Forests help climate

21 November 2008


You may think of forests as  nice place to walk the dog, or a useful source of wood for furniture or paper, but researchers writing in the Proceedings of the National Academy of Sciences have found that forests may influence the planet's climate in important and previously unknown ways.

It all boils down to two things - reflectiveness and nitrogen.  When sunlight hits the Earth's surface, it is either absorbed and heats the planet up. Alternatively it gets reflected back into space and doesn't affect the Earth's temperature. Now Scott Olinger and his team have found that the amount if sunlight reflected back into space by forests is directly related to the levels of nitrogen in the trees' foliage.

While scientists have long known that nitrogen-rich foliage plays an important role in pulling CO2 out of the atmosphere, this discovery highlights a new role for nitrogen in controlling climate.  So nitrogen-rich trees have a doubly-whammy effect on the climate by simultaneously absorbing more CO2, and also by reflecting more sunlight.

The researchers made their discovery by poring over six years of data collected across North America, noticing that the overall reflectivity of forest foliage, a property known as albedo, rose and fell in line with levels of nitrogen in the leaves.

The newly discovered link adds an interesting new twist to our understanding of climate and raises important questions about how ecosystems interact with it. Changes in climate, air pollution, land use, and species mix can all affect nitrogen levels in foliage, and all of these may be important for considering in climate models - which they haven't been until now.


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