Aspects of Stability and Change in Biogeographical CommunitiesAuthor(s): J. R. FlenleySource: Area, Vol. 16, No. 1 (Mar., 1984), p. 72Published by: The Royal Geographical Society (with the Institute of British Geographers)Stable URL: http://www.jstor.org/stable/20002006 .

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72 Annual Conference

showed how a model representing rainfall, initial conditions and internal transformations could mimic flood distributions, although poor results were obtained for very large flows on the Wye, suggesting modifications for localised heavy rain. J. B. Thornes presented analytical and simu lation results on 'Gully growth and bifurcation'. A gully head was treated as a kind of shock

wave and the conditions for bifurcation explored for parabolic, cubic and quartic contours. ' Some geomorphological rules derived from a theoretical model' were proposed by F. Ahnert (RWTH Aachen), drawing on experience with his program SLOP3D. He argued that relief, slope forms and soils frequently tend towards dynamic equilibrium, approached in different ways for wash and slow mass movement. A lively discussion exposed our ignorance of the relationship between regolith thickness and bedrock weathering. Finally A.C. Armstrong (MAFF Field Drainage Experimental Unit, Cambridge) considered 'Slope development and boundary conditions', examining the effects of basal conditions on hillslope profiles in a simulation model. He showed how important these can be in affecting forms, and, conversely, how similar forms can arise in response to a variety of process and boundary assumptions.

N. J. Cox and I. S. Evans University of Durham

Aspects of stability and change in biogeographical communities The purpose of the session was to be iconoclastic, and an alternative title 'The Death of the Climax' had been proposed, and would in some ways have proved very appropriate.

Although biologists mostly gave up using the Clements-Tansley theory of succession to climax decades ago, the concept has hung on in geography. G. Jones (Strathclyde) argued that a stable climax was impossible according to cybernetic theory, since the probability of something upset ting the stability could never be zero. J. R. Flenley (Hull) showed that it was possible by popu lation-biology theory alone to construct something close to a British postglacial pollen diagram,

without reference to succession or climax. Interglacial pollen diagrams also failed to show the expected mixed oak forest to be a climax, since it was succeeded by other dominants. Tropical pollen diagrams did not show any long-term stability. B. Huntley (Durham) showed by means of isopoll maps that European tree taxa had behaved in a highly individualistic (Gleasonian) manner during the Late Quaternary, and thus did not support the Clementsian 'organismal' concept which is a corollary of the climax theory. M. B. Usher (York, UK) also found individ ualistic behaviour in two differing communities (African termites and Breckland grassland), analysing the data by means of Markov chains.

Three papers broadened the scope. M. C. Kellman (York, Ontario) showed how savanna trees could be important concentrators of nutrients, thus providing nuclear points for immigration of forest trees. Over the slightly longer timescale since neo-glaciation, R. J. Whittaker (Cardiff) examined the vegetation of a glacier foreland in Norway; stability had not been reached in 230 years. P. E. O'Sullivan (Plymouth Poly) considered stability and succession in freshwater lakes, and concluded that the end-point of lake ontogeny did not have to be either eutrophy or oligo trophy; this is contrary to existing theories.

Although the audience was rather small, this was a lively and interesting session, which has helped to bring biogeography up to date. In the words of one speaker: ' the whole climax theory is to biogeography what the Davisian cycle of erosion was to geomorphology: a great theoretical idea, but one which just happens not to be true in practice. I suggest that biogeographers would do well to drop the term climax and all compounds of it entirely from their jargon, and that Clements' theory should be laid to rest alongside that of Davis in the graveyard of great geographical theories.

J. R. Flenley University of Hull

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