Experiments under controlled conditions have established that ecosystem functioning is generally positively related to levels of biodiversity, but it is unclear how widespread these effects are in real-world settings and whether they can be harnessed for ecosystem restoration. We used remote-sensing data from the first decade of a long-term, field-scale tropical restoration experiment initiated in 2002 to test how the diversity of planted trees affected recovery of a 500-ha area of selectively logged forest measured using multiple sources of satellite data. Replanting using species-rich mixtures of tree seedlings with higher phylogenetic and functional diversity accelerated restoration of remotely sensed estimates of aboveground biomass, canopy cover, and leaf area index. Our results are consistent with a positive relationship between biodiversity and ecosystem functioning in the lowland dipterocarp rainforests of SE Asia and demonstrate that using diverse mixtures of species can enhance their initial recovery after logging.
NbS Approach: Forest Landscape Restoration
Forest landscape restoration
This article updates our previous comprehensive meta-analysis of what drives and stops deforestation (Busch and Ferretti-Gallon 2017). By including six additional years of research, this article more than doubles the evidence base to 320 spatially explicit econometric studies published in peer-reviewed academic journals from 1996 to 2019. We find that deforestation is consistently associated with greater accessibility (as influenced by natural features such as slope and elevation and built infrastructure such as roads, cities, and cleared areas) and with higher economic returns (from agriculture, livestock, and timber). Some demographic variables are consistently associated with less deforestation (e.g., Indigenous people, poverty, and age) or more deforestation (e.g., population), and others are not associated with the level of deforestation (e.g., education and gender). Policies that directly influence allowable land-use activities are associated with less deforestation (e.g., protected areas, enforcement of forest laws, payments for ecosystem services, community forest management, and certification of sustainable commodities). But policies and institutions that primarily seek other ends are not consistently associated with more or less deforestation (e.g., democracy, general governance, conflict abatement, and land-tenure security). We introduce reforestation and forest degradation as new dependent variables alongside deforestation. Greater population is consistently associated with more forest degradation, whereas steeper slope, greater distance from cities, and lower population are consistently associated with more reforestation.
The European Union’s Biodiversity and Forest Strategies for 2030 mandate protecting all remaining old-growth forests across the EU, increasing the area of habitat patches set aside within forests harvested for timber, and limiting clear-felling in timber-producing landscapes (1). Although saving old-growth forests is critical, stand-alone policies can produce unintended consequences (2). Without simultaneously reducing demand for forest products or increasing supply from plantations and secondary forests, such measures can lead to increased harvesting elsewhere, often in tropical countries, to accommodate demand. Shifting logging activities to countries with weaker legal protections aggravates biodiversity and carbon losses and exacerbates existing inequities in environmental burdens (3). Isolated policies displacing production will also undermine the EU’s recent Deforestation Regulation to halt imports of deforestation-linked tropical products (4).
The consistent monitoring of trees both inside and outside of forests is key to sustainable land management. Current monitoring systems either ignore trees outside forests or are too expensive to be applied consistently across countries on a repeated basis. Here we use the PlanetScope nanosatellite constellation, which delivers global very high-resolution daily imagery, to map both forest and non-forest tree cover for continental Africa using images from a single year. Our prototype map of 2019 (RMSE = 9.57%, bias = −6.9%). demonstrates that a precise assessment of all tree-based ecosystems is possible at continental scale, and reveals that 29% of tree cover is found outside areas previously classified as tree cover in state-of-the-art maps, such as in croplands and grassland. Such accurate mapping of tree cover down to the level of individual trees and consistent among countries has the potential to redefine land use impacts in non-forest landscapes, move beyond the need for forest definitions, and build the basis for natural climate solutions and tree-related studies.
European forests are facing multiple natural and anthropogenic pressures that are expected to become more severe in the next decades. Tree diversity is projected to decline in many areas across the continent. How this will affect the provision of forest services remains an open question, whose answer depends, among others, on the practical and theoretical challenges of incorporating assisted migration into climate adaptation strategies. Here, we tackle the issue by combining a large dataset of tree species occurrences, future climatic projections, and data on tree functional traits and tree-specific forest services into a novel modelling framework.
Old growth forests continue to decline.
