I appreciate your reply, and will use it! What bothers me most about the criticisms of Clements is the simple fact that Clements is criticized for taking positions he never takes in his major publications. For example, the superorganism idea. That comes from the notion that communities (formations) have an ontogeny and a phylogeny, and he is trying to plug into recapitulationism. He claims communities have an ontogeny (succession) and a phylogeny (they are descended from ancestral comminutes). And that's it. That's the Clementsian superorganism. Other people took the concept other places maybe, but the idea Clements proposed went no further than that.
Clements is also criticized for being Lamarckian. I'd like to see some references to Clements on that issue. In Plant Succession, Clements states that current communities evolved from past comminutes, but he does not take a stand on the mechanism. Most people in that day accepted the inheritance of acquired characters, and Darwin made it a foundation of his theories; but we understand Darwin. We trash Clements for being "Lamarckian" even though he does not base his succession ideas on Lamarkianism. Clements is sometimes trashed for not being Darwinian even though he accepts Darwinian evolution as matter of fact in Plant Succession, but does not take a stand on mechanism. Probably good politics, because you had Mendelists vs Darwinists and strict selectionists vs Lamarkians...and Clements really didn't need to propose how the climate formed the vegetation, only state that it did, which it does, as we know today, by natural selection! Just because Clements does not propose specifically a selectionist model to explain how communities evolve doesn't make him anti evolutionary or anti Darwinian in his thinking. As far as Gleason is concerned, he is simply unfair. Clements speaks of the forms of the vegetation, not the species composition. He acknowledges that some communities in a given climax are very diverse while others are not. Clements does not predict a specific species composition for a climax, he predicts a specific form for the formation (community). Clements describes the differences in species composition between the marshy areas of Minnesota and the marshy areas of Louisiana, for example. Clements also states quite clearly that the species that will make up a formation (community) will be locally dispersed, and that long distance dispersal probably makes a negligible contribution to any community. Finally, Clements also makes a point of discussing small scale disturbances and habitat heterogeneity. He speaks of the importance of disturbances as small as wheel ruts, and variation like altitude and aspect on a mountain slope, and goes on at length on how habitat heterogeneity and small scale disturbances will affect community composition. He even talks at length about gradation of one community into another on even very small scales. Gleason states "It has often occurred to the writer that much of the structural variation in an association will disappear if taxonomic units which have the same vegetational form and behavior could be considered as a single ecological unit". Gleason has no arguement from this point on. Clements is in fact considering taxonomic forms which have the same form and behavior as single ecological units to the point of suggesting that herbaria be organized to reflect the common form and behavior of plants, which had to rankle systematists who want classification to reflect phyogeny only. If Gleason were to propose that the destruction of large sections of a temeprate broad leaved deciduous forest would be followed by something other than a succession leading to a temerate broad leaved deciduous forest climax, all else being equal, he would have something. In the end though, he attacks Clements for saying something Clements did not say; that the species composition of a climax community is constant. Clements nevcer makes that claim. I could go on for a while, as there is a lot more I can say here! "So easy it seemed once found, which yet unfound most would have thought impossible" John Milton ________________________________________ Robert G. Hamilton Department of Biological Sciences Mississippi College P.O. Box 4045 200 South Capitol Street Clinton, MS 39058 Phone: (601) 925-3872 FAX (601) 925-3978 >>> Skip Van Bloem <[EMAIL PROTECTED]> 2/20/2007 12:15 AM >>> I get Ecolog posts in digest form, so usually when I am tempted to comment it is already a day late, and so I don't. But this time I'll make an exception in defense of Henry Gleason (and also in defense of Clements) though probably not in time to forestall Dr. Hamilton's "trashing" of Gleason to his class. It is very much worthwhile to consider not only the state of ecology back in 1916 and in the 1930s, but also to consider the backgrounds of both Clements and Gleason. I would argue that based on their experience both men would have no choice to come up with their respective interpretations of succession and that if you flipflopped their experience, both men would have developed the others' theories. Clements primarily worked mostly in temperate and montane environments in the USA (Neb, Min, Col, Calif, Ariz). Gleason began his research in Ill, following up on work by Cowles, and continued in Michigan and at the NY Botanical Garden. Most importantly for this post, Gleason spent time putting together a botanical survey for Puerto Rico and worked in the Asian tropics. He had already begun to question the association model of Clements by 1927, but his tropical trips resulted in a more complete criticism. From PR, Gleason published on plant ecology and noted that multiple transects or plots would seldom result in similar species compositions. (Gleason, H.A. and M.T. Cook, Plant ecology of Porto Rico. Scientific Survey of Porto Rico and the Virgin Islands, 1927. 