D4.2.15 Climax communities and arrested succession (HL) Notes

Climax Communities and Arrested Succession

1. A thriving forest represents a climax community, the final stage of ecological succession.
2. However, human activities like grazing or draining wetlands can disrupt this process, preventing the ecosystem from reaching its potential.
3. These ecosystems experience minimal changes in species composition and are highly efficient in energy use and nutrient cycling.

Key Characteristics of Climax Communities

1. Stability: Species composition remains relatively unchanged unless disturbed.
2. Biodiversity: A wide variety of plants, animals, and microorganisms coexist.
3. Efficient Nutrient Cycling: Decomposers recycle nutrients effectively.
4. Energy Balance: Energy input (e.g., sunlight) matches energy output (e.g., heat loss).

Arrested Succession: When Progress Stops

1. Human activities can halt natural succession, creating a stable but less biodiverse system known as arrested succession.
2. Two primary causes are grazing and wetland drainage.

Grazing Halts Forest Development

1. In grassland ecosystems, livestock like cattle or sheep graze heavily, preventing trees and shrubs from growing.
2. Impacts of Grazing:
   1. Selective Feeding: Grasses survive, while tree saplings and shrubs are eliminated.
   2. Soil Compaction: Livestock movement compacts soil, reducing water infiltration and seedling growth.
   3. Ecosystem Shift: Instead of evolving into a forest, the ecosystem stabilizes as grassland.

Example

Bison grazing on the Great Plains of North America maintains open grasslands by preventing tree colonization.

Draining Wetlands Alters Succession

1. Wetlands naturally progress toward swamp forests as part of their succession.
2. However, drainage for agriculture disrupts this process.
3. Impacts of Wetland Drainage: