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Nancy Golubiewski, Ph.D.Advisor: Carol Wessman, Ecology and Evolutionary Biology Carbon in Conurbations: Afforestation and Carbon Storage as Consequences of Urban Sprawl in Colorado's Front RangeIn the arid western United States, urbanization transforms landscapes from sparsely vegetated grasslands with tree-lined riparian corridors into matrices of asphalt, concrete, turf grass, and multi-strata wooded stands. This research sought to understand the consequences of urbanization upon carbon pools in the Front Range of Colorado, a metropolitan area undergoing expansive urban transformation. Vegetative and soil carbon, as well as biomass and other soil physical/chemical properties, were measured throughout the Denver-Boulder metropolitan area in 2000 and 2001. Anthropogenic activities leave clear signatures on all three carbon compartment measured. The comparison of carbon storage in the vegetated spaces of urban areas to that in grasslands and agricultural fields reveals a marked increase as well as a proportional shift in storage from belowground to aboveground. Lawn grass produces more biomass and stores more carbon than local prairie or agricultural fields. Introduced woody vegetation comprises a substantial carbon pool in urban greenspaces and represents a wholly new ecosystem feature. Established green-spaces harbor larger carbon pools than native grasslands on a per area basis. Rather than map the urban land-cover types, high spectral resolution images from NASA's Airborne Visible/Infrared Spectrometer were used to determine the distribution of built surfaces, grass, trees, soil and water in Boulder. Carbon values measured in the field were then applied to the classified imagery, as well as to land-use/land-cover catgories from a USGS analysis of historical aerial photography (1930s-1990s). A carbon hotspot exists in the urbanized areas where well-established urban vegetation occupies residential neighborhoods, urban greenspaces, and city streets. Other hotspots exist along riparian corridors and on vegetated foothills. Between 1930 and 1990, developed land almost quintupled in area in the Front Range of Colorado. During the same time period, estimates of the carbon pool trajectory range from -3% to +18%. The true direction, given the local context, is surmised to be neutral or positive. |
