126
WILLIAM MACNAE
The shore profile may also affect the manner of deposition of silt,
etc., carried in suspension by the tide, and so control the distribution
of animals and plants.
All shores of sand or mud show a tendency to flatten out at one or
more intertidal levels. I n regions with a large intertidal range there is
usually a succession of flats at different levels. This phenomenon has
been shown by Macnae and Kalk (1962) to influence the apparent
distribution of plants and animals across the flats at Inhaca, off
Lourenqo Marques, and Macnae (1966) (Fig. 31) has shown an extreme
example at and near St. Lawrence in the Broad Sound region of central
Queensland.
I n many mangrove-bearing coasts visited by the author the same
peculiarity is evident. On coasts where material is accruing one
normally will find a continuity of slope downwards from the landward
fringe to the seaward edge of the mangal. But on others there seems to
have been an alternation of periods of accretion and periods of erosion.
This naturally gives rise to a differentiation in levels. I n such areas,
as for example on the northern shores of Pulau Ketani off Port Swettenham, this will result in a bruguiera forest coming up against a fringe of
Sonneratia colonizing a new lower level (Fig. 32).
Such an easy explanation is not always offered. I n Sandakan Bay,
north Borneo, as much as three-quarters of the mangal is occupied by
a forest dominated by Rhizophora apiculata. Only a narrow zone
dominated by Bruguiera parvi$ora with Ceriops tagal and Xylocarpus
granatum and with a few scattered bushes of N y p a fruticans and fewer
trees of Heritiera littoralis intervenes between the rhizophora forest
and the local facies of rain forests growing on sloping ground.
This pattern is also shown within the mangals along the western
coast of peninsular Thailand between Ranong and Phangnga. Here
Ceriops tagal and C. decandra are more abundant in the understorey
than is Rruguiern parvi$ora.
I n these areas the shore has tended to flatten out at the level of the
rhizophora forests and here only, for the landward fringe and the
seaward fringes are quite narrow.
In the estuary of the Lubok river west and slightly north of Sandakan Bay and in other places in Borneo extensive nypa swamps occur in
addition to, and following directly on, the rhizophora forests (Figs. 9
and 10). Here, then, the apparent flattening of the shore has extended
into a zone under more marked freshwater domination.
Along much of the west coast of Malaya the widest zones in the
mangal are the zones of bruguiera forests which are separated from the
sea by avicennia or sonneratia fringes.
WILLIAM MACNAE
The shore profile may also affect the manner of deposition of silt,
etc., carried in suspension by the tide, and so control the distribution
of animals and plants.
All shores of sand or mud show a tendency to flatten out at one or
more intertidal levels. I n regions with a large intertidal range there is
usually a succession of flats at different levels. This phenomenon has
been shown by Macnae and Kalk (1962) to influence the apparent
distribution of plants and animals across the flats at Inhaca, off
Lourenqo Marques, and Macnae (1966) (Fig. 31) has shown an extreme
example at and near St. Lawrence in the Broad Sound region of central
Queensland.
I n many mangrove-bearing coasts visited by the author the same
peculiarity is evident. On coasts where material is accruing one
normally will find a continuity of slope downwards from the landward
fringe to the seaward edge of the mangal. But on others there seems to
have been an alternation of periods of accretion and periods of erosion.
This naturally gives rise to a differentiation in levels. I n such areas,
as for example on the northern shores of Pulau Ketani off Port Swettenham, this will result in a bruguiera forest coming up against a fringe of
Sonneratia colonizing a new lower level (Fig. 32).
Such an easy explanation is not always offered. I n Sandakan Bay,
north Borneo, as much as three-quarters of the mangal is occupied by
a forest dominated by Rhizophora apiculata. Only a narrow zone
dominated by Bruguiera parvi$ora with Ceriops tagal and Xylocarpus
granatum and with a few scattered bushes of N y p a fruticans and fewer
trees of Heritiera littoralis intervenes between the rhizophora forest
and the local facies of rain forests growing on sloping ground.
This pattern is also shown within the mangals along the western
coast of peninsular Thailand between Ranong and Phangnga. Here
Ceriops tagal and C. decandra are more abundant in the understorey
than is Rruguiern parvi$ora.
I n these areas the shore has tended to flatten out at the level of the
rhizophora forests and here only, for the landward fringe and the
seaward fringes are quite narrow.
In the estuary of the Lubok river west and slightly north of Sandakan Bay and in other places in Borneo extensive nypa swamps occur in
addition to, and following directly on, the rhizophora forests (Figs. 9
and 10). Here, then, the apparent flattening of the shore has extended
into a zone under more marked freshwater domination.
Along much of the west coast of Malaya the widest zones in the
mangal are the zones of bruguiera forests which are separated from the
sea by avicennia or sonneratia fringes.