Climate-related benefits of afforestation depend on the balance of the often-contrasting effects of biogeochemical (carbon sequestration) and biogeophysical (radiation balance) effects. These effects are known to vary at the continental scale (e.g., from boreal to tropical regions). Here, we show in a four-year study that the biogeochemical vs. biogeophysical balance in paired forested and non-forested ecosystems across short distances (approximately 200 Km) and steep aridity gradient (aridity index 0.64 to 0.18) can change dramatically. The required time for the forestation cooling effects via carbon sequestration, to surpass warming effects associated with the forests’ reduced albedo and suppressed longwave radiation, decreased from 213 years in the driest sites to 73 years in the intermediate and 43 years in the wettest sites. Climate-related benefits of forestation, previously considered at large-spatial scales, should be considered at high-spatial resolutions in climate-change mitigation programs aimed at taking advantage of the vast non-forested dry regions.
During December 2020, a crowdsourcing campaign to understand what has been driving tropical forest loss during the past decade was undertaken. For 2 weeks, 58 participants from several countries reviewed almost 115 K unique locations in the tropics, identifying drivers of forest loss (derived from the Global Forest Watch map) between 2008 and 2019. Previous studies have produced global maps of drivers of forest loss, but the current campaign increased the resolution and the sample size across the tropics to provide a more accurate mapping of crucial factors leading to forest loss. The data were collected using the Geo-Wiki platform (www.geo-wiki.org) where the participants were asked to select the predominant and secondary forest loss drivers amongst a list of potential factors indicating evidence of visible human impact such as roads, trails, or buildings. The data described here are openly available and can be employed to produce updated maps of tropical drivers of forest loss, which in turn can be used to support policy makers in their decision-making and inform the public.
To counteract undesirable impacts of climate change, several different mitigation instruments have been proposed to sequester carbon through reforestation or avert greenhouse gas emissions due to land use change through forest carbon offset projects. Such projects will require an explicit focus on equitable benefit sharing to generate sustainable and alternative livelihoods. However, research on the impacts of forest carbon offset projects for individuals and communities has often been conducted without baseline data or counterfactuals built into the research methods. We conducted a study in a small Indigenous community in eastern Panama with participants and non-participants in a forest carbon offset project, across wealth groups. In this mixed methods study, participants and non-participants completed surveys before, during, and after implementation over 14 years to assess changes to natural and financial assets. We also assessed major concerns and perceived benefits of the carbon offset project via open-ended questions. Quantitative data show that participants continued to engage in reforestation practices even after payment cessation. Quantitative data also suggest carbon offset payments provided financial stability for poorer participants to diversify into other sources of income over time, while income inequality remained stable across wealth groups. Qualitative data indicate that the greatest benefit of the carbon offset project for participants was economic security for future generations, while concerns about basic needs like food and money declined over time for both participants and non-participants. This research suggests that forest carbon offset projects can be effective for encouraging long-term adoption of forestry practices, specifically reforestation and agroforestry, while providing social co-benefits for rural livelihoods, across wealth dimensions.
Meeting the Paris Agreement’s climate objectives will require the world to achieve net-zero CO2 emissions around or before mid-century. Nature-based climate solutions, which aim to preserve and enhance carbon storage in terrestrial or aquatic ecosystems, could be a potential contributor to net-zero emissions targets. However, there is a risk that successfully stored land carbon could be subsequently lost back to the atmosphere as a result of disturbances such as wildfire or deforestation. Here we quantify the climate effect of nature-based climate solutions in a scenario where land-based carbon storage is enhanced over the next several decades, and then returned to the atmosphere during the second half of this century. We show that temporary carbon sequestration has the potential to decrease the peak temperature increase, but only if implemented alongside an ambitious mitigation scenario where fossil fuel CO2 emissions were also decreased to net-zero. We also show that non-CO2 effects such as surface albedo decreases associated with reforestation could counter almost half of the climate effect of carbon sequestration. Our results suggest that there is climate benefit associated with temporary nature-based carbon storage, but only if implemented as a complement (and not an alternative) to ambitious fossil fuel CO2 emissions reductions.
