Climate Change and...
- Climate Variability
- Climate Models
Effects of Climate Change
Urban Land Use and Development
ABSTRACT: During the past few decades, urban and suburban developments have grown at unprecedented rates and extents with unknown consequences for ecosystem function. Carbon pools of soil and vegetation on landscaped properties were examined in the Front Range of Colorado, USA, in order to characterize vegetation and soils found in urban green spaces; analyze their aboveground biomass, vegetative C storage, and soil C storage; and compare these suburban ecosystem properties to their counterparts in native grassland and cultivated fields.
Anthropogenic activities leave clear signatures on all three C compartments measured. Management level dominates the response of grass production, biomass, and N tissue concentration. This, in turn, influences the amount of C and N both stored in and harvested from sites. The site age dominates the amount of woody biomass as well as soil C and N. Soil texture only secondarily affects total soil carbon and total bulk density.
Established urban green spaces harbor larger C pools, more than double in some cases, than native grasslands or agricultural fields on a per-area basis. 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 green spaces and represents a new ecosystem feature. After an initial decrease with site development, soil organic carbon (SOC) pools surpass those in grasslands within two decades. In addition to the marked increase of C pools through time, a shift in storage from belowground to aboveground occurs. Whereas grasslands store ̃90% of C belowground, urban green spaces store a decreasing proportion of the total C belowground in soils through time, reaching ̃70% 30–40 years after construction. Despite the substantial increase in C pools in this urban area, it is important to recognize that this shift is distinct from C sequestration since it does not account for a total C budget, including increased anthropogenic C emissions from these sites.
DESCRIPTION: In the contiguous 48 states of the United States, urban areas increased twofold between 1969 and 1994 and currently occupy 3.5% of the land, or 2.81 x 107 ha (Dwyer et al., 1998). On a global scale, more than 476,000 ha of arable land are converled annually to urban areas (World Resources Institute, 1996). This conversion has the potential to greatly modify soil organic carbon (SOC) pools on regional scales and to a lesser extent on a global scale (Pouyat et al., 2002).
ABSTRACT: We used data available from the literature and measurements from Baltimore, Maryland, to (i) assess inter-city variability of soil organic carbon (SOC) pools (1-m depth) of six cities (Atlanta, Baltimore, Boston, Chicago, Oakland, and Syracuse); (ii) calculate the net effect of urban land-use conversion on SOC pools for the same cities; (iii) use the National Land Cover Database to extrapolate total SOC pools for each of the lower 48 U.S. states; and (iv) compare these totals with aboveground totals of carbon storage by trees. Residential soils in Baltimore had SOC densities that were approximately 20 to 34% less than Moscow or Chicago. By contrast, park soils in Baltimore had more than double the SOC density of Hong Kong. Of the six cities, Atlanta and Chicago had the highest and lowest SOC densities per total area, respectively (7.83 and 5.49 kg m–2 ). On a pervious area basis, the SOC densities increased between 8.32 (Oakland) and 10.82 (Atlanta) kg m–2 . In the northeastern United States, Boston and Syracuse had 1.6-fold less SOC post- than in pre-urban development stage. By contrast, cities located in warmer and/or drier climates had slightly higher SOC pools post- than in pre-urban development stage (4 and 6% for Oakland and Chicago, respectively). For the state analysis, aboveground estimates of C density varied from a low of 0.3 (WY) to a high of 5.1 (GA) kg m–2 , while belowground estimates varied from 4.6 (NV) to 12.7 (NH) kg m–2 . The ratio of aboveground to belowground estimates of C storage varied widely with an overall ratio of 2.8. Our results suggest that urban soils have the potential to sequester large amounts of SOC, especially in residential areas where management inputs and the lack of annual soil disturbances create conditions for net increases in SOC. In addition, our analysis suggests the importance of regional variations of land-use and land-cover distributions, especially wetlands, in estimating urban SOC pools.
ABSTRACT: Based on field data from 10 USA cities and national urban tree cover data, it is estimated that urban trees in the coterminous USA currently store 700 million tonnes of carbon ($14,300 million value) with a gross carbon sequestration rate of 22.8 million tC/yr ($460 million/year). Carbon storage within cities ranges from 1.2 million tC in New York, NY, to 19,300 tC in Jersey City, NJ. Regions with the greatest proportion of urban land are the Northeast (8.5%) and the southeast (7.1%). Urban forests in the north central, northeast, south central and southeast regions of the USA store and sequester the most carbon, with average carbon storage per hectare greatest in southeast, north central, northeast and Pacific northwest regions, respectively. The national average urban forest carbon storage density is 25.1 tC/ha, compared with 53.5 tC/ha in forest stands. These data can be used to help assess the actual and potential role of urban forests in reducing atmospheric carbon dioxide, a dominant greenhouse gas.