Ecological Succession

1. Ecological Succession Succession after the Yellowstone fires. Succession at Mt. St. Helens. Ecological succession is theseries ofchanges that occur over time in a new or disturbed ecosystem.

2. Primary Succession • occurs when there is only bare rock in an area • when land is formed from lava erupting from a volcano • when land is scraped down to bedrock by a glacier • First, moss & lichen (pioneer species) grow. • Moss & lichen die, decompose and form soil. • Grasses grow from seed spread by wind and animals. • Shrubs grow • Small trees grow • Larger trees grow • Climax community (stable community at the end of succession

3. Primary Succession at Glacier Bay, Alaska A climax community is the stable community at the final stage of succession.

4. Secondary Succession • occurs when there is an existing ecosystem that is disturbed, often by a natural disaster or human activity • Volcanic eruption (Mount St. Helens) • Forest fire (Yellowstone National Park) • Tree cutting by humans • Takes less time than primary succession because soil is already present. • Starts with soil. • Grasses grow from seed spread by wind and animals. • Shrubs grow • Small trees grow • Larger trees grow • Climax community (stable community at the end of succession

5. Secondary Succession on Mt. St. Helens after it erupted in 1980 Land covered by ash from the eruption Grasses & shrubs have rooted and grown