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Photograph by © WWF-Canon/William F. RODENBURG |
The Southeast Asian
rainforests are the oldest, consistent rainforests on Earth,
dating back to the Pleistocene Epoch 70 million years ago.
It has a biological richness and diversity unequaled by that
of the Amazon or African rainforests. Yet Southeast Asia is
losing its rainforests faster than any equatorial region,
and has the fewest remaining primary rainforests. It is
projected that most of the primary rainforests of Southeast
Asia will be destroyed in the next 10 years. Southeast Asia is a
3,100 mile long chain of about 20,000 islands strung between
Asia and Australia. It covers and area of 1,112,000 square
miles, almost twice the size of Alaska. The area lies from
latitude 20° north and 16° south, and longitude
95° to 105° east. The average daily temperature
varies from 70°F to 90°F. Humidity is always
high. Millions of years
ago, as the rest of the world went through cooling and
warming periods, the climate of the Southeast Asian region
remained more or less the same. This was due mainly because
of its location on the equator and being surrounded by
water. Because the climate on the equator doesn't change
much and the surrounding oceans provide plenty of moisture
in the form of rain, the region was able to have consistent
forests over very long periods of time. As sea levels rose
and fell through warming and icing cycles, small pockets of
forests survived as "forest refugia", or reservoirs of
wildlife from which various species could reestablish
themselves. Malaysia and the islands of Borneo, Sumatra and
Java were all part of the same landmass during the last ice
age. When the glaciers melted and sea levels rose many of
these reservoirs were cut off from each other. This forced
species to developed their own distinctive evolutionary
paths in response to local environments, leading to an
amazing diversity of species of every kind. One interesting
feature of the lowland rainforests of Malaysia, Borneo and
Sumatra is the dominance of one family of trees, the
Dipterocarpaceae. Dipterocarp are emergent trees and can
reach heights of 120 feet. Their crowns are supported on
large straight trunks. Many epiphytes, like orchids and
ferns grow on the trees. Lianas, vines and strangler
figs cling
to the trees as they grow towards the sunlight. The emergent
species is the tualang (Koompassia excelsa)which can
reach heights of 280 feet. It is the 3rd tallest tree
species in the world, and is almost never cut down because
of its hard wood and massive buttresses. But most
importantly it is home to large honey bees (Apis
dorsata)whose honeycombs hang like enormous wedges from
the underside of its branches. These trees are worth more
money when left standing. Trees and shrubs in
the lower canopy have elongated crowns as the leaves reach
for light. Shade tolerant species flourish here. Leaves are
set at the best angle to receive light. Special swollen
joints at the base of the stem, called pulvinus, rotate the
leaf to follow the sun. On the forest floor
the soil is shallow with most nutrients close to the
surface. Leaf litter and dead trees are quickly consumed and
broken down by fungi, insects, and other decomposers. The
nutrients decomposition creates are immediately taken up by
the biomass of the forest. Because the nutrients are close
to the surface, roots don't grow down very far, and trees
have adapted by growing buttressed roots up to 30 ft high,
or stilt roots which hang down from their trunks and
branches. There are many
mutualistic relationships within the ecosystem of the
rainforest. Dawn
Bats are the
prime pollinators of the durian
tree. Each of the hundreds of fig species have their own
species of pollinating wasp (Agaoninae spp), without which
they would quickly fade into extinction and vise versa.
Silvery
Gibbons
(Hylobates moloch)live their entire lives in the high
canopies of the dipterocarp forests, never descending to the
ground. Their survival depends on the dipterocarp and fig
trees which house and feed them throughout the year. Links
within the tropical rainforest ecosystem extend to thousands
of plants which support mammals and birds. If a keystone
species is eliminated, additional losses will be triggered
and create a dominoes effect of extinctions. Trees don't flower
and come into fruit at the same time in the Southeast Asian
rainforest. Some trees only fruit once every three years,
some only every ten year. The short nutrient cycle makes it
difficult for trees to produce large amounts of fruit at
regular intervals. Many trees complete the flowering cycle
in only one day, and are only receptive for a few hours
during the day or night. Very few trees depend on the wind
for pollination since there is little air under the dense
canopy. These trees depend on animals and insects to
pollinate and disperse their seeds. Emergent trees like the
Kapok (Ceiba pentandra), dipterocarps, or Tualang
which can grow to heights of 240 ft, can afford to have
air-borne seeds. Their crowns grow high above the canopy and
are exposed to the winds that blow there. When seeds drop to
the ground they almost always need to germinate in shady
conditions. The forest floor is a difficult place to begin
life, and many seeds surround themselves with fleshy,
aromatic pulp as an immediate source of food. Smell plays an
important part of a plant's life cycle, and many plants will
have strong smelling flowers and fruits. The Rafflesia
smells like a rotting corps, and the durian fruit smells
almost too bad to eat, although it is known as the King of
Fruit and tastes delicious. The powerful smell attract
animals and insects that eat and disperse the seeds far from
their parent tree. Hundreds of animal
and plant species are on the brink of extinction in
Southeast Asia. The critically endangered two-horned
Sumatran
rhinoceros
survives in small forest pockets of Sumatra and Borneo.
