Addressing critiques refines global estimates of reforestation potential for climate change mitigation

Abstract

Reforestation is a prominent climate change mitigation strategy, but available global maps of reforestation potential are widely criticized and highly variable, which limits their ability to provide robust estimates of both the locations and total area of opportunity. Here we develop global maps that address common critiques, build on a review of 89 reforestation maps created at multiple scales, and present eight reforestation scenarios with varying objectives, including providing ecosystem services, minimizing social conflicts, and delivering government policies. Across scenarios, we find up to 195 Mha (million hectares) are available (2225 TgCO₂e (teragrams of carbon dioxide equivalent) per year total net mitigation potential), which is 71-92% smaller than previous estimates because of conservative modeling choices, incorporation of safeguards, and use of recent, high-resolution datasets. This area drops as low as 6 Mha (53 TgCO₂e per year total net mitigation potential) if only statutorily protected areas are targeted. Few locations simultaneously achieve multiple objectives, suggesting that a mix of lands and restoration motivations will be needed to capitalize on the many potential benefits of reforestation.

Fig. 1. Conceptual diagram of the process of mapping reforestation potential.

Reforestation mapping generally follows the following steps: (1) defining forest, (2) mapping forest potential (where forest can occur), (3) mapping reforestation potential within the potential forest, first as maximum reforestation potential, and then as constrained reforestation potential (maximum reforestation potential with safeguards), and (4) using overlays to provide additional information so that decision makers can evaluate the feasibility and desirability of the maximum or constrained reforestation potential given specific circumstances. Critiques from the literature associated with these steps are shown to the left. Details from unique existing global reforestation maps and this analysis are shown in columns.

Fig. 2. Datasets used in reforestation maps.

Suitability, exclusion, and overlay datasets used by peer-reviewed reforestation maps that were published 2011–2022 (n = 89), and by this analysis. Datasets are partly sorted by prevalence in a given geography, top to bottom (sorting global first, then regional, then national, then subnational). Some datasets are used consistently across scales. For example, forest loss is always used to define suitability, and economic factors are always used as an overlay. However, other datasets are used in different ways depending on the individual product and scale of the analysis. For example, croplands are used as suitability, exclusion, and overlay factors in different products or within the same product.

Fig. 3. Agreement (intersection) of reforestation scenarios and scenario combinations in this analysis, with example maps.

a Comparison of the area of seven scenarios to the constrained reforestation potential, and the area of agreement of 25 select scenario combinations (area shown in bars, identity of scenario combinations shown below the bars by circles), b percent land area in the constrained reforestation potential scenario by one-degree cells, and c percent land area where all avoiding social conflicts scenarios agree (intersect) within the constrained reforestation potential by one-degree cells. Panel c has less total area than panel b due to removal of areas with low individual rights, insecure land tenure, and/or potential conflict with nature-dependent livelihoods. Note that 102 other possible scenario combinations are not shown in a.