When the fields of modern botany, ecosystem biology, forestry, and fire science were being created, a theory developed about how natural systems arose, and where they went. If plants and animals went through phases where they developed, matured, spent time as a relatively-unchanging adult, and then died, perhaps plant and animal communities did the same thing. In the late 1800s and early 1900s, the idea of the “climax state” developed. This was the ideal, the goal (so to speak) of the development of what we today would call an ecosystem. The Great Plains, for example, developed from bare ground and brush toward their ideal state of tall-grass prairies.
It was OK for the time, but had some flaws. Flaws which are still seen today, even after actual biological science has moved away from the model.
Frederic Clements is credited with coining the term “climax state” to describe a mature ecosystem, one that had reached it’s final form and would remain in that state unless acted upon by a major disaster or outside force (fire, huge floods, ice sheet, humans plowing everything). He didn’t actually use the term, and his idea was a lot more subtle and had more variations, including allowing for shifts in climate that would lead to shifts in community composition. However, well into the 20th century, the implication of an ideal climax state for any given ecosystem had become entrenched, at least in popular literature. I encountered it in high school biology in the late 1980s, although our textbooks were at least ten years out of date. I read it in popular science books as well.
The climax state works, to a point. Certain environments do support certain kinds of plant and animal groupings, and others don’t. You won’t get tall-grass prairies in the equatorial tropics, because of the soil chemistries and rainfall patterns. You won’t find mountain sheep thriving in the eastern Great Plains, or in the southeastern long-leaf pine forests, either. The presence and absence of fire, seasonal and secular rainfall and drought patterns, soil chemistries, all sorts of things affect the ecosystems and the sorts of things that thrive. If you suppress fire in the Great Plains, you get upland forests and brush. If you suppress fire in the short grass steppe, you get dense stands of grass that choke themselves out, and then brush moves in, but no trees. Rainfall has a lot to do with it.
However, we didn’t know what we didn’t know when Clements and others did the pioneering research. Now we have had more time and better tools to observe, and we know that climax states are not as tidy as initially theorized. Nor are they ever permanent.
The modern environmental movement won’t accept that. They stick with the old model. There is, in their mind, a perfect environment, it existed before humans moved in (or before modern industrial society moved in), and any change in that primordial condition is bad. They see the planet as having been in a climax state at perfect equilibrium. Their goal is to return the planet to that state, whatever it was, by eliminating anything that caused the changes. Meaning modern humans living a first world lifestyle.
If you ask serious ecologists, or botanists, landscape restoration experts, or environmental historians, we’ll tell you that change is constant. However, the rate of change varies a great deal, and humans as a keystone species do a lot to change our habitats. Is that good or bad? It depends on what you think is good and bad. But we all agree that change happened before humans developed, and change will continue long after the cockroaches, salt-cedar, and Keith Richards inherit the Earth.
In many ways, the environmental movement as seen in the media lives in the scientific past. They stick with old theories because those fit what they want to believe. In their way of thinking, there was a perfect state of equilibrium. There are predetermined ecosystems that, once reached, continue in perpetuity (until the Sweet Meteor of Doom or Deccan Traps change things). And it was very good, until modern humans loused everything up.* There once was a climax state and all things lived therein and it was Good.
Science says not really, no. Within the environmental constraints of a region, certain biota are more likely to develop in certain ways. But they are ever changing unless they are maintained in that state, the way Native Americans maintained the tall-grass prairies, or Europeans maintained certain forest and meadow ecosystems.
For more information:
The following are a little technical, but go into the details of the theory of climax and succession.
*Or what I call the Ben Rumson view of the world. “G-d made the mountains. G-d made the sky./ G-d made the people, G-d knows why./ He fixed up the planet as best that he could/ And then come the people and gum it up good!” (from “The First Thing You Know” in the movie Paint Your Wagon)