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Changes in Ecosystems: Ecological Succession
1.05 Determine the interaction of organisms within an ecosystem.
Ecological Succession
• Ecological Succession is the natural, gradual changes in the types of species that
live in an area; can be primary or secondary
• The gradual replacement of one plant community by another through natural
processes over time
Primary Succession
Primary succession is the beginning of a community where few, if any, living
things exist, or where earlier communities were wiped out.
Begins in a place without any soil
o Sides of volcanoes
o Landslides
o Flooding
Starts with the arrival of living things such as lichens that do not need soil to
Called PIONEER SPECIES – The first species living in an otherwise lifeless
Soil starts to form as lichens and the forces of weather and erosion help break
down rocks into smaller pieces
When lichens die, they decompose, adding small amounts of organic matter to the
rock to make soil
A pioneer community is the first community thriving in a once lifeless area.
Simple plants like mosses and ferns can grow in the new soil
The simple plants die, adding more organic material
The soil layer thickens, and grasses, wildflowers, and other plants begin to take
These plants die, and they add more nutrients to the soil
Shrubs and tress can survive now
Insects, small birds, and mammals have begun to move in
What was once bare rock now supports a variety of life
Secondary Succession
• Begins in a place that already has soil and was once the home of living organisms
• Occurs faster and has different pioneer species than primary succession
• Example: after forest fires
Climax Community
• A stable group of plants and animals that is the end result or final stage of the
succession process
• Does not always mean big trees
– Grasses in prairies
– Cacti in deserts
Primary vs. Secondary
• No soil
• Pioneer species
• Weathering & decomposition
• Humus and sand increase over time
• End = climax community
• Soil already exists
• Seeds have suitable soil conditions.
• Occurs much faster
• Climax community.
Key concepts:
• Pioneer species—first species to begin a succession.
• Climax community—the final stage in a succession.
Ecological succession — Change of environment involving a series of species
replacements in a community.
Primary succession — occurs where there is no soil, e.g. after a volcanic eruption or a
glacial retreat
• “pioneer organisms”
• Simple plants first – no or shallow roots.
• Gradual influx of more complicated and larger plants as the habitat changes.
• Ends with a “climax community” – ecosystem stays constant, provided there are
no changes in abiotic influences.
Secondary succession — begins in an area where soil is already present, (e.g. a once
cultivated field or after a forest fire.)
Old field succession:
grasses + weedsÆ taller grasses + golden rodÆ small trees (cherries, dogwood,
sumac) Æ mature climax forest (oak, beech-maple, hickory)