7(1-2): p. 1-173.) Granted, a series of plots or transects may only be descriptive, but PR at the time that Gleason was here was already a highly fragmented habitat, severely affected by land use history. The Spanish had been here for >400 years. Agriculture was already well on its way to deforesting 96% of the island (a level reached within 25 yr of Gleason's visit) but some marginal lands and former crown lands were already developing secondary forests. We have aerial photos of the island from 1936 that show clear patchworks of forest fragments of various ages witihin an agricultural matrix. Gleason was a bright fellow, was well trained by Cowles and in Clementsian succession before arriving in PR, and would have recognized the value of sampling in what we would now recognize as a chronosequence. I would argue that chronosequence sampling is in fact experimental, but that is probably another topic for Ecolog. Finally, I think if you read more of Gleason's work, you'll find that he is cut more from a modeler's mold. If you blindfold yourself and run through a mature forest in Michigan, it's pretty sure that you'll run into a majority of beeches and maples, or oaks and hickories, etc. If you do the same in mature forests in Puerto Rico, you won't run into a majority of anything, except trees, and our flora is "depauperate" compared to continental tropical tree floras. In fact, we do refer to "tabonuco" or "colorado" forests, but these aren't dominant species in the temperate sense, they are better understood as species that one might frequently find in mature lowland or lower montane (respectively) wet forests. They are indicators of a forest type, rather than a successional association. If you go into a mature (>80 year old) forest in the tropics and predict the species of tree next to the one you are standing under, you'll need a long list to be correct--much longer than in most temperate/alpine regions. On the other hand, Clements did not work in the tropics, as far as I know. As such, he would have a shorter list of species to work with and a set of "climax" forests that were very predictable in dominant species--even in species from earlier successional stages, as Marks so well illustrated in Pennsylvania. A most reasonable explanation of these patterns would be plant associations. When forced to explain "exceptions" due to waterlogged soil, sandy patches, etc. Clements defined smaller associations. Perhaps the tropical forests represent ever more smaller associations due to edaphic and other factors, but it is very hard not to believe that our forests are more individualistic and our species are more interchangeable. Gleason began his career in Illinois using a Clementsian approach and found cracks in it, even from his descriptive work. Perhaps Clements' calls for more experimentation were a smokescreen to diminish the attention paid to his critics. Perhaps it was genuine. Regardless, in hindsight, it was ahead of the curve to call for manipulative support for successional concepts. On the other hand, 10 years after the publication of Clements' seminar work, Gleason would have had ample experience with very controlled observations in much different systems to both support his individualistic hypothesis and criticize superorganisms. So there is my 2c. and as it's after midnight, this post will probably miss yet another day in the life of ecolog digests, but thanks for letting me provide a postscript. Skip J. Van Bloem, PhD Dept. of Agronomy and Soils University of Puerto Rico at Mayaguez > Date: Sat, 17 Feb 2007 13:51:50 -0600 > From: Robert Hamilton <[EMAIL PROTECTED]> > Subject: Re: 1916 Clements reference in electronic version? > > The problem I see with Gleason is that his argument is purely > rhetorical. He does use examples, but no experimental analyses of any > sort. A key point, again JMHO, is that Gleason talks of SPECIES while > Clements talks more of life forms. Clements does not predict rigid > SPECIES compositions, however one of the problems with a lot of Clements > work is the attempt to define smaller and smaller scale associations of > life forms. > > I could rant on almost indefinitely! Reading Gleason reveals a person > who is consumed with description only; there is no attempt at any sort > of experimental analysis. Clements continually insists on experimental > analysis. The 1916 paper, for example, includes a lot of data. One needs > to remember where Ecology was in 1916. We had no Evolutionary Synthesis, > but rather Darwinists vs Mendelists. We had no concept of any sort of > Functional Ecology outside Clements and his group. Clements challenged > people who just wanted to describe; Clements wanted experimental > analysis.
