Yellowstone National Park, 1988
Succession is the gradual process of
community development. It involves species
in one stage being replaced by different
species. The time involved in succession is on
a scale of tens, hundreds and thousands of
years.
Abiotic factors such as windstorms, droughts and fire can
cause change in a community of plants and animals.
Biotic Factors also change communities over time. Insect
epidemics can kill trees. Overgrazing can selectively
remove species of plants from a forest.
Environmental disturbances have natural and man-made
causes. This picture was taken in Mesa Verde, Colorado in
2000
This picture was taken after the fire. What plant life will
emerge? What plants will succeed after this environmental
change? Forest fires are a natural part of the life cycle
of the community.
After a major change in an environment, grasses, mosses
and lichens begin to colonize. It is the first step in the
process of succession.
0
5 yrs
The first species to colonize or grow in an area are called pioneer
species. Only pioneer species are able to grow after a major
disturbance in a community due to the lack of soil or nutrients.
Examples: lichens and mosses
Animals begin to inhabit the area. Usually, insects appear first, then
rodents and larger mammals are the last to appear.
0 yrs 5 yrs 15 yrs
Opportunistic species take advantage of the work done by
the pioneer species. Pioneers modify the environment in
such a way that it becomes less suitable for their growth
but more suitable for other species. Opportunists
eventually replace pioneer species. Examples: grasses & weeds
0 yrs 5 yrs 15 yrs
25 yrs
Over time, the decay of pioneer species, grasses and
shrubs adds nutrients to the forest floor allowing more
complex species to grow.
0 yrs 5 yrs 15 yrs
25 yrs
50-80 yrs
The biodiversity of a community continues to increase as it
ages. A variety of plants and animals will inhabit the
area.
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25yrs
50-80 yrs
150+
Succession takes hundreds of years before completion. Species
replacement continues until the community is dominated by
competitively superior species. Once the community reaches a
stable state of maturity it is called a climax community.
Timeline
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Lichens & Mosses
Timeline
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15yrs
Grasses & Shrubs
Timeline
0yrs 5yrs
15yrs
25yrs
Dwarf Trees
Timeline
0yrs 5yrs
15yrs
25yrs
50-80yrs
Immature Forest
Timeline
0yrs 5yrs
15yrs
25yrs
50-80yrs
150+
Mature Forest
Timeline
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15yrs
25yrs
50-80yrs
150+
Biodiversity
Two Types of Succession
Primary succession- a change in an environment where soil
never existed before. Examples include recently formed
volcanic lava and rock revealed when glaciers melt. Lichens
and mosses first grow on the rock then soil forms from
decayed mosses. Eventually, shrubs and trees follow.
Two Types of Succession
Secondary succession also occurs on smaller scales. When
Secondary succession- a change in an environment where
one giant emergent tree falls, sunlight reaches the forest
soil already exists. Examples include areas destroyed by
floor. This brings many changes to this section of the
forest fire, clear-cutting, or insect epidemics.
rainforest.
More roads are being built in undeveloped areas. Farmers
clear land for crops and easier access to the main road.
What type of succession do new roads cause? How would it
affect the plants and animals?
Deforestation in Madagascar’s rainforest: because of poor
soil conditions, savannahs often form once rainforests have
been cleared for crops or cattle. What type of succession
is pictured here?