33© INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



State of more or less dynamic equilibrium with the local environment, 

 though minor adjustments go on all the time. For life, as we have 

 seen, can never be static, and the climax is only relatively so when 

 compared with other stages of the succession. So besides the obvious 

 differences in space, which are often attributable to diversification 

 of the habitat, the climax inevitably shows some variation with time, 

 its state remaining dynamic to that extent. This variation may be 

 no more than that which results from the death and decay of indi- 

 viduals especially of the dominant species — the disappearance of a 

 big tree, for example, leaving a gaping hole in the forest canopy — 

 followed by replenishment. If, on the other hand, there is a pro- 

 gressive change, then we will have a continuing succession. 



The climax must at least be sufficiently stable and lasting to out- 

 live the life-span of the dominant species. It commonly consists 

 of patches or phases of different but related composition. However, 

 these are normally at most representative of cyclic changes comprising 

 upgrade and downgrade parts that nevertheless return to much the 

 same climax type. If they do not do so, then a succession or retro- 

 gression must be involved, examples of the latter being the coloniz- 

 ation of eroded heaths by Lichens and of coniferous forests by Bog- 

 mosses. It is supposed by some that even these changes represent 

 parts of a long-term cycle, but for such generalization the evidence 

 seems inconclusive. We cannot wait long enough to see the true 

 situation, which might take millennia to emerge ! 



In nature we expect to see some kind of ' regional ' or ' prevailing ' 

 climax developed in local-climatically suitable situations at least on 

 undisturbed tracts of the better soils of a region. But besides the 

 complications already mentioned, there may be more important local 

 variations of soil, biota, treatment, and so forth, causing the sere to 

 be arrested, after being deflected, at some stage before the climax, 

 and so constituting a subclimax. This is an imperfect stage in which 

 the dominants are of lower life-form or competition-impress than 

 those of the climax, the vegetation being ' held back ' by artificial 

 or natural causes other than the climate. For the immediate site 

 or ecological peculiarity may largely determine the actual growth. 

 Examples are the subclimaxes due to such treatments as persistent 

 burning or grazing (often called disclimaxes, being due to disturbance, 

 or plagioclimaxes, owing to the deflection involved), or to marked 

 differences in the rocky or other substratum. This last instance may 

 if desired be termed an ' edaphic climax ' by those who doubt whether 

 it will ever attain (or even if there is such a thing as) a ' regional 



