Soil Ecosystems (DP IB Environmental Systems & Societies (ESS)): Revision Note

Soil Ecosystems

Soil Ecosystem Succession

• Soil ecosystems undergo changes over time through a process known as succession

• Succession in this context refers to the predictable sequence of changes in the composition and structure of a soil ecosystem

• The process of succession is influenced by factors such as climate, vegetation, and interactions between biotic and abiotic components

   Primary Succession

• Primary succession occurs in areas where soil development starts from bare rock where there is no organic matter

• Pioneer species, such as lichens and mosses, colonise the bare substrate and begin the process of soil formation

• These pioneer species are well adapted to harsh conditions and can tolerate low nutrient availability

• As these pioneer species establish and grow, they begin to break down rocks and organic matter, contributing to the formation of the initial thin, nutrient-poor soil layer

• Over time, the accumulated organic matter and the process of weathering lead to the development and deepening of the soil layer

• This soil can be colonised by herbaceous plants and shrubs - these plants have slightly higher nutrient requirements compared to pioneer species and contribute to the further enrichment of the soil

• As the soil becomes more fertile, it can support the growth of larger plants, such as trees

• The establishment of trees marks the later stages of succession, known as climax communities, where the soil ecosystem reaches a stable state

   Changes in Soil Characteristics

• As succession progresses, there are significant changes in soil characteristics

• Initially, the soil may be nutrient-poor and have a low organic matter content

• However, as vegetation and organic matter increase, the soil becomes enriched with nutrients, organic compounds, and microbial communities

• The soil structure improves, leading to increased water-holding capacity and better nutrient availability for plant uptake

• Soil pH may also change as different plants and microbes affect nutrient cycling processes

• Additionally, soil erosion becomes less of a risk as the soil becomes more stabilised and protected by vegetation

The general process of succession resulting in the creation of new soils

Fertile Soil and Nutrient Cycles

• Fertile soil contains a diverse community of organisms, including bacteria, fungi, insects, and earthworms, that play essential roles in maintaining functioning nutrient cycles

• Decomposers, such as bacteria and fungi, break down organic matter, releasing nutrients back into the soil

• Nutrient cycling involves the movement of essential elements, such as nitrogen, phosphorus, and carbon, between living organisms, organic matter, and the soil

• This cycling ensures the availability of nutrients for plants, supporting their growth and productivity

Resistance to Soil Erosion

• A well-developed and fertile soil ecosystem is resistant to soil erosion (the process by which soil is transported away by wind or water)

• The presence of vegetation, particularly deep-rooted plants, helps to stabilise the soil, preventing erosion

• Soil organisms, such as earthworms, contribute to soil structure by creating channels and burrows that improve water infiltration and soil porosity, reducing the likelihood of erosion

• The organic matter content in fertile soil enhances its ability to retain moisture, reducing surface runoff and erosion risks