Rethinking Reforestation: Why the Real Opportunity is Much Smaller than We Thought

By Abdul Ahad NazakatReviewed by Laura ThomsonOct 14 2025

Reforestation has long been promoted as a leading “natural climate solution”, a way to restore forests, enhance ecosystems, and capture carbon from the atmosphere. But estimates of how much land is available for reforestation, and how much carbon it can sequester, have varied significantly. A new paper by Fesenmyer et al. (2025) attempts a more cautious, evidence-based reassessment in this context.¹

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This article reviews the study’s methodology, findings, and implications for global climate mitigation. It also considers the future of reforestation and complementary strategies for achieving sustainable climate goals.

Key Advances in Methodology

The authors reviewed 89 existing reforestation or restoration opportunity maps, many of which reinforce high-profile climate and biodiversity initiatives. The maps differ in how they define “forest,” what data they use to exclude or include lands, and how they address risks like fire, biodiversity trade-offs, or conflicts with agriculture and communities.

To improve on previous work, Fesenmyer et al carried out the following:

1. Adopt a conservative forest definition. They only count areas that can support dense tree cover (≥ 60 % canopy cover) rather than including sparser woodland or savanna ecosystems, thus reducing risks of mislabeling open ecosystems as forestable lands.
2. Combine multiple existing forest-potential layers. They require agreement between the Bastin and Walker maps and low uncertainty to accept a pixel as forest-potential.
3. Integrate fire frequency data. Areas experiencing frequent non-agricultural fires are excluded because such disturbance regimes challenge long-term forest viability.
4. Apply “exclusions” and safeguards. After establishing a maximum reforestation potential (i.e. where forests could be added), they impose precautionary exclusions for croplands, wetlands, peatlands, built-up areas, and where the albedo effect may lead to net climate harm.¹

These steps collectively reduce overoptimistic estimates and help avoid perverse or harmful outcomes such as planting forests in areas that damage biodiversity or displace agriculture.

Realistic Revised Estimates

The more conservative approach shrinks the global “constrained reforestation potential” estimate to 195 million hectares (Mha) of land, with a corresponding net mitigation potential of 2225 teragrams CO2-equivalent per year over 30 years of regrowth. That is 71–92 % lower than earlier high-end estimates, which ranged from ~678 to 2509 Mha depending on methods.¹

In contrast, their “maximum” reforestation potential (without all exclusions) is 305 Mha (≈ 3114 TgCO2e/year)— still considerable, but far more modest than some prior maps suggested.¹ The drop-off between maximum and constrained totals highlights how many practical, ecological, and social constraints must be heeded.

In their “constrained” scenario, about 98 million people live in areas considered suitable for reforestation under the model. Recognizing that local priorities vary, the authors do not attempt to prioritize which lands should be reforested. Instead, they generate a suite of eight scenarios (e.g., prioritizing minimizing social conflict, securing biodiversity, focusing on water quality) to illustrate how one’s objectives would affect which lands are targeted.¹

One telling result is that very few lands satisfy all criteria. Only 15 Mha meet all seven of the authors’ scenario constraints simultaneously; only 0.5 Mha meets all eight.¹ This suggests that trade-offs are inevitable: one cannot maximize carbon, biodiversity, social justice, and other goals all at once.

Strengths, Limitations, and Implications of the Study

The study’s strengths lie in its clear response to critiques of earlier mapping exercises. By adopting more strict definitions, incorporating fire dynamics, emphasizing low-uncertainty consensus, and applying precautionary exclusions (e.g., for albedo, croplands), the authors produce a more defensible “floor” estimate for reforestation potential. They also provide full datasets and code for replication or modification, which enhances transparency and adaptability to local contexts.

At the same time, the authors fully acknowledge uncertainties and limitations. Their exclusion rules are necessarily judgment calls, for example, how many fires constitute “too many”, or how strictly to define canopy cover. Sensitivity analyses show that relaxing tree-cover thresholds or not excluding fire zones can dramatically increase estimated potential (e.g., by 36–481 %).¹ The reliance on global-scale datasets may overlook nuanced local conditions or opportunities (e.g. marginal croplands, degraded soils, silvopasture.

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Moreover, translating map-based potential into real-world reforestation projects demands local knowledge, community engagement, socio-economic incentive structures, secure land tenure, and ecological monitoring. The authors caution that reforestation must add above and beyond baseline recovery of forests; i.e. new planting must not simply mimic what would have regrown naturally.

Overall, the study clarifies that earlier, more optimistic assessments have likely overstated the scale of safe reforestation opportunities. However, it also reaffirms that modest but meaningful gains remain possible when done carefully.

Reforestation in the Future

Smarter, Locally Grounded Reforestation

Looking forward, the challenge is not just identifying where to reforest but also how to do it in a sustainable, equitable, and resilient way. This study's more conservative estimates can serve as a realistic constraint, helping governments, NGOs, and funders avoid overcommitment to unattainable goals.

Key imperatives include:

• Fine-scale planning and stakeholder engagement: Global maps can guide broad priorities, but local ecological, social, and cultural contexts ultimately determine success.
• Institutional strengthening of land tenure and rights: One scenario with heavy reductions in area is due to insecure land tenure. Ensuring clear, enforceable rights is essential to avoid conflicts and guarantee long-term forest protection.
• Complementary ecological safeguards: Monitoring fire regimes, biodiversity baselines, and carbon permanence is crucial to ensure that reforestation is durable and beneficial.
• Prioritizing co-benefits: In many settings, restoration that supports water quality, erosion control, habitat connectivity, or agroforestry may deliver more local value than carbon alone.

The ~195 Mha figure suggests a “doable but limited” scale within these constraints. Properly targeted reforestation could contribute up to ~2225 TgCO2e per year of net mitigation. However, this was only around 5 % of global fossil fuel and land-use emissions in 2022.¹. Thus, reforestation alone will not suffice to achieve climate goals.

Alternatives and Complementary Options

As reforestation alone is insufficient, other strategies must complement it. Some alternatives or supplements include:

• Enhancement of carbon storage in existing forests: Rather than focusing only on new forests, we can improve management of current forests (e.g., reduce degradation, improve growth, and protect).
• Afforestation in novel ecosystems: While the study excludes many afforestation options, planting trees beyond native forest zones (if carefully designed) may be viable in some contexts.
• Technological carbon removal: Approaches like direct air capture, engineered carbon capture and storage, or enhanced weathering may serve as backstops if biological options saturate.
• Avoided emissions and demand-side reductions: The most reliable climate strategy is reducing fossil emissions and land-use conversion in the first place; reforestation should not be a "carbon offset crutch."

Final Thoughts

Fesenmyer et al.'s work offers a realistic view of reforestation’s global potential. Their carefully constrained 195 Mha and associated mitigation estimate provide a more credible benchmark than earlier projections. However, the study emphasizes that reforestation is not a silver bullet; it is one tool among many and must be managed.

Success will depend on combining robust global modeling with locally informed planning, strong institutions, diverse restoration strategies, and continued innovation in climate mitigation. In an era of urgent emissions reductions, reforestation can still play an important supporting role, but only if deployed wisely in combination with broader decarbonization and ecosystem strategies.

References and Further Reading

1. Fesenmyer, K.A., Poor, E.E., Terasaki Hart, D.E. et al. Addressing critiques refines global estimates of reforestation potential for climate change mitigation. Nat Commun 16, 4572 (2025). https://doi.org/10.1038/s41467-025-59799-8

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