关键词: 城市林业, 植被生态, 碳储存, 碳排放, 管理措施, 生命周期, 绿地

Abstract: Urban vegetation is an important sink for carbon cycling in urban ecosystems. This study aims to promote the understanding of carbon sequestration in urban ecosystems. The literature analysis software HistCite was used, to review current status of studies on carbon sequestration in urban ecosystems both in China and abroad. The review highlighted research methodology, capacity of carbon sequestration and influential factors, and priorities of carbon sequestration studies were identified. Study of carbon sequestration in urban vegetation started in the early 1990s and attracted increasing attention since 2009. The existing literatures focus on regional assessment and reduction in carbon emission. Ground survey and estimation based on remote sensing images were the main methods used in studying carbon sequestration in urban vegetation. Currently the ground survey mainly uses the methodology of forest ecological survey. However, due to different growing conditions and higher spatial heterogeneity in urban vegetation in comparison to natural forests, it is necessary to develop a new method for estimating carbon sequestration that is adaptive to urban ecosystems. The remote sensing method is better for large-scale analysis and is spatially explicit. Nevertheless, it also suffers from relatively low accuracy in land-cover classification in urban ecosystems. Even high spatial-resolution images are available, it is often very costly. Urban vegetation can reduce carbon concentration in the atmosphere directly via biomass accumulation or indirectly through the reduction in fossil fuel consumption. Such indirect pathways include the reduction in energy consumption of urban infrastructure, the alleviation of hot island effect, and the promotion of green transportation etc. In recent years, focus of the studies is shifting from carbon sequestration capacity assessment to the underlying mechanisms of its dynamics under both human and natural disturbance. Factors that influence carbon sequestration in urban vegetation mainly include plant growth and replacement, land cover and land use changes, human modification and management. Some clear results are:urban vegetation has a higher carbon sequestration capacity in its early growth stage; the change from forests to constructed areas in humid regions will reduce carbon sequestration; urban vegetation helps to offset the reduction in carbon sequestration in constructed areas; Garden maintenance and management increases carbon sequestration but its own carbon emission cannot be ignored. With improvement in understanding of carbon sequestration of urban vegetation, there will be more cities conducting assessments. Existing data are difficult to aggregate due to differences in methods of survey and estimation, becoming a bottleneck for the development of this research field. Using garden waste to produce biofuel may help to offset the carbon emission from garden maintenance and management. Research priorities for the next step should be set to methods for life cycle assessment and accounting for the carbon emission from human design and management.

Key words: urban forestry, vegetation ecology, carbon storage, carbon emissions, management practices, life cycle, green space