Amiro and co-workers have measured carbon dioxide release after disturbances in North-American forests at 180 locations. The disturbance were either harvesting, fire, windfalls, insect outbreaks, or thinning. Large differences were found depending on latitude and forest type. It takes 10-20 years after harvest or other large scale disturbances before the forest land becomes a carbon sink again. Read the whole article in Journal of Geophysical Research.