94
WILLIAM MACNAE
A variant of this develops on firm soils of uneven surface. The tree
layer contains Xylocarpus granatum, Heritiera littoralis, Ficus retusa,
Intsia bijuga with Nypa in muddy gullies. The undergrowth is a thick
layer of Derris he~erophylla (Willd.) Back. and Acrostichum sp.
A third variant occurs on moderately firm soils with a tree layer
including Bruguiera sexangula, Dolichandrone spathacea (L.f.) K.
Schum., Barringtonia racemosa, Terminalia catappa, Ficus microcarpa,
Lngerstroemia speciosa Pers., Corypha utan Lam. and along the creeks
X ylocarpus granatum and Oncosperma jilanzentosum B1. A dense
undergrowth comprises Acanthus ilicifolius L., Derris heterophylla,
Acrostichum sp. and Crinum sp.
These three associations seem in some unrecorded way to have been
determined by the nature of the soil and, in addition, show an increasing
dependence on fresh water; they may be considered to be variants
merging into the barringtonia racemosa association as described below
or into peat swamp forest.
The relationship between nature of soil and its associated vegetation
in the mangrove areas is hinted at but not definitely shown by some
unpublished observations made in Sarawak by Anderson (personal
communication). He has demonstrated that, in a transect from the
seaward mangrove fringe to fully developed peat forest, there is a
transition from almost purely mineral soils in the seaward avicennia
fringes, to muck soils (with up to 65% humic material) supporting an
association containing Nypa fruticans, Avicennia officinalis, Acanthus
ilicifolius, Sonneratia caseolaris, Acrostichum sp. and with Bruguiera
sexangula as the dominant tree, and finally into peat soils with around
95% organic matter. These latter occur only just above high water
mark.
Comments relating one species or another to more friable sandy soils
or to clays are common in the literature but without definition of what
is meant.
I n Australia a luxuriant mangal occurs only in the wettest parts of
Queensland between the Hinchinbrook channel and the Daintree
river, and there only on heavy volcanic soils. Its development is not so
lush on quartzitic soils in this same area. In eastern Africa such an
association occurs only at the mouth of the Rufiji delta and on Mafia
Island, where the rainfall is higher than even a few miles inland.
I n north Queensland and in the Rufiji delta the landward fringe
contains specimens of each and every mangrove tree occurring in the
area, no one species is dominant. Most trees are well grown and only a
few saplings are present. This is the area where Heritiera littoralis is
normally to be found both in eastern Africa south to Inhambane and
WILLIAM MACNAE
A variant of this develops on firm soils of uneven surface. The tree
layer contains Xylocarpus granatum, Heritiera littoralis, Ficus retusa,
Intsia bijuga with Nypa in muddy gullies. The undergrowth is a thick
layer of Derris he~erophylla (Willd.) Back. and Acrostichum sp.
A third variant occurs on moderately firm soils with a tree layer
including Bruguiera sexangula, Dolichandrone spathacea (L.f.) K.
Schum., Barringtonia racemosa, Terminalia catappa, Ficus microcarpa,
Lngerstroemia speciosa Pers., Corypha utan Lam. and along the creeks
X ylocarpus granatum and Oncosperma jilanzentosum B1. A dense
undergrowth comprises Acanthus ilicifolius L., Derris heterophylla,
Acrostichum sp. and Crinum sp.
These three associations seem in some unrecorded way to have been
determined by the nature of the soil and, in addition, show an increasing
dependence on fresh water; they may be considered to be variants
merging into the barringtonia racemosa association as described below
or into peat swamp forest.
The relationship between nature of soil and its associated vegetation
in the mangrove areas is hinted at but not definitely shown by some
unpublished observations made in Sarawak by Anderson (personal
communication). He has demonstrated that, in a transect from the
seaward mangrove fringe to fully developed peat forest, there is a
transition from almost purely mineral soils in the seaward avicennia
fringes, to muck soils (with up to 65% humic material) supporting an
association containing Nypa fruticans, Avicennia officinalis, Acanthus
ilicifolius, Sonneratia caseolaris, Acrostichum sp. and with Bruguiera
sexangula as the dominant tree, and finally into peat soils with around
95% organic matter. These latter occur only just above high water
mark.
Comments relating one species or another to more friable sandy soils
or to clays are common in the literature but without definition of what
is meant.
I n Australia a luxuriant mangal occurs only in the wettest parts of
Queensland between the Hinchinbrook channel and the Daintree
river, and there only on heavy volcanic soils. Its development is not so
lush on quartzitic soils in this same area. In eastern Africa such an
association occurs only at the mouth of the Rufiji delta and on Mafia
Island, where the rainfall is higher than even a few miles inland.
I n north Queensland and in the Rufiji delta the landward fringe
contains specimens of each and every mangrove tree occurring in the
area, no one species is dominant. Most trees are well grown and only a
few saplings are present. This is the area where Heritiera littoralis is
normally to be found both in eastern Africa south to Inhambane and