To address climate change and meet global commitments, nature-based climate (NbCS) solutions i.e. actions that aim to address climate change in sustainable way, are becoming increasingly popular. This is often expressed in so called “green pledges” that promote large scale programs of tree planting, often in plantations. Establishment of such plantations could deliver benefits to biodiversity, but this is not guaranteed, and recommendations on how to manage nature-based solutions (NbS) for biodiversity are limited and not embedded in scientific knowledge. Evidence from landscape ecology can inform general principles of NbCS design. Here, we synthesise evidence and make recommendations that can help “green pledges” to benefit biodiversity conservation. We call for an integrated approach, where NbCS tree planting projects move beyond carbon storage to create functional and diverse habitats providing multiple long-term services while safeguarding biodiversity.
Forest restoration is being scaled-up globally to deliver critical ecosystem services and biodiversity benefits, yet we lack rigorous comparison of co-benefit delivery across different restoration approaches. In a global synthesis, we use 25,950 matched data pairs from 264 studies in 53 countries to assess how delivery of climate, soil, water, and wood production services as well as biodiversity compares across a range of tree plantations and native forests. Carbon storage, water provisioning, and especially soil erosion control and biodiversity benefits are all delivered better by native forests, with compositionally simpler, younger plantations in drier regions performing particularly poorly. However, plantations exhibit an advantage in wood production. These results underscore important trade-offs among environmental and production goals that policymakers must navigate in meeting forest restoration commitments.
Quantifying how well Nature-based Solutions can offset anthropogenic climate change impacts is important for adaptation planning, but has rarely been done. Here we show that a widely-applied Nature-based Solution in South Africa – invasive alien tree clearing – reduces the impact of anthropogenic climate change on drought streamflow. Using a multi-model joint-attribution of climate and landscape-vegetation states during the 2015–2017 Cape Town “Day Zero” drought, we find that anthropogenic climate change reduced streamflow by 12–29% relative to a counterfactual world with anthropogenic emissions removed. This impact on streamflow was larger than corresponding reductions in rainfall (7–15%) and reference evapotranspiration (1.7–2%). Clearing invasive alien trees could have ameliorated streamflow reductions by 3–16% points for moderate invasions levels. Preventing further invasive alien tree spread avoided potential additional reductions of 10–27% points. Total clearing could not have offset the anthropogenic climate change impact completely. Invasive alien tree clearing is an important form of catchment restoration for managing changing hydroclimatic risk, but will need to be combined with other adaptation options as climate change accelerates.
Forest carbon projects can deliver multiple benefits to society. Within Southeast Asia, 58% of forests threatened by loss could be protected as financially viable carbon projects, which would avoid 835 MtCO2e of emissions per year from deforestation, support dietary needs for an equivalent of 323,739 people annually from pollinator-dependent agriculture, retain 78% of the volume of nitrogen pollutants in watersheds yearly and safeguard 25 Mha of Key Biodiversity Areas.
Fire-prone dry forests often face increasing fires from climate change with low resistance and resilience due to logging of large, old fire-resistant trees. Their restoration across large landscapes is constrained by limited mature trees, physical settings, and protection. Active restoration has been costly and shown limited effectiveness, but lower cost passive restoration is less studied. I used GIS and machine learning to see whether passive restoration of old trees could overcome constraints in time, by 2060, across 667,000 ha of montane forests in the San Juan Mountains, Colorado, where temperatures are increasing faster than the global average. Random Forest models of physical locations of reconstructed historical old growth (OG) and relatively frequent fire (RFF) show historical OG with RFF was favored between 6.1 and 7.9℃ annual mean temperatures. Random Forest models projected that similar temperature-suitable locations were moved into the current middle montane ca 2015, and would be extended to just below the upper limit of the montane if the Paris 1.5℃ goal is reached, but beyond if not. US Forest Service common stand exam data, which covered ~15% of the study area and included 26,149 tree ages, show the highest potential for restoring resistance and resilience from old trees is a ≥120-year age class. This class could become a ≥160-year age class, which meets old-growth age criteria, over 81% of the area by ca 2060, nearly fully restoring historical old-growth levels. Half this age class is already protected, and much of the remainder could be retained using evidence-based diameter caps. Datasets thus are sufficient to show that passive restoration of old-tree resistance and resilience to fire is feasible by ca 2060 across a large montane landscape, although contingent on global success in achieving the Paris 1.5℃ goal. Passive restoration may be viable elsewhere.
