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J. M. LAMBERT AND M. B . DALE
site-definition as well as a species-definition, so that the physical
properties of the relevant sites can also be invoked for purposes of
recognition of similar units elsewhere ; although the habitat factors are
thus involved as a secondary step, their inclusion adds to the pool of
common information. The idea of simultaneous definition of vegetationunits on both species and habitat together is by no means new, since both
criteria have long appeared in common terms like “reedswamp”. However, most systems of vegetational classification which have hitherto
made use of environmental features have tended to use the two kinds
of criteria separately at different stages in a single hierarchical system ;
in contrast, the present proposal is to erect both definitions simultaneously by independent analyses.
The essence of nodal analysis as we conceive the situation is that the
noda finally abstracted are separate units separately related to the
sites on which they occur, so that any one sample of vegetation can
contain a number of noda. Perhaps the chief stumbling-block to any
earlier emergence of conceptions of this type has lain in the common
phytosociological practice of regarding the whole complement of species
at a given site as an inviolable unit for purposes of classification. However, the idea of “noda” in our sense seems to have something in
common with the long-established concept of “synusiae”, which have
been variously defined but which appear to have the common property
of representing tightly-knit groups of species of similar ecological
requirements. Nevertheless, the direct comparison fails in that the
usual concept of synusiae does not appear to embody the idea of
physical intermingling of different synusiae ; the closest approximation
is seen when the term is applied to different layers in stratified vegetation, since here there is at least some coincidence of site in a horizontal
sense.
Since the noda are also separately related to the groups of ecologically similar species from which they are derived, their erection as
abstract units also allows us to accommodate the concept of physical
overlap of groups of species of different ranges of ecological tolerance.
The idea of these doubly-defined noda thus to some extent effects a
compromise between the opposing concepts of “vegetational continua”
and discrete communities ; but whether the new concept will prove as
useful in practice as it appears in theory still remains to be seen.
We have already mentioned (p. 87) possible practical advantages
accruing from the concentration of the properties of each nodum into
a single characteristic species and a single characteristic site. Although
the idea of a “characteristic site” is new, the concept of a “characteristic
species” is long-established and has led to widespread argument in
phytosociological circles : “dominance”, “constancy” and “fidelity”
J. M. LAMBERT AND M. B . DALE
site-definition as well as a species-definition, so that the physical
properties of the relevant sites can also be invoked for purposes of
recognition of similar units elsewhere ; although the habitat factors are
thus involved as a secondary step, their inclusion adds to the pool of
common information. The idea of simultaneous definition of vegetationunits on both species and habitat together is by no means new, since both
criteria have long appeared in common terms like “reedswamp”. However, most systems of vegetational classification which have hitherto
made use of environmental features have tended to use the two kinds
of criteria separately at different stages in a single hierarchical system ;
in contrast, the present proposal is to erect both definitions simultaneously by independent analyses.
The essence of nodal analysis as we conceive the situation is that the
noda finally abstracted are separate units separately related to the
sites on which they occur, so that any one sample of vegetation can
contain a number of noda. Perhaps the chief stumbling-block to any
earlier emergence of conceptions of this type has lain in the common
phytosociological practice of regarding the whole complement of species
at a given site as an inviolable unit for purposes of classification. However, the idea of “noda” in our sense seems to have something in
common with the long-established concept of “synusiae”, which have
been variously defined but which appear to have the common property
of representing tightly-knit groups of species of similar ecological
requirements. Nevertheless, the direct comparison fails in that the
usual concept of synusiae does not appear to embody the idea of
physical intermingling of different synusiae ; the closest approximation
is seen when the term is applied to different layers in stratified vegetation, since here there is at least some coincidence of site in a horizontal
sense.
Since the noda are also separately related to the groups of ecologically similar species from which they are derived, their erection as
abstract units also allows us to accommodate the concept of physical
overlap of groups of species of different ranges of ecological tolerance.
The idea of these doubly-defined noda thus to some extent effects a
compromise between the opposing concepts of “vegetational continua”
and discrete communities ; but whether the new concept will prove as
useful in practice as it appears in theory still remains to be seen.
We have already mentioned (p. 87) possible practical advantages
accruing from the concentration of the properties of each nodum into
a single characteristic species and a single characteristic site. Although
the idea of a “characteristic site” is new, the concept of a “characteristic
species” is long-established and has led to widespread argument in
phytosociological circles : “dominance”, “constancy” and “fidelity”