Forests constitute an important part of the “Carbon World Bank.” The organic matter in their leaves, wood, roots and soil stores a great deal of carbon absorbed from the atmosphere.
When a forest burns with light intensity, or is thinned, there’s a short-term withdrawal from that bank—for a while, the forest releases more carbon than it takes up.
But such management can increase how much water and nutrients are available for the remaining trees. Just three or four years later, the forest as a whole is likely to grow more vigorously than before, putting that forest patch back in the black in terms of carbon storage.
This kind of carbon banking helps to counteract rising carbon dioxide levels in the global atmosphere. But when stand-replacing crown fires happen in forests not adapted to them, the forest carbon bank breaks down.
Near Kendrick Park, north of Flagstaff, pine forest has been converted into sparse grassland in the wake of severe fires more than 15 years ago. Northern Arizona University researchers have measured there how carbon dioxide moves between atmosphere into ecosystem. And they’ve found that even after many years the former forest’s dead roots, stumps, and logs have continued to release more carbon than new growth takes up.
In a world of climate change, that’s not good news. It suggests that some severely burned areas may require a conscious investment—deliberate tree planting—if they are to once again play their important role of banking some of the atmosphere’s excess carbon.