A New Approach to Quantify and Map Carbon Stored, Sequestered and Emissions Avoided by Urban Forests

By E. Gregory McPherson, Qingfu Xiao, and Elena Aguaron

Davis, CA (September 8, 2013) – A new U.S. Forest Service study looks at quantifying and mapping stored carbon in trees. Using test sites in Sacramento and Los Angeles, this new approach provides a better understanding of the science behind stored carbon in our urban forests.

Field surveys, biometric information, and remote sensing were used to improve estimates of carbon storage and avoided emissions. These techniques and results can then be used for climate action planning, identifying conservation areas and determining prospective areas of canopy expansion.

Findings for Los Angeles and Sacramento illustrate the complex role of regional and local determinants. Although average tree density and size were substantially greater in Los Angeles, the mean C storage density (8.15 t ha-1) was 53 percent of Sacramento’s (15.4 t ha-1). In Sacramento, native oaks with very high wood densities (815 kg m-3) accounted for 30 percent of total basal area. In Los Angeles, the most dominant taxa had relatively low wood densities (350 – 550 kg m-3).

The inclusion of relatively more wooded land in the Sacramento study area may partially explain higher C storage levels. In Los Angeles, where development is relatively dense, 14 percent of all trees surveyed shaded more than one building compared to only 2 percent in Sacramento. Consequently, the transfer function for avoided emissions in Los Angeles (2.77 t ha-1 UTC yr-1) exceeded Sacramento (2.72 t ha-1 UTC yr-1).

The approach described here improves C estimates and increases the resolution at which C can be mapped across a region. It can be used to map baseline C storage levels for climate action planning, identify conservation areas where UTC densities are highest and determine where opportunities for expanding UTC are greatest.

Download the research.