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Succession
Succession
• Disturbances such as fires, landslides,
hurricanes, and floods trigger a sequence
of changes in the composition of a
community.
• Certain species flourish immediately after
the disturbance and are replaced by
others etc.
Succession
• Succession is the gradual sequential
growth of species in an area.
• There are two types of succession that are
recognized.
– Primary succession – The development of a
community that has not previously supported
life.
• Examples – bare rock, sand dunes, an island
formed from volcanic eruption.
Succession
– Secondary succession - The sequential
replacement of species that follow the
disruption of an existing community.
• Examples – Natural disasters, development,
logging, farming, mining.
– Pioneer Species – Species that predominate
early succession. They tend to be small, fast
growing, and hardy.
• Examples – ragweed, crabgrass
Primary Succession
• Often occurs slowly because the minerals
for plant growth are unavailable.
– Rock may take many years of repeated
freezing and thawing to eventually break
down.
– Example is the Canadian Shield formed from
retreating glaciers 12000 years ago leaving
barren bedrock.
– Eventually lichens formed and their decay
provided nutrients for succeeding plant forms.
Secondary Succession
•
Secondary succession takes about 100
years for the original ecosystem to return
through well defined stages.
1.
2.
3.
4.
Annual grasses
Shrubs
Smaller trees such as dogwoods or pines
Deciduous forest
Stages of Succession
Succession
• The traditional description says that the
community proceeds through a predictable
series until it reaches a Climax community .
• Meaning that each stage is replaced by new
species more suited to the changing community
until it reaches a climax of stable individuals.
• Current observations indicate that succession is
a continual process and climax communities
may never be reached.
Question?
• How would a fire alter succession in a
community?
Question?
• Why do the plants that we think of as
weeds make excellent pioneer species?
Question?
• What is the difference between a
pioneer species and a climax
community?
Question?
• Describe the geological process of soil
formation as it relates to succession.