Ecological succession refers to predictable changes in the structure of a community over time. Primary succession occurs on new areas without soil, like after a volcano, where pioneer species establish and create soil for more complex plants. Secondary succession follows a disturbance, like a fire, that reduces an existing ecosystem and leaves soil intact, allowing the area to transition back to its original state. Succession proceeds through early, middle, and late stages as species composition changes from small, fast reproducing pioneers to longer-lived plants and animals of a mature ecosystem.

1. Succession Ecological succession refers to more-or-less predictable and orderly changes in the structure of an ecological community.

2. Primary Succession Primary succession is the first stage of the ecological succession of plant life from barren land with no soil to fully functioning plant ecosystems. In primary succession, pioneer plants like mosses and lichen, start to "normalize" the habitat, creating conditions nearer the optimum for plant growth. These pioneer plants are then dominated by more complex plants like grasses and shrubs. A good example of primary succession takes place after a volcano has erupted. The barren land is first colonized by simple pioneer plants which pave the way for more complex plants, such as hardwood trees by creating soils and other necessities.

3. Secondary Succession Secondary succession is a process started by an event (e.g. forest fire, harvesting, hurricane) that reduces an already established ecosystem (e.g. a forest or a wheat field) to a smaller population of species. Secondary succession occurs on preexisting soil whereas primary succession usually occurs in a place lacking soil. A harvested forest going back from being a cleared forest to its original state is an example of secondary succession.

4. Secondary succession occurs after disturbance that leaves the soil intact. 1988 fires in Yellowstone

5. Diagram of bog succession.

6. Stages of Succession Early: plants typically small with short lifecycles and rapid seed dispersal, Middle: plants typically longer lived, slower seed dispersal, and in woodland systems Late: plants and animal species are those associated with older, more mature ecosystem. A seral community (sere ) is the name given to each group of plants within the succession. A pioneer species is a plant species which colonizes previously uncolonized land, usually leading to ecological succession.

7. Graphs showing changes in biomass and diversity with succession.

8. Moraine Succession Moraine is the general term for debris of all sorts originally transported by glaciers or ice sheets that have since melted away. retreating glaciers leave moraines. autotrophic bacteria are first colonizers. mosses and lichens are first macroscopic autotrophs. soil forms gradually pioneering plant species are next

9. Moraine Succession Succession continues until a climax community is formed. spruce replace alder and cottonwood final stage is a spruce and hemlock forest