Premium
Inconsistent definitions of “urban” result in different conclusions about the size of urban carbon and nitrogen stocks
Author(s) -
Raciti Steve M.,
Hutyra Lucy R.,
Rao Preeti,
Finzi Adrien C.
Publication year - 2012
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/11-1250.1
Subject(s) - impervious surface , environmental science , vegetation (pathology) , land use , biomass (ecology) , metropolitan area , forestry , ecosystem , land cover , urban forest , geography , soil water , ecology , hydrology (agriculture) , soil science , biology , medicine , geotechnical engineering , archaeology , engineering , pathology
There is conflicting evidence about the importance of urban soils and vegetation in regional C budgets that is caused, in part, by inconsistent definitions of “urban” land use. We quantified urban ecosystem contributions to C stocks in the Boston (Massachusetts, USA) Metropolitan Statistical Area (MSA) using several alternative urban definitions. Development altered aboveground and belowground C and N stocks, and the sign and magnitude of these changes varied by land use and development intensity. Aboveground biomass (live trees, dbh ≥ 5 cm) for the MSA was 7.2 ± 0.4 kg C/m 2 (mean ± SE), reflecting a high proportion of forest cover. Vegetation C was highest in forest (11.6 ± 0.5 kg C/m 2 ), followed by residential (4.6 ± 0.5 kg C/m 2 ), and then other developed (2.0 ± 0.4 kg C/m 2 ) land uses. Soil C (0–10 cm depth) followed the same pattern of decreasing C concentration from forest, to residential, to other developed land uses (4.1 ± 0.1, 4.0 ± 0.2, and 3.3 ± 0.2 kg C/m 2 , respectively). Within a land use type, urban areas (which we defined as >25% impervious surface area [ISA] within a 1‐km 2 moving window) generally contained less vegetation C, but slightly more soil C, than nonurban areas. Soil N concentrations were higher in urban areas than nonurban areas of the same land use type, except for residential areas, which had similarly high soil N concentrations. When we compared our definition of urban to other commonly used urban extents (U.S. Census Bureau, Global Rural–Urban Mapping Project [GRUMP], and the MSA itself), we found that urban soil (1 m depth) and vegetation C stocks spanned a wide range, from 14.4 ± 0.8 to 54.5 ± 3.4 Tg C and from 4.2 ± 0.4 to 27.3 ± 3.2 Tg C, respectively. Conclusions about the importance of urban soils and vegetation to regional C and N stocks are very sensitive to the definition of urban used by the investigators. Urban areas, regardless of definition, are rapidly expanding in their extent; a systematic understanding of how our development patterns influence ecosystems is necessary to inform future development choices.