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