These two approaches to the description of plant communities can be
expressed graphically in the form shown in Fig, 3.1, where the distributions
of individual species are depicted along an environmental gradient. This
may represent any environmental factor such as soil moisture, acidity, alti-
tude, and so on. All species have their optimum for a given factor (see Fig.
2.18) and have their ecological limits within which survival and growth are
possible; some may have a narrow range of tolerance, and others may have a
wide range of tolerance and hence, potentially, a wider distribution. If the
elements model is correct, then we would expect that a number of species
might coincide in their optima and limits, as shown in Fig. 3.1a. But if the
individualistic concept of Cleason is more realistic, the expected pattern
should be as shown in Fig. 3.1b, where there is little coincidence between
species. Most field studies have demonstrated that the Gleason model is
closer to the truth, but the two concepts are not totally mutually exclusive.
These two approaches to the description of plant communities can be expressed graphically in the form shown in Fig, 3.1, where the distributions of individual species are depicted along an environmental gradient. This may represent any environmental factor such as soil moisture, acidity, alti- tude, and so on. All species have their optimum for a given factor (see Fig. 2.18) and have their ecological limits within which survival and growth are possible; some may have a narrow range of tolerance, and others may have a wide range of tolerance and hence, potentially, a wider distribution. If the elements model is correct, then we would expect that a number of species might coincide in their optima and limits, as shown in Fig. 3.1a. But if the individualistic concept of Cleason is more realistic, the expected pattern should be as shown in Fig. 3.1b, where there is little coincidence between species. Most field studies have demonstrated that the Gleason model is closer to the truth, but the two concepts are not totally mutually exclusive.
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