Worldwide, Indigenous peoples are leading the revitalization of their/our cultures through the restoration of ecosystems in which they are embedded, including in response to increasing “megafires.” Concurrently, growing Indigenous-led movements are calling for governments to implement Indigenous rights, titles and treaties, and many settler-colonial governments are committing to reconciliation with Indigenous peoples and to implementing the United Nations Declaration on the Rights of Indigenous Peoples. Yet, despite growing recognition that just and effective conservation is only possible through partnerships with, or led by, Indigenous peoples, decolonizing approaches to restoration have received insufficient attention. However, reconciliation will be incomplete without Indigenous-led restoration of Indigenous lands, knowledges, and cultures. In this article, we introduce the concept of “walking on two legs” to guide restoration scientists and practitioners in advancing the interconnected processes of Indigenous-led restoration and reconciliation in Indigenous territories. As an action-oriented framework articulated by Secwépemc Elder Ronald E. Ignace, “walking on two legs” seeks to bring Indigenous knowledges into balance with western scientific knowledge in service of upholding an Indigenous stewardship ethic that is embedded in Indigenous ways of relating to land and embodies principles of respect, reciprocity, and responsibility. Grounding this discussion in the context of fire-adapted ecosystems of western Canada and unceded and traditional Secwépemc territory, Secwepemcúl̓ecw, we argue that walking on two legs, along with principles of reconciliation, offers a pathway to uphold respectful relationships with Indigenous peoples, knowledges, and territories through Indigenous-led restoration.
- Restoring the degraded Atlantic Forest is one of the biggest conservation challenges in Brazil. In a biome with high human presence, understanding the potential for restoration approaches, such as agroforestry, to provide benefits to smallholder farmers and biodiversity is essential in developing equitable restoration strategies.
- Smallholder or family farmers are essential to national food security, producing most fruit and vegetables consumed in Brazil. Their farms can also provide ecological stepping stones for biodiversity. To better understand their role in Atlantic Forest restoration, this study explores the use of agroforestry by smallholder farmers from the Movimento Sem Terra (MST), the Rural Landless Workers’ Movement, in Pontal do Paranapanema.
- We use quantitative and qualitative data to assess farmer perceptions of the measures which support agroforestry farming, barriers to implementation and its impact on indicators of wellbeing. We find agroforestry farmers report significant benefits in 8 of 18 tested indicators. Attitudes to agroforestry are varied, but common themes emerge including the high value of tree cover for shade and cooling effects, and the difficulties in selling agroforestry products. Our results show lack of policy support and initial investment needs are the biggest constraints to agroforestry, but opportunity cost is not considered a large barrier.
- Tailored policies and financial measures are needed to integrate thousands of smallholder farmers into the Atlantic Forest restoration agenda, helping to reach biome restoration targets while supporting rural livelihoods and national food security. Further research is required into links between additional socio-economic and biogeographical variables and agroforestry uptake in the region
Adverse effects of climate change are increasing around the world and the floods are posing significant challenges for water managers. With climate projections showing increased risks of storms and extreme precipitation, the use of traditional measures alone is no longer an option. Nature-Based Solutions (NBS) offer a suitable alternative to reduce the risk of flooding and provide multiple benefits. However, planning such interventions requires careful consideration of various factors and local contexts. The present paper provides contribution in this direction and it proposes a methodology for allocation of large-scale NBS using suitability mapping. The methodology was implemented within the toolboxes of ESRI ArcMap software in order to map suitability for four types of NBS interventions: floodplain restoration, detention basins, retention ponds, and river widening. The toolboxes developed were applied to the case study area in Serbia, i.e., the Tamnava River basin. Flood maps were used to determine the volume of floodwater that needs to be stored for reducing flood risk in the basin and subsequent downstream areas. The suitability maps produced indicate the potential of the new methodology and its application as a decision-support tool for selection and allocation of large-scale NBS.
