Introduction and General Description of U.S. Forests
Terrestrial ecosystems are a major sink for carbon. Carbon dioxide is removed from the atmosphere by the photosynthetic process and stored in the plant biomass. Forest stands are manipulated in many ways such as thinning, clear-cutting, introduction of exotic tree species, forest fertilization, forest fire prevention, inputs of nutrients from rainfall deposition, acid rain, and introduction of nonnative insects. In contrast to clearing for agriculture, which takes land out of forest cover for a period of time, forest management practices can include clear-cutting or partial cutting followed by reforestation. As forest systems are so diverse, there are no standard sets of assumptions that can describe the effects of possible climate change. About 120 Mha of forestlands have been converted to other uses, and much of that land is now productive agriculture land. The chapter also presents an overview of the key concepts discussed in this book.