Measuring the detoriation of the environment is not easy. The surveilance of tropical forests has mainly been based on interpretation of satelite imageniary. This basically estimate the extent of the tree canopy - an area measure, assuming that what is below is unchanged. A new study shows that this assumption is dificient - a lot of forest degradation takes place below the canopy.

This error of estimate is alarming as tropical forest seems not to be the major carbon sink we have envisaged. Rather the other way around: Taking what goes on under the canopy into consideration turns tropical forests into a major carbon source. More carbon seems to be lost to degradation and disturbance than to deforestation proper.