114
WILLIAM MACNAE
East Asia A . marina (known locally as A . intermedia) occurs on the
seaward fringe of a mangal facing the sea rather than a channel, creek
or river.
Since these beaches face
seaward and are exposed to light wave action the substratum is
relatively firm. Behind, this passes into a forest of Bruguiera cylindrica.
Along the entrance to channels, etc., A. marina gives way to A . alba
and since wave action is less the substratum is very soft. I n the area of
overlap individual trees may be difficult to identify as one species or
the other. Behind the forest of A . alba, one finds a forest of Rhizophora
mucronata.
I n India, around Bombay, only A . alba is present and it occupies the
entire, or almost the entire, mangal. The trees are kept short by cutting
and the young branches fed to water buffalo.
I n the absence of A . alba, A. marina occupies the entire seaward
fringe.
Moldenke (1960) recognizes a third species in this ecological group,
Avicennia eucalyptifolia Zipp. ex Miq., and most of the localities from
which he records this species are in the vicinity of coral reefs (Fig. 26)
or off-shore coral islands from the Philippines to Queensland.
On stable coasts the seaward avicennia fringe is very narrow, often
only one to three trees deep. On accrescent coasts it may be more
than 4 km (4 mile) wide. This is the case on many shores along the
Straits of Malacca and parts of Borneo and New Guinea. On such
shores seedlings of A. marina or of A . alba colonize the new banks of
alluvium, develop into saplings, young trees and finally a well-developed
orchard of tall avicennia trees under the shelter of which seedlings of
species of Rhizophora develop.
The substratum is firmer than the mud banks in front. This
firmness is due to the dense mat of nutritive roots lying some 10-35 cm
below the surface. Anderson (unpublished data) has shown that in
Sarawak the alluvium on which these avicennia trees develop is
deficient in organic material which represents only 5-15% of the soil
content.
On the shore of Trinity Bay near Cairns in north Queensland
saplings of Aegiceras corniculaturn occurred with the saplings of
Avicennia marina. At this level a considerable quantity of seepage
water came out on to the beach, and presumably kept the salinity of
the soil water within the range preferred by Aegiceras (Macnae, 1966).
The thickets of saplings and seedlings extend down almost to mean
sea-level. At the lower levels many seedlings get coated with fine silt,
deposited by the tide-these seedlings die. Seedlings and saplings of
Avicennia cannot grow well under conditions of shade. Macnae (1963)
On such beaches it is a pioneer.
WILLIAM MACNAE
East Asia A . marina (known locally as A . intermedia) occurs on the
seaward fringe of a mangal facing the sea rather than a channel, creek
or river.
Since these beaches face
seaward and are exposed to light wave action the substratum is
relatively firm. Behind, this passes into a forest of Bruguiera cylindrica.
Along the entrance to channels, etc., A. marina gives way to A . alba
and since wave action is less the substratum is very soft. I n the area of
overlap individual trees may be difficult to identify as one species or
the other. Behind the forest of A . alba, one finds a forest of Rhizophora
mucronata.
I n India, around Bombay, only A . alba is present and it occupies the
entire, or almost the entire, mangal. The trees are kept short by cutting
and the young branches fed to water buffalo.
I n the absence of A . alba, A. marina occupies the entire seaward
fringe.
Moldenke (1960) recognizes a third species in this ecological group,
Avicennia eucalyptifolia Zipp. ex Miq., and most of the localities from
which he records this species are in the vicinity of coral reefs (Fig. 26)
or off-shore coral islands from the Philippines to Queensland.
On stable coasts the seaward avicennia fringe is very narrow, often
only one to three trees deep. On accrescent coasts it may be more
than 4 km (4 mile) wide. This is the case on many shores along the
Straits of Malacca and parts of Borneo and New Guinea. On such
shores seedlings of A. marina or of A . alba colonize the new banks of
alluvium, develop into saplings, young trees and finally a well-developed
orchard of tall avicennia trees under the shelter of which seedlings of
species of Rhizophora develop.
The substratum is firmer than the mud banks in front. This
firmness is due to the dense mat of nutritive roots lying some 10-35 cm
below the surface. Anderson (unpublished data) has shown that in
Sarawak the alluvium on which these avicennia trees develop is
deficient in organic material which represents only 5-15% of the soil
content.
On the shore of Trinity Bay near Cairns in north Queensland
saplings of Aegiceras corniculaturn occurred with the saplings of
Avicennia marina. At this level a considerable quantity of seepage
water came out on to the beach, and presumably kept the salinity of
the soil water within the range preferred by Aegiceras (Macnae, 1966).
The thickets of saplings and seedlings extend down almost to mean
sea-level. At the lower levels many seedlings get coated with fine silt,
deposited by the tide-these seedlings die. Seedlings and saplings of
Avicennia cannot grow well under conditions of shade. Macnae (1963)
On such beaches it is a pioneer.