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Land Use / Land Cover Change
| The following are some of the USGCRP's major accomplishments
related to Land
Use / Land Cover Change during Fiscal Year 2002:
National Land Cover Database:
A 1992 National Land Cover Database (NLCD) was completed, validated to determine accuracy, and released via a seamless Internet map server. The development of the NLCD was supported by four USGCRP agencies. The NLCD was produced using 1992 Landsat Thematic Mapper satellite data; it included the categorization of 21 general land cover types, spanned the 48 contiguous states, and had 30- meter spatial resolution. The dataset was designed to support a wide range of environmental assessments, including analysis of the rates of land cover change, impacts of land cover change on water quality, and the evaluation of ecosystem form and function. Its national and regional applications include watershed management, environmental inventories, transportation modeling, fire risk assessment, and land management. Access to the data is through the USGS Land Cover Characterization Program.
Land Use/Land Cover Change in U.S. Ecological Regions:
An analysis of land-use and land-cover change in nine eastern U.S. ecological regions has been completed. In the first phase of a study to document land-use and land-cover change for five periods from 1973 to 2000 (1973, 1980, 1986, 1992, and 2000) for 84 U.S. ecological regions, Landsat satellite data were interpreted to determine the contemporary rates of change. During the nearly 30-year period, land use/land cover changed over approximately 20 percent of the area of in the Mid-Atlantic Coastal Plain and Southeastern Plain, due to the rapid, cyclic harvesting and replanting of forests. The adjacent Piedmont region also showed substantial change in forest cover. Urbanization was the dominant conversion in the northern Piedmont and Atlantic Coast Pine Barrens. The two Appalachian regions studied (Blue Ridge and North Central Appalachia) experienced comparatively low levels of change, with the primary transformations being urban development and forest conversion, respectively. The early results of this national study provided evidence of the distinctive regional character and variation in the rates and characteristics of land-use and land-cover change. (See Figure 7.1.)
Land Use/Land Cover Change and Changes in Soil Carbon and Nitrogen:
Recent satellite and ground based studies in the southern United States indicate that woody encroachment into grasslands can significantly alter biogeochemical cycling in arid to semi-arid ecosystems. Specifically, shifts from grasslands to shrublands and forestland in northern Texas have increased substantially during the past 70 years, contributing to increases in plant and soil carbon and nitrogen stocks in the region. These changes have occurred primarily as the result of abandonment of agricultural and pasture lands as well as changing fire and grazing practices. Together, these changes have implications for future land management.
Fire Disturbance and Forest Carbon Storage:
Increasing atmospheric CO2, climatic variation, and fire disturbance all play roles in the historical carbon cycle dynamics of Alaska. Analyses of the distribution of the ages of tree stands in Alaska indicate that fire has likely become less frequent since 1950, compared to the first half of the 20th Century. Quantitative results from application of the Terrestrial Ecosystem Model (TEM) indicate that the key factor responsible for the substantial carbon storage in Alaska during the 1980s was regrowth under a less frequent fire regime. In the context of the overall U.S. carbon budget, the analyses with TEM indicate that Alaska is likely to be an important region of carbon storage. The applications of mechanistic models, such as TEM, represent complementary tools to atmospheric analysis, with the potential to provide information on the quantity of changes in carbon storage at finer spatial scales, and also to provide information on factors responsible for changes in carbon storage. This information may be useful in evaluating policy options related to the U.S. carbon budget.
Forest Cover Increase and Carbon Sequestration:
Forest cover increases averaging 7 percent per decade between about 1970 and 1990 have been found in analyses of the U.S. Upper Midwest. Data from 136 representative study sites were collected using satellite data, aerial photography, and field data, combined with regional Geographic Information System-based models. The results indicate increased carbon sequestration, because forest cover is primarily replacing pastures and croplands. Forest regrowth and planting in the temperate forests of the Northern hemisphere due to land-use change may account for some of the "missing sink" in carbon budgets. The observed increase in the Upper Midwest resulted primarily from the abandonment of marginal agricultural lands as the farm economy in the region has declined. A significant decade-scale lag effect was observed between abandonment and regrowth. A countervailing trend is extensive dispersed rural development in the region, driven by demand for recreation and retirement destinations as well as for seasonal homes. This work highlights, and also raises questions about, the dependence of land-use change and consequent carbon sequestration on agriculture policies, infrastructure investments, and regional and local planning efforts. (See Figure 7.2)
7.2. Forest cover increase and abandonment of marginal
agricultural lands in the Upper Midwest
Land Use/Land Cover Change and Native Species Viability:
Analyses of Landsat imagery, along with aerial photographs, indicate that conifer forests expanded by more than 7 percent in the Greater Yellowstone Ecosystem during 1975-95.The major land-cover changes were a 347 percent increase in urban area and a 400 percent increase in rural residences. A key finding is that hot spots for native species overlap with intensive land use in the same small portion of the landscape. A critical consequence is that development on private lands threatens the viability of some native species in Yellowstone National Park and other nature reserves. Another key finding is that human population and economic growth are associated with changes in ecosystem attributes; rapid change has important implications for carbon storage and biodiversity. Information from this study can be used to better manage the urban-park interface to ensure conservation of natural resources while encouraging regional economic activity.