S U C C E S S I V E A P P R O X I M A T I O N I N D E S C R I P T I V E E C O L O G Y
37
related t o it. The classes of triangle, quadrangle, pentagon etc. can be
perfectly defined and there is, by their very nature, no possibility of
intermediates between them. This is a very different situation from that
of colours, for example, where the common categories of yellow, red and
so on are capable of every shade of gradation and cannot be separated
from one another except by arbitrary dividing lines in certain physical
variables such as wavelength. Yet even in phenomena such as colour
some classification is essential and even the crude categories of subjective impression are invaluable and constantly used.
Vegetation is among the more difficult phenomena to classify (cf.
Goodall, 1954b). The difficulty is of two kinds - in the construction of
the classes and in the principles t o be applied t o the later grouping of
the classes. Some of the divergent views which have been expressed on
these topics will be discussed later.
Most working ecologists have concluded as a result of extensive field
experience that, in any region, plant communities may be found which
occur many times with more or less similar structure and species composition and which grow in similar habitats. These are usually communities which occupy large areas; for the area of a vegetation type is
often a reliable indication of its stability. Significant and stable communities, however, may sometimes occupy small areas ; and, in regions
which have recently suffered from intense biotic influence or catastrophic disturbance, most of the vegetation may be labile. Not all the
vegetation of a region can, therefore, be attributed to these stable communities (in extreme instances only a small proportion). Nevertheless, on the grounds of their similarity to one another, they can be combined into a class, an abstract community type, about which generalizations may be made. There are various reasons why these communities
may occur repeatedly ; but the logicel processes of classification and
generalization are independent of any possible explanation of their
occurrence. I think that this is the essence of the plant sociological
approach to vegetation classification. It does not attempt t o produce
classes into which all vegetation must be fitted but it does distinguish
abstract types where there is a sufficient degree of similarity and consistency between communities t o warrant the construction of classes.
Classification not only organizes and systematizes the findings of any
science, but can also be used as a research tool because it throws into
relief the similarities and differences between phenomena. Only broad
generalizations can be made from broad classifications, but the more
precise the classification, t'he more accurate the generalization. Reasoning such as this is implicit in most phytosociologiml methods, but its
value seems t o be little a{preciated. Poore (1956) examined phytosociological methods and suggested that, by utilizing these principles
37
related t o it. The classes of triangle, quadrangle, pentagon etc. can be
perfectly defined and there is, by their very nature, no possibility of
intermediates between them. This is a very different situation from that
of colours, for example, where the common categories of yellow, red and
so on are capable of every shade of gradation and cannot be separated
from one another except by arbitrary dividing lines in certain physical
variables such as wavelength. Yet even in phenomena such as colour
some classification is essential and even the crude categories of subjective impression are invaluable and constantly used.
Vegetation is among the more difficult phenomena to classify (cf.
Goodall, 1954b). The difficulty is of two kinds - in the construction of
the classes and in the principles t o be applied t o the later grouping of
the classes. Some of the divergent views which have been expressed on
these topics will be discussed later.
Most working ecologists have concluded as a result of extensive field
experience that, in any region, plant communities may be found which
occur many times with more or less similar structure and species composition and which grow in similar habitats. These are usually communities which occupy large areas; for the area of a vegetation type is
often a reliable indication of its stability. Significant and stable communities, however, may sometimes occupy small areas ; and, in regions
which have recently suffered from intense biotic influence or catastrophic disturbance, most of the vegetation may be labile. Not all the
vegetation of a region can, therefore, be attributed to these stable communities (in extreme instances only a small proportion). Nevertheless, on the grounds of their similarity to one another, they can be combined into a class, an abstract community type, about which generalizations may be made. There are various reasons why these communities
may occur repeatedly ; but the logicel processes of classification and
generalization are independent of any possible explanation of their
occurrence. I think that this is the essence of the plant sociological
approach to vegetation classification. It does not attempt t o produce
classes into which all vegetation must be fitted but it does distinguish
abstract types where there is a sufficient degree of similarity and consistency between communities t o warrant the construction of classes.
Classification not only organizes and systematizes the findings of any
science, but can also be used as a research tool because it throws into
relief the similarities and differences between phenomena. Only broad
generalizations can be made from broad classifications, but the more
precise the classification, t'he more accurate the generalization. Reasoning such as this is implicit in most phytosociologiml methods, but its
value seems t o be little a{preciated. Poore (1956) examined phytosociological methods and suggested that, by utilizing these principles