Nature‐based Solutions to tackle climate change and restore biodiversity

Abstract

Climate change and biodiversity loss dominate concerns over anthropogenic modification of the natural world. For the last 40 years, each decade has been successively warmer than the last; the most recent with global surface temperatures 1.09°C higher than before the industrial era, c. 1850–1900 (IPCC, 2021). In addition to a changing climate, life on Earth is under extreme pressure from habitat change, invasive species, over-exploitation and pollution (Hautier et al., 2015; Millennium Ecosystem Assessment, 2005). As a result, it has been estimated that 1 million species will likely go extinct in the coming decades, coinciding with declines in overall biomass (IPBES report, 2019; Lotze et al., 2019). Together, these worrying trends of climate change and biodiversity loss define the Anthropocene era (Crutzen, 2002). The coming years will see a strong push for the development of large-scale solutions to reduce atmospheric carbon dioxide levels and air pollution to mitigate climate change, while also reversing trends in biodiversity decline. For example, the 2021–2030 UN Decades on Ecosystem Restoration (https://www.decadeonrestoration.org/) and Ocean Science for Sustainable Development (https://www.oceandecade.org/) are two of the key programmes designed to help deliver the United Nations Sustainable Development Goals by 2030, which include climate change mitigation and biodiversity protection. Furthermore, the Intergovernmental Panel on Climate Change (IPCC) and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) published their first-ever joint report (Portner et al., 2021) in recognition of climate change and biodiversity loss being inexorably intertwined (Pettorelli et al., 2021). The joint report is a call to action, making it clear that there is no time to lose in implementing strategies with a combined approach to reverse trends in environmental degradation (Pettorelli et al., 2021), and is expected to inform discussions and policy decisions at the upcoming Conferences of Parties (COP), COP 15 (biodiversity) and COP 26 (climate change) at the end of 2021. Nature-based Solutions (NbS) are a promising approach to address a broad range of societal challenges, such as reducing atmospheric carbon dioxide while increasing habitat and biodiversity. They are defined by the International Union for the Conservation of Nature (IUCN) as: ‘Actions to protect, sustainably manage, and restore natural or modified ecosystems, that address societal challenges [such as climate change] effectively and adaptively, simultaneously providing human well-being and biodiversity benefits’. A report by the British Ecological Society on NbS found that it can never be a substitute for the need to reduce fossil fuel emissions to achieve net zero emissions and halt climate change, but NbS could make a valuable contribution, while providing a range of other benefits (Stafford et al., 2021). To realise these benefits, uncertainties associated with the implementation of NbS, and evidence regarding their benefits to biodiversity, need to be addressed (Pettorelli et al., 2021). The extent to which NbS can aid in climate mitigation also needs clarification as estimates of contributions vary widely, and because some proposed actions may not provide human wellbeing or biodiversity benefits—a key tenet of NbS (Portner et al., 2021). This Special Feature brings together new scientific research to help understand the co-benefits of NbS and how they should be implemented. The articles in this Special Feature cover NbS in five countries across three continents—from forestry projects in Brazil to human-modified landscapes in Europe, these studies show just a few of the myriad aspects that must be considered when designing NbS. In this Editorial, we discuss some of the main results obtained and provide a perspective on what is required for successful NbS. A popular application for NbS is climate change mitigation. Although NbS include both terrestrial and marine initiatives (Fourqurean et al., 2012) many projects focus on tree planting or woodland regeneration (www.wwf.panda.org; Holl & Brancalion, 2020; Seddon et al., 2021; Seymour, 2020). Recent studies are starting to focus also on restoration of wetlands or peatlands (e.g. Bossio et al., 2020; Bradfer-Lawrence et al., 2021; Griscom et al., 2017). In one of the studies in this Special Issue, Bradfer-Lawrence et al. (2021) conducted a mapping exercise to precisely examine the contribution of peatland restoration, saltmarsh creation and woodland creation for mitigating the effects of climate change. They used the United Kingdom as a case study, and their main aim was to investigate the extent to which these NbS would contribute to the UK's net zero emissions target. Their results show that even under the most ambitious interventions, woodland creation can remove up to −602.9 Mt CO2e (CO2 equivalent) and saltmarsh creation could lead