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Hevea brasiliensis is a tropical tree. It is native to
the Amazon Basin in Brazil and adjoining countries. In the
early stages (that is up to about 1910) most rubber was
harvested from "wild trees" growing in the Amazon
Basin and to a lesser extent from other natural sources
of natural rubber (such as Ficus elastica) growing in the
Congo Basin of Africa. Hevea was taken from the Amazon to
South Asia (Sri Lanka) and South East Asia (Singapore and
Malaysia) by the British Colonial Office where it was grown
experimentally and later on plantations (see history). Subsequently,
cultivation spread to what was then Indochina (Vietnam and
Cambodia), the Dutch East Indies (Indonesia) and Thailand,
and subsequently to Africa (Liberia, Nigeria, Cote d'Ivoire).
Initially cultivation took place on plantations, but smallholders
rapidly adopted it as a source of income.
Climatic factors
Hevea brasiliensis is a tropical tree. It grows best at
temperatures of 20-28°C with a well-distributed annual
rainfall of 1,800-2,000 mm. It grows satisfactorily up to
600 metres above sea level (but is capable of growing much
higher - to at least 1000 metres near the Equator), and
will perform on most soils provided drainage is adequate.
Hevea tends to be damaged by high winds. Its required temperature
and rainfall define its prime growing area as between the
10° latitudes on either side of the equator, but is
cultivated much further north (Guatemala, Mexico and China)
and south (Sao Paulo region of Brazil). Further discussion
on environmental factors is available.
Maturity
Mature Hevea trees on rubber plantations are 20-30 metres
high, with graceful upwards-extending branches and a relatively
slim trunk. Such trees flower once a year, and after insect
cross-pollination produce large fruits containing several
thimble-sized seeds with hard outer coats. If satisfactorily
germinated and planted within 2-3 weeks, seeds grow to produce
seedling plants. Depending on conditions, the latter then
take 5-10 years to reach 'maturity', which is defined as
the stage when tapping can be started. In practice, this
is the time when the trunk has about 500 mm circumference
at 1 metre above ground level.
Biosynthesis
Hevea trees convert inorganic nutrients from the soil,
and carbon dioxide from the atmosphere, into organic carbohydrates
which are then turned into rubber latex. The latter passes
up the tree through millions of capillary vessels or tubes
located in the soft outer bark.
Wintering
At least once a year the leaves of the tree, which are
the sites of carbohydrate formation, die and fall off in
wintering, and new leaves are formed. During wintering,
which lasts for sixteen weeks, the metabolism of the tree
and the constitution of its latex are substantially affected.
The yield is also reduced, and this, together with other
climatic factors, accounts for marked seasonal variations
in NR production in producing countries.
Further pages:
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