As cities increasingly turn to nature-based solutions to address key urban socio-ecological challenges, approaches to their governance, planning and implementation are increasingly important for ensuring their effectiveness. Nature-based solutions are multifunctional, and so their planning and implementation are by necessity interdisciplinary. As such, to support urban transitions with nature-based solutions, the role of intermediary actors deserves research attention. Intermediaries play key roles in linking between sectors, across different levels of government and between disciplines and policy domains. We identified three key points for research and planning nature-based solutions through intermediaries as key agents for change: intermediaries are creators of enabling institutional spaces needed for mainstreaming nature-based solutions in cities; intermediaries as actor configurations are dynamic over time and in context, and intermediation has to be understood as a fundamental governance activity in cities that want to scale up their climate adaptation planning with nature-based solutions. Using a case study of the development and initial implementation of the metropolitan urban forest strategy in Melbourne Australia, we analyze the multi-actor landscape that emerged, through the lens of intermediation. We systematically investigated which actors, partnerships and platforms acted as intermediaries in the transformative agenda of the Urban Forest strategy, how these actors interacted over the course of the strategy’s development and how their roles and functions shifted during the early implementation stages of the strategy. We found that an ‘ecology of intermediaries’ adopted a range of roles to support key functions including building collaboration, informing and disseminating policy learning, and strengthening political support. While intermediaries’ roles and functions shifted across the strategy’s development, their contributions were critical in the complex metropolitan governance context. Collaborative planning and governance for nature-based solutions in cities require intermediaries to remain topical, focused and inclusive/open to new ideas and lessons from innovations both emerging and driven.
Several Andean countries have planned to restore forest cover in degraded land to enhance the provision of multiple ecosystem services in response to international commitments such as the Bonn Challenge. Hydrological services, e.g. water supply, hydrological regulation and erosion mitigation, are particularly important to sustain the life of more than fifty million Andean people. While rapid and important forest cover changes have occurred during recent decades, critical information on the impact of forestation on hydrological services has not yet been synthesized in the context of Andean ecosystems. We define forestation as the establishment of forest by plantation or natural regeneration on areas that either had forest in the past or not. To help improve decision-making on forestation in the Andes, we reviewed the available literature concerning the impacts of forestation on water supply, hydrological regulation and mitigation of erosion and landslides. We also examined available data on the most relevant hydrological processes such as infiltration, evapotranspiration and runoff in forest stands. Hydrological services from native forests were also included as a reference state for comparing processes and services provided by forestation. Following systematic review protocols, we synthesized 155 studies using different methods, including meta-analyses and meta-regressions. Results show that forestation has had clear impacts on degraded soils, through reducing water erosion of soils and risk of moderate floods, increasing soil infiltration rate by 8 and topsoil organic matter (SOM). We found that 20 years of tree plantation was sufficient to recover infiltration rate and sediment yield close to the levels of native forests whereas SOM, soil water storage and surface runoff of native forests could not be recovered by forestation in the time scales examined. The benefits in terms of hydrological regulation are at the expense of a reduction in total water supply since forest cover was associated with higher water use in most Andean regions. Forestation with native species was underrepresented in the reviewed studies. The impact of forestation on landslides has also been largely overlooked in the Andes. At high elevations, exotic tree plantations on Andean grasslands (e.g. páramo and puna) had the most detrimental consequences since these grasslands showed an excellent capacity for hydrological regulation and erosion mitigation but also a water yield up to 40% higher than tree plantations. People engaged in forest restoration initiative should be aware that hydrological services may take some time for society and the environment to show clear benefits after forestation.
Earth is approaching environmental thresholds that, if crossed, will create serious disruptions to ecosystems, economies, and society. To avoid the devastating effects of climate change and biodiversity loss, humanity must protect and restore native ecosystems. International conventions and organizations support forest restoration as a method for mitigating hazardous environmental shifts, but questions remain as to where and how to focus such restoration efforts. On page 76 of this issue, Bastin et al. describe a new approach that advances our understanding of global tree distribution.
Over 140 Mha of restoration commitments have been pledged across the global tropics, yet guidance is needed to identify those landscapes where implementation is likely to provide the greatest potential benefits and cost-effective outcomes. By overlaying seven recent, peer-reviewed spatial datasets as proxies for socioenvironmental benefits and feasibility of restoration, we identified restoration opportunities (areas with higher potential return of benefits and feasibility) in lowland tropical rainforest landscapes. We found restoration opportunities throughout the tropics. Areas scoring in the top 10% (i.e., restoration hotspots) are located largely within conservation hotspots (88%) and in countries committed to the Bonn Challenge (73%), a global effort to restore 350 Mha by 2030. However, restoration hotspots represented only a small portion (19.1%) of the Key Biodiversity Area network. Concentrating restoration investments in landscapes with high benefits and feasibility would maximize the potential to mitigate anthropogenic impacts and improve human well-being.
