Landscape carbon budgets and planning guidelines for greenspaces in urban residential lands.

Abstract

There is increasing concern about the predicted negative effects of a future CO₂ doubling on the earth. This concern has evoked interest in the potential for urban greenspace to help reduce the levels of atmospheric carbon. The purpose of this study was to quantify landscape-related carbon storage and annual carbon fluxes for urban residential landscapes and to suggest proper planting and management guidelines to improve direct and indirect removal of atmospheric carbon by urban greenspace, based on models of alternative landscape scenarios. For detailed quantification, the scale of this study was limited to two residential blocks in northwest Chicago having a significant difference in vegetation cover. Total carbon storage in greenspace was about 26.15 kg per m² of greenspace in study block 1, and 23.20 kg per m² of greenspace in block 2. Of the total, soil carbon accounted for about 78.7 percent in block 1 and 88.7 percent in block 2. Trees and shrubs in block 1 and block 2 accounted for 20.8 percent and 10.6 percent, respectively. The carbon storage in grass and other herbaceous plants was only about 0.5 to 0.7 percent in both blocks. Total annual net carbon input to block 1 and block 2 by all the greenspace components was 0.48 kg per m² of greenspace in block 1 and 0.31 kg per m² of greenspace in block 2. The principal net carbon release in greenspace of the residential landscapes was from grass maintenance. Models of alternative landscape scenarios suggest that an ecological landscape, characterized by full tree plantings in the available growing spaces, with no landscape management, is the best landscape type to maximize annual net carbon sequestration in Chicago with its long heating season. Differences between the two blocks in the size of greenspace area and vegetation cover resulted in great differences in total carbon storage and annual carbon uptake. An effective way to increase the carbon storage and uptake in urban areas is to secure as large greenspace as possible and to plant as many trees as possible.