2.6. 7: What controls the Climax?
American ecologist F.E. Clements in the early years of the 20th Century developed a theory in which the community acted almost like a single organism. He concluded that with enough time the community anywhere that experienced the same climate over a large area would develop to the same end point or climax. Clements believed that the only factor controlling the climax was the regional climate. (Clements, F. E., 1936: Nature and Structure of the Climax. J. Ecol. 24: 252-84.)
This is a great over simplification of the factors that control the type of climax community that can form. According to Clements view the climax community for the whole of Western Europe would be a fairly uniform mixed deciduous woodland dominated by Oak. For much of this area Oak is the dominant tree species, but it is not the only dominant species. Also where Oak does dominate, the assemblage of other plants in the community varies from place to place. (Polunin, O. & Walters, M., 1985: A guide to the vegetation of Britain and Europe. Oxford University Press)
Soil or Edaphic factors have as important a role in deciding what climax community can establish in any one area. Variations in pH, original parent rock, humid content, water holding capacity and aspect all greatly effect which plant species can thrive.
In Great Britain there is a divide between the North and West of the Country compared to the South and East. The former is cooler and wetter with a greater tendency for acidic soils to form where as the latter is dryer and warmer with more base rich (alkaline) soils, though both soils types can be found within each climatic area. Between these two extremes there are intermediate woodland types that form on often water logged soils as well.
|
Cool and Wet North Western | ||||||||
| Warm and Dry South Eastern | |||||||||
| Base rich soils | Low base soils | Acidic soils | |||||||
The table above summarizes the main variations found in British woodlands. As can be seen these depend both on the climatic influence and the influences of the soils in the region.1
- after Rodwell, J.S., Editor, 1991. British Plant Communities, Volume 1 Woodlands and Scrub. Cambridge: Cambridge University Press [↩]