Succession is a series of changes that take place
in a comunitiy as it gets older. Often, smaller, less competitive plants get
replaced by larger more competitive plants which take up all the water from
the ground and shade the smaller ones. The change in plants in the community
as succession occurs thus determines what animals live there.
Community: All the populations of plants and
naimals that live in a certain area.
Climax Community: The last or final stage of
succession in a community. This stage is often called "old growth"
in the Pacific Northwest. In Pacific Northwest forests, the old growth trees
might be Douglas Fir and Red Cedar, while in the sagebrush desert east of the
Cascades, the old growth might consist of sagebrush or juniper.
Primary Succession: Succession that occurs on
an area that never had life on it before. The soil in such areas is bare rock
(recently exposed by volcanic action, or exposed by the melting of glaciers).
Therefore, soil must develop before plants can live there.
Pioneer Plants: Pioneer plants are the 1st plants
that livein an area after a disturbance. Their seeds are carried to the area
by the wind, by the action of water, or accidently in the guano (birdy doo doo)
of birds or stuck to the feathers or fur of animals (remember some seeds have
stickery outer coats to help move them to new areas!).
During primary succession, the first plants to live on bare rock include bacteria
and blue-green algae (where moist), and lichens. Lichens are common pioneer
plants on rock. They are an example of 2 creatures that live together and help
each other (mutualism). One is a fungus which provides
a home on the rock and absorbs minerals and water from the rock. The other is
an algae which lives inside the fungus and makes food via photosynthesis.
Lichens help break down rock by releasing carbon dioxide which makes an acid
when mixed with water. This acid dissolves rock particles, and breaks big rocks
down into sand. The wind then blows the sand grains into cracks where it collects.
As pieces of lichen die, they are blown into the cracks too, mixed with sand,
and these then make soil which larger plants may live in.
Secondary Succession: Succession where the community
of plants that exists in an area is changed after a disturbance. Such changes
include fires (including natural forest fires), floods, earthquakes, landslides,
and such human caused phenomena as farming, logging, road building, and home
or building construction.
The key factor in secondary succession is that the soil already exists, so
that succession can quickly resume and rebuild the area with plants and animals.
The pioneer plants after disturbances during secondary succession include mosses,
grasses, and weeds.