October 23, 2017

Ecological succession rehabilitated

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Ecology, so as to be made scientifically respectable and also compatible with the paradigm of modernism, has become reductionistic, mechanistic and quantified. To achieve this has meant seeking to discredit the basic principles of ecology, formulated by the great early ecologists such as Thoreau, Clements and Shelford.

One such basic principle is that of ‘ecological succession’. The author shows that the real reasons for ‘discrediting’ this principle, rather than being objective, as science is supposed to be, were in fact largely ideological and political.

The old well-established principle of ecological succession to a climax must be rehabilitated.

Published in The Ecologist Vol. 15 No. 3 1985.

An important principle of ecology is that ecosystems develop in a series of stages which must all occur in the right order – a process referred to as ‘succession’ which continues until a ‘climax’ is reached – a situation from which there is then little change, as it is the most stable one achievable in the circumstances.

The idea is an old one. In the 18th century, naturalists observed the process of succession in Scandinavian bogs. As Worster writes:

“water-loving hydrophytes would settle a pond and, by trapping mud with their roots, would eventually modify the environment to one more suited to mesophytes, or even xerophytes. The pond or lake would become a bog and then dry land covered by a dense forest.” [1]

The principle of succession was clearly formulated by Warming. He considered that it proceeded in a definite direction – towards a climax formation or final community. This notion Warming regarded as central to the new discipline of ecology.

Later (1899) H. C. Cowles made his pioneer studies of succession of plants on the sand dunes of Lake Michigan, while V. E. Shelford studied succession among animal populations. Both studies showed that as the dunes became older, so were the species of plants and animals inhabiting them completely replaced by different species.

Succession was regarded by Frederick Clements as fundamental to the developing science of ecology. Nature, he considered, did not move aimlessly but as a steady flow toward stability. In a specific environment, a clear progression could be plotted by the scientist through what Clements called a “sere” that begins in the pioneering stages with an unbalanced and relatively unstable assemblage and ends with a complex and stable equilibrium community, one that is capable of sustaining itself indefinitely.

Clements accentuated the role of climate in determining the nature of the sere and also established the principle that in any given habitat the sere could only end in a single climax (monoclimax). He was later to be seriously attacked on both these counts.

As Worster notes, Clement’s theory of succession and the climax undoubtedly reflected his

“underlying, almost metaphysical faith that the development of vegetation must resemble the growth process of an individual plant or animal organism.” [2]

This view is unacceptable to modern science and hence to modern scientific ecology on a number of counts:

  • Firstly, it tends to confirm the unacceptable idea that an ecosystem is a “superorganism” as Clements maintained, or at least that it resembles an organism in a significant way.
  • Secondly, it implies that the development of an ecosystem is not the result of random changes selected by an undefined environmental ‘invisible hand’ in accordance with their competitive skills (as all life processes tend to be viewed today) but occurs instead according to an orderly strategy.
  • Thirdly, it implies that this strategy is carefully co-ordinated by the ecosystem. This means that ecological development is at once teleological and holistic – a nightmarish thought for our scientists and hence for our scientific ecologists who are ideologically committed to a random and atomised world.

It is unacceptable for yet another closely associated reason, which is that it implies that the goal of ecological development is the achievement of stability, whereas our modern industrial society is committed to perpetual change in a single direction, which can only occur by reversing the successional process or sere, or by artificially maintaining the ecosystem at its most productive pioneering stage, which happens to be, ecologically, the least advanced – the stage most marked by discontinuities such as floods, droughts, epidemics, population explosions and wars.

To accept the principle of ecological succession to a climax is thus to accept the destructive nature of economic development which, from the ecological point of view, rather than being identified with ‘progress’ must, on the contrary, be classified as ‘regress’.

It was mainly – though perhaps subconsciously – for these reasons that ecologists imbued with the paradigm of modernism, eventually came to reject Clement’s thesis. Clements may have gone too far – for instance, climate is clearly not the only factor in determining the nature of a climax – nevertheless, his basic thesis is obviously correct.

Gleason, not surprisingly, was one of the first to reject it. In 1910 he wrote:

“it is impossible to state whether there is one definite climax association in each province: it seems probable that there are several such associations, each characteristic of a limited portion.” [3]

And in 1927 he said

“. . . succession is an extraordinarily mobile phenomenon whose processes are not to be stated as fixed laws, but only as general principles of exceedingly broad nature, and whose results need not, and frequently do not, ensue in any definitely predictable way.” [4]

Succession, in this way, ceased to be a directive process tending towards a definite goal. Gleason tended to regard it, instead, as a random process just as he regarded the association as a random arrangement of individuals. “In the centre of an association”, he wrote, “we see only the fluctuations in structure from year to year.” [5] He even suggested that succession might be retrogressive.

