Download Ecology Name - Plain Local Schools

Environmental Science
Chapter 3, section 3.5
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NOTES
How Ecosytems Change
Scientists refer to ecological change as Succession
ex: As you walk through a forested area, you see many different kinds of plants and animals. Your grandparents
and great-grandparents may have walked through the same forested area and saw many of the same plants and
animals; however, that area may not have always been a forest. It may have been a meadow or even a shallow
lake.
Ecological Succession
• Succession is a regular pattern of changes over time in the types of species in a community.
• May take hundreds or thousands of years.
• As each new community arises, the previous one dies.
ex: Tall pines trees shade the ground. Pine seedlings need
light but the taller trees block the sunlight. Maples
and oaks can grow in less light, so they replace the
pine trees.
• The community that eventually forms if the land is left undisturbed is called the climax community.
Secondary Succession
• In 1980, Mount St. Helens (Washington State) erupted, burning and flattening 18,000 hectares (about 44, 460
acres) of land.
• Today, if you were to visit, the forest has already begun to regenerate.
• Succession that occurs on a surface where an ecosystem has previously existed is call secondary succession.
Fire and Secondary Succession
Old-field Succession
Primary Succession
• Succession that occurs on surfaces where no ecosystem existed before is called primary succession.
• Occurs on new islands created by volcanic eruptions and in areas exposed when a glacier retreats.
• Primary succession is much slower to progress than secondary succession because there is no soil. It takes several
hundred to several thousand years to produce fertile soil naturally.
• After soil forms, seeds of small plants are able to germinate and grow.