FAUNA A N D FLORA O F MANGROVE SWAMPS
93
landward fringe of the mangal also contains tall trees-in other words
the rain forest continues into the littoral, but there will be an abrupt
change in species at the level of extreme high water (see Fig. 8). There
may, in fact, be a slight “ salting cliff ” marking the change. Observations in Australia (Macnae, 1966) suggest that such a rain forest mangal
will only develop in areas with a rainfall of over 2 000 mm (80 in) and
then only when there is an appreciable fall during the drier season.
I n Malaya the landward fringe constitutes Watson’s (1928) class
(v), which is inundated by extreme high tides, and the upper part of
his class (iv), inundated by normal high tides. It corresponds also with
de Haan’s (1931) classes A3 and A4. Each of these three shows slight
differences from the others. The forests studied by Watson were
clearly under marine domination and the dominant trees were mangroves. Those studied by de Haan appear to have been less saline for
the trees of the barringtonia racemosa association were dominant.
Watson reports that Bruguiera gymnorhiza may be dominant if the
soil is heavy and wet; and with it may occur old trees of Rhizophora
apiculata, of Xylocarpus moluccensis Roem. and good stands of Intsia
bijuga (Colebr.) 0. Kunz.; lianas and other climbers and also various
epiphytes will be common. Avicennia oficinalis L. is common, occasionally abundant a t this level in South East Asia from the Indus delta
to New Guinea. I n eastern Africa A. marina extends up to this level.
I n the levels reached by normal spring tides Xylocarpus granatum and
Lumnitzera littorea Voigt form large trees : Bruguiera parvijlora W & A
and B. cylindrica may form dense stands and B. sexangula Poir. may
occur with B. cylindrica ; Avicennia lanata Ridl. is also, on the eastern
shores of the Malayan peninsula and on the island of Singapore, characteristic of this level. There is almost always an undergrowth of ferns,
the short Acrostichum speciosum Willd. in shade, and the larger A.
aureum L. in clearings where it may form a stand 3 m high. If the soil
is friable R. apiculata will be dominant. Degraded forests of this sort
occurring just above high water mark in the centre of “mangrove
islands ” off the west coast of Malaya are known to foresters as hutan
darat-dry forest.
De Haan recognizes three variants, firstly a lumnitzera littorea
association which develops on firm shallow soils with banks of marl,
with a very uneven surface. The tree layer is thin with occasional
well-grown trees of Bruguiera gymnorhiza, Lurnnitzera littorea, Xylocarpus granatum, Heritiera littoralis, Ficus microcarpa L. f., Terminalia
catappa L. and Barringtonia racemosa. The undergrowth is a thick
wilderness of Xcyphiphora hydrophyllacea Gaertn. and of Acrostichum
sp. (de Haan does not distinguish between A. aureum and A. speciosum).
93
landward fringe of the mangal also contains tall trees-in other words
the rain forest continues into the littoral, but there will be an abrupt
change in species at the level of extreme high water (see Fig. 8). There
may, in fact, be a slight “ salting cliff ” marking the change. Observations in Australia (Macnae, 1966) suggest that such a rain forest mangal
will only develop in areas with a rainfall of over 2 000 mm (80 in) and
then only when there is an appreciable fall during the drier season.
I n Malaya the landward fringe constitutes Watson’s (1928) class
(v), which is inundated by extreme high tides, and the upper part of
his class (iv), inundated by normal high tides. It corresponds also with
de Haan’s (1931) classes A3 and A4. Each of these three shows slight
differences from the others. The forests studied by Watson were
clearly under marine domination and the dominant trees were mangroves. Those studied by de Haan appear to have been less saline for
the trees of the barringtonia racemosa association were dominant.
Watson reports that Bruguiera gymnorhiza may be dominant if the
soil is heavy and wet; and with it may occur old trees of Rhizophora
apiculata, of Xylocarpus moluccensis Roem. and good stands of Intsia
bijuga (Colebr.) 0. Kunz.; lianas and other climbers and also various
epiphytes will be common. Avicennia oficinalis L. is common, occasionally abundant a t this level in South East Asia from the Indus delta
to New Guinea. I n eastern Africa A. marina extends up to this level.
I n the levels reached by normal spring tides Xylocarpus granatum and
Lumnitzera littorea Voigt form large trees : Bruguiera parvijlora W & A
and B. cylindrica may form dense stands and B. sexangula Poir. may
occur with B. cylindrica ; Avicennia lanata Ridl. is also, on the eastern
shores of the Malayan peninsula and on the island of Singapore, characteristic of this level. There is almost always an undergrowth of ferns,
the short Acrostichum speciosum Willd. in shade, and the larger A.
aureum L. in clearings where it may form a stand 3 m high. If the soil
is friable R. apiculata will be dominant. Degraded forests of this sort
occurring just above high water mark in the centre of “mangrove
islands ” off the west coast of Malaya are known to foresters as hutan
darat-dry forest.
De Haan recognizes three variants, firstly a lumnitzera littorea
association which develops on firm shallow soils with banks of marl,
with a very uneven surface. The tree layer is thin with occasional
well-grown trees of Bruguiera gymnorhiza, Lurnnitzera littorea, Xylocarpus granatum, Heritiera littoralis, Ficus microcarpa L. f., Terminalia
catappa L. and Barringtonia racemosa. The undergrowth is a thick
wilderness of Xcyphiphora hydrophyllacea Gaertn. and of Acrostichum
sp. (de Haan does not distinguish between A. aureum and A. speciosum).