Field of Science

From carbon dioxide to carbon dioxide - lesson from the tropics

Here in the rain forest life is a pretty dramatic process. While the great towering giants of wood have a aura of permanence about them, the tree turn over in a wet tropical forest is 2 to 3 times as fast as in temperate forests. Trees are great store houses of carbon dioxide, relatively short term reservoirs, and it is hard for people to rap their brains around the fact that all that stuff is primarily built out of a colorless, tasteless gas that only makes up a fraction of one percent of the atmosphere.

In the temperate zone we are used to seeing mushrooms pop up out of the ground, reproductive structures that are dwarfed by the huge filamentous organisms hidden from sight. And of course such fungi are the primary recyclers of cellulose and the other stuff trees and plants are built from. So you might expect to see lots of fungi on the ground in rainforests, but such is not the case. Decomposition is so fast here, no organic material builds up in or on the soil. Most of the fungi you see are growing right out of decomposing plant material. The fungi shown here are called "dead man's fingers", cute, eh? And they are growing out of a log that is pretty far along in terms of decomposition. The Phactor is not an expert on fungi, but he seems to remember that this fungus is called appropriately enough Xylaria, after xylem, wood. And so after being stored in this log for decades or in some cases even centuries, all that carbon dioxide is going back into the air. And if, as some of
the best data indicates (see for link), even a slight increase in temperature causes a higher rate of tree mortality, then you have a very scary scenario where an increasing concentration of carbon dioxide is driving an increase in tree mortality and more carbon dioxide is being released.

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