The Development of a Climax Community

...And the Confusion Surrounding a Climax Forest

A California climax forest
Giant Sequoia serial forest. Steve Nix

Defining a Climax Community

A climax community by is a relatively stable and undisturbed biological community of animals, plants, and fungi that have evolved into a "steady state" of development which secures the stability of all the collective communities. Through a natural successional process of instability, all individual organism ecosystems simultaneously transition through a series of more stabilizing stages where they all finally maintain their individual positions in the community and where they become stable from "egg and seed to maturity".

So, all biotic communities on earth engage in a forward-moving evolutionary process that takes place in several major defined steps or stages. Until climax completion, these transitional stages are each called a "serial stage" or a  "sere".  In other words, a sere is an intermediate stage found in ecological succession in an ecosystem advancing towards a particular organism's climax community. In many cases, there is more than one serial stage to pass through before climax conditions are attained.

A serial community is a name given to each group of biota within the succession. A primary succession describes primarily the plant communities that occupy a site that has not previously been vegetated. These plants can also be described as the vegetative pioneer community. 

Defining Plant Succession

To understand a climax plant community, you must first understand plant succession which is simply the replacement of one plant community by another.

This can occur when soils and sites are so harsh that few plants can survive and takes a very long time for plants to establish a root-hold to begin the process of succession. When destructive agents like fire, flood and insect epidemic destroy an existing plant community, plant establishment can happen very rapidly.

Primary plant succession starts on raw unvegetated land and usually exists as a sand dune, an earth slide, a lava flow, a rock surface or a retreating glacier. It is obvious that these harsh conditions for plants would take eons for this type of exposed earth to decompose to support higher plants (with the exception of the earth slide which would start plant succession fairly quickly).

Secondary plant succession generally starts on a site where some "disturbance" has set back a previous succession. The sere can be continually setback which then lengthens the period to a potential final plant community climax condition. Agricultural practices, periodic logging, pest epidemics and wildland fire are the most common agents of secondary plant succession setbacks.

Can You Define a Climax Forest?

A plant community that is dominated by trees representing the last stage of natural succession for that specific locality and environment, to some, is considered a climax forest. The name usually given to any particular climax forest is the name of the primary existing tree species and or its regional location.

To be a climax forest, the trees growing within a particular geographic region should remain essentially unchanged in terms of species composition for as long as the site "remains undisturbed".

But, is this really a climax forest or just another late sere that has avoided disturbance the longest. Do foresters who only manage trees over decades know enough to determine a climax forest and assume it to be the equivalent of late stage succession? Should speculative ecologists conclude that there can never be a climax forest because cyclical disturbance (both natural and human-caused) will always be a constant in North American forests?

The Climax Debate is Still With Us

The first published discussion(s) on the existence of climax communities started nearly a century ago with foundational papers written by two ecologists, Frederick Clements and Henry Gleason. Their ideas were debated over decades and definitions of a "climax" changed with a greater understanding of a new science called ecology.

Political winds also confused the topic with terms like "virgin forests" and "old-growth forests".

Today, most ecologists agree that climax communities are not common in the real world. They also agree that most exist in space and time and can be observed on large time scales of many decades and on wide ranges of an area, from a dozen acres to thousands of acres. Others believe that there can never be a real climax community because of constant disturbance over time.

Foresters have adopted a silviculturally practical approach when managing large stable communities of climax tree species. They use and name a "climax" forest to be the final sere in terms of the stabilization of major tree species. These conditions are observed on a human timescale and can maintain specific tree species and other plants over hundreds of years.

Examples of some of these are:  

  • the coniferous forests of the Pacific Northwest
  • the wetlands in North America
  • the redwood (Sequoia sempervirens) forests
  • beech-maple of the North American Northeast