The environment may be altered in substantial ways through the activities of humans, other living things, or when natural disasters occur, such as climate changes and volcanic eruptions.

Although these changes are sometimes occur very quickly, in most cases species replace others gradually, resulting in long-term changes in ecosystems.

These gradual long term changes in altered ecosystems are called ecological successions.

Ecosystems tend to change with time until a stable system is formed.

The type of succession which occurs in an ecosystem depends upon climatic and other limitations of a given geographical area.

A Typical New York State Succession Pioneer organisms are the first organisms to reoccupy an area which has been disturbed by a disruption.

Typical pioneers in a succession include grasses in a plowed field or lichens on rocks.

These pioneer organisms modify their environment, ultimately creating conditions which are less favorable for themselves, but establishing conditions under which more advanced organisms can live.

Over time, the succession occurs in a series of plant stages which leads to a stable final community which is very similar to the plant community which originally existed in the ecosystem.

This final stable plant community is called a climax community.

This community may reach a point of stability that can last for hundreds or thousands of years.

A Pond Succession Sequence It has been observed that when natural disasters occur, such as a floods or fires, the damaged ecosystem is likely to recover in a series of succession al stages that eventually result in a stable system similar to the original one that occupied the area.

A Typical New York State Succession This chart represents a typical succession which is observed in New York State.

The annual grasses represent the pioneer or first organisms in this succession.

The beech-maple forest would represent a typical Northern New York climax community.

The climax community will last hundreds or thousands of years unless again disrupted.

A forest containing oak and/or hickory trees would be a more typical Southern New York climax community.