Ecosystems 7 - Plant Succession Theories

1. Plant Succession Theories
The classical plant succession theory
suggests that once the climatic climax
vegetation is reached then the community
remains in a steady state – is this likely to be
the case?

2. MonoClimax Theory
•The monoclimax theory was an invention of the
American ecologist F.E. Clements (e.g. 1916).
This states that every region has only one climax
community, toward which all communities are
evolving and that, given sufficient time and
freedom from interference, a climax vegetation
of the same general type will be produced
irrespective of the earlier site conditions.
Clements believed that it was climate, and
climate alone that determined the final "forest-
type".

4. Is such a monoclimax succession towards a climatic climax community inevitable?

5. The classical plant succession theory
suggests that once the climatic climax
vegetation is reached then the community
remains in a steady state – is this likely to be
the case?

6. Polyclimax Theory
•The polyclimax theory arose as as an obvious reaction.
A.G. Tansley (1939) was an early proponent. There are
many different climax communities that can be recognised
in a particular region. These climaxes are controlled by
soil moisture, mineral ions, activity of animals,
topography, and other factors.
The difference is the time factor applied in measuring
relative stability. In the view of the supporters of the
monoclimax theory, given enough time, a single climatic
climax community would be achieved, eventually
overcoming the edaphic and other climaxes.

7. Climax
Vegetation
Plagioclimax
subclimax (after
deforestation,
ploughing, burning)
Secondary
succession
Primary
succession
New inorganic
(non-vegetated
surface)
Biotic
subclimax
Edaphic (soil)
subclimax
THE
POLYCLIMAX
THEORY
1
2
2
3
4
1
2
3
4
Primary succession
natural interruptions in primary

succession
Retrogressive succession due to

disturbance (natural or human)
Secondary succession

8. This begs the question, should
we consider time on an ecological
or geological scale?
However we consider time, is the
climate stable?

9. Climax Pattern Hypothesis
•R.H. Whittaker (1953) proposed a variation of the polyclimax
idea, the climax pattern hypothesis. This emphasises that a
natural community is adapted to the whole pattern of
environmental factors in which it exists. In addition to climatic
factors, e.g. wind, there are a whole range of edaphic factors,
fire, and biotic factors, including grazing, disease and
mutualistic and competitive interactions.
•Whereas the monoclimax theory allows one climatic climax in
a region and the polyclimax theory allows several climaxes in
the same area, the climax pattern hypothesis allows a
continuity of climax types, varying gradually along
environmental gradients and not neatly packaged into
discrete climax types.
•The climax is recognised as a steady-state community in
dynamic balance with the environment in all its gradients.
Rather than referring to a climatic climax, the correct term is
prevailing climaxes and these are determined by climate, soil,
topography and biotic factors as well as fire, wind, salt spray
and other influences, including "chance".