How much carbon was stored in Seattle’s urban vegetation?

Details

Most of the global population and its CO₂ emissions can be attributed to urban areas. Urbanization changes terrestrial carbon stocks and fluxes, which in turn affect ecosystem functions and atmospheric CO₂ concentrations.

Using the Seattle, Washington, region as a case study, the researchers explored how aboveground carbon stocks relate to land cover in an urbanizing area. Their objectives were to estimate aboveground live and dead terrestrial carbon stocks across multiple land cover classes and quantify relationships between urban cover and vegetation across an urbanization gradient. They established 154 sample plots in the Seattle region to assess carbon stocks by distance from the urban core and by land cover: heavily, moderately and lightly urbanized areas, mixed forest, and conifer forest.

Regional mean aboveground live biomass was 89±22 Mg C ha⁻¹, with an additional 11.8±4 Mg C ha⁻¹ in coarse woody debris biomass; the figures are means with 95% confidence intervals. Average live biomass was 140±40 Mg C ha⁻¹ in forested land covers and 18±14 Mg C ha⁻¹ in urban land covers, while regional mean vegetated canopy cover was 57%. Both total carbon stocks and mean vegetated canopy cover were surprisingly high, even in heavily urbanized areas, well exceeding observations in other urbanizing areas and average US forested carbon stocks.

As urban land covers and populations continue to grow rapidly worldwide, the researchers concluded that vegetation in urbanizing areas is important to consider in the terrestrial carbon cycle.