | Chemical weathering; organic matter begins | < 1 cm | Very low |
| Mosses | Moisture retention; more organic matter | 1-5 cm | Low |
| Herbs | Deeper roots; N-fixing species; more organic matter | 5-20 cm | Moderate |
| Shrubs | Dense root systems; higher biomass; more species | 20-50 cm | High |
| Climax forest | Deep soil; closed canopy; self-perpetuating | >50 cm | Moderate (shade-specialist) |
Facilitating mechanisms at each transition:
- Lichens → Mosses: Lichens create mineral soil + moisture retention for moss establishment
- Mosses → Herbs: Mosses deepen soil and organic matter; herbs can establish in thicker soil
- Herbs → Shrubs: Herb matter builds soil; shrubs outcompete herbs for light
- Shrubs → Trees: Trees shade out shrubs; long-lived competitive dominants take over