Forests in Flux

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Published on: Jun. 2, 1996

Last revision: Oct. 21, 2010

What does a perfect forest look like? Most of us, if asked that question, would probably think of an open woodland with towering, 300-year-old trees. When we talk about forest conservation, that is the forest we want to save from destruction.

Forests begin with a few plants and go through the process of "succession," ultimately arriving - ideally - in a climax or old-growth state. But disturbances like fires, tornadoes or diseases crash the party, interrupting succession and creating something far different from the perfect forest with the 300-year-old giant trees.

During most of the past century, ecologists have known and talked about forests as communities continually changing toward a "climax" condition. This climax forest was thought to be as perfect as a forest gets. It fully occupied all the sites and niches available for occupation and made maximum use of environmental resources. A climax forest was considered to be at the peak of productivity, which it maintained in a condition of a dynamic equilibrium, or steady state.

The Climax Forest

Under ideal conditions, each successive collection of plants and animals would move into a forest and dominate available space for a few years or a few centuries and be replaced by a later succession of organisms. Plants in each stage would change environmental conditions to the point that another group of plants was better able to grow there, before giving way to these new plants.

Changing environmental conditions include shading the ground, accumulation of organic matter and moisture and different forest animals and microorganisms. Succession would continue toward a climax forest. A full array of species would be present in this climax forest - more species diversity than in any of the pre-climax or successional forests. The climax forest would be relatively stable. Sure drought, flood or wind would come along from time to time, but their effects would be temporary. The forest would soon recover.

Human disturbances were thought to have more serious and long lasting effect. Cutting, burning, land clearing, use of herbicides, pollution and erosion are more frequent and severe; they are outside the range of tolerance of the natural forest and would scar the forest forever. But if a forest was unaltered by human presence, it would eventually develop into a dynamic equilibrium - a climax forest.

The Disturbed Forest

Other ecologists have a somewhat different view of a forest. Rather than succeeding toward a climax steady state, forests are continually set back to

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