Germinating Success

Biodiversity creates Dangers

Living Planet

I know, it’s easy for us to think of biodiversity as a wonderful thing. But the pressures that create this biodiversity make the rainforest a very dangerous place. Especially when it comes to the survival of the forest’s youngest inhabitants.

Let’s think about it from the plant’s point of view. I’ve collected about 15 different types of tree seed here, all of which have come from this small patch of forest behind me. Now, imagine that each of these seeds represents a tree. And imagine that the forest was made up of a single species. Like this one, that the locals call prischaco. What you’d have is a monoculture. But in the pest infested rainforest, this doesn’t happen. And here’s why.

You see, imagine you are a seedling trying to germinate and grow here. We know that each of these tree species has a highly specialised set of herbivores which attack it. So this one will be accessible to all of the herbivores living on these trees. Not a good situation at all.

But what if you were a different species of tree germinating here? Then you wouldn’t be susceptible to this particular set of herbivores, and that would confer a real advantage to you. Then there’s a far greater chance that it would prosper through to maturity, that it would survive. And in fact… If another tree species were to grow here, it to would enjoy the same advantages. Reduced susceptibility to this type of herbivore attack.

The strategy spreads like wildfire through the forest. What we end up seeing… Is a complete mosaic of species. A seedling is far more likely to survive if it germinates in isolation, far away from the parent tree, surrounded by different tree species.

So how do plants get their precious seeds away to safety, away from their set of voracious pests? To find the answer, I’m going to the jungles of Borneo.

The Jungles of Borneo. Home to some of the largest animals in any rainforest. In the Kinabatangan river, a group of pygmy elephants. Among the herd is a baby, born only a few weeks ago. Nearby in the Sepilok Sanctuary, this young orang-utan is just days old. They don’t know it, but these youngsters are incredibly important. Because not only are both species rare, but both will play a crucial role in this ecosystem.

Orang-utans. Absolutely extraordinary animals. So easy to see why we generate so much affection for them. And when you look into their eyes, it’s like a reflection in a not-so-distant mirror.

But that is another reason why we should value both orang-utans and elephants. If you’re a tree, seed dispersal and germination is a pretty risky business. After all, you’re covered with pests, all of which want to gobble up those seeds or snap up any tasty germinating seedling. Your only chance is to get your seeds as far away from yourself and those pests as possible. The question is, how do you do it?

They both face the same problem… How to find enough food. The solution, as the baby is starting to realise, is that they never stop moving. She will have to work hard to keep up with the herd. You see, these elephants are on the lookout for fruit.

Overhead, orang-utan’s search for fruit in the canopy. And thanks to their agility, they can reach almost all of it. But for the young elephant, even low-hanging fruit can be just out of reach. Her mother shows him how to get them.

But what’s important here is that this elephant can smell some fruit from way over a kilometre away. And there are some plant species here that have specifically evolved to attract elephants.

For instance, this jackfruit is so large that nothing else can really deal with it. His huge gut will take a couple of days to digest that meal, by which time he may have travelled over 10 kilometres. Between them, the orang-utan and the elephant disperse thousands of species of fruit. Not only will these seeds be supplied with the ready-made fertiliser, they will germinate safely away from the threat of attack from the mother tree’s pests.

Rainforests, more than any other ecosystem, rely on animals to spread their seeds over large distances. But paradoxically, this has created a nightmare.