We currently face both an extinction and a biome crisis embedded in a changing climate. Many biodiverse ecosystems are being lost at far higher rates than they are being protected or ecologically restored. At the same time, natural climate solutions offer opportunities to restore biodiversity while mitigating climate change. The Bonn Challenge is a U.N. programme to restore biodiversity and mitigate climate change through restoration of the world’s degraded landscapes. It provides an unprecedented chance for ecological restoration to become a linchpin tool for addressing many environmental issues. Unfortunately, the Forest and Landscape Restoration programme that underpins the Bonn Challenge, as its name suggests, remains focused on trees and forests, despite rising evidence that many non-forest ecosystems also offer strong restoration potential for biodiversity and climate mitigation. We see a need for restoration to step back to be more inclusive of different ecosystem types and to step up to provide integrated scienti c knowledge to inform large-scale restoration. Stepping back and up will require assessments of where to restore what species, with recognition that in many landscapes multiple habitat types should be restored. In the process, trade-offs in the delivery of different ecosystem services (e.g. carbon, biodiversity, water, albedo, livestock forage) should be clearly addressed. We recommend that biodiversity safeguards be included in policy and implemented in practice, to avoid undermining the biophysical relationships that provide ecosystem resilience to climate change. For ecological restoration to contribute to international policy goals will require integrated large-scale science that works across biome boundaries.
Land-based greenhouse gas removal (GGR) options include afforestation or reforestation (AR), wetland restoration, soil carbon sequestration (SCS), biochar, terrestrial enhanced weathering (TEW), and bioenergy with carbon capture and storage (BECCS). We assess the opportunities and risks associated with these options through the lens of their potential impacts on ecosystems services (Nature’s Contributions to People; NCPs) and the United Nations Sustainable Development Goals (SDGs). We find that all land-based GGR options contribute positively to at least some NCPs and SDGs. Wetland restoration and SCS almost exclusively deliver positive impacts. A few GGR options, such as afforestation, BECCS, and biochar potentially impact negatively some NCPs and SDGs, particularly when implemented at scale, largely through competition for land. For those that present risks or are least understood, more research is required, and demonstration projects need to proceed with caution. For options that present low risks and provide cobenefits, implementation can proceed more rapidly following no-regrets principles.
Despite substantial increases in the scope and magnitude of biodiversity conservation and ecological restoration, there remains ongoing degradation of natural resources that adversely affects both biodiversity and human well- being. Nature-based Solutions (NbS) can be an effective framework for reversing this trend, by increasing the alignment between conservation and sustainable development objectives. However, unless there is clarity on its evolution, definition and principles, and relationship with related approaches, it will not be possible to develop evidence-based standards and guidelines, or to implement, assess, improve and upscale NbS interventions globally. In order to address this gap, we present the definition and principles underpinning the NbS framework, recently adopted by the International Union for Conservation of Nature, and compare it to (1) the Ecosystem Approach that was the foundation for developing the NbS definitional framework, and (2) four specific eco- system-based approaches (Forest Landscape Restoration, Ecosystem-based Adaptation, Ecological Restoration and Protected Areas) that can be considered as falling under the NbS framework. Although we found substantial alignment between NbS principles and the principles of the other frameworks, three of the eight NbS principles stand out from other approaches: NbS can be implemented alone or in an integrated manner with other solutions; NbS should be applied at a landscape scale; and, NbS are integral to the overall design of policies, measures and actions, to address societal challenges. Reversely, concepts such as adaptive management/governance, effectiveness, uncertainty, multi-stakeholder participation, and temporal scale are present in other frameworks but not captured at all or detailed enough in the NbS principles. This critical analysis of the strengths and weaknesses of the NbS principles can inform the review and revision of principles supporting specific types of NbS (such as the approaches reviewed here), as well as serve as the foundation for the development of standards for the successful implementation of NbS.