sunnuntai 22. helmikuuta 2009

"Nature" - sademetsien biomassa lisääntymässä

Carbon cycle: Sink in the African jungle

Helene C. Muller-Landau1
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Apparently pristine African tropical forests are increasing in tree biomass, making them net absorbers of carbon dioxide. Is this a sign of atmospheric change, or of recovery from past trauma?

The lush vegetation of tropical forests is a large and globally significant store of carbon1. Because tropical forests contain more carbon per unit area than any alternative land cover, cutting them down releases carbon into the atmosphere. For the same reason, growing forests take up carbon from the atmosphere. Of course, trees cannot grow for ever, and neither can forests: in the absence of disturbances that kill trees en masse — such as fires, hurricanes or logging — every forest will eventually reach a point at which tree growth and death are in equilibrium, and at which the average change in tree carbon stocks is zero.

It is thus surprising that undisturbed tropical forests currently do not seem to be at equilibrium. If you measure the size of trees in a given area, calculate their carbon stocks, and then repeat the process some years later, you will on average find that the forest holds more carbon than it did before. This was first reported for Amazonian tropical forests2, and on page 1003 of this issue Lewis et al.3 show that ...

Nature 457, 969-970 (19 February 2009) | doi :10.1038/457969a; Published online 18 February 2009

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