Increase the extent of forest cover within urban areas

Urban forests include developed sites adjacent to streets and buildings, open spaces in parks, residential areas, and schools, as well as natural areas designated as preserves and large urban parks. Urban forestry can be an important mechanism for increasing stored carbon as trees in urban areas can have significant biomass and carbon sequestration (Nowak et al. 2013). Carbon sequestration rates in individual trees within urban areas can exceed those in natural forests due to greater foliar biomass and reduced competition from lower tree densities, as well as irrigation and fertilization (Jo and McPherson 1995)—and a changing climate may be further accelerating these growth rates in urban areas (O’Brien et al. 2012; Pretzsch et al. 2017). Trees can have an additional important influence on carbon mitigation in urban zones by reducing the energy requirements for building heating in winter due to wind protection and summer cooling from tree shading (Nowak et al. 2010).

Carbon stocks often reach their highest density in forested ecosystems compared to other ecosystem types or land uses (Liu et al. 2012; Liu et al. 2014). Actions that maintain the integrity of forested ecosystems or re-establish forest cover can have some of the most significant benefits for maintaining carbon in both above- and belowground pools, as well as improving the ability of the ecosystems to sequester carbon into the future. This strategy seeks to sustain or enhance carbon stocks at broad spatial scales through maintaining forest vegetation, increasing forest stocking, or re-establishing forest cover on non-forested lands.