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:
   1. Water Removal: Draining lowers water levels, killing aquatic plants.
   2. Soil Changes: Exposed soils dry out and compact, making re-colonization by wetland plants difficult.
   3. Invasive Species: Drier conditions favor invasive plants over native wetland species.

Why Do Climax Communities Matter?

1. Climax communities provide critical benefits:
   1. Biodiversity: They host diverse species, promoting ecosystem resilience.
   2. Ecosystem Services: Wetlands filter water and store carbon, forests regulate climate and provide habitat.
   3. Stability: Mature ecosystems are better equipped to withstand disturbances like droughts or wildfires.

Sustainable Grazing Practices

1. Rotational Grazing: Move livestock to prevent overgrazing in one area.
2. Buffer Zones: Protect sensitive areas, like riverbanks, from grazing.
3. Mixed Grazing: Use diverse livestock species to reduce selective feeding.

Example

In the UK, rotational grazing helps maintain species-rich grasslands while supporting farming.

Wetland Restoration Strategies

1. Rewetting: Restore natural water levels to revive wetland ecosystems.
2. Invasive Species Control: Remove non-native plants to allow native species to recover.
3. Protected Areas: Designate wetlands as conservation zones to prevent future drainage.

Why Does This Matter?

1. Human activities often arrest succession, altering ecosystems.
2. However, with informed management, we can restore natural processes, ensuring the resilience and sustainability of ecosystems for future generations.