Reforest lands that have been deforested and afforest suitable lands

Reforestation is the intentional replanting of understocked forestlands (stands in which the growing space is not effectively occupied by crop trees). Here, we also include the establishment of forest vegetation on non-forested lands (also called afforestation). Sample et al. (2017) estimate that reforestation of understocked forested lands could result in 13.3 TgC∙yr-1 (13.3 million metric tons C) of additional carbon stored in aboveground biomass in the U.S, while Hoover and Heath (2011) suggest that 11.3 TgC∙yr-1 could be sequestered from increased stocking levels in just within the seven states of the northeastern U.S. The contribution of forest soils to this additional carbon sink strength with reforestation is equally significant. Nave et al. (2018) estimate that reforestation could contribute an additional 13-21 TgC∙yr-1 (13-21 million metric tons C) within forest soils. Carbon sequestration rates can be increased when non-forested lands, such as marginal crop lands, are converted to forests. For example, nearly half of the carbon sequestered in the U.S. in 2005 came from the regrowth of forests on former crop lands, with reported rates of carbon accrual of 0.14 ̶ 0.34 MgC∙ha-1∙yr-1 (Post and Kwan 2000).

Carbon stocks often reach their highest density in forested ecosystems compared to other ecosystem types or land uses. 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.