Controversy over the dustbowl

The whole question came to a head during the debate over the great dustbowl in the late 1930s. Ecologists, at the time, showed that the crisis was a man-made one. Ploughing the southern plains, which should clearly never have been done, caused them to divert from their climax state and the dustbowl was the consequence. During the debate that followed, the very notion of a ‘climax’ came under attack. Tansley, the Oxford ecologist, was particularly keen to discredit the concept. He insisted that man, with his great ingenuity, was capable of creating his own climax, an “anthropogenic climax” as he called it, which was superior to the natural variety.

Tansley’s motive was clear. To quote Worster, he

“did not want to accept any climax achieved by purely natural processes as an ideal for man to respect and follow. His concern was not to re-establish man as a part of nature, but to put down the threat to the legitimacy of human empire, posed by the natural climax theory. If Tansley was right and there were no meaningful differences between the balance achieved by nature and that contrived by man – if the two systems were at least equals in quality and performance – then what reasonable objection could there be to man’s rule over the biological community, or to the further extension of his empire? The effect of Tansley’s proposal, in other words, would be to remove ecology as a scientific check on man’s aggrandising growth. The Clement’s stand of the climatic climax must be replaced, he was saying, by a kind of environmental relativism: there would then be no exterior model against which the artificial environment could be evaluated scientifically. The yardstick would be tossed away, and man would again be free to design his own world.” [6]

Clement’s climax was also attacked very bitterly by the agricultural historian James Malin in 1956. According to Worster, it was the latter’s purpose over a number of decades, to defend the battered reputation of the farmers “against the ‘Evangelical conservationists’ “. Malin insisted:

“No more brazen falsehood was ever perpetrated upon a more gullible public, than the allegation that the dust storms of the 1930s were caused by the ‘plough that broke the plains’.” [7]

On the contrary, large-scale mechanised agriculture was a step forward. The Plains had benefited from it, nature needed to be ploughed up, and

“blowing dirt around was necessary for it to remain vigorous and fertile.” [8]

Frederick Clements was the bogey man. His writings provided the rationale for the “hysterical” conspiracy against progress. It had to be totally discredited. In 1953 Malin wrote,

“The conventional or traditional concept of the state of nature must be abandoned – the mythical, idealised condition, in which natural forces, biological and physical, were supposed to exist in a state of virtual equilibrium, undisturbed by man.” [9]

This in fact is what scientific ecologists have since succeeded in doing.

Malin succeeded in persuading himself that dust storms were:

“natural phenomena of the great plains, they are part of the economy of nature and are not in themselves necessarily abnormal, at least, not in the sense in which the subject was exploited during the drought decade of the 1930s.” [10]

It is easy to see what motivated Malin to write such nonsense. As Worster put it:

“Like Tansley in England, Malin was unhappy with what seemed, in ecology, to be a prejudice against civilisation: a belief that ‘only civilised man was evil’ and that he had no moral right to alter the natural order. The preservationist’s oft-repeated charge of ‘rape’ for what modern man had done to the grassland especially enraged him, in part because it implied that nature is more than a mere thing, that it has personal character, that it is female and vulnerable. Nor would he accept any distinction between the environmental impact of the Indian and of the White man.” [11]

Neither James Malin, nor his associate Carl Sauer, even bothered to disguise their motives. The idea of the climax, they asserted, “assumes the end of change” – which they had been clearly taught to see as providing a panacea to every possible problem. [12]

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The position of modern scientific ecologists

Ironically, it is the anti-ecological ideas of Gleason, Tansley and Malin that have come to be regarded as the ecological orthodoxy. This is clear from the writings of Ricklefs:

“In recent years, the concept of the climax as an organism or unit, has been greatly modified to the point of outright rejection by many ecologists, with the recognition of communities as open systems whose composition varies continuously over environmental gradients.” [13]

It is also clear from the writings of Simberloff:

“The deterministic path of succession, in the strictest Clementsian monoclimax formulation, is as much an ideal abstraction as is a Newtonian particle trajectory. There is a tidiness, an ease of conceptualisation, to well-defined ideals moving on perfect paths, that is as appealing, both aesthetically and functionally, in ecology as it was in genetics and evolution. Unfortunately, it is as poor a description of ecological, as of evolutionary reality.” [14]

