THE USE O F STATISTICS I N PHYTOSOCIOLOCIY
89
that decisions as to the initial data to be collected, and the analytical
methods to be used, ultimately depend on.the recognition of this
distinction.
The second basic concept is that the plant component of most
vegetation consists of separately identifiable units, differing in properties
other than mere spatial position. Without this assumption, the science
of phytosociology would have no meaning, and we must therefore accept
it as a necessary assumption for any phytosociological work. However,
the categorization of the units to be recorded is a matter for personal
decision, and must be determined by the purpose of the investigation.
We have already indicated (p. 67) that definition of the units by
reference to generally accepted taxonomic categories (i.e. species) is
likely to be most generally useful, but this does not deny the possibility
of using other categories of units for specific purposes.
The decision to use species as the categories of plants to be recorded
leads us inevitably to a further assumption based on common experience. Our existing knowledge of vegetational systems all points to the
fact that, even in very limited areas, there will be some variation in
floristic composition from site to site, with some species absent from
many of the sites. Since the existence of qualitative differences of this
sort immediately imposes a degree of heterogeneity (p. 71) on the
vegetation, we can make the assumption that we are dealing with a
basically heterogeneous system; and this will help us to decide on the
most effective methods of analysis.
The question of whether vegetation is fundamentally “continuous”
or “discontinuous” is less easy to resolve from common observation;
as Poore (1962, p. 53) has pointed out, “workers who have long famitiarity with vegetation and who have examined the question critically
can come to quite opposite conclusions.” However, we ourselves believe
(p. 72) that much of the confusion has arisen from a general reluctance
among ecologists to define precisely the terms which they are using, so
that “discontinuity” and “heterogeneity” are frequently confounded.
Since the assumption of heterogeneity is itself sufficient to swing the
balance in favour of classification rather than ordination techniques for
primary analysis, we do not feel that either of the opposing concepts
of discrete communities or “vegetational continua” is particularly
useful as a basis for investigation; we prefer instead to make no assumption either way, but to use only the concept of heterogeneity as a
working tool.
If no initial assumption of the existence of discrete communities is
made, then any sampling method used must be independent of this
assumption. This in itself destroys the basis for the traditional phytosociological practice of subjectively selecting “stands” of “homo-
89
that decisions as to the initial data to be collected, and the analytical
methods to be used, ultimately depend on.the recognition of this
distinction.
The second basic concept is that the plant component of most
vegetation consists of separately identifiable units, differing in properties
other than mere spatial position. Without this assumption, the science
of phytosociology would have no meaning, and we must therefore accept
it as a necessary assumption for any phytosociological work. However,
the categorization of the units to be recorded is a matter for personal
decision, and must be determined by the purpose of the investigation.
We have already indicated (p. 67) that definition of the units by
reference to generally accepted taxonomic categories (i.e. species) is
likely to be most generally useful, but this does not deny the possibility
of using other categories of units for specific purposes.
The decision to use species as the categories of plants to be recorded
leads us inevitably to a further assumption based on common experience. Our existing knowledge of vegetational systems all points to the
fact that, even in very limited areas, there will be some variation in
floristic composition from site to site, with some species absent from
many of the sites. Since the existence of qualitative differences of this
sort immediately imposes a degree of heterogeneity (p. 71) on the
vegetation, we can make the assumption that we are dealing with a
basically heterogeneous system; and this will help us to decide on the
most effective methods of analysis.
The question of whether vegetation is fundamentally “continuous”
or “discontinuous” is less easy to resolve from common observation;
as Poore (1962, p. 53) has pointed out, “workers who have long famitiarity with vegetation and who have examined the question critically
can come to quite opposite conclusions.” However, we ourselves believe
(p. 72) that much of the confusion has arisen from a general reluctance
among ecologists to define precisely the terms which they are using, so
that “discontinuity” and “heterogeneity” are frequently confounded.
Since the assumption of heterogeneity is itself sufficient to swing the
balance in favour of classification rather than ordination techniques for
primary analysis, we do not feel that either of the opposing concepts
of discrete communities or “vegetational continua” is particularly
useful as a basis for investigation; we prefer instead to make no assumption either way, but to use only the concept of heterogeneity as a
working tool.
If no initial assumption of the existence of discrete communities is
made, then any sampling method used must be independent of this
assumption. This in itself destroys the basis for the traditional phytosociological practice of subjectively selecting “stands” of “homo-