1. Ecological Succession
How do ecosystems respond following a disturbance?

2. Vocabulary
Climax Forest Lichen Pioneer Species Primary Succession Secondary Succession

3. ecological succession: series of changes that occur over time in an ecosystem
primary succession: succession that occurs on surfaces where no soil exists
secondary succession: succession that occurs following a disturbance that changes an existing community without removing the soil

4. Primary Succession
Occurs when bare rock is exposed by a retreating glacier or created by cooled lava. – The soil is gone!
pioneer species: first species to populate a previously uninhabited area (mosses, lichens)

5. Mosses and Lichens: Fungus/algae that can grow on bare rock

6. Succession progresses from pioneer species to more complex ecosystems and longer-lived trees, ultimately resulting in a Climax Community

7. This process may take hundreds of years from the first plants until a climax forest is reached.

8. Craters of the Moon National Monument
Idaho, US

9. Craters of the Moon National Monument
Idaho, US

10. Secondary Succession
Occurs following natural or human-caused disturbances: wildfires, clearing of land for agriculture or development, wind storms, lakes that dry up, etc.
The soil is still in place

11. Secondary succession is quicker than primary because the soil is in place.
It may start with grasses as pioneer species.

12. South side of Mount St. Helens and Shoestring Glacier prior to the 1980 eruption.
(USGS, D. Miller)

14. Muddy River lahar deposit following the Mount St. Helens eruption.
(USDA Forest Service,
 F. Valenzuela, 1981)

15. Fresh pyroclastic flow deposits directly north of the crater at Mount St. Helens.
(USGS, 1980)

16. Twenty-five years later the Pumice Plain north of the crater is covered in wildflowers.
(USDA Forest Service,
P. Frenzen, 2004)

17. Mount St. Helens Washington, US Eruption May 1980
Photos taken August 2005