Transcript Unit 2A Ch 5 S3- How Ecosystems Changex

HOW ECOSYSTEMS WORK
Ch. 5, Section 3: How Ecosystems Change
Standards: SEV1a, b, d, e, SEV5c
WHAT IS ECOLOGICAL SUCCESSION?
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A gradual process of
change and
replacement of some or
all of the species in a
community.
Can take 100’s or
1000’s of years.
Ends in a climax
community
WHAT IS A CLIMAX COMMUNITY?
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Final, stable community.
Generally remains the
same if undisturbed
Type of climax community
will vary depending on
ecosystem
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Climax community for a
desert is different from
tropical rainforest
Both primary & secondary
succession end with a
climax community.
WHAT ARE THE TWO TYPES OF SUCCESSION?
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PRIMARY
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occurs on a surface
where no ecosystem
existed before
Ex: rocks, sand dune,
new island
SECONDARY
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Occurs on a surface
where an ecosystem
has previously existed.
Ex: after fire, volcano,
flood, abandoned farm
WHAT ARE THE STEPS OF PRIMARY
SUCCESSION?
Typical primary succession of forest:
 Rock is physically & chemically
weathered & broken down to make soil.
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Physical- frost wedging- frozen water
expands & creates cracks
Chemical- pioneer species like lichens &
moss can secrete acids to dissolve rock.
Thin soil can support grasses
As grasses die & decompose they
contribute to soil layer and soil gets
thicker.
As soil thickens it can support larger
plant life like shrubs
First trees that grow are usually sun
loving trees like pines
As pines grow tall they shade their
saplings, saplings can’t get sun and die
off.
Shade loving trees like deciduous trees
(oak, hickory) grow under pines,
eventually outgrowing and replacing
pines.
WHAT ARE THE STEPS OF SECONDARY
SUCCESSION?
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Soil is already established so it
doesn’t have to be created.
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Takes less time than primary
More common than primary
succession
Pioneer species- grasses,
weeds
Shrubs
Pine trees
Deciduous trees
3 examples:
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After a fire
After a field is abandoned
Pond becomes a forest
FIRE & SECONDARY SUCCESSION
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Some ecosystems rely on
natural fires to maintain the
ecosystem.
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Ex: grasslands, chaparral
Fires are actually
beneficial:
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Jack pine trees need intense
heat of fire to release seeds
Animals eat new, soft plants
that sprout right after fire
when soil is nutritious
Minor forest fires burn
accumulation of brush &
deadwood that would
otherwise contribute to major
fires.
OLD FIELD SECONDARY SUCCESSION
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Farmers field becomes
a forest.
Pioneer species of
grasses establish
quickly due to rich soil.
POND TO FOREST SUCCESSION
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Ponds can fill in and
become a forest if not
maintained.
Pond fills in with dead
leaves, debris, eroded
sediment.
Makes pond more shallow.
Sunlight helps plants grow
in shallow pond
Eventually fills in completely
with sediment & secondary
succession continues.
QUESTIONS TO ASK YOURSELF…
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What is the difference
between primary and
secondary succession?
What role does a pioneer
species play during the
process of succession?
Why would putting out forest
fires be damaging in the long
run?
What role do lichens play in
primary succession?
How are lichens similar to the
pioneer species that colonize
abandoned farm areas? How
are they different?