How Ecosystems Change

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How Ecosystems Change

• Understanding how ecosystems change can help you
  predict what can happen to the land around you in
  the years to come.

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Essential Questions

• How do ecosystems change over time?
• How do new communities begin in areas without
  life?
• How do pioneer species compare to climax
  communities?

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Ecological Succession

• Succession refers to the normal, gradual changes
  that occur in the types of species that live in
  an area.
• Succession is a process by which one biotic
  community is replaced by another until a climax
  community develops.

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Succession from Rock to Forest

• Some 240 years ago a glacier began retreating in
• Glacier Bay, Alaska
• The glacier left behind a rocky terrain
  completely devoid of organic matter
• The process that begins in a place without any
  soil is called Primary Succession

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• An Example of Primary Succession Glacier Bay,
  Alaska

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Primary Succession

• Pioneer organisms such as microbes,
  lichens, and mosses are the first to inhabit a
  rock promoting soil formation.

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Primary Succession

• Eventually, enough soil is built up so that
  grasses can succeed the pioneer organisms.

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Primary Succession

• Grasses are replaced by shrubs, which are
  replaced by fast-growing trees.

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Primary Succession

• Coastal Sitka Spruce Forest, Southeast Alaska

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Succession occurs differently in different places
around the world.The types of grasses,
fast-growing trees, and climax-community plants
vary with the location and climate of an area.
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A Climax Community Is Not Truly Final

• Humans or nature can destroy it.

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A Climax Community Is Not Truly Final

• In this case, succession starts over with grasses
  as Secondary Succession.

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Secondary Succession

• After a forest fire, not much is left except dead
  trees and ash-covered soil.
• However, these places do not remain lifeless for
  long.

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Secondary Succession

• The topsoil, which may have taken 1000s of years
  to form, is not destroyed.
• Spores and seeds which lie dormant are then
  allowed to develop.
• Sequence may be crabgrass, tall grass and
  horseweed, softwood then hardwood.

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Secondary Succession

• The soil already contains the seeds of weeds,
  grasses, and trees.
• More seeds are carried to the area by wind and
  birds.
• Other wildlife may move in.
• Succession that begins in a place that already
  has soil and was once the home of living
  organisms is called
• secondary succession.

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Secondary Succession

• Secondary succession occurs faster and has
  different pioneer species than primary succession
  because soil is already present.
• The cause may be a natural disturbance such as a
  forest fire or farming.
• In 1850, Connecticut was almost entirely open
  land cleared for farming or timber.
• Today, Connecticut has been mostly reforested
  through the process of secondary succession as
  farming has left the state since the 1800's.

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Secondary Succession

• This photo shows three succession stages.
• The trees in the background.
• The area on the right behind the fence, in front
  of the trees.
• The area in the foreground, in front of the
  barbed wire fence.

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Secondary Succession

• In the background are the trees of an eastern
  hardwood
• forest. This area has not been cleared in over
  fifty years.
• These trees represent the climax community for
  the rainfall,
• temperature and soil of this area.

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Secondary Succession

• The area on the right, behind the fence, in front
  of the trees, has not
• been mowed in about ten years. Shrubs and
  evergreen trees have
• moved in. These are the intermediate species.

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Secondary Succession

• The area in the foreground, in front of the
  barbed wire fence, has
• been mowed within the last year. The plants are
  all annuals or
• herbaceous perennials. These are the pioneer
  species.

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Climax Communities

• A community that has reached a stable stage of
  ecological succession is called a climax
  community.
• It is a combination of plants and animals that
  use the available resources most efficiently.
• Diversity and balance are maintained in a climax
  community because as trees die, they provide
  nutrients for new communities of organisms.

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How do ecosystems change over time?

• Ecosystems change over time by a process know as
  succession in which one biotic community is
  replaced by another until a climax community
  develops.
• Succession is often caused by changes in the
  environment brought about by the current
  community.
• Succession can also occur because of changes in
  climate and natural catastrophes such as fire,
  hurricanes, floods, and volcanic eruptions.
• Humans cause succession by cutting down forests,
  polluting the environment and overdeveloping an
  area.

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How do new communities begin in areas without
life?

• By a process known as primary succession. Pioneer
  organisms such as microbes, lichens, and mosses
  are the first to inhabit a rock promoting soil
  formation.
• They survive drought, extreme heat and cold, and
  other harsh conditions and start the
  soil-building process.
• Soil begins to form as lichens and the forces of
  weather and erosion help break down rocks into
  smaller pieces.
• When lichens die, they decay, adding small
  amounts of organic matter to the rock.
• Plants such as mosses and ferns can grow in this
  new soil.
• Thus begins the process for higher order plants.

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How do pioneer species compare to climax
communities?
Pioneer species are the first organisms to occupy
an area and do not need soil to survive.
Examples of pioneer species would be organisms
such as microbes, lichens, and mosses. Climax
communities are the last communities to occupy an
area. Climax communities are a combination of
plants and animals. They tend to be stable and
self-perpetuating.
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Ecological Succession
Lichens
Mosses
Microbes
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Ecological Succession
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Ecological Succession
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Ecological Succession
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Ecological Succession
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Ecological Succession