Battle for the Light
In Southern Asia’s lush forests one remarkable group of trees cast their pervasive shadows over the extraordinary array of plants and animals living below.
At the Equator dawn arrives with astonishing speed. In the rainforests of Sumatra and Borneo, it’s the tops of giant dipterocarp trees which catch the first rays of intense sunlight. After 12 hours darkness the abrupt return of the light is greeted by the operatic displays of the gibbons; just part of a dawn chorus as varied and overpowering as any on the planet.
Nurtured by equatorial heat and year-round rainfall, the forest stretches up to 80 metres tall. The huge canopy trees have straight pillar-like trunks and umbrella-shaped crowns, which influence all the lives below. Not only do these “selfish giants” catch much of the sunlight and monopolise the nutrients from the forest floor; their leaves produce poisons making them unpalatable. So their massive resources are locked away from most forest creatures. What’s more the gaps between their gigantic trunks create aerial canyons that must be crossed – in astounding ways. These forests are home to acrobatic apes, leaping lizards and gliding squirrels – all precisely adapted to travelling amongst the forest giants. The much heavier orangutans must use their strength to flex saplings and pole vault across the gaps.
Beneath the dipterocarps, fruiting trees proliferate using very different tactics. Tropical fig trees invest their extra energy to produce a rich harvest, feeding a procession of birds and primates in return for some seed scattering. Equatorial Asia is home to many tasty and pungent smelling fruits like the infamous durian, whose odour attracts orangutans and elephants from great distances. A rain of
half-eaten smaller fruits, dropped by monkeys, benefits a surprising range of forest floor dwellers – from bearded pigs to the rare Sumatran rhino and even fresh water fish. The abundance of the fruit scavengers in turn provide prey for the shy fishing cat and the mighty tiger.
For bottom-dwelling plants, the greatest struggle is to obtain enough light on the gloomy forest floor. Only 2 percent of the powerful equatorial sunlight makes it this far.
Forest floor plants are superbly adapted to capture the weakest rays of scattered light. Once a forest giant falls, creating a light gap, the battle for light becomes more obvious. Dormant seedlings spring in to action, surging upwards until new foliage closes the light gap. The window of opportunity passes.
After dark the dipterocarp forest’s most mysterious resident emerges. The colugo has strange elastic skin membranes between its limbs and tail, enabling it to glide 120 metres, easily crossing forest gaps and avoiding ground predators. Not only has it conquered the aerial canyons, the colugo appears to have conquered the selfish giants poisons as well, feeding on tender leaf tips and sap from their mighty trunks. Perhaps the colugo is the creature best adapted to life in the shadows of the forest giants of equatorial Asia.