D4.2.13 Changes occurring during primary succession (HL) Notes

Pioneer Species Begin Soil Formation

1. Primary succession starts in lifeless areas such as bare rock, sand, or clay left by glaciers or volcanic eruptions.
2. Bacteria, lichens, and mosses are the first colonizers.
3. These organisms:
   1. Break down rock into smaller particles.
   2. Add organic matter as they die and decompose, forming the first thin soil layer.

Herbs and Grasses Stabilize the Soil

1. Once some soil is present, herbs and grasses can establish themselves.
2. Their roots:
   1. Anchor the soil, preventing erosion.
   2. Improve water retention.
3. As these plants die, they add more organic material, enriching the soil further.

Shrubs and Trees Enrich the Habitat

1. As the soil deepens, shrubs and small trees take root.
2. These plants:
   1. Provide shade, creating microhabitats for shade-tolerant species.
   2. Enhance nutrient cycling, as their fallen leaves and branches decompose.

Climax Communities Represent Stability

1. Over time, ecosystems reach a climax community, which is stable and diverse.
2. Characteristics include:
   1. Large trees, such as spruce or oak.
   2. Complex food webs, supporting a wide range of species.
   3. Efficient nutrient cycling, maintained by decomposers.

Primary Succession Increases Ecosystem Complexity

1. Biodiversity Expands: New species join the community, leading to diverse plants, animals, and microorganisms.
2. Primary Production Rises: Larger plants capture more sunlight, increasing photosynthesis and energy flow.
3. Food Webs Grow More Intricate: Interactions among species become more complex, creating stable ecosystems.
4. Nutrient Cycling Becomes More Efficient: Decomposers recycle organic matter, enriching the soil and supporting plant growth.

The Next Wave: Small Plants and Grasses

1. As soil begins to form, it can support small plants like grasses and herbs.
2. These plants:
3. Stabilize the Soil: Their roots prevent erosion and hold the soil in place.
4. Increase Nutrients: They add more organic matter to the soil as they grow and decompose.

Building Complexity: Shrubs and Small Trees

1. With more soil and nutrients available, larger plants like shrubs and small trees begin to grow.
2. These plants:
3. Provide Shade: This creates microhabitats for shade-tolerant species.
4. Enhance Nutrient Cycling: Their leaves and branches contribute to a richer, more fertile soil.

The Climax Community: A Stable Ecosystem

1. Over time, the ecosystem reaches a climax community, a stable and mature stage with high biodiversity.