Succession in
Ecosystems
AP Environmental Science
Successiona series of changes in a
community in which new
populations of organisms
gradually replace existing ones
Predictable and orderly
changes in the structure of an
ecological community over time
Reasons for succession
Response to
natural and human
disturbances
Community
dynamics change
as older organisms
die out and new
ones move in
Primary succession
Growth occurs on newly
exposed surfaces where no soil
exists: takes place on bare rock
Primary succession
New bare rock comes from 2
sources:
1. volcanic lava flow cools
and forms rock
Primary succession
New bare rock comes from 2
sources:
2. Glaciers retreat and expose
rock
Pioneer organisms
the first organisms
to colonize a new
site
lichens are the
first to colonize
lava rocks
Takes several
hundred years to
produce fertile
soil naturally.
Pioneer organisms
As the rocks breaks apart,
water freezes and thaws
on the cracks, which
breaks up the rocks
further.
When the lichens die, they
accumulate in the cracks.
Then mosses begin to grow
and die, leading to the
creation of fertile soil.
Fertile soil is made up of
the broken rocks, decayed
organisms, water, and air.
Primary Succession-
Climax community
a stable, mature community that
undergoes little or no
succession
Climax community
Example
In most of
Virginia,
the climax
community
would be a
deciduous
oak–
hickory
forest
Primary succession
Secondary successionsequence of community changes
that takes place when a
community is disrupted by
natural disaster or human
actions – takes place on
existing soil
Secondary successionExample:
A fire levels
portions of a
forest
Secondary successionExample:
A farmer
plows his
field
Secondary succession
Secondary succession-
Secondary Succession:
Mt. St. Helens
Erupted in 1980.
44,460 acres were
burned and flattened.
After the eruption,
plants began to
colonize the volcanic
debris.
Pioneer species: the
first organism to
colonize any newly
available area and
begin the process of
ecological
succession.
Secondary Succession:
Mt. St. Helens
Over time, pioneer
species makes the
area habitable by
other species.
Today, Mt. St. Helens
in the process of
secondary
succession.
Plants, flowers,
new trees and
shrubs have started
to grow.
Fire and Secondary Succession
Natural fire caused
by lightening are a
necessary part of
secondary
succession.
Foresters allow
natural fires to
burn unless they
are a threat to
human life or
property.
Fire and Secondary Succession
Some species of
trees (Jack pine
and lodgepole
pine) can only
release their
seeds after they
have been exposed
to the intense heat
of a fire.
Fire and Secondary Succession
Minor forest
fires remove
brush and
deadwood.
Preventing fire
allows
underbrush to
thicken.
Fire and Secondary Succession
When a fire
does come the
fire burns
hotter and
longer
because of the
underbrush
killing large
trees that
would
normally have
survived
Fire and Secondary Succession
Some animals
depend on
fires because
they feed on
the newly
sprouted
vegetation.
Fire and Secondary Succession