|Vegetation Climax, Western Ghats 2009|
ECOLOGICAL PAPERS WRITTEN IN THE 1930S are the Burgess Shale of the discipline. As in that middle-Cambrian fossil bed of primordial forms, everything is already there and often piled pretty closely together. Arthur Tansley’s 1935 paper “The use and abuse of vegetation concepts and terms” appeared in the journal Ecology and re-reading it three-quarters of a century later opens a window on the debates in the early years of discipline. Tansley’s proximate concern is to chastise the younger South African ecologist John Phillips, whose views on vegetation development had chagrined him. In the background is the powerful figure of Frederic Clements, the senior American ecologist and archdeacon of the concepts of “succession” and the “complex organism”, whose views Phillips was advocating and justifying. These days Tansley’s paper is primarily remembered for introducing the term “ecosystem”; however, other debates swirl around it, including questions concerning the degree to which we might regard the largest entities of nature as “super-organisms”. (For an account of this paper go here) Is the plant community correctly seen as a large independent organism that grows, matures, and reproduces in the way an individual plant or animal does? Debates about this matter – a storm in arcane scientific teacup – prefigure more contemporary debates about Gaia: can the planet itself be regarded as a single super-organism?
THE ECOSYSTEM CONCEPT WAS PROPOSED to serve two functions. Firstly, the ecosystem is an ecological category in which the all the organisms of a region (“biome”) and the non-living components of the environment are in “relatively stable dynamic equilibrium” – the ecosystem is thus an entity with investigable properties (Tansley’s interests were, after all, primarily methodological). The ecosystem is also one of a suite of concepts – plant community, succession, development, and climax – that Tansley regarded as providing the essential framework for studying the processes for governing change. So the ecosystem is both a relatively stable entity in nature but is also one that emerges from, and is simultaneously part of, the ongoing, and often progressive, dynamics of nature.
The two provinces of ecological thought represented most forcefully in Tansley’s review of ecological terms – the production of stable entities, and change – have drifted further apart since that time. However, even though they are not always considered in an integrated way, the themes remain central to contemporary ecological enquiry. Drawing upon Tansley’s review I consider each in turn before considering how each of these perspectives has subsequently developed in ecological thought and finally ask how they might be drawn together again (the last two of these tasks will be the work of future postings).
PERHAPS IT COULD BE OTHERWISE; perhaps matter in this universe could be spread out like jam on toast, instead, though, it is clumpy like Dundee marmalade. Indeed, not only is matter clumpy, on most scales it is composed of clumps within clumps within clumps. Cells aggregate to form tissues, tissue to organs, organs to organ systems, organ systems to bodies etc. When Tansley proposed the ecosystem it was, he said, “one category of the multitudinous physical systems of the universe, which range from the universe as a whole down to the atom.” That is, the ecosystem is but one of the units ranging in size from the very smallest to the largest of all, part of the hierarchy of nature in which entities are arranged like Chinese boxes, the smaller ones contained in progressively larger one.
As one contemplates the properties of each of the categories of natural entity should one expect them to have similar attributes despite their difference in scale?
Frederic Clements (1874 -1945), the principle early theorizer of successional change in vegetation, and his acolyte John Phillips against whom Tansley railed in his 1935 paper, believed precisely this: common attributes from organism to landscape-scale ecological entity should reasonably be expected to have several important properties in common. The climax community – the vegetation unit reflecting the stable endpoint of development in a given climatic zone – could be regarded as a “complex organism”. This complex organism had, in the view of Clements and Phillips, attributes in common with “organisms” as more commonly understood by biologists (i.e. individual animals, plants etc.). In an important summation of his writing on succession and the concept of climax vegetation Clements writes in a 1936 paper: “[like] other but simpler organisms, each climate not only has its own growth and development in terms of primary and secondary succession, but also has evolved out of a preceding climax.” He goes on to write “[the climax as a complex organism] possesses an ontogeny and phylogeny that can be quantitatively and experimentally studied, much as with the individuals and the species of plants and animals.” Phillips is likewise emphatic on this point. One of the subsections of a paper for 1935 is on the thesis that:
“The plant or biotic community behaves as, and actually is, an integrated whole: a complex organism, which exhibits various life phenomena in a manner similar to an individual organism.”
Like the developmental processes of individual organisms, the adult complex organism, assuming that its growth is non-pathological, is “born, grows, matures, reproduces, and carries out various other biotic phenomena” and is directed inexorably towards a pre-ordained final form, one which is stably in equilibrium with the climate of the region.
In his 1936 summary paper Clements asserted that a detailed analysis of North America vegetation and the successful application of the concept of climax and complex organism by researchers around the globe leave the assertions he originally made in his 1916 monograph intact and fully supported. In the 1936 paper Clements included in the reference section Tansley’s 1935 Use and Abuse paper in which the notion of a complex organism had been acerbically attacked, but significantly Clements does not refer to that paper in the text. It is as if he were indicating to the good Professor Tansley that his critique had been noted but blithely dismissed.
Another factor that lent strong support to Clements’ views on the climax community and the complex organism was, in Clements’ opinion, the rise of notions of emergent evolution and holism. These ideas were originally developed by Jan Christiaan Smuts, a statesman and philosopher, and Phillips fellow South African, who coined the term holism to describe "[the] tendency in nature to form wholes that are greater than the sum of the parts through creative evolution." John Phillips applied these ideas to vegetated communities. Holism was especially suited to transforming the rather loose analogy of the climax community to the individual organism since holism provides a mechanism for the complex organism to invariably emerge from earlier successional stages. Holism in Phillips’ reading of it could be “conceived as the basic principle underlying the universal tendency to synthesis: the principle responsible for the origin and development of whole.” The complex whole, it would seem, can serve as a cause. The “factor of holism [is] innate in the very being of the community, a factor of cause.” Phillips thus provides a philosophical justification for the assumption that the climax community could act as causal agents.
Tansley reacted to this defense by Phillips of the complex organism more vehemently than he does to any other part of Phillips’ thesis. He manfully struggles to understand Phillips’ meaning; one must grant Tansley this. Can a community be the “cause of its own activities?” Mystified Tansley kicks the ball to the touchline saying that the “philosophical question of the meaning of causation” is something that he cannot attempt to discuss in his paper. He cautioned though that to remember “that these activities of the community are in analysis nothing but the synthesized actions of the components in association.” Tansley both tries to understand him – he draws back from accusing him of vitalism, but ultimately he is not sold on the idea. He ends the section with some blistering comments directed at the younger Professor Phillips: I quote him in full:
“It is difficult to resist the impression that Professor Phillips' enthusiastic advocacy of holism is not wholly derived from an objective contemplation of the facts of nature, but is at least partly motived by an imagined future "whole " to be realised in an ideal human society whose reflected glamour falls on less exalted wholes, illuminating with a false light the image of the "complex organism."”
THE ISSUE OF WHAT COUNTS AS AN ECOLOGICAL ENTITY, what properties each entity has, are these properly regarded as “emergent” properties, how the stability (where it exists) of the entity is maintained, and how these entities develop, remains a significant question for the ecology. The insights are at times quite odd and at times are discussed in the margins of the discipline. We will discuss these developments next. It can be said, however, that in spirit these discussions have not strayed from the spirit of the testy exchanges between Tansley and his colleagues.