The knowledge gap database compiles an evidence base for Nature-based Solutions, to support defining research and innovation avenues, and bolster policy and practitioners’ knowledge and knowledge-implementation. This database, first published in 2021 and updated in June 2024, aggregates knowledge gaps and research needs identified through extensive desk research, drawing from academic and non-academic sources. For a detailed explanation of the methodology and analysis behind the 2024 update, please refer to this NetworkNature report. For more context on the initial database see the NetworkNature report on practical, research, and innovation needs.
The updated database includes additional 619 gaps categorised into 32 broad topics and 11 types of approaches. This marks a significant expansion from the initial database, established in 2021, which contained 172 knowledge gaps. Covering gaps from 2017 to March 2024, this database will be continually updated throughout the duration of NetworkNature+.
| Gap description | Origin of source | Source | Resource | Broad topic | Types of approaches | |
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| A strong scientific evidence base, particularly quantitative socioeconomic assessments and economic cost–benefit analyses, is needed for ecosystem-based approaches. Comprehensively