FAUNA AND FLORA OF MANGROVE SWAMPS
97
shores. These two plants also occur together in the lagoons of small
rivers in southern Natal, just behind the coastal dunes through which
the rivers break, when occasional floods raise the level in the lagoon
sufficiently (personal observation).
b. The nypa association
The nypa association constitutes one of the most important, and
from the air most conspicuous, features of the mangal throughout the
Indo-Malaysian and South East Asiatic regions (Fig. 10). It occupies
extensive, often very extensive, areas in the region flooded by the
highest spring tides (Fig. 19). A notable feature of the area occupied
by the association is the large number of huge (up to 3 m high) mounds
of Thalassina anomala and these affect considerably the facies shown
by the association.
When nypa is very dense there may be little else, for other plants
are shaded out. I n such an area the palms present a veritable wall
along the banks of rivers or creeks. Occasional trees of Heritiera
littoralis, of Xylocarpus granutus, X . moluccensis, Bruguiera sexangula,
B. gymnorhixa or of Lumnitzera littorea may stand out conspicuously
at higher levels and trees of Rhixophora apiculata a t only fractionally
lower levels. Excoecaria agallocha, Bruguiera cylindrica and Sonneratia
caseoluris are frequent associates. Hibiscus tiliaceus and species of
Pandanus will also occur in places where the water is almost fresh.
The mounds cast up by Thalassina often reach heights above high
water mark. At levels where they may occasionally be flooded they are
colonized by Acrostichum speciosum and by the lianas Clerodendron
inerme (L.) Gaertn., Cynanchum carnosum Hort., Entada scheferi Ridl.
( ? = E. phaseoloides) as well as by rotans, Calamus aquatilis Ridl. and
these will sprawl over the trees rather than over the nypa of which the
slippery leaves seem to offer little to grasp.
At higher levels terrestrial plants may colonize. I have seen a
juvenile coconut tree on such a mound in the Sarawak river delta.
Because of its uses to man as thatch and for various other purposes
including sugar production, the nypa association is often kept artificially clear. Though not in the usual sense of the word cultivated, it is
cared for and as a result of leaf cutting access between palms is easier.
Usually the creeks and rivers are lined by a dense wall of the palms
but various mangroves may develop between ; these include Avicennia
oficinalis, Kandelia Icandel, Brownlowia tersa (L.) Kost., Aegiceras
corniculatum and most characteristically, Sonneratia caseolaris.
The ecotone or zone of passage between the nypa association and the
freshwater swamp forest is often indicated by a narrow and continuous
97
shores. These two plants also occur together in the lagoons of small
rivers in southern Natal, just behind the coastal dunes through which
the rivers break, when occasional floods raise the level in the lagoon
sufficiently (personal observation).
b. The nypa association
The nypa association constitutes one of the most important, and
from the air most conspicuous, features of the mangal throughout the
Indo-Malaysian and South East Asiatic regions (Fig. 10). It occupies
extensive, often very extensive, areas in the region flooded by the
highest spring tides (Fig. 19). A notable feature of the area occupied
by the association is the large number of huge (up to 3 m high) mounds
of Thalassina anomala and these affect considerably the facies shown
by the association.
When nypa is very dense there may be little else, for other plants
are shaded out. I n such an area the palms present a veritable wall
along the banks of rivers or creeks. Occasional trees of Heritiera
littoralis, of Xylocarpus granutus, X . moluccensis, Bruguiera sexangula,
B. gymnorhixa or of Lumnitzera littorea may stand out conspicuously
at higher levels and trees of Rhixophora apiculata a t only fractionally
lower levels. Excoecaria agallocha, Bruguiera cylindrica and Sonneratia
caseoluris are frequent associates. Hibiscus tiliaceus and species of
Pandanus will also occur in places where the water is almost fresh.
The mounds cast up by Thalassina often reach heights above high
water mark. At levels where they may occasionally be flooded they are
colonized by Acrostichum speciosum and by the lianas Clerodendron
inerme (L.) Gaertn., Cynanchum carnosum Hort., Entada scheferi Ridl.
( ? = E. phaseoloides) as well as by rotans, Calamus aquatilis Ridl. and
these will sprawl over the trees rather than over the nypa of which the
slippery leaves seem to offer little to grasp.
At higher levels terrestrial plants may colonize. I have seen a
juvenile coconut tree on such a mound in the Sarawak river delta.
Because of its uses to man as thatch and for various other purposes
including sugar production, the nypa association is often kept artificially clear. Though not in the usual sense of the word cultivated, it is
cared for and as a result of leaf cutting access between palms is easier.
Usually the creeks and rivers are lined by a dense wall of the palms
but various mangroves may develop between ; these include Avicennia
oficinalis, Kandelia Icandel, Brownlowia tersa (L.) Kost., Aegiceras
corniculatum and most characteristically, Sonneratia caseolaris.
The ecotone or zone of passage between the nypa association and the
freshwater swamp forest is often indicated by a narrow and continuous