Mains Paper II · 4 Environment & Ecology · 4.1 Ecology and ecosystems
4.1.5 Ecological succession: primary, secondary and climax
Ecological succession is the gradual, fairly predictable change in the species of an area over time, until a stable climax community in balance with the climate is reached.
- APPSC Group 2 · Mains Paper II
- Advanced level
- 7 min read
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Core facts
- Succession: a gradual and fairly predictable change in the species composition of an area.
- Pioneer species: the first species to colonise a bare area.
- Sere: the entire sequence of communities that replace one another in an area.
- Seral stages (seral communities): the individual transitional communities in a sere.
- Climax community: the final, stable community that is in near equilibrium with the environment (mainly the climate).
- Primary succession: starts where no soil or life existed before: bare rock, newly cooled lava, newly formed sand dunes, a newly created pond or reservoir.
- Secondary succession: starts where a community was destroyed but soil remains: abandoned farmland, burned or cut forest, flooded land.
- Secondary succession is faster than primary succession, because soil, seeds and roots are already present.
- Pioneers on bare rock: usually lichens. They secrete acids that dissolve rock and start soil formation. Mosses follow.
- Pioneers in water: usually phytoplankton.
- Hydrarch succession: in water; progresses from wet (hydric) to mesic conditions.
- Xerarch succession: in dry areas; progresses from dry (xeric) to mesic conditions.
- The idea of succession and the climax was developed by F.E. Clements (1916).
Explained
Stages of succession
| Hydrarch (water) | Xerarch (bare rock) |
|---|---|
| Phytoplankton | Lichens (crustose, then foliose) |
| Rooted submerged plants | Mosses |
| Rooted floating plants | Herbs and grasses |
| Reed swamp and sedges (marsh-meadow) | Shrubs |
| Shrubs | Trees |
| Forest (climax) | Forest (climax) |
- Both sequences lead towards mesic conditions (medium moisture): water bodies fill up and become drier; bare rock builds soil and holds more water.
What changes during succession
- Soil depth and organic matter increase.
- The number and diversity of species increase.
- Total biomass increases.
- Niches become more specialised and food webs more complex.
- Nutrient cycles become more closed; less is lost from the system.
- The community moves from r-selected pioneers (small, fast-growing) to K-selected climax species (large, long-lived).
Primary versus secondary succession
| Feature | Primary | Secondary |
|---|---|---|
| Starting point | No soil, no life | Soil present, life removed |
| Examples | Bare rock, lava, new pond | Abandoned field, burned forest |
| Pioneers | Lichens, phytoplankton | Grasses and herbs, from seeds in soil |
| Speed | Very slow (centuries or more) | Faster (decades) |
Deeper
Types by cause and energy
- Autogenic succession: change is driven by the community itself (for example, plants building soil and shade).
- Allogenic succession: change is driven by outside forces (fire, flood, siltation, climate change).
- Autotrophic succession: dominated by green plants from the start; biomass rises over time.
- Heterotrophic succession: dominated early by heterotrophs, for example on a dead log or in a sewage-rich pond; organic matter falls over time.
Views of the climax
| Theory | Proposed by | Idea |
|---|---|---|
| Monoclimax | F.E. Clements | Each climatic region has only one climax, set by climate |
| Polyclimax | A.G. Tansley | Several climaxes can exist in one region, set by soil, topography, fire and so on |
| Climax-pattern | R.H. Whittaker | The climax is a continuous pattern that varies with the environment |
Mechanisms (Connell and Slatyer, 1977)
- Facilitation: early species change conditions in ways that help later species.
- Tolerance: later species tolerate lower resource levels and simply outlast earlier ones.
- Inhibition: early species hold the site and block later ones until they die or are disturbed.
Disturbance resets succession. Fire, cyclones, grazing and shifting cultivation hold many Indian landscapes at a seral stage. For example, many grasslands persist only because of regular fire or grazing.
Real examples: after the 1883 eruption of Krakatoa (Indonesia) wiped out life on the island, it became a classic study of primary succession. Abandoned jhum (shifting cultivation) plots in north-east India show secondary succession back towards forest.
Common traps
- ✗ "An abandoned farm is primary succession." ✓ It is secondary succession, because soil remains.
- ✗ "Mosses are the pioneers on bare rock." ✓ Lichens are the pioneers; mosses follow.
- ✗ "Hydrarch succession moves from dry to wet." ✓ Hydrarch moves from wet to mesic; xerarch moves from dry to mesic.
- ✗ "Primary succession is faster because there is less competition." ✓ Secondary succession is faster, because soil is already present.
- ✗ "A sere is the final community." ✓ A sere is the whole sequence; the final stable stage is the climax.
Quick revision
- Succession: gradual, predictable change in species composition.
- Pioneer → seral stages → climax; the whole sequence = sere.
- Primary: no soil (rock, lava, new pond). Secondary: soil remains (abandoned field, burnt forest).
- Secondary is faster.
- Pioneers: lichens on rock; phytoplankton in water.
- Hydrarch: wet → mesic. Xerarch: dry → mesic.
- Clements (1916): monoclimax. Tansley: polyclimax. Whittaker: climax-pattern.
- During succession, diversity, biomass and soil increase.
Go deeper: Mains writing (beyond what APPSC Group 2 usually asks)
Mains writing Mains writing
- Frame: succession is nature's own restoration. Ecological restoration works best when it speeds up natural succession instead of planting a single species.
- Analysis points:
- Monoculture plantations (eucalyptus, acacia) freeze succession and support little diversity, although they add "green cover" on paper.
- Shifting cultivation: long fallow cycles allow secondary succession to restore soil. Shorter cycles under population pressure degrade land.
- Mining and quarry sites need active help (topsoil, pioneer species, nitrogen-fixing plants) to restart succession.
- Wetlands naturally fill up through hydrarch succession, and siltation from deforested catchments speeds this up.
- Way forward:
- assisted natural regeneration with native species
- protect seed sources and soil
- restore with mixed species in stages
- leave natural regeneration areas free of grazing and fire for some years
- Example: degraded forest restored by stopping grazing and fire often recovers faster and with more native diversity than land planted with one fast-growing exotic species.
Practise this topic. Questions on Ecology & ecosystems, with answers explained.
All Ecology and ecosystems notes · APPSC Group 2 syllabus · APPSC G2 Prelims Mock 1 with answers · Start free
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