Topic #4: Ecological Succession KEY
Ecosystems are constantly changing in response to natural and human disturbances. As an ecosystem
changes, older inhabitants gradually die out and new organisms move in, causing further changes in the
community. This series of predictable changes that occurs in a community over time is called ecological
succession. Ecological succession is slow and gradual; it occurs over a period of many years. As ecological
succession occurs, types of species present in a community will change in response to changing
environmental conditions such as fires, climate change, and the clearing of forests to plant crops.
Pioneer species arrive first. As environmental conditions change, they are replaced by other
species, and later these species may be replaced by another set of species. Primary Succession:
Succession that occurs on surfaces where no soil exists. It leads to the gradual establishment of biotic
communities in lifeless areas.
• Rock weathers and crumbles into particles, releasing nutrients.
• Physical and chemical breakdown of rock
• Soil slowly forms
• Initial pioneer species: lichens, mosses.
• Next you will see: Herbs, grasses, low shrubs.
• Climax Community: Trees.
Secondary Succession: Ecological succession in an area where natural vegetation has been removed or
destroyed but the soil or bottom sediment has not been destroyed. Secondary succession may follow a
disturbance that destroys a community without destroying the soil.
