Reforestation offers an immense opportunity to sequester additional carbon and help keep global warming below 20C, but we need better estimates of how much climate mitigation potential exists, through reforestation at actionable scales.
Here, we produced a state-of-the-art spatial map of reforestation opportunity in the conterminous United States (US) . We calculated maximum mitigation potential, based on the biophysical factors, as well as feasible mitigation potential, based on multiple safeguards such as biodiversity protection and food security.
We defined reforestation as the conversion of non-forested areas (less than 25% forest cover) to forested areas (more than 25% forest cover), in areas that were forested historically. We followed a two-step approach of (i) mapping reforestation opportunity areas and (ii) calculating carbon sequestration rates to calculate mitigation potential.
To map reforestation opportunity, we started with historically forested areas and applied a series of spatial and non-spatial deductions eliminating areas where reforestation is unlikely to occur. These deductions included intensive human development, major roads, and impervious surfaces. Additionally, we removed urban areas and peat lands to align with other carbon accounting systems. Lastly, we retained less than 1% of reforestable croplands to protect food production. The resulting area is the maximum potential for reforestation are in the US. We further evaluated feasible mitigation potential by removing 92% of pastureland, in order to reduce effects on livestock production. Finally, we calculated ecoregionally-appropriate carbon sequestration rates, accounting for different forest types in the US.
Results/Conclusions
Our findings indicate that the maximum potential for reforestation in the US is 79 Mha, while 63 Mha (95% CI: 34 to 91.8) represents the feasible reforestation opportunity. We calculated the average area-weighted carbon sequestration rate as 1.33 MgCha-1 yr-1 (95% CI: 0.17 to 5.01). Therefore, we estimate that the maximum mitigation potential is 380 TgCO2e yr-1 and the feasible mitigation potential is 306 TgCO2e yr-1.
The findings of this study have shed light on the enormous potential of reforestation activities to mitigate climate change in the US. These findings would support national and state level policies and evidence-based decision-making related to climate change. Our future work would entail refining the spatial analysis of reforestation opportunity and determining the cost and policies that would hinder or support reforestation activities across the US. We hope that this information will provide the data required by multiple stakeholders, including government, non-profit, and business actors, to implement reforestation activities.