The stages in ecological succession

The changes that take place during any form of succession depend
on a variety of environmental factors, such as the amount of moisture,
temperature, and wind. One possible scenario for primary succession
might begin with the appearance of simple plants, such as lichens and
mosses. Such plants are able to spring up in tiny cracks in the rocks in
which water and dissolved minerals collect.
When these pioneer plants die, they decompose and begin to form
soil in which other, more complex plants can begin to grow. The second
stage of plants might consists of grasses, herbs, and small shrubs. A characteristic
of these plants is that they devote a great deal of energy producing
huge numbers of seeds. They may live only one year, and spend
the greatest part of their energy to ensuring that offspring will arise the
following year. Species of this kind are known as opportunist species.
Grasses are a common example of opportunist species.
Plants that make up the early stages of succession also die, decompose,
and contribute to the growing layer of soil. This process takes place
over hundreds or thousands of years, however. Eventually, the soil is able
to support more complex plants, such as larger shrubs and small trees including
aspen, black spruce, and jack pine. These plants gradually take
over from earlier communities since they are taller, have more leaves, and
can capture more sunlight that was originally captured by simpler plants.
In the final stages of succession, taller trees begin to grow. They, in
turn, block out the sunlight needed by smaller trees and replace them. The
final stage of ecological succession is known as a climax community. A
climax community in the scenario outlined here might consist of birch,
white spruce, and balsam fir.