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The expansion of agroforestry could provide substantial climate change mitigation (up to 0.31 Pg C yr−1), comparable to other prominent natural climate solutions such as reforestation. Yet, climate-focused agroforestry efforts grapple with ambiguity about which agroforestry actions provide mitigation, uncertainty about the magnitude of that mitigation and inability to reliably track progress. In this Perspective, we define agroforestry as a natural climate solution, discuss current understanding of the controls on farm-scale mitigation potential and highlight recent innovation on emergent, high-resolution remote sensing methods to enable detection, measurement and monitoring. We also assess the status of agroforestry in the context of global climate ambitions, highlighting regions of underappreciated expansion opportunity and identifying priorities for policy and praxis.In this Perspective, the authors highlight agroforestry as a natural climate solution, discussing definitional refinements, controls on mitigation potential and remote sensing innovations. They assess the status of agroforestry in the context of climate ambitions, identifying key areas and opportunities.

Summary Climate change is dramatically altering the distribution and abundance of many species. An examination of traits may elucidate why some species respond more strongly to climate change than others, particularly when ecophysiological thresholds set range limits. Mangrove forests are expanding polewards. Although multiple environmental factors influence mangrove distributions, freeze tolerance is hypothesized to determine their poleward extent. To investigate how trait variation influences mangroves’ responses to a warming climate, we examined how freeze tolerance and associated traits varied along a latitudinal cline for three co‐occurring mangrove species. We sampled individuals along >200 km of Florida, USA's eastern coast, from the mangroves’ most northern populations, where freeze events were historically common, to southern populations where freeze events continue to be rare. We measured a suite of traits in field‐collected adults and their garden‐reared offspring, and assessed their responses to an experimentally imposed freeze event. We asked whether freeze tolerance and other traits varied predictably among species, with latitude, and between life stages. Species and populations varied dramatically in freeze tolerance, with the highest freeze tolerance in the northernmost species and populations, and the lowest freeze tolerance in the southernmost species and populations. Additionally, leaves of all three species were drier, tougher, thicker and more freeze‐tolerant at the range edge. Tolerance to freezing appears to set the range limits for these mangrove species. All three species converged on a similar phenotype at the range edge, but species‐level variation in freezing resistance was conserved. Thus, these species are likely to continue migrating at different rates in response to climate warming, potentially leading to the dissolution of typically co‐occurring species and creating ‘no analogue’ coastal mangrove–marsh communities. Lay Summary

The role of tree diversity in restored forests and its impact on key ecological processes like growth and resistance to herbivory has become increasingly important. We analyzed height growth and white-tailed deer Odocoileus virginianus browsing damage to saplings of 16 broadleaved tree species in a large-scale (13 ha) reforestation experiment in Maryland, USA, where we manipulated tree diversity in 70 1,225-m² plots. After four growing seasons, higher plot-level tree richness led to increased deer browsing damage (i.e., associational susceptibility). Despite increased deer damage to saplings in mixed plots, tree richness had no overall effect on sapling height growth. However, diversity–height relationships were related to species functional traits. Light demanding species with large leaves and faster growth rates had reduced heights in mixtures, whereas shade-tolerant, slower-growing species generally had either increased or unchanged height growth in diverse tree communities, likely related to increased canopy closure in mixtures relative to monocultures. We show that tree diversity can improve growth of late successional species despite exacerbated mammalian herbivore damage. By facilitating the establishment of species with a range of life-history strategies, increased tree diversity may enhance ecosystem multi-functionality in the early stages of forest restoration.

Restoring forest cover is a key action for mitigating climate change. Although monoculture plantations dominate existing commitments to restore forest cover, we lack a synthetic view of how carbon accumulates in these systems. Here, we assemble a global database of 4756 field-plot measurements from monoculture plantations across all forested continents. With these data, we model carbon accumulation in aboveground live tree biomass and examine the biological, environmental, and human drivers that influence this growth. Our results identify four-fold variation in carbon accumulation rates across tree genera, plant functional types, and biomes, as well as the key mediators (e.g., genus of tree, endemism of species, prior land use) of variation in these rates. Our nonlinear growth models advance our understanding of carbon accumulation in forests relative to mean annual rates, particularly during the next few decades that are critical for mitigating climate change. Tree planting is a promising yet controversial natural climate solution. Here the authors perform a global analysis of aboveground C accumulation in tree monocultures, identifying key predictors such as prior land use, taxonomic identity, and plant traits.

Constraining the climate crisis requires urgent action to reduce anthropogenic emissions while simultaneously removing carbon dioxide from the atmosphere. Improved information about the maximum magnitude and spatial distribution of opportunities for additional land-based removals of CO₂ is needed to guide on-the-ground decision-making about where to implement climate change mitigation strategies. Here, we present a globally consistent spatial dataset (approximately 500-m resolution) of current, potential, and unrealized potential carbon storage in woody plant biomass and soil organic matter. We also provide a framework for prioritizing actions related to the restoration, management, and maintenance of woody carbon stocks and associated soils. By comparing current to potential carbon storage, while excluding areas critical to food production and human habitation, we find 287 petagrams (PgC) of unrealized potential storage opportunity, of which 78% (224 PgC) is in biomass and 22% (63 PgC) is in soil. Improved management of existing forests may offer nearly three-fourths (206 PgC) of the total unrealized potential, with the majority (71%) concentrated in tropical ecosystems. However, climate change is a source of considerable uncertainty. While additional research is needed to understand the impact of natural disturbances and biophysical feedbacks, we project that the potential for additional carbon storage in woody biomass will increase (+17%) by 2050 despite projected decreases (−12%) in the tropics. Our results establish an absolute reference point and conceptual framework for national and jurisdictional prioritization of locations and actions to increase land-based carbon storage.

