Study concludes forests are decreasing, but how good is the data?

Using data from 541 randomly selected 18.5 by 18.5 km blocks, an analysis of Landsat-7 satellite data has concluded that 3% of the forests (1 million square kilometer) present in 2000 were gone by 2005. See map at http://www.sciencenews.org/view/download/id/58673/name/WHEN_A_TREE_FALLS . The researchers...