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Are old forests a net source of carbon?

The early morning air swirling around Matteo Detto’s gumboots is saturated with carbon. Before daybreak on his rainy season hikes along the ridgeline of Panama’s Barro Colorado Island, forest floor CO2 can top 500 parts per million − 20 percent more than the 400−ppm mark earth’s atmosphere hit not long ago.

The forest floor exhales CO2. It pools overnight in the still air and is swept into the atmosphere with the daytime breezes. This is one component of the complex forest carbon cycle studied by Detto, an associate scientist at STRI.

Detto’s outdoor laboratory centers on a 48−meter tower that juts out of the forest canopy. On the ground, Detto’s automated equipment samples soil outflows of CO2. Atop the tower, at the interface of the forest canopy with the atmosphere, another device measures the flux of atmospheric carbon and other greenhouse gases − 10 times per second, every second of the year.

"By measuring these gases with such high frequency, we can estimate how much carbon is coming in and out of the forest," says Detto, high above the forest floor surrounded by sweeping views of Barro Colorado and the Panama Canal. "Is the forest, at the ecosystem scale, a carbon source or carbon sink?"

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Asner Wright Hall Muller Winter Potvin
Turner Detto Hubell Rubinoff Davies