Their entire population is thought to be only 300 to 500
individuals. The Javan rhinoceros has already slipped into
extinction. The Sumatran tiger, like its cousin the Javan
tiger will soon be extinct as well. The Asian elephant is
another large forest herbivore which needs large amounts of
forest to survive. Human encroachment and logging are
shrinking their habitat to the extent that they can no
longer support the elephants. The Malayan tapir is the
largest of the 4 species of tapir still alive and no more
than 50 animals still live in the wild. Another animal found
only on Sumatra and Borneo is the orangutan, or "man of the
forest". They were once found on mainland Asia from Thailand
to southern China. They feed mostly on fruit and move
through the forest following the fruiting trees. There are
thirteen separate species of primates in Borneo's lowland
forests alone. Most have overlapping home ranges but have
different diets and foraging methods. The climate of
Southeast Asia is classified as a tropical wet climate in
the Köppen climate zone system. The climate is
influenced by maritime wind systems which originate in the
Indian Ocean and the South China Sea. It has two monsoon
seasons. The northeastern monsoon occurs from October to
February and brings heavy rains to the eastern side of the
islands. These storms carry the same punch as Atlantic
hurricanes but spend much of their energy over the
Phillipines. The southwestern monsoon is more powerful and
occurs from April to August. Heavy rains saturate the
western side of the island chain. Rain shadow effects create
dryer but windy conditions on the opposite sides of the
islands and the Malaysian peninsula during monsoon seasons.
There are two inter-monsoon seasons between the two main
monsoon seasons. Southeast Asian rainforests get an average
of 79 inches of rain annually. Any change in the
monsoon cycle can have devastating results. In 1992-1993 one
of the largest fires ever burned in Kalimantan. Widespread
logging had degraded the primary forest and made it prone to
fire. The drought brought on by the El Niño of that
year created a catastrophe when agricultural fires got out
of control. Twentyseven thousand square km burned out of
control. The same events
unfolded in 1998. The El Niño of that year created a
very weak monsoon season. Thousands of forest fires burned
over Malaysia and the Indonesian archipelago, destroying
rainforests and the plants and animals within them. A haze
of smoke spread for thousands of miles across the region.
Untold mutualistic relationships may have been destroyed,
keystone species eliminated. It is still unclear what
effects the events of 1998 had on the ecosystem of the
rainforests. Unfortunately, in the year 2002 another strong
El Niño is developing over the Pacific. Political
instability in the Indonesian archipelago has resulted in
little law enforcement within protected wildlife areas. In
1992, feeling betrayed by the government of President
Suharto, local people took control of the land and began
indiscriminate logging and farming in the dipterocarp
rainforests. Little regard has been given for the long-term
environmental effects, and at the present rate of
destruction there will be no primary lowland rainforests
remaining in Indonesian Borneo by the next
decade. In Indonesia illegal
logging has led to a "biological catastrophe" affecting
thousands of plant and animal species and upsetting the
natural biologic equilibrium that keeps a rainforest healthy
and stable. The mutualism that sustains numerous species has
been destabilized and could lead to massive extinctions. For
the plants and animals and the myriad species that inhabit
the rainforests of Southeast Asia it may be too late and
there is no "forest refugia" left from which to replenish
their species. Fragmentation of habitats will cause more
interaction of animals with humans, and many animals will be
killed or captured for the pet trade. Huge numbers of
species will become extinct before their role in the
rainforest will have become known, and the rainforest
ecosystem of Southeast Asia will collapse. E. Benders-Hyde
2002
bibliography: "Rainforests",
http://passporttoknowledge.com/rainforest/GEOsystem/Maps/se_asia.html,
(3/18/02). "[Biome - Living
Worlds] :: Rainforest :: Plants", http://library.thinkquest.org/C0113340/text/biomes/biomes.rainforest.plants.html,
(3/18/02). "[Biome - Living
Worlds] :: Rainforest", http://library.thinkquest.org/C0113340/text/biomes/biomes.rainforest.animals.html,
(3/18/02). [Biome - Living
Worlds] :: Impact :: Rainforest :: Social Impact",
http://library.thinkquest.org/C0113340/text/impact/impact.rainforest.html,
(3/18/02). [Biome - Living
Worlds] :: Rainforest :: Climate", http://library.thinkquest.org/C0113340/text/biomes/biomes.rainforest.climate.html,
(3/18/02). "Rainforest Plants",
http://www.zoorainforst.co.nz/plantsprint.html,
(3/18/02). "Earth Floor:
Biomes", http://www.cotf.edu/ete/modules/msese/earthsysflr/rforest.html,
(2/8/02).
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