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New Study: A Carbon Surprise in Old-Growth Forests

Thursday, March 5, 2015
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Most forests in the eastern U.S. are young and growing fast. A new study published this week in the journal Ecology  shows the potential for younger forests to maintain their valuable carbon 'sink' capacity for many decades to come -- but not in the way you might expect. 

To explore the potential for young forests to store carbon over time, HF ecologist Jonathan Thompson, along with his graduate student Jennifer McGarvey and colleagues from the University of Virginia, looked instead at old forests. They measured carbon in the scattered fragments of remaining old-growth forest throughout the mid-Atlantic states, hoping to determine the upper limit of how much carbon a forest can store. 

They found that the old-growth forests store 30% more carbon than surrounding younger forests. And a striking amount of that carbon is found in dead wood - in downed logs and standing snags. In fact, there was eighteen times more carbon stored in dead wood in the old-growth stands (almost 20% of the total carbon stored) than in the younger stands. 

They found that tree species matters, too. Stands dominated by tulip poplar (Liriodendron tulipifera) store the most live biomass, while stands of mixed oak (Quercus spp.) store more dead wood.

The scientists note that today's younger forests will likely have a different trajectory than today's old-growth forests. These young stands originated in abandoned agriculture fields, and have not had time to build up generations of dead wood stores. But tree pests and pathogens, such as the hemlock woolly adelgid, may accelerate the build-up of the dead wood pool, leading to more carbon storage over time.

(Photo: Rebecca Walker, Jennifer McGarvey, and Stevie Gildehaus measure old growth carbon stores at Belt Woods near Annapolis MD. Photo by Jonathan Thompson.) 

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