Natural climate solutions can mitigate climate change in the near-term, during a climate-critical window. Yet, persistent misunderstandings about what constitutes a natural climate solution generate unnecessary confusion and controversy, thereby delaying critical mitigation action. Based on a review of scientific literature and best practices, we distill five foundational principles of natural climate solutions (nature-based, sustainable, climate-additional, measurable, and equitable) and fifteen operational principles for practical implementation. By adhering to these principles, practitioners can activate effective and durable natural climate solutions, enabling the rapid and wide-scale adoption necessary to meaningfully contribute to climate change mitigation. Natural climate solutions can mitigate climate change but misunderstandings about what constitutes a natural climate solution generate unnecessary confusion and controversy. This Perspective distills five foundational principles of natural climate solutions and fifteen operational principles for practical implementation.

Restoring tree cover changes albedo, which is the fraction of sunlight reflected from the Earth’s surface. In most locations, these changes in albedo offset or even negate the carbon removal benefits with the latter leading to global warming. Previous efforts to quantify the global climate mitigation benefit of restoring tree cover have not accounted robustly for albedo given a lack of spatially explicit data. Here we produce maps that show that carbon-only estimates may be up to 81% too high. While dryland and boreal settings have especially severe albedo offsets, it is possible to find places that provide net-positive climate mitigation benefits in all biomes. We further find that on-the-ground projects are concentrated in these more climate-positive locations, but that the majority still face at least a 20% albedo offset. Thus, strategically deploying restoration of tree cover for maximum climate benefit requires accounting for albedo change and we provide the tools to do so. Restoring tree cover is a prominent climate solution but can cause global warming due to changes in albedo. This paper maps albedo and carbon changes from restoring tree cover to highlight where the greatest net climate benefits can be achieved.

Achieving the 1.5–2.0 °C temperature targets of the Paris climate agreement requires not only reducing emissions of greenhouse gases (GHGs) but also increasing removals of GHGs from the atmosphere1,2. Reforestation is a potentially large-scale method for removing CO2 and storing it in the biomass and soils of ecosystems3–8, yet its cost per tonne remains uncertain6,9. Here, we produce spatially disaggregated marginal abatement cost curves for tropical reforestation by simulating the effects of payments for increased CO2 removals on land-cover change in 90 countries. We estimate that removals from tropical reforestation between 2020–2050 could be increased by 5.7 GtCO2 (5.6%) at a carbon price of US$20 CO2–1, or by 15.1 GtCO2 (14.8%) at US$ 50 tCO2–1. Ten countries comprise 55% of potential low-cost abatement from tropical reforestation. Avoided deforestation offers 7.2–9.6 times as much potential low-cost abatement as reforestation overall (55.1 GtCO2 at US $20 tCO2–1 or 108.3 GtCO2 at US$ 50 tCO2–1), but reforestation offers more potential low-cost abatement than avoided deforestation at US$20 tCO2–1 in 21 countries, 17 of which are in Africa.There is a growing need to find cost-effective options for greenhouse gas abatement. In this study, spatially disaggregated marginal abatement cost curves are developed to facilitate economic appraisal of tropical reforestation.

Better land stewardship is needed to achieve the Paris Agreement's temperature goal, particularly in the tropics, where greenhouse gas emissions from the destruction of ecosystems are largest, and where the potential for additional land carbon storage is greatest. As countries enhance their nationally determined contributions (NDCs) to the Paris Agreement, confusion persists about the potential contribution of better land stewardship to meeting the Agreement's goal to hold global warming below 2°C. We assess cost-effective tropical country-level potential of natural climate solutions (NCS)—protection, improved management and restoration of ecosystems—to deliver climate mitigation linked with sustainable development goals (SDGs). We identify groups of countries with distinctive NCS portfolios, and we explore factors (governance, financial capacity) influencing the feasibility of unlocking national NCS potential. Cost-effective tropical NCS offers globally significant climate mitigation in the coming decades (6.56 Pg CO2e yr−1 at less than 100 US$ per Mg CO2e). In half of the tropical countries, cost-effective NCS could mitigate over half of national emissions. In more than a quarter of tropical countries, cost-effective NCS potential is greater than national emissions. We identify countries where, with international financing and political will, NCS can cost-effectively deliver the majority of enhanced NDCs while transforming national economies and contributing to SDGs. This article is part of the theme issue ‘Climate change and ecosystems: threats, opportunities and solutions’.

Forests are major components of the global carbon (C) cycle and thereby strongly influence atmospheric carbon dioxide (CO 2 ) and climate. However, efforts to incorporate forests into climate models and CO 2 accounting frameworks have been constrained by a lack of accessible, global-scale synthesis on how C cycling varies across forest types and stand ages. Here, we draw from the Global Forest Carbon Database, ForC, to provide a macroscopic overview of C cycling in the world’s forests, giving special attention to stand age-related variation. Specifically, we use 11 923 ForC records for 34 C cycle variables from 865 geographic locations to characterize ensemble C budgets for four broad forest types—tropical broadleaf evergreen, temperate broadleaf, temperate conifer, and boreal. We calculate means and standard deviations for both mature and regrowth (age < 100 years) forests and quantify trends with stand age in regrowth forests for all variables with sufficient data. C cycling rates generally decreased from tropical to temperate to boreal in both mature and regrowth forests, whereas C stocks showed less directional variation. Mature forest net ecosystem production did not differ significantly among biomes. The majority of flux variables, together with most live biomass pools, increased significantly with the logarithm of stand age. As climate change accelerates, understanding and managing the carbon dynamics of forests is critical to forecasting, mitigation, and adaptation. This comprehensive and synthetic global overview of C stocks and fluxes across biomes and stand ages contributes to these efforts.