Ecological Succession Examples of Changing Ecosystems A forest

Ecological Succession

Examples of Changing Ecosystems • A forest could have been a shallow lake a thousand years ago. • Mosses, shrubs, and small trees cover the concrete of a demolished building.

Ecological Succession • Gradual process of change and replacement of the types of species in a community. • May take hundreds or thousands of years.

• Newer communities make it harder for the older ones to survive. • Example: Younger birch trees will have a harder time competing with taller, older birch trees for sun, but a shade loving tree may replace the smaller birch trees.

Primary Succession • Type of succession that occurs where there was no ecosystem before. • Occurs on rocks, cliffs, and sand dunes.

• Primary succession is very slow. • Begins where there is no soil. • Takes several hundred years to produce fertile soil naturally. • First species to colonize bare rock would be bacteria and lichens.

Lichens • Do not require soil. • Colorful, flaky patches. • Composed of two species, a fungi and an algae. • The algae photosynthesize and the fungi absorbs nutrients from rocks and holds water. • Over time, they break down the rock.

• As 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.

Mosses on rocks

• Primary succession can be seen happening on the sidewalks. • If left alone, even NYC would return to a cement filled woodland.

Secondary Succession • More common • Occurs on a surface where an ecosystem has previously existed. • Occurs on ecosystems that have been disturbed or disrupted by humans, animals, or by natural processes such as storms, floods, earthquakes, and volcanoes.

Secondary Succession: Mt. St. Helens • Erupted 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.

• Over time, the 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. • If this continues, over time they will form a climax community.

• Climax community: the final and stable community. • Climax community will continue to change in small ways, but left undisturbed, it will remain the same through time.

Fire and Secondary Succession • Natural fire caused by lightening are a necessary part of secondary succession. • Some species of trees (ex: Jack pine) can only release their seeds after they have been exposed to the intense heat of a fire. • Minor forest fires remove brush and deadwood.

Fire and Secondary Succession • Some animals depend on fires because they feed on the newly sprouted vegetation. • Foresters allow natural fires to burn unless they are a threat to human life or property.

Old-field Succession • Occurs in farmland that has been abandoned. • Grasses and weeds grow quickly, and produce many seeds that cover large areas.

• Over time, taller plants grow in the area, shading the light and keeping the pioneer species from receiving any light. • The longer roots of the taller plants deprive the pioneer species from water. • The pioneer species die.

• Taller trees begin to grow and deprive the taller plants of water and light. • Followed by slow growing trees (oaks, maples) takeover the area. • After about a century, the land returns to a climax community.