NbS Triple Win Toolkit: Economics and Finance 69 reforestation is taking place due to the high value of alternative land uses. This may make reforestation less cost-effective than avoided deforestation since establishment costs may be higher, although this is context specific and depends on local land use (i.e. deforestation rates per country or region), efficiency and transaction costs65,66,69. Reforestation offers the second most cost-effective NbS option inthe tropics70, with the greatest reforestation potential arising inBrazil, India, Mexico, Myanmar, Colombia, and Indonesia.Cost estimates are reported to vary between $8/tCO2e(USD) in Indonesia and $25/tCO2e (USD) in Brazil69. Non-monetised benefits Provision of habitat Local climate control or cooling effects Air quality Reduced soil erosion Cultural and traditional values and well-being Food and water security Further discussion Reforestation may be undertaken in a variety of ways but can come with many pitfalls. Monoculture plantations can cause adverse effects, reducing biodiversity and increasing water insecurity if the species chosen is maladapted to the local ecosystem71,7. Reforestation does not include afforestation – establishing forest through planting or seeding on land that was not previously classified as forest – but it can encompass both new deliberate/ artificial planting as well as natural regeneration. Natural regeneration is seen as passive management, whereby a previously forested area is allowed to naturally re-seed or develop. Natural regeneration often encourages greater diversity at multiple levels, resilience to climate change, and structural heterogeneity70. Natural regeneration is also more likely to becost-effective since the only costs associated are opportunitycosts and maintenance costs are lower69,72. Utilising reforestation as a cost-effective tool for carbon sequestration is widespread, as evidenced in literature and the evidence base of case studies. This evidence base does not suggest that reforestation is the most cost-effective or most effective intervention; simply that it is often selected. It can offer short-term benefits for carbon sequestration at low costs62,67, but can also result in biodiversity loss, greater water insecurity, and potential reductions in income from switching from agriculture to forest-based activities72,73,74. A focus on reforestation can also obscure the benefits from initially protecting intact ecosystems and forests, and can divert resources away from other ecosystems potentially more efficient at carbon sequestration71,7. Peatlands are often raised as one such example. Only two case studies in the database focused on peatland while sixty-two focused on tropical forests, temperate forests, or montane ecosystems including forests. Avoiding the destruction of or restoring peatlands has comparable carbon sequestration potential to reforestation65. However, re-wetted peatlands may also be a net contributor of methane, a powerful greenhouse gas (GHG), an effect also influenced by climate change and seasonal variation75. While forests cover more of the globe, in terms of the efficiency of carbon sequestration and potential for biodiversity benefits, there are other ecosystems and interventions that warrant as much study and application as has been awarded reforestation efforts.