Was Clements Right for the Wrong Reasons?

Frederic Clements was an important plant ecologist of the early twentieth century. His influence virtually dominated the development of plant ecology. He understood plant communities (such as a deciduous forest, or a desert) as being analogous to organisms, and the process of ecological succession (recovery of a plant community from disruption) as being analogous to a body healing itself. Succession reached a “climax” at a single vegetation type that was best suited to the local environment.

Clements could command assent to his views by means of his strong character. You can see that character even in his signature, which I scanned from an actual letter that I have since sent to the Ecological Society archives.

Starting with scientists such as Henry Gleason, many plant ecologists criticized the Clements view of ecological climax. Gleason said that there were no discrete plant communities. Each species of plant had its own distribution. What we call a forest was where many forest species of plants happened to have overlapping individual distributions.

The plant ecology laboratory of Fakhri Bazzaz, where I got my Ph.D. in 1987, was so strongly influenced by Gleason’s viewpoint that he called it The Gleason Laboratory. We thought it was kind of funny that Clementsian ecologists would refer to an oak forest as a Quercetum (as if, like a species, it should have a Latin name), a pine forest a Pinetum, etc.

But maybe Clements was on to something, though he could not have understood why. Recent research by ecologists such as Suzanne Simard has shown that an entire forest—even the different species—can be interconnected by means of mycorrhizae, the fungi that often live in roots. Hormone messages, minerals, even water and calories, can pass through these connections. In this way, a forest can really be an interconnected whole, in which some of the plants take partial care of other plants the way some organs of your body take care of others. She focused on coniferous forests with birches and alders. While I remain unsure about, say, a cross-timbers oak forest being an interconnected net of mycorrhizae, I can think of several ways in which an alder thicket, such as those on the Blue River that I have studied, form an integrated unit. They live in a habitat where floods frequently wash away the soil, and where underground connections between the plants might be particularly valuable.

Being trained in a lab that saw a forest as individual trees, I resisted Simard’s viewpoint a little at first, and then when I became convinced of it, it was a new revelation to me. Although Clements did study fungi (and wrote a book about them), I have found no evidence that he understood mycorrhizae as a method of making an oak forest into a Quercetum. But if he were alive today (he died in 1945) and read Simard’s book, he might have said, “Told you so.”

Among the letters now at the Ecological Society archives, I ran across copies of correspondence between University of Illinois ecologist Arthur Vestal and other prominent figures in the history of ecology, not only Clements but also Henry Cowles, Cornelius Muller (whom I met), and Liberty Hyde Bailey, who (as author of The Holy Earth) was a big thinker to rival Clements. These were interesting though not significant documents. They show the humorous and human side of these prominent scientists. In the letter from Clements to Vestal, which contained the signature above, Clements was urging Vestal to get a portable typewriter to take with him into the field. It was much better for taking field notes than paper, which can get damp. You can carry a portable typewriter right out to the places you are studying. In another letter, Vestal wrote to Charles Shull that “You will think me a reprehensible discombobulator for not sending you the seeds…” In another letter, Vestal lamented that, with the beginning of the Fall 1926 semester, he was in a disagreeable mood because, instead of having time for his beloved research, he had to teach 200 freshmen. (I enjoyed teaching before my retirement, but many scientists do not.)

These great minds, fumbling through issues that we today take for granted, are now lost to the general awareness even of other scientists, although a few science historians will run across their archives. But these old scientists helped form the ground upon which we now build our work. It’s just that, sometimes, we might have to do a little deconstruction (for example of the idea that each tree is a separate individual struggling for its own existence) before we can continue our construction.