by EG McPherson, Q Xiao, E Aguaron
Landscape and Urban Planning 120:70-842013
Although the urban tree canopy in California is an important sink for approximately 163 million tons of carbon emissions, official statewide greenhouse gas inventories frequently exclude urban forests. This paper examines overall carbon storage, sequestration, and emissions avoided by city trees to determine the impact of urban forests on inventory estimates. To accurately quantify and map stored, sequestered, and avoided carbon emissions, the authors utilized field surveys, biometric information, Geographic Information System data sets, and remote sensing of urban tree canopy for 370 plots in Los Angeles and 300 plots in Sacramento. The Urban Forest Effects Model (UFORE) field sampling method and urban tree canopy (UTC)-based transfer functions were employed for quantification and mapping at high spatial resolution. After applying multiple derivations of UTC-based transfer functions, the authors were able to estimate that California urban forests account for 2 and 12 percent of total carbon stored and sequestered annually. When including avoided emissions, city trees were responsible for 20 percent of total reductions. The results suggest that the UFORE field sampling method used in conjunction with UTC-based transfer functions can be utilized for mapping baseline carbon storage levels and identifying conservation areas with considerable tree density. This identification is useful for determining the greatest opportunities for urban tree canopy expansion. By further examining the relationship between carbon and temporal dimensions of land use and age classes, future studies could potentially predict change in baseline carbon storage as neighborhoods age. Based on this research, it is evident that urban forests help mitigate climate change by offsetting carbon emissions and modifying urban climate; making city trees an effective adaptation strategy for climate action planning.