Emergy Basis of Forest Systems

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Tilley, David
University of Florida
A major question in natural resource management is how to integrate economic-use activities with the supporting ecosystems to maximize performance of the ecological-economic system. In this dissertation, the natural wealth of forested systems of three different sizes was evaluated with emergy: two watersheds of the Southern Appalachians, Macon County (N.C.), and North Carolina. Emergy is the total amount of energy of one form that was required directly and indirectly to make another form of energy. Values are reported as emdollars (Em$) which represent the economic activity resulting from resource use. Benefits provided by forested watersheds were quantified based on emergy required to develop and maintain each service or product. Total wealth contributed by the multiple-use Wine Spring Creek (WSC) watershed was 4300 Em$/ha/y, and was divided among scientific research (3450 Em$/ha/y), water yield (2060 Em$/ha/y), recreation (1880 Em$/ha), and timber (1440 Em$/ha/y). In the 1990's, timber accounted for 3% of world emergy use, 1% in the United States, 9% in North Carolina, 14% in Macon County, and 8% in the WSC watershed. Forest ecosystems captured 53% of environmental emergy in North Carolina, 81% in Macon County, and 100% in the WSC watershed. The importance of forest ecosystems to the U.S. economy were evaluated based on emergy flows of the U.S. forest products industry and international trade of forest products in North America. In 1993, the U.S. had an annual trade surplus in forest products worth 63 billion Em$. Simple models were developed to explore the temporal and spatial dynamics of emergy and transformity in forested watersheds. Transformity is the ratio of emergy to energy; it measures position in the energy hierarchy of energy forms. Temporally, transformity and emergy lagged energy levels in reaching steady-state. Spatially, emergy from mountain uplands converged to the stream network, making water and its carved basin locations of high empower density. A model, MULTIBEN, evaluated forest empower of multiple benefits given various combinations of economic investment in recreation and timbering. Maximum empower was found at an intermediate level of economic investment, suggesting that an optimum intensity of forest development exists.