Factors Influencing Succession (HL) (DP IB Environmental Systems & Societies (ESS))

Factors Influencing Succession

• Succession refers to the gradual process by which ecosystems change and develop over time

  • Various abiotic and biotic factors influence the succession process and the type of community that forms

Climatic factors

• Climate plays a key role in determining the direction and speed of succession

  • Areas with high rainfall and warm temperatures generally experience faster succession, as conditions favour plant growth

  • Cold climates or areas with limited rainfall may experience slower succession due to harsh growing conditions

• Wind and extreme temperatures can impact which species are able to survive in a given area, therefore shaping the community

  • For example, in desert ecosystems, high winds and extreme heat can:

    • Slow down plant growth

    • Allow only drought-tolerant species to thrive

Local bedrock and soil properties

• The type of bedrock and soil in an area affect nutrient availability and water retention

  • This directly influences the plant species that can grow, for example:

    • Sandy soils drain quickly, favouring species that tolerate dry conditions

    • Clay-rich soils retain more water, favouring moisture-loving species

• Soil pH is another important factor

  • Acidic soils (such as those found over granite) support different plants compared to alkaline soils (such as those over limestone).

    • For example: in calcareous grasslands found on limestone, many species are adapted to high pH and calcium-rich conditions

Geomorphology and topography

• Steep slopes can restrict soil development because rainwater and gravity cause erosion

  • This makes it difficult for plants to establish and soil to accumulate

    • For example, mountain ecosystems often have thin soils on slopes, supporting hardy plant species like grasses and shrubs

• Waterlogging occurs when the land is poorly drained

  • This prevents oxygen from reaching plant roots

  • This leads to the development of wetland ecosystems with specialised plants like reeds, rushes, and mosses

• Geomorphology also includes the shape and structure of the land, which influences water flow, drainage patterns, and sunlight exposure, affecting plant growth

Fire and weather-related events

• Fires can significantly influence succession, creating new opportunities for different species to dominate

  • Some ecosystems, like savannahs or Mediterranean scrublands, are fire-adapted

    • They contain plants that can regrow quickly after being burned

    • Fire helps the seeds of some plant species break dormancy and germinate

    • Fires can also clear away competing vegetation and create nutrient-rich ash in which new plants can sprout and thrive

• Storms, floods, or droughts also shape the direction of succession by removing dominant species or altering the landscape

  • These events create conditions for new species to establish

  • For example, hurricanes can knock down trees in a forest, allowing light to reach the forest floor, promoting the growth of shade-intolerant species

Biotic influences (top-down effects)

• Herbivores and carnivores can have top-down effects on the community structure during succession

• Primary consumers, like grazing animals, can limit plant growth by consuming young plants

  • This can alter which plant species dominate the ecosystem

  • For example, in Yellowstone National Park, the reintroduction of wolves controlled elk populations, allowing vegetation like willow and aspen to regenerate

• Keystone species (species that have a disproportionate effect on their environment) often drive changes in succession

  • For example, elephants in African savannahs knock down trees

  • This opens up space for grasses and other shrubs to thrive, maintaining the grassland ecosystem

Human impacts on succession

• Deforestation, urbanisation, and agriculture can halt natural succession

  • These actions convert natural landscapes to human-dominated systems

  • For example, agricultural fields are frequently disturbed, preventing natural succession from occurring, and crops are continuously planted instead of allowing a forest or grassland to regrow