62
M. E. D. POORE
Within a small area, this is easy, for floristic composition and ecology
usually alter together and consistently with one another. The change
in the Scottish mountains from a Rhacomitrium-Cares bigelowii
sociation t o one of Rhucomitrium and Juncus tri$idus is regularly correlated with a particular shift in environment. The whole floristic composition usually reflects finer differences than does either the dominant
or the structure of the community. Moreover the physiognomy can be
reconstructed from a good description in floristic terms, but floristics
cannot be inferred from a description of structure.
On a global scale, however, this method does not apply because areas
which appear t o be ecologically equivalent have different floristic
histories. A truly ecological classification would unite the equatorial
forests of Malaysia, Central Africa and Tropical America more closely
than any one of them t o the sub-tropical savannahs adjoining it. A
physiognomic classification would do the same because of the striking
homoplastic evolution of vegetation structure in response to habitat.
A classification based on floristics would, on the other hand, separate
them widely.
These considerations lead t o the conclusion that classification of
communities within one relatively uniform floristic region should be
based on floristic comparison, but that classification on a larger scale
should be based on physiognomic-ecological criteria. For this the
system proposed by Gams in 1918 supplemented by the decisions of the
International Botanical Congress (Du Rietz, 1936) still seem t o be
the most satisfactory.
Taken together these recommend that there should be separate
classifications of synusiae and phytocoenoses. The units of these two
systems, within a uniform floristic region, being as follows.
Synusiae
Phyto- (bio-) coenoses
Society
Sociation
Union
Association
Federation
Alliance
When this system is extended outside a uniform floristic region, the
following concepts and terms are appropriate.
For synusiae : isoecia; abstract units built up of ecologically equivalent but floristically different synusiae of different regions.
For phytocoenoses : isocoenoses ; abstract units built up of floristically
different but ecologically indentical consociations.
E. DEFINITIONS OF UNITS
Definitions of units should be precise so that there is no doubt
whether or not a community falls into a named unit. If we accept the
M. E. D. POORE
Within a small area, this is easy, for floristic composition and ecology
usually alter together and consistently with one another. The change
in the Scottish mountains from a Rhacomitrium-Cares bigelowii
sociation t o one of Rhucomitrium and Juncus tri$idus is regularly correlated with a particular shift in environment. The whole floristic composition usually reflects finer differences than does either the dominant
or the structure of the community. Moreover the physiognomy can be
reconstructed from a good description in floristic terms, but floristics
cannot be inferred from a description of structure.
On a global scale, however, this method does not apply because areas
which appear t o be ecologically equivalent have different floristic
histories. A truly ecological classification would unite the equatorial
forests of Malaysia, Central Africa and Tropical America more closely
than any one of them t o the sub-tropical savannahs adjoining it. A
physiognomic classification would do the same because of the striking
homoplastic evolution of vegetation structure in response to habitat.
A classification based on floristics would, on the other hand, separate
them widely.
These considerations lead t o the conclusion that classification of
communities within one relatively uniform floristic region should be
based on floristic comparison, but that classification on a larger scale
should be based on physiognomic-ecological criteria. For this the
system proposed by Gams in 1918 supplemented by the decisions of the
International Botanical Congress (Du Rietz, 1936) still seem t o be
the most satisfactory.
Taken together these recommend that there should be separate
classifications of synusiae and phytocoenoses. The units of these two
systems, within a uniform floristic region, being as follows.
Synusiae
Phyto- (bio-) coenoses
Society
Sociation
Union
Association
Federation
Alliance
When this system is extended outside a uniform floristic region, the
following concepts and terms are appropriate.
For synusiae : isoecia; abstract units built up of ecologically equivalent but floristically different synusiae of different regions.
For phytocoenoses : isocoenoses ; abstract units built up of floristically
different but ecologically indentical consociations.
E. DEFINITIONS OF UNITS
Definitions of units should be precise so that there is no doubt
whether or not a community falls into a named unit. If we accept the