The Emerald Band
Rainforest Network
In Asia, rainforests cover hundreds of islands – some small, some vast.
New Guinea, Java, Sumatra. Amongst them, some of the remotest places on the planet. Across the Indian Ocean, Africa and the rainforests of the Congo
Basin. Farther west still and we reach the Americas, home to the Amazon rainforest, the largest unbroken expanse of trees in the tropics. Together,
these jungles form an Emerald band that circles our globe.
The Emerald Band
Here on the equator, there are virtually no seasons. It's hot and wet all year round. Humidity barely drops below 90%… and the sunlight is more
intense than anywhere else on the planet, day in and day out. All of this rain and all of this sun results in a phenomenon on a scale unseen
anywhere else.
It's happening here, in these leaves, in all of these billions of leaves. and even if you're a really hard-nosed biologist, really pragmatic about
life, it's nothing short of miraculous.
It's the chemical process of photosynthesis. What plants are doing is combining two very abundant ingredients – carbon dioxide in the air, and water. Two
ingredients that are almost impossible to combine.
If we take carbon dioxide and water and mix them together, even under great pressure, all we get is fizzy water. On the other hand, when plants mix
carbon dioxide and water, they get something else. They get food. They get sugar. More of these sugars are produced an a given area of rainforest
than in any other habitat because of the sheer quantities of water and solar energy. In fact, the energy captured by rainforests in one year alone
could power the UK for over a million years.
All of that energy is turned into food, quite literally out of thin air. It's a bit like the botanical equivalent of turning water into wine.
Photosynthesis might explain why we have so much life here. But it doesn't explain why there are so many different types of life.
There's one very special animal that I'd like you to meet. She's a leafcutter ant, and she's an ant with a challenge. You see, her problem is that
she can't digests leaves on her own. She needs to take them back to her nest. But what possible effect could a tiny pest like her have on this
immense forest?
There are plenty of plant pests in temperate forests, but there is one crucial difference, temperate forests have winters and each winter, the cold
kills off creatures like the ants and they have to rebuild their colonies and start from scratch each spring.
But here in the rainforest, there is no winter and as a consequence, the plants here are under almost relentless attack. Our ant is just one worker
among thousands in a single colony. Each ant deposits or leaf fragment deep within the nest. There it will be, composted and
turned into a fungal food for the whole colony.
Added together, the impact of all of these thousands of ants is enormous. It's relatively easy to work out just how much these ants are harvesting.
We know there's around 100,000 in every nest, and scientist counted the number of journeys they made every day carrying pieces of leaf. 374,200.
They also measured the leaf area – the total being carried each day by the ants – 11 square metres. Multiply that up and during the course of a
year, it adds up to 3855 square metres and that is 20% of the leaf cover that is produced here in the area of the forest where these little guys
are foraging. That's one fifth of all the leaves here destroyed by nothing more than ants. And that's just the ants. Grasshoppers, caterpillars,
slugs and snails… Everything seems to be eating its greens here.
Wherever you look in the forest, it's almost impossible to find a leaf that hasn't been attacked by pests. The simple fact that there's no winter to
kill off these pests is a huge problem for plants. So to stand any chance of survival, every single plant in the rainforest is armed. And many are
filled with toxic chemicals which render them inedible. All of this has had a profound effect on the evolution of the animals that live here.
Take a closer look at these creatures. What do you notice? Many of them are plain weird. They are unlike anything else. And one of the strangest of
all is found here in Latin America. Here it is, and what an amazing animal. Really charming as well. But if we take a closer look at it, you can see
exactly what I mean by weird. This is a female three-toed sloth. And she's embarking on a 20-metre vertical climb to find food. She is charming, but
she's also quite unlike any other animal.
So why is she so weird? Well, it's a direct result of a very peculiar diet. You see, she is a very fussy eater. Feeding on only one or two trees, the
leaves of which are tough and full of toxins. But her gut has evolved to host bacteria which are specially equipped to break down these otherwise inedible
leaves.
