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Bakau
Rhizophora sp.
Family Rhizophoraceae
Bakau is a common mangrove tree on Chek Jawa. Bakau can be immediately
recognised by its arching prop and stilt roots. It grows best in wet,
muddy and silty sediments.
Stilt and Prop Roots: Bakau has
stilt and prop roots. These roots not only hold up the tree in soft
mud, but also absorb air and thus help the tree to breathe. The roots
also have special ultrafiltration membranes to exclude salt so that
the water absorbed is less salty. Any salt that does get through is
stored in old leaves which are then shed.
Dotty Leaves: Bakau leaves are
thick and waxy to store and conserve water. Bakau leaves have tiny
black dots on the underside, while other mangrove trees with similarly-shaped
leaves do not.
Flowers: Bakau flowers have white
thick sepals and delicate petals which wither away quickly. The flowers
are wind-pollinated and thus have no fragrance but produce lots of
powdery pollen. Bakau is also self-pollinating.
Long Seedlings: The fruit does
not fall away when it ripens. Instead, the single seed within the
fruit starts to germinate while it is still on the mother tree, and
the mother tree channels nutrients to the growing seedling (vivipary).
The seedling forms a stem (called a hypocotyl). When the seedling
finally falls, at first it floats horizontally, and drifts with the
tide. It can survive for long periods at sea. After some weeks, the
tip gradually absorbs water and the seedling floats vertically and
starts to sprout its first leaf from the top, while tiny roots grow
from the bottom. When it hits mud, it grows more roots to anchor itself
upright, and then more leaves. Bakau seedlings grow tall rapidly to
avoid being submerged at high tide. They can grow by 60cm in the first
year.
Two species of Bakau are common on Chek Jawa.
Bakau minyak (Rhizophora apiculata)
has a red stipule and reddish leaf stalk.
Bakau kurap (Rhizophora mucronata)
has a whitish stipule. Its Malay name refers to the pimply skin of
the seedling: 'kurap' means 'warty'.
Role in the habitat: Its arching
stilt and prop roots provides plenty of living spaces for other plants
and animals in the mangroves. At high tide, you can be sure to see
mudskippers and crabs clinging onto the roots.
Human uses: Bakau is well used
by traditional coastal communities. It is said that the young shoots
can be eaten and the juice made into wine. But honey collected from
the flowers is said to be poisonous. The timber is heavy, difficult
to saw and not durable unless it is dried for a long time. Nevertheless,
it is used for construction, to make fish traps, house frames, pilings
and poles. In Singapore in the past, Bakau poles were used extensively
as scaffolding for building construction and renovations. Bakau wood
is the preferred mangrove wood for firewood and to make charcoal.
It produces an even heat and is easy to split for firewood. It is
also chipped and used in commercial paper and rayon production in
Indonesia and East Malaysia. Tannins are extracted from the bark;
a black to chestnut dye is obtained from the leaves. Bakau is fast
growing and thus often used to replant mangroves either for conservation
or as part of a managed forest to produce timber for construction
or charcoal. Bakau is also used extensively in traditional medicines.
Various parts of the tree is used to treat digestive problems, bleeding
and other ailments.
Status and threats: Unlike some
other mangrove trees, new growths from Bakau trees only emerge from
branch tips and not the trunk. So they can be killed by excessive
collection of branches for firewood or other uses. Although Bakau
is still commonly seen in our mangroves, the mangroves as an ecosystem
is threatened by development, reclamation and other destructive human
activities. |
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Stilt
and prop roots
Bakau minyak
R. apiculata
has red stipules
Flower of
Bakau kurap
R. mucronata
Seedling of
Bakau kurap
Long seedlings of Bakau Kurap |
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quick
facts
To about 25m tall, stilt and prop roots, common in the mangroves
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