Video: Mt. St. Helens
Directions
1. As you watch the video, think about these
two questions:
– How does an ecosystem recover from a
natural (or human-related) disaster?
– Identify two to three events that you feel are
critical to this “restoration” process.
Mt.
St.
Helens
https://www.youtube.com/watch?v=-H_HZVY1tT4
Activity
Directions: In pairs, you will:
1. Work together to put the cards in the
correct order (step)
2. Some steps may contain two cards (but
no more than two)
3. Five minutes to complete.
Questions to consider
• Before you start sequencing, think of what you
expect to see at the beginning, the middle, and
the end.
• While you sequence, think:
– Does it make sense if we order the cards this way?
– What needs to happen before/after this step can
occur?
– Does this layout match what we planned out at the
beginning?
Changes in Ecosystems:
Ecological Succession
Objectives
SWBAT:
1. Identify and describe the stages and specific organisms
of primary and secondary succession.
2. Differentiate between primary and secondary
succession.
3. Describe the role of pioneer species in ecological
succession.
4. Apply knowledge of terrestrial succession to freshwater
succession.
Vocabulary
1. Ecological succession
2. Primary succession
3. Secondary succession
4. Pioneer species
5. Climax community
Definition:
• Natural, gradual changes in the types of
species that live in an area
– The gradual replacement of one plant
community by another through natural
processes over time
– Predictable in time and types of species*
Types of Ecological Succession
• Primary Succession
• Secondary Succession
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Primary Succession
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Primary Succession: Step 1
• Begins in a place without any soil, like
after:
– Volcano eruption
– Landslide
– Glacier retreat
• Known as “bare rock”
Primary Succession: Step 2
• Lichen and moss are first to colonize and
establish
– Called PIONEER SPECIES
• These set the foundation for the rest
http://www.saguaro-juniper.com/
http://botit.botany.wisc.edu
Importance of lichen and moss
• Why lichen and moss?
• Require little soil for survival
• Secrete acid that breaks
down rock, creating soil
• Contain nitrogen-fixing bacteria to adapt to
low nutrient availability
• Their death returns
nutrients to soil
Primary Succession: Step 3
• Small plants, such as grasses and weeds,
establish
• Die and decompose, improving nutrient quality
of soil
Primary Succession: Step 3
• New home for organisms
– Insects
– Small rodents
– Birds
Primary Succession: Step 4
• Plants like shrubs and flowers can grow in
the higher nutrient soil
• These plants die, adding more organic
matter to the soil
Primary Succession: Step 4
• Medium sized organisms are indicative of
this step of ecological succession
Primary Succession: Step 5
• “Soft-wood” trees establish and grow
– Alders, pines, willows, or birches
Birch forest in Ord Ban
Red alder forest
Primary Succession: Step 6
• Climax Community: mature and complex
community of plants and animals
– Always competition for resources
– Prone to disturbance and change
These are Climax Communities
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Primary Succession: Review
Check for Understanding
1. What do pioneer species do that
make them an integral part of
ecological succession?
What if?
What if?
• An avalanche?
What if?
• Deforestation?
Secondary Succession
• Begins in a place that already has soil and
was once the home of living organisms
Secondary Succession: Step 1
• Soil and some vegetation remain after
disturbance
Secondary Succession: Step 2
• Some seeds in the
soil begin to grow.
– Seeds “awakened” by
fire/heat
Secondary Succession: Step 3
• Larger shrubs move in.
Secondary Succession: Step 4
• Fast growing trees (such as pines) move
in
Secondary Succession: Step 5
• These are followed by slower-growing
hardwood trees
A summary of changes that occur during
succession:
•
Pioneer species colonize a bare or disturbed site. Soil building.
•
Changes in the physical environment occur (e.g., light,
moisture, soil, etc.).
•
New species of plants displace existing plants because their
seedlings are better able to become established in the changed
environment.
•
Newly arriving species alter the physical conditions, often in
ways that enable other species to become established.
•
Animals come in with or after the plants they need to survive.
•
Eventually a climax community that is more or less stable will
become established and have the ability to reproduce itself.
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Disturbances will start the process of succession again.
Checking for Understanding
1. Which step of ecological succession
is most vulnerable to
disturbance/change? Explain.
Comparison
Directions: With your partner from earlier,
1. Differentiate between primary vs.
secondary succession
1. Focus on characteristics unique to each
2. Not on steps
Primary vs. Secondary
Freshwater Succession
Directions:
• Apply what you know about primary and
secondary succession to describe
succession in freshwater ecosystems.
– Draw each step and include a brief
description of what is happening.
– Start off with a lake
Vocabulary
1. Ecological succession
2. Primary succession
3. Secondary succession
4. Pioneer species
5. Climax community
6. Hydrosere succession
Freshwater Succession
Directions:
• Apply what you know about primary and
secondary succession to describe
succession in freshwater ecosystems.
– Draw each step and include a brief
description of what is happening.
Freshwater Succession
• Known as hydrosere
succession
– Gradual transition
from lake/pond to
wooded ecosystem
Hydrosere Succession Overview
Think-pair-Share
• How does the size of a pond or
lake affect the rate (speed) at
which hydrosere succession
occurs?
Question:
• Does ecological succession occur
at a constant and predictable
rate?
Objectives
1. Compare the mechanisms of ecological
succession.
2. Explain the concept of ecological
succession using the mechanisms of
ecological succession.
Vocabulary
1. Facilitation model
2. Tolerance model
3. Inhibition model
a. Known as “mechanisms of ecological
succession”
Jigsaw
Directions: In threes,
1. Designate person A, B, and C
a. Person A reads Facilitation Model
b. Person B reads Tolerance Model
c. Person C reads Inhibition Model
2. Answer the question to your section
3. Share answer/section with group
4. As a group, answer #4, 5, and 6 (Venn
Diagram)
Facilitation Model
• The current species make it easier and
possible for the incoming species to
establish and survive
Tolerance Model
• Some species can withstand stress due to
competition for resources, like sunlight
 Jack pine
are shade
intolerant
(need lots of
sunlight)
Red spruce 
are shade
tolerant (do
not need
much sunlight)
Inhibition Model
• Some species inhibit, or prevent, other
species from establishing
– Allelopathy
Quick Write
• Write a summary what you
learned today about ecological
succession.
– Primary, secondary, & hydrosere
succession
– mechanisms of ecological succession
(facilitation, tolerance, and inhibition
models).