Ecological Succession
Ecological Succession
• Ecosystems are constantly changing due
to natural and human disturbances
Examples:
• Natural disturbances
– Forest fires
• Human disturbances
– Clearing a forest for agriculture
Ecological Succession
• Succession- orderly, natural
changes and species replacements
that occur in an ecosystem
– Basically, older organisms die out and
new organisms move in, causing further
changes in the community
Steps in Succession
1. Grass gets taller and weeds start to grow

area looks like a meadow
Steps in Succession
2. Bushes grow, trees appear

Different animals enter the area to live
Steps in Succession
3. Less light now reaches the ground

Grass slowly disappears
Steps in Succession
4. 30 years later, area will resemble a forest
Succession
• At each stage, different species of plants
and animals may be present
– Conditions at each stage are suitable for
some, but not others
2 types of Succession
• Primary and Secondary
• Primary Succession- takes place on land
where there are no living organisms
– Ex: when lava from a volcano cools and forms
new land
Primary Succession
• Pioneer species- first organisms to occupy
new land
– Ex: lichens
• Decaying lichens and other pioneer
species combine with bits of rock to make
soil
Lichen on
Rock
Primary Succession
• Seeds move into small patches of soil and
begin to grow
Primary Succession
• Primary succession slows down and
community becomes stable
• Climax community- a stable, mature
community that undergoes little or no
species change
Secondary Succession
• Secondary Succession – occurs when
community is destroyed or altered but soil
is still there
– Ex – fire, clear cutting
– Regrows to mature, stable community called
climax community
– May take less time than primary succession
Forest Fire Regrowth