Transcript Ecological Succession

Ecological Succession
Examples of Changing Ecosystems
• A forest could have been a shallow lake a
thousand years ago.
• Mosses, shrubs, and small trees cover the
concrete of a demolished building.
Ecological Succession
• Gradual process of change and
replacement of the types of species in a
community.
• May take hundreds or thousands of years.
• Newer communities
make it harder for the
older ones to survive.
• Example: Younger
birch trees will have a
harder time
competing with taller,
older birch trees for
sun, but a shade
loving tree may
replace the smaller
birch trees.
Primary Succession
• Type of succession
that occurs where
there was no
ecosystem before.
• Occurs on rocks,
cliffs, and sand
dunes.
• Primary succession is very slow.
• Begins where there is no soil.
• Takes several hundred years to produce
fertile soil naturally.
• First species to colonize bare rock
would be bacteria and lichens.
Lichens
• Do not require soil.
• Composed of two species, a fungi and an
algae.
• The algae photosynthesize and the fungi
absorbs nutrients from rocks and holds
water.
• Over time, they break down the rock.
• 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.
Mosses on rocks
• Primary succession
can be seen
happening on the
sidewalks.
• If left alone, even
NYC would return to a
cement filled
woodland.
Secondary Succession
• More common
• Occurs on a surface where an
ecosystem has previously existed.
• Occurs on ecosystems that have been
disturbed or disrupted by humans,
animals, or by natural processes such as
storms, floods, earthquakes, and
volcanoes.
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.
• Over time, the 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.
• If this continues, over time they will form a
climax community.
• Climax community: the final and stable
community.
• Climax community will continue to change in
small ways, but left undisturbed, it will remain
the same through time.
Fire and Secondary Succession
• Natural fire caused by lightening are a
necessary part of secondary succession.
• Some species of trees (ex: Jack pine) can
only release their seeds after they have
been exposed to the intense heat of a fire.
• Minor forest fires remove brush and
deadwood.
Fire and Secondary Succession
• Some animals depend on fires because
they feed on the newly sprouted
vegetation.
• Foresters allow natural fires to burn unless
they are a threat to human life or property.
Old-field Succession
• Occurs in farmland
that has been
abandoned.
• Grasses and weeds
grow quickly, and
produce many seeds
that cover large
areas.
• Over time, taller plants grow in the area,
shading the light and keeping the pioneer
species from receiving any light.
• The longer roots of the taller plants
deprive the pioneer species from water.
• The pioneer species die.
• Taller trees begin to
grow and deprive the
taller plants of water
and light.
• Followed by slow
growing trees (oaks,
maples) takeover the
area.
• After about a century,
the land returns to a
climax community.
Your Turn
Lets go outside at determine where the woods
are in the succession process.
Did they form from Primary or Secondary
succession?