the gradual, sequential regrowth of a community of species...
TRANSCRIPT
The gradual, sequential regrowth of a
community of species in an area is called
ecological succession.
You can see early stages of succesion in
vacant lots, along roads, and even in
sidewalks or parking lots where weeds are
pushing up through cracks in the concrete.
Mt St Helens eruption and 12 years later
Is the development of a community in an
area that has not supported life previously,
such as bare rock, a sand dune, or an island
formed by a volcanic eruption.
Soil is not initially present.
Mt St Helens primary succession
Is the sequential replacement of species that
follows disruption of an existing community.
Disruption may stem from a natural
disturbance, such as a forest fire or a strong
storm, or from human activity, such as
farming, logging or mining.
Occurs where soil is already present.
A species that colonizes an uninhabited area
and that starts an ecological cycle in which
many other species become established
Occurs in areas that been recently exposed
to the elements and lack soil.
Primary succession typically proceeds from
lichens and mosses to a climax community
Occurs in areas where the original ecosystem
has been cleared by a disturbance.
Secondary succession typically proceeds from
weeds to a climax community.
The traditional description of succession is
that the community proceeds through a
predicatable series of stages until it reaches
a stable end point, called the climax
community.
A recently abandoned agricultural field is
being pioneered by weeds. Eventually, taller
plants and shrubs will compete with the
pioneers. If no further disturbances occur, a
forest of pine or cottonwood may follow,
succeeded by a hardwood forest. The whole
process will take about 100 years.
Primary succession starts when bare rock is
colonized by pioneer species such as lichens
which build up soil.
Secondary succession starts when
disturbance allows pioneer species such as
weeds to grow in existing soil. These
pioneers are later followed by shrubs and
trees until a climax community is
established.
Play Glacier Bay which took 200 years