New Study Raises Estimates of Deforestation in Amazon

Back to Map Page April, 1999 Deforestation in Brazil's Amazon River basin has been a dominant theme of global environmental concern in recent years. A new study published in the April 8 issue of Nature says that current methods of estimating Amazonian deforestation fails to identify at least half of the badly damaged (but not completely removed) forests each year. This report found that annual deforestation rates are at least twice as great as previously thought--and three times greater in drought years, when forest fires exacerbate deforestation by logging. Logging, agriculture, and other activities are making large areas of the Amazon rainforest susceptible to fire. The study, conducted by Brazilian and American ecologists, points out that existing estimates of deforestation use satellite data that detect new clear cuts well but fail to identify subtler forms of deforestation. In particular, satellite data cannot identify overgrown clear cuts, forests damaged by the removal of just the larger trees, and small patches of forest burned for ranching and farming. Satellite sensors gather information on the wavelengths of energy reflected from the earth's surface. Forests, water, pavement, and other surfaces reflect characteristic wavelengths, so where the satellite records areas with these wavelengths, the corresponding land uses can be mapped with reasonable accuracy. But sometimes very different types of landcover can reflect very similar wavelengths, which makes them look the same to a satellite sensor. Disturbed and partly-logged forests, for example, can be hard to distinguish from pristine, undisturbed forest. Even worse, a five-year-old clearcut in the tropical Amazon quickly grows thick, weedy new cover, which can look just like a mature forest to a satellite sensor. Satellite data are a cost-effective means of estimating deforestation in the huge, largely inaccessible rainforest regions of Brazil, but because of these technological limitations, these data also fail to identify extensive areas of damaged forest. Badly damaged forest is a problem because it dries out and quickly becomes susceptible to fire. The new study estimated deforestation rates using a combination of spot checks by airplane and inteviews with loggers and lumber mill owners. The authors estimated that in 1998 drought associated with El Nino about 17,000 square miles of forest were lost or badly damaged, about three times the official Brazilian estimate of 5,700 square miles. Overall, the new study raises the estimate of total deforestation from the official 13% to 16%, or 217,000 square miles in a 1.3 million square mile rainforest region. Deforestation in Brazil's rainforest is a concern because of lost biodiversity and also because of expected contributions to global warming. Global warming is understood to result mainly from concentrations of carbon dioxide in the atmosphere. When forests burn, they release carbon dioxide (formerly carbon stored in the wood and leaves of the living trees) into the air. When forests grow they take carbon dioxide from the air in order to build new wood and leaves. A forested region the size of the Amazon basin, then, can either take up or release tremendous amounts of carbon dioxide. Climatologists are therefore very interested in understanding the extent of deforestation (or carbon storage) in this region. Although deforestation is proceeding rapidly in many other environments, including North American rain forests and dry tropical forests, tropical rain forests are a subject of special concern because of their tremendous biodiversity. Ecologists estimate that about one third of all the world's plant and animal species live in tropical rain forests, many of these still undiscovered and undescribed. No one knows what resources are lost as these species disappear with their forest habitat. Brazil and other countries in the Amazon River basin share one of the most important rainforest regions in the world. Other major regional tropical rainforests occur in equatorial Africa and Southeast Asia. For more information, see these related web sites: Protest against tropical forest product consumption in the United States Greenpeace update on environmental events in the Amazon region News from the journal Nature (free registration required for access to site) To read more, see Environmental Science, a Global Concern, Cunningham and Saigo, 5th ed. Loss of tropical forests: p. 297-302 Map of megadiversity regions: p. 272 Map of human disturbance: 104 Environmental Science, Enger and Smith, 6th ed. Tropical forests and farming: p. 81 Forests and deforestation: p. 194-96 Back to Map Page feedback form | permissions | international | locate your campus rep | request a review copy digital solutions | publish with us | customer service | mhhe home Copyright ©2001 The McGraw-Hill Companies. Any use is subject to the Terms of Use and Privacy Policy. McGraw-Hill Higher Education is one of the many fine businesses of the The McGraw-Hill Companies.