By Frank Landis, CNPS-SD Conservation Committee Chair
Just to be different, I thought I’d go back to my roots as a plant community ecologist and explain why I dislike that particular label so much. I will be going into what the words plant community and vegetation mean, and why vegetation community is such an ugly and ill-thought neologism.
First, vegetation: it simply means all the plants in a defined area. That’s what Julie Evens (my former lab mate and now CNPS Fellow) maps for CNPS, and I’m glad she does. Plant community also means all the plants in an area, but it comes attached to a rather problematic and disproved theory that I will describe below.
The third term I will add is ecosystem, which means all the organisms in a particular area, plus their abiotic environment. This may seem to be a non-sequitur, but if this is new to you, you’re probably going to raise one of some very common objections. Most of those objections actually refer to ecosystems, not plant communities. Please keep this in mind. Plant community and vegetation refer only to plants.
The concept of plant communities was proposed by the pioneering ecologist Frederic Clements (1874-1945), and it’s part of his climax theory of plant succession. He was a popular scientist with a number of students, and his ideas dominated the first half of the century and were resurrected by GIS boffins and planners in the late 20th Century. However, as we’ve learned with current politics, just because an old idea gets resurrected doesn’t mean it was or is right, and that’s why I’m going to go into some detail about what Clements meant by plant community.
Succession is change in the composition of a plant community through time. You’re likely aware of this idea: after a disturbance, pioneer species come in. They’re followed by species that grow up in their shade (herbs giving way to shrubs, which in turn give way to trees). In the absence of disturbance, the plant community comes to a climax state, where the plants in it continue to reproduce themselves. This climax state is determined by the climate, and lasts indefinitely unless the plant community is disturbed, at which point it undergoes succession again. And if the plant community is disturbed too often, it gets stuck in a “disclimax.”
Does this sound reasonable? Unfortunately, it isn’t, but to see why it’s not just unreasonable but damaging, we need to walk through some history.
For one thing, Clements published about plant succession back in 1916. This was a point at which many biologists wererejecting Darwinian evolution, because Darwin’s ideas didn’t seem to gibe with Mendel’s genetic theory. The “Grand Synthesis” of the two was decades in the future. Moreover, Clements was a proponent both of Lamarckism (the idea that evolution happens through the inheritance of acquired characteristics) and superorganism theory. He’d also not heard of climate change or symbiosis. While both were known by then, anthropogenic climate change was thought to be an issue for the distant future and ice ages were in the distant past, while symbiosis was literally considered to be a communist plot that good capitalists rejected (that’s a story for another day). This was the heyday of evolution via competition, the “nature red in tooth and claw” school.
Clements theorized that plant communities were literally superorganisms composed of multiple plant species. That superorganism, when disturbed, regenerated itself through succession. Since he also thought that climate was constant, he assumed that which plant community superorganism established itself on a site depended largely on climate, and that it took centuries to reach climax under a constant climate.
At this point, some people who know a little about mycorrhizae and have heard the expression “wood wide web” are getting angry, because a current incarnation of the superorganism is that all the plants in a forest are tied together by their mycorrhizal web, just like the internet ties us all together into one beautiful global community. The sarcasm is intentional, because the “wood wide web” metaphor popped up early in the days of the World Wide Web, and by now everyone who is online knows that the internet not only does not make civilization into a superorganism, it divides us. And that’s true about plant-fungal relations too. They’re complicated. To get back to the second paragraph, if you’re invoking fungi to tie a plant community together, that’s an ecosystem of plants and fungi, not a plant community. Plant communities are nothing but plants, and that’s part of the problem with them.
One of Clements’ most persistent critics was a botanist named Henry Gleason. He started off with Clementsian views, but by 1926, he objected to them. Gleason proposed instead the idea of vegetation in associations. Vegetation is simply all the plants growing in a defined area, while associations are repeated patterns of associating plants. This is purely descriptive, and no one theory is attached to why some associations are common, or why they occur where they occur. Gleason thought that plant species followed individualistic patterns, growing where they could on environmental gradients like light, moisture, and nutrients, and that there were no superorganismal plantcommunities. Clements’ followers so hounded Gleason that heeventually left plant ecology altogether and went on to a successful career in plant taxonomy.
Now we turn to the University of Wisconsin, where I got my PhD. In 1959, John Curtis, a professor at UW and head of the Plant Ecology Lab, published The Vegetation of Wisconsin: An Ordination of Plant Communities. In it, he tested Clements’ notion of succession to climax against Gleason’s idea of plants acting individualistically. Curtis and his students did this by sampling putative plant communities along environmental gradients across Wisconsin, and ordinating plant occurrences along the gradients. If Clements was right and the landscape was composed of superorganisms, Curtis expected to see multiple plant species following the same patterns on environmental gradients. If Gleason was right, each plant would have its own pattern of abundance along each gradient.Long story short, Gleason was right, and there aren’t any plantsuperorganisms out there.
But Clements didn’t fade into history. The Vegetation of Wisconsin is still a standard textbook in Wisconsin, but most people outside the state haven’t read it and don’t realize that it was actually testing Clements against Gleason. So, plant succession to climax is still taught, even though it was debunked back in 1959.
Succession theory causes trouble. For example, it’s behind the long-held belief that Sierran “climax” forests shouldn’t burn at all, while chaparral “disclimax” has to burn frequently, or it will get overgrown by later-successional trees. We know this is wrong now, as billion-dollar fires sweep California due to mismanagement prompted, in part, by Clements’ ideas.
Clements’ theory also assumes that climates are stable over a scale of centuries. Now we know they never have been. The longest-lived trees survive fairly drastic climate changes, and only reproduce successfully when the climate is favorable for seedlings to survive. This is the exact opposite of what Clements thought, as is our modern realization that disturbance is normal, not an aberration.
Those are a few of the many reasons why I much prefer vegetation, and why CNPS and CDFW use vegetation, not plant communities. It’s a more correct, neutral term.
As for “vegetation community?” That bureaucratic neoplasm apparently emerged from the GIS and planning worlds. The people pushing this phrase had to deal with arguments about whether to use plant community or vegetation. Apparently because they didn’t have the time to understand the history, they made Solomonic decisions to split the baby and thereby begat “vegetation community.” It’s a meaningless buzzword that makes trained people cringe, the more so because vegetation is the neutral term, while plant community is loaded and problematic. Unfortunately, the well-intentioned folk using vegetation community control things like funding and employment opportunities, so it has spread invasively throughout the bureaucracies. It is cringeworthy bad science, and it would be nice to see it discarded with so many other problematic terms.
(Editor’s Note: I review the Science Daily listings to find current articles that pertain to California native plants, could apply to ecosystems in our chapter’s area, and might be interesting to newsletter readers. If you know of other such peer-reviewed science articles, please send the link to me. Thanks!)