April 13, 2012

Spiders in Borneo: Trees that grow from sky to ground

This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American

The first time I arrived to the Amazon rainforest decades ago, I was astounded at the intensity. Everywhere I looked, there was a story unfolding -- predation, decay, camouflage, parasitism. As a biologist, I felt as if I'd arrived to the center of the biological world, like a country boy arriving wide-eyed to New York City or Beijing. Tropical rainforests have high pressure, relentless ecological drama. Even as the magnificent trees here in Borneo reach for the sun, termites are gnawing at their trunks, too impatient to wait for the tree's death.

Even the plants are murderous. Trees grow from the ground toward the sky, correct? Well, not all. Strangler figs grow from the sky toward the ground. A strangler fig begins life as an epiphyte, a small plant perched on the branches of another tree. It drops roots from the canopy down toward the ground. As it grows, it drops more and more roots, which gradually thicken and begin to surround the trunk of the host tree. Eventually these coalesced roots can form a sheath around the host trunk, the host tree dies, and the strangler fig stands on its coalesced roots. The coalesced roots form a cylinder, hollow in the center where the host trunk used to be. Here's a strangler fig we saw at Mulu, its "trunk" like a braided rope.

We humans find ourselves part of the drama. I've already posted about leeches, and you can imagine the mosquitoes. Most of the things that want to eat you in a tropical forest are not tigers, but tiny things, from fungi to bugs. "Hi, we are here to recycle you. Are you ready? May we have a piece?"

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A tropical forest is constantly turning over, so dynamic that if you try to sit still, you will be moved anyway, cell by cell. One of the reasons that clearing tropical forests for agriculture usually yields disappointing results is that their nutrient richness does not extend deep into the soil, as in a temperate prairie, but rather is bound up almost entirely in the living organisms. The nutrients are traded quickly from one life to another. Remove the organisms, and the richness is gone.

Tropical forests may sound scary, but they are amazing. And really, you decay slowly enough to enjoy the forest while you last.

Previously in this series:

Spiders in Borneo: Introduction

Spiders in Borneo: Undiscovered biodiversity

Spiders in Borneo: The guests of honor: Salticidae

Spiders in Borneo: Team Salticid

Spiders in Borneo: Mulu National Park

Spiders in Borneo: Dreaming about salticid spiders

Spiders in Borneo: Jumping spiders in the forest

Spiders in Borneo: Beating around the bushes

Spiders in Borneo: Spiders in leaf litter

Spiders in Borneo: A Vertical Life