Ecological Succession

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Ecological Succession
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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.

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Ecological Succession

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

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• 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.

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Primary Succession

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

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• 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.

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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.

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• 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.

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

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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.

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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.

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• 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.

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• 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.

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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.

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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.

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Old-field Succession

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

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• 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.

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• 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.

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Your Turn HW

• Create two flowcharts. One illustrating the steps
  of primary succession, one illustrating the steps
  of secondary succession.
• You may use either pictures or words.
• Use the following terms in your charts