Episode one - Tropical Worlds

More kinds of plants are crammed together in the tropical forests than anywhere else on earth. The result is beauty and intense competition - a plant battleground.

Most plants live high in the canopy. The upper branches of giant trees support magical sky gardens, where an almost infinite variety of flowers compete for the attention of hummingbirds and insects.

Plants need light but the forest floor is dark. When an old tree falls, sunlight floods in, firing the starting gun on a race for the canopy. Seedlings battle with lassoes, grappling hooks and giant leaves, which cast others into the shade. In this episode Sir David Attenborough visits South America to see the Balsa Tree, which grows several metres a year, sacrificing strength for fast growing, brittle wood.

Plants use leaves to capture light and carbon dioxide, which they turn into food. But leaves attract leaf-eaters. The greatest is an underground fungus. It enlists an army of ants to march out, chop up leaves and bring them back, to create a mulch which it feeds off. Plants retaliate by flooding their leaves with toxins.

When it comes to reproduction, the short-lived Balsa Tree outcompetes the rest, growing huge flowers brimming with super-strength nectar, irresistible to animal pollinators. The parasitic Corpse Flower is irresistible too - but only to flies. It mimics a dead animal, down to its teeth, hair and foul stench.

Tropical forests even create their own weather. Fungi release spores - tiny reproductive grains - a billion per square metre, which attract moisture as they float above the forest. The result? Most raindrops in a tropical forest have a fungal spore at their heart.

Today tropical forests are being chopped into ever smaller fragments, each a fragile reservoir of diversity. Yet there is hope. Left to its own devices tropical forest can recover. Grazing land left to regrow in Costa Rica has, in 20 years, become forest again, rejoining many fragments.

Key stories

New / Remarkable behaviour

Fight For Light - new technologies gives us a more detailed and dynamic experience of plant battles than ever before.

The battle between plants after a giant tree falls and light hits the forest floor.

New / Remarkable behaviour

Fungus/leaf cutter ants – new technologies made this possible to capture

The biggest leaf eater in the forest is a fungus, which lives underground. Leaf cutter ants do its bidding, going out and cutting fragments of leaf which the ants bring back for the fungus. The attacked plants then fight back by releasing toxins into their leaves that the fungus doesn’t like and tells the ants to collect from a different plant.

New / Remarkable behaviour

A bat and a flower are tied together in mutual dependency - this has never been filmed before.

The bat is a nectar feeder and for a large part of the year the seven-hour flower is the only source of nectar. Equally the bat is the flowers only pollinator. Each flower only provides a little nectar, forcing the bat to travel through the forest visiting many flowers (and pollinating them) every night.

Rafflesia

A parasitic plant without leaves or even a stem. This plant plugs into a vine and takes all it needs from it. It grows a huge bud for several years. Eventually it opens out into the world’s biggest flower that will last just one night. Its texture and colour mimics an animal carcass and it smells like one too. This attracts carrion flies, that crawl around inside it, looking for meat to lay their eggs on. In the process they get a dollop of pollen stuck on their backs, which they carry to another flower, so pollinating it.

Fungi

This is both a plant’s greatest ally in the forest and a great enemy. Fungi break down dead plants and release nutrients that living plants need to grow. However some fungi also attack and kill plants. But the most remarkable things fungi do is create rain. Each fungus releases thousands of spores which float through and over the rain forest. They attract moisture until this falls as rain. 90% of tropical raindrops have a fungal spore at their heart.

Filming locations

Danum Valley, Borneo - Dipterocarps

A private reserve on the edge of Mount Kinabalu NP Borneo - Raflessia

La Selva Biological Station and Reserve, Costa Rica - Leaf Cutter Ants

Osa conservation reserve, Osa Peninsular, Costa Rica - Balsa Tree

Private reserve in the Heredia province, Costa Rica - Glowing Fungus

Filmed species

Balsa
Kinkajou
Vine in fight for light
Fungus
Leaf cutter ant
Rafflesia
Orchids various
Dipterocarp
Underwoods’ bat and seven-hour flower

Behind the scenes

On location in Borneo filming the masting dipterocarps in Danum Valley, the crew accidentally disturbed a nest of Asian Giant Hornets. The swarm attacked the crew and one of our researchers was stung three times.

In Costa Rica, the Tropical Worlds team spent three weeks in the same spot watching their camera take several thousand shots of leaf cutter ants.