170
become more and more important. These are
accompanied by Ceratophyllum demersum and
often by species of Myriophyllum, Najas,
Vallisneria , etc. Further, when marked eutrophication results from pollution by sewage or
from run-off from fertilised agricultural land,
an increase in phytoplankton leads to a decrease
in transparency. There is also consequent compression of the zonation of macroscopic plants.
Mosses and, perhaps, Charophyceae tend to
disappear.
8.3.3 Relationship of Size
of Individuals to Density
of Populations
In Lake Taltowisko, Bernatowicz and Pieczyn’ska
( 1965 ) had found a clear negative relationship
between the weight of the stem of Phragmites
australis and the density of the population.
8.3.4 Illumination
The maximum depth at which autotrophic AM
can grow, irrespective of their nature, clearly
does depend on the transparency of the water.
However, the fact that no autotrophic plants
will occur below their biogeochemical compensation points does not mean that the zonation is necessarily determined solely by light
penetration
8.4
Phytosociology
The associations of plants in lakes and wetlands
have been classifi ed according to the methods of
the various schools of plant sociology. These
classifi cations do permit the characterization of
certain complex entities which can be recognised
as occurring over and over again in different
localities or regions.
The fi rst of these schools is the European or,
more strictly, the Zurich–Montpellier approach
associated with Braun-Blanquet and had been
used extensively for aquatic communities by
Koch ( 1926 , 1928 ), Krausch ( 1964 ), etc.
The second is the North American approach
associated with Clements ( 1916 ) and adapted by
Pearsall ( 1918b ) in English Lakes and, in a more
modern form, in an important study of the
Scottish lochs by Spence ( 1964 ).
8.4.1 The Continental European
Approach
It could be said that the basic vegetational unit
is the ‘association’. It is distinguished by dominant species and by rarer species of high fi delity. It is also distinguished by its physiognomy
or overall general appearance and by the life
forms, relative to the seasonal cycle, of the
important plants present.
Oberdorfer ( 1957 ) reported about two associations, namely, the Wolffi io-Lemnetum gibbae
or Lemno-Spirodeletum of somewhat varying
composition, with a variant, and the LemnoSpirodeletum salvinietosum where Salvinia is
signifi cantly present. On the other hand, Muller
and Görs ( 1960 ) had recognised eight associations, which include the larger pleuston of the
Hydrocharitetum morsus-ranae .
8.4.2 The Clements–Pearsall
Approach
The detailed use of the continental system had
not appealed to the English-speaking ecologists. As such, the most eminent student of synecology of lacustrine plants, namely, Pearsall
( 1917 , 1918a , b , 1920 ), had based his approach
and terminology on that of Clements ( 1916 ).
All the plant communities of a lake are regarded
as serial stages of a hydrarch succession, progressing landward from the vegetation of the
deepest part of the euphotic zone through the
various infralittoral, eulittoral and fully terrestrial communities until the local climax is
reached. Zonation may, therefore, be considered to be a spatial equivalent of succession in
8 Aquatic Macrophytes in Lakes
become more and more important. These are
accompanied by Ceratophyllum demersum and
often by species of Myriophyllum, Najas,
Vallisneria , etc. Further, when marked eutrophication results from pollution by sewage or
from run-off from fertilised agricultural land,
an increase in phytoplankton leads to a decrease
in transparency. There is also consequent compression of the zonation of macroscopic plants.
Mosses and, perhaps, Charophyceae tend to
disappear.
8.3.3 Relationship of Size
of Individuals to Density
of Populations
In Lake Taltowisko, Bernatowicz and Pieczyn’ska
( 1965 ) had found a clear negative relationship
between the weight of the stem of Phragmites
australis and the density of the population.
8.3.4 Illumination
The maximum depth at which autotrophic AM
can grow, irrespective of their nature, clearly
does depend on the transparency of the water.
However, the fact that no autotrophic plants
will occur below their biogeochemical compensation points does not mean that the zonation is necessarily determined solely by light
penetration
8.4
Phytosociology
The associations of plants in lakes and wetlands
have been classifi ed according to the methods of
the various schools of plant sociology. These
classifi cations do permit the characterization of
certain complex entities which can be recognised
as occurring over and over again in different
localities or regions.
The fi rst of these schools is the European or,
more strictly, the Zurich–Montpellier approach
associated with Braun-Blanquet and had been
used extensively for aquatic communities by
Koch ( 1926 , 1928 ), Krausch ( 1964 ), etc.
The second is the North American approach
associated with Clements ( 1916 ) and adapted by
Pearsall ( 1918b ) in English Lakes and, in a more
modern form, in an important study of the
Scottish lochs by Spence ( 1964 ).
8.4.1 The Continental European
Approach
It could be said that the basic vegetational unit
is the ‘association’. It is distinguished by dominant species and by rarer species of high fi delity. It is also distinguished by its physiognomy
or overall general appearance and by the life
forms, relative to the seasonal cycle, of the
important plants present.
Oberdorfer ( 1957 ) reported about two associations, namely, the Wolffi io-Lemnetum gibbae
or Lemno-Spirodeletum of somewhat varying
composition, with a variant, and the LemnoSpirodeletum salvinietosum where Salvinia is
signifi cantly present. On the other hand, Muller
and Görs ( 1960 ) had recognised eight associations, which include the larger pleuston of the
Hydrocharitetum morsus-ranae .
8.4.2 The Clements–Pearsall
Approach
The detailed use of the continental system had
not appealed to the English-speaking ecologists. As such, the most eminent student of synecology of lacustrine plants, namely, Pearsall
( 1917 , 1918a , b , 1920 ), had based his approach
and terminology on that of Clements ( 1916 ).
All the plant communities of a lake are regarded
as serial stages of a hydrarch succession, progressing landward from the vegetation of the
deepest part of the euphotic zone through the
various infralittoral, eulittoral and fully terrestrial communities until the local climax is
reached. Zonation may, therefore, be considered to be a spatial equivalent of succession in
8 Aquatic Macrophytes in Lakes