Source: Tana E. Wood, USDA Forest Service, International Institute of Tropical Forestry, Tel. 1-434-242-0881
Oct. 24, 2012 • A new study shows that widely available satellite imagery can be used to map tropical rain forests with much more detail than was previously thought possible. The work is important because tropical countries need to produce detailed forest maps for REDD+, which is a mechanism that gives countries financial incentives for Reducing carbon Emissions from Deforestation and Degradation. This new mapping allows better forest management to sustain biodiversity and enhance carbon stocks for REDD+ efforts.
Detailed maps of forest types are essential, including maps that distinguish among forest types, but until now scientists have assumed that tropical forest tree communities are too similar to each other in most satellite imagery to be mapped. Although satellite imagery is commonly used to map tropical forests over large areas, only a few forest types are usually identified. This study, however, showed that if many dates of imagery are available, as in newly available satellite image archives, clues to distinguishing among forest patches containing different groups of tree species can be found.
Working in Trinidad and Tobago, the study authors, led by Dr. Eileen Helmer of the USFS International Institute of Tropical Forestry, searched through the recently opened archives of Landsat satellite imagery and through the very high resolution satellite images viewable with Google Earth™. They discovered that the spatial distributions of many tree communities thought to be indistinguishable in satellite imagery can in fact be revealed, but only in imagery from unique times, such as that collected during periods of severe drought, or when a particular tree species is flowering. Other forest types were distinct in very high resolution imagery because of unique canopy structure. The study also brought to light extensive abandoned agricultural areas that have transitioned to forest. This trend of increasing forest cover will likely continue in Trinindad and other Caribbean islands, because much agriculture, including one of the key agricultural products, sugar cane, is no longer profitable in the region.
Maps and data resulting from the study, including a new country-wide set of topographic maps, are available at http://fsgeodata.fs.fed.us/rastergateway/caribbean. These are the first maps for an entire tropical country that show the distributions of communities of tropical forest tree species.
The study, “Detailed maps of tropical forest types are within reach: forest tree communities for Trinidad and Tobago mapped with multiseason Landsat and multiseason fine-resolution imagery”, appears in the September issue of Forest Ecology and Managementby lead author Dr. Eileen Helmer with co-authors from Colorado State University and the Forestry Division of the Republic of Trinidad and Tobago.