Succession in Ecosystems

AP Environmental Science

Succession-

a series of changes in a community in which new populations of organisms gradually replace existing ones Predictable and orderly changes in the structure of an ecological community over time

Reasons for succession

Response to natural and human disturbancesCommunity dynamics change as older organisms die out and new ones move in

Primary successionGrowth occurs on newly exposed surfaces where no soil exists: takes place on bare rock

Primary succession

New bare rock comes from 2 sources:

1. volcanic lava flow cools and forms rock

Primary succession

New bare rock comes from 2 sources:

2. Glaciers retreat and expose rock

Pioneer organismsthe first organisms to colonize a new site

lichens are the first to colonize lava rocks Takes several hundred years to produce fertile soil naturally.

Pioneer organismsAs the rocks breaks apart, water freezes and thaws on the cracks, which breaks up the rocks further.When the lichens die, they accumulate in the cracks. Then mosses begin to grow and die, leading to the creation of fertile soil.Fertile soil is made up of the broken rocks, decayed organisms, water, and air.

Primary Succession-

Climax community

a stable, mature community that undergoes little or no succession

Climax community

ExampleIn most of Virginia, the climax community would be a deciduous oak–hickory forest

                                                                                                                                

Primary succession

Secondary succession-

sequence of community changes that takes place when a community is disrupted by natural disaster or human actions – takes place on existing soil

Secondary succession-

Example: A fire levels portions of a forest

Secondary succession-

Example: A farmer plows his field

Secondary succession

Secondary succession-

Secondary Succession: Mt. St. HelensErupted in 1980.44,460 acres were burned and flattened.After the eruption, plants began to colonize the volcanic debris.Pioneer species: the first organism to colonize any newly available area and begin the process of ecological succession.

Secondary Succession: Mt. St. HelensOver time, pioneer species makes the area habitable by other species. Today, Mt. St. Helens in the process of secondary succession.Plants, flowers, new trees and shrubs have started to grow.

Fire and Secondary Succession

Natural fire caused by lightening are a necessary part of secondary succession.Foresters allow natural fires to burn unless they are a threat to human life or property.

Fire and Secondary Succession

Some species of trees (Jack pine and lodgepole pine) can only release their seeds after they have been exposed to the intense heat of a fire.

Fire and Secondary Succession

Minor forest fires remove brush and deadwood.Preventing fire allows underbrush to thicken.

Fire and Secondary Succession

When a fire does come the fire burns hotter and longer because of the underbrush killing large trees that would normally have survived

Fire and Secondary Succession

Some animals depend on fires because they feed on the newly sprouted vegetation.

Fire and Secondary Succession