The Hydrosere and Current Concepts of the Climax

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Abstract
The chief factors controlling vegetation are considered and the validity of the view that climate is the only one controlling the climax is questioned. A distinction is drawn between climate and what may be called environmental climate. The merits of the monoclimax and polyclimax theories are considered; the latter is deemed less likely to obscure facts by over-simplification. Sere and climax are terms which refer to differences in rate of change, rather than to anything more absolute. The environmental climate of submerged habitats is characterized in outline, and it is considered useful to distinguish lakes from ponds in a qualitative way by the greater intensity of wave action in the former. A generalized account of the probable course of evolution of lakes in humid and arid regions is given; they present habitats which are probably at least as stable as terrestrial ones. The plant communities which are found in lakes are therefore best regarded as forming a sere reaching a climax dominated by submerged angiosperms in moderate depths of water where wave action is slight and illumination fairly good. A brief account of the probable course of this succession is given and the post-climax development of land vegetation in bays is shown to be a true post-climax as it is limited to the original extent of the special conditions. It is proposed to call the sere in lakes ending in climax under water a limnosere and to restrict the term hydrosere to the succession in small bodies of water which has a climax on land. A few examples of hydroseres which have been described from lakes are examined and are shown to apply only to limited areas in which conditions favor development of a post-climax. The normal discontinuity between the vegetation in a lake and that on its shores is pointed out and changes in the vegetation in 2 senile lakes are summarized. Habitat conditions in the littoral region of the sea are similar to those in lakes and consideration of marine plant communities agrees with and confirms the position taken in interpreting lake communities. It is doubtful if a succession in the ordinary sense can be said to occur in the sea.