It is equally clear from the writings of Whittaker:

“The more closely vegetational dynamics are observed, the less clear-cut becomes the distinction between climax and successional communities. Vegetation does not really consist of climaxes and successions leading toward them. In a long-range perspective, the vegetation of the earth’s surface is in incessant flux; what we observe in the field are not simply successions and climaxes, but only different kinds and degrees of vegetational stability and instability, different kinds and rates of population change.” [15]

Elsewhere, he makes the same points somewhat differently:

“If one seeks to view this complexity in perspective in terms of species populations in space and successional and evolutionary change and without the intervention of man’s ecological abstractions, then the view of the forest is not one of clear and orderly associations, successions and phylogeny. It is one of a veritable shimmer of populations in space and time.” [16]

It is also clear from the writings of Pickett:

“The classical interpretation of succession as development of vegetation through discreet stages culminating in a regional climax. . . has been abandoned by modern ecologists.” [17]

Though he has the grace to admit that “no ecological complete, contemporary model has replaced it.”

In line with current scientific dogma, ecological succession tends to be explained today in terms of competition and in terms too of the properties of populations rather than of whole ecosystems. This is pointed out by Connell and Slayter for instance, [18] and also by Pickett. [19] It is also the view of Putnam and Wratten. Pioneering species, the latter tell us, are replaced

“not just because the environment does not suit them but because they are poor competitors and competition is more intense in climax ecosystems.” [20]

It is difficult to see how they can really believe this. The operation of all sorts of internally generated negative-feedback mechanisms which Odum even refers to as “environmental hormones” [21] and which inhibit the growth of species that are replaced by other species in the succession towards a climax, is clearly visible to all but the most prejudiced eye.

Ricklefs alludes to the operation of such a mechanism when describing the process of succession on abandoned farmland in the Piedmont region of North Carolina. He describes how “Decaying horseweed roots stunt the growth of horseweed seedlings” and how “this self-inhibiting effect, whose function and origin is not understood, cuts short the life of horseweed in the sere”.

Such growth inhibitors presumably are the by-product of other adaptations that increase the fitness of horseweed during the first year of succession:

“If horseweed plants had little chance of persisting during the second year, owing to invasion of the sere by superior competitors, self-inhibition would have little negative selective value.” [22]

Putnam and Wratten also refuse to see the development of an ecosystem and the achievement of a climax as the result of a long-term strategy; indeed not even in terms of any of the intrinsic features of a developing ecosystem.

If ecosystem development is not in this way an orderly strategy, then the climax cannot be its logical outcome; instead it must be seen as ‘thrust upon’ the system from the outside. For this reason they suggest that we abandon the use of the term climax altogether and use instead the term “end community”. [23]

How then does their version of succession occur? Putnam and Wratten offer but the most simplistic answers – the only ones, as one might have guessed, that can be quantified and modelled by systems ecologists, the only ones reconcilable too with the simplistic view of life adopted by modern science today.

What they actually suggest is that succession is simply the result of “an accumulation of biomass” which stops when there is no opportunity to accumulate any further biomass, because the process has in fact come up against gross features of the environment that are immutable – physical barriers – a shortage of resources for further growth. Alternatively they see it in purely energetic terms as

“an imbalance within the energy relations of the community resulting in the accumulation of biomass by the community.” [24]

Both these explanations are based on the notion that the behaviour of an ecosystem is random, mechanistic, individualistic and hence uncoordinated, and also passive and externally controlled, as indeed must be all life processes if they are to be fitted, Procrustean-like, into the paradigm of modernism.

Putnam and Wratten then reveal their ideological bias still more clearly. Productivity, they tell us, is often low in a climax by comparison to that of earlier stages in the succession “due to the complexity of web-design, cycling of materials through the system is extremely slow.” [25]

Such features of a climax have traditionally been regarded as beneficial. But Putnam and Wratten wonder if they really are. [26] They point out that there are “many examples of far more productive, indeed far more diverse communities characteristic of earlier, pre-climax seral(sic) stages.” They then ask whether a climax is in fact “tantamount to over-maturity?” [27]

The argument assumes that productivity is the yardstick for judging ecosystems. This also was the argument of Tansley and Malin – of those, if we remember, who opposed the application of any constraints on man’s ecologically destructive activities. It is the ultimate irony that those who advance it should call themselves ‘ecologists’.

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