Carbon in conurbations: Afforestation and carbon storage as consequences of urban sprawl in Colorado's Front Range.

摘要

In 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 edaphic C, 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 C compartments measured. The comparison of C 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 C than local prairie or agricultural fields. Introduced woody vegetation comprises a substantial C pool in urban greenspaces and represents a wholly new ecosystem feature. Established urban greenspaces harbor larger C pools than native grasslands on a per area basis.; Rather than map the urban land-cover types, regional detection of the proportion of the urbanized landscape occupied by vegetated and anthropogenic components extracted biophysical information of the urban/rural matrix. Convex geometry and partial unmixing algorithms were used to extract major landscape elements from an AVIRIS image of Boulder, including six vegetation endmembers. Other scene components were also identified, including soil, water, and five impervious surfaces. The fractional abundance of urban vegetation equaled or exceeded that of vegetation in surrounding areas.; In order to understand the effect of the per-area C increase in anthropogenic landscapes regionally, the distribution of carbon in land covers across the landscape was investigated. Regional C estimates were based on both fractional abundances and land-use/land-cover categories. 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.