to a removal of a meagre −2.7 Mt CO2e by 2100. Peatland restoration would have the most dramatic impact, potentially avoiding the emission of 663 Mt CO2 by 2100 (Bradfer-Lawrence et al., 2021). However, it is important to note that there were no scenarios where peatland restoration would lead to net carbon sequestration, only avoided emissions. In other words, while carbon emissions are much higher in degraded than in restored peatlands, peatland restoration in itself does not sequester additional carbon. Woodland and saltmarsh creation, on the other hand, would lead to carbon sequestration. The total cumulative mitigation by 2100 is equivalent to 3 years' worth of UK emissions at current levels. These results are show NbS is not a sole solution to climate change, but can contribute meaningfully to the UK's goal to reach net zero emissions. There are other NbS that can be used in conjunction with restoration and tree planting which can help boost carbon sequestration. Improved Forest Management (IFM) is another form of NbS that stands alongside reforestation and avoided forest conversion to offset greenhouse gas emissions (Griscom et al., 2017; Fargione et al., 2018). IFM includes silvicultural practices such as extended rotation, managing stand density, retaining logging debris, reducing the intensity of harvests and soil management, but so far, only extended rotation has been assessed for its use as an NbS. Kaarakka et al. (2021) reviews a range of silvicultural practices within IFM and discuss how they could help increase carbon sequestration in live vegetation and soil. The authors also discuss how many of these practices come with trade-offs. For instance, extended rotation can be an attractive option to increase carbon storage in the short term, however, it can also increase the risk of fire or diseases in the future. On the other hand, thinning could decrease total carbon storage in the short term but provide increased storage in the long term. This study particularly focuses on how soil carbon is often overlooked when creating forest management guidelines (Case et al., 2021), despite the potential of these stocks to represent 56% of ecosystem carbon on managed lands in the continental United States (Domke et al., 2017). The authors discuss how harvesting intensity, for instance, is a key factor affecting soil carbon stocks both directly by removing biomass and indirectly through disturbance, but harvesting intensity is rarely designed to maximise soil carbon stocks in forested areas. Both the Bradfer-Lawrence et al. (2021) and Kaarakka et al. (2021) studies highlight the variety of NbS approaches that can be used to help mitigate climate change, from ecosystem restoration, to tree planting, to soil management. These approaches will contribute to achieving net zero carbon emissions when used alongside societal changes to reduce carbon emissions. Importantly, these practices also have the potential to provide essential co-benefits, such as biodiversity, however, evidence on best management techniques to achieve this is still lacking (Di Sacco et al., 2021; Pettorelli et al., 2021). One of the most important potential ecological co-benefits of NbS is how it can support local biodiversity and slow global losses. A wide diversity of living organisms is essential to maintain the health and function of an ecosystem. Ecosystem functions are all the processes that maintain life, and these can be as varied as nutrient cycling, pollination or seed dispersal. Some of these ecosystem functions are also particularly relevant for humans; for instance, it is estimated that animals pollinate two-thirds of all crops grown for human consumption (Klein et al., 2007). This positive relationship between biodiversity and ecosystem functioning is shown by Beaumelle et al. (2021) in their contribution to this Special Feature. This study demonstrates the advantages of increasing plant diversity on a local scale to improve biological pest control services, using vineyards as the test crop habitat due to its high use of pesticides. The authors show that diverse, flowering crop cover has more beneficial effects on natural predators for pest control in simple (less natural) habitats compared to complex and more natural landscapes. From an ecological perspective, this research corroborates previous studies that increased plant diversity can trigger a bottom-up cascade that is positive to overall biodiversity and the provision of pest control. Ultimately, this study provides evidence that increasing diversity of plant species in extremely simplified terrestrial systems, such as existing monocultures, is an effective NbS for reducing the use of pesticides. Increasing plant diversity in highly modified aquatic systems can also trigger a bottom-up cascade and increase benefits to humans, as shown by Van Leeuwen et al. (2021) who reports the progress of the restoration of a man-made freshwater ecosystem in the Netherlands. Lake Markermeer was initially formed by creating an estuary for flood protection. While this lake initially provided high levels of ecosystem services, its ecological integrity declined over time such that biodiversity of higher trophic levels significantly declined. Unlike the aim of many restoration projects, returning this lake to its original conditions is not an option given the continued need for flood risk protection. Instead, the Marker Wadden project was created to enhance the food web from the bottom up. The project created new islands which provided ‘natural’ shorelines with gradual land–water transition, promoting the colonisation of plants and nesting areas for rare bird species, as well as recreation opportunities for people. The suspension of fine sediments, which was one of the main issues reducing light availability for phytoplankton, was improved in some areas which also triggered an increase in zooplankton, fish and aquatic birds. Again, this study adds to evidence that sometimes small modifications towards a more natural habitat can improve a broader array of environmental conditions. The importance of considering trophic interactions is clear from the benefits seen in the man-made systems studied in Beaumelle et al. and Van Leeuwen et al., but the same remains true for natural and regenerating systems. Villar and Medici (2021) conducted experiments to address the buffering effects of large herbivores on plant communities in the Atlantic Forest of Brazil. Large herbivores were excluded from 18 m2 exclosures which were left open at the top and bottom to allow small mammals entry. The experiment ran from 2004 to 2014, with sampling twice-yearly in the first half, and annually in the second half. The results showed a collapse in plant community biodiversity resulting from large herbivore (tapir, peccary and deer) exclusion in both old-growth and secondary forests, although a trend of decreasing diversity over time was seen in plots with and without treatment, likely due to ongoing defaunation. Large herbivores modulate the plant community through herbivory but also through seed dispersal (Edwards et al., 2014; O'Farrill et al., 2013), and rewilding is yet another type of NbS that could be most effective at increasing plant diversity in restoration sites. The studies in this Special Feature have given examples of the extent to which NbS can help mitigate climate change and biodiversity loss. However, those practices must also benefit humans locally, and some studies in this Special Feature show how easily those practices can become harmful if socio-economic impacts are not considered during project planning. For instance, although IFMs have many positive effects, small-scale farmers can be disadvantaged by improvements to silvicultural management in the United States (Kaarakka et al., 2021). This is because IFM can be expensive when compared to traditional forestry practices, due to delayed harvests and higher management costs. Kaarakka et al. (2021) discuss the importance of expanding financial incentives to ensure that these increased costs are offset, enabling participation from lower income stakeholders such as family farmers, who own 36% of the forestland in the United States. Schemes which raise awareness of carbon market opportunities and support participation by removing financial and logistical barriers (Marland et al., 2017) could reduce some of the socio-economic impacts of NbS. Similarly, NbS can also be harmful to small-scale farmers in South America if the social context of interventions is not explicitly modelled (Gastauer et al., 2021). The Atlantic Forest of Brazil is the focus of one of the most ambitious restoration targets in the world, with potentially up to 22 million hectares undergoing forest restoration. At such large scales, passive restoration strategies, such as natural forest regrowth, are usually the main target given their lower economic costs. However, Gastauer et al. (2021) showed that large-scale restoration projects targeting areas with the highest potential for passive restoration also inadvertently harm marginalised communities. This is because this type of intervention targets specific types of land use and small properties that may not be very productive, but are the only source of income for their landholders (Gastauer et al., 2021). Gastauer et al. (2021) show that there are other strategies, which may be more costly in terms of implementation, but are socially fairer and improve compliance with environmental policies. In addition to this, interventions which foster local ownership and empowerment are also more likely to result in favourable ecological outcomes (Hajjar et al., 2021; Oldekop et al., 2016). An effective NbS should be a place-based partnership between people and nature (Seddon et al., 2021). Welden et al. (2021) argue that if the discourse on NbS is constrained to the lexicon of ecosystem services, that is, what nature can do for people, then the potential of resulting schemes will be inherently limited. Instead, they present a core framework for NbS which highlights the intertwined relationship between people and nature and brings together previously siloed disciplines. Their contribution to this Special Feature offers a perspective on how holistic, interconnected and inclusive core framing is urgently needed to shape global discourses on NbS across research, policy and practice. A vital consideration in this perspective is how, if properly framed, NbS can create space for a transformation of Western worldviews to one in which humans and non-human nature are interconnected and mutually dependent (Welden et al., 2021). Considering economic, social and environmental aspects when designing NbS may appear prohibitively complex, but many of the papers in this Special Feature show how the oversimplification of natural systems and the problems they face can lead to biodiversity declines and project failure. The use of more complex ecosystem service models in decision making would help prevent negative outcomes of NbS, particularly those that include socio-economic dimensions (Welden et al., 2021). As models are only as good at the data behind them, long-term monitoring of existing examples of how NbS might change a habitat, and the consequences for society, are paramount. Observations must also monitor the entire ecosystem, and not just the target species (such as the plant responsible for carbon storage or the predator of a specific pest). Trophic cascades up and down food chains can destabilise ecosystems, and ignoring these could have negative consequences, as shown by Lake Merkemeer in the Netherlands which was designed for flood protection but ultimately reduced lake biodiversity (Van Leeuwen et al., 2021). It is not trivial to determine the most suitable habitat and location for an NbS. As this Editorial has shown, targeting diverse and natural habitats with NbS may not guarantee the best outcome of an ecosystem service. The benefits of diversifying flora for natural pest control were most effective in simple, manipulated habitats (Beaumelle et al., 2021), although desirable characteristics such as terrestrial carbon storage is greater in more complex habitats (Kaarakka et al., 2021). Social impacts are also significant, and prioritising external perspectives and knowledge over local ones (Seddon et al., 2021) can constrain positive social outcomes (Woroniecki et al., 2020) and jeopardise the effectiveness of interventions (Scheba & Mustalahti, 2015). If a scheme does not adequately cover human needs, there will be resistance to adoption (Bradfer-Lawrence, et al., 2021). The vital task of ongoing management of NbS schemes will also be more challenging if local communities are not engaged and involved with ongoing management (Holl & Brancalion, 2020). Interventions which foster local ownership and empowerment are more likely to lead to positive ecological outcomes (Hajjar et al., 2021; Oldekop et al., 2016; Van Oosten et al., 2014). Ultimately, considering the varied impacts of an NbS, which will differ spatially and temporally, is crucial prior to implementing an NbS scheme. NbS a can be part of many solutions to sequester carbon, increase biodiversity and provide options for adaptation to some of the inevitable global changes we are already beginning to see. The co-benefits of NbS can be great, including increased biodiversity from habitat restoration and benefits to humans through increasing accessible natural space. The success of an NbS will depend on the location of habitat transformation, and can differ widely. Whichever site is ultimately chosen, long-term monitoring and management of restored areas is needed to ensure the benefits of the NbS outweigh any costs. Communicating with stakeholders, and considering all the ecological and societal impacts is also crucial. If humans are considered a part of nature, rather than apart from it, the socio-economic dimension of projects and policy can be considered more holistically. The importance of an inclusive and well-established lexicon is part of ensuring good practice. Put simply by Bradfer-Lawrence et al. (2021) ‘Avoidance of perverse outcomes can be made more certain by emphasising the “nature” in NbS’, which includes not only the physical world around us, but also humans and their interactions with it. We thank the British Ecological Society Policy Committee for initiating this Special Feature. Special thanks to Emma Ransome and Jos Barlow for their comments on an earlier version of this article. E.L.C. was funded by an Imperial College Research Fellowship. H.F.-T. is funded by NERC. C.B.-L. and E.L.C. are members of the British Ecolohical Society (BES) Policy Committee, and E.L.C. had a minor involvement in the BES NbS report. All authors were involved in planning and writing of the editorial. H.F.-T. and C.B.-L. summarised the articles of this Special Feature, and H.F.-T. wrote the core text surrounding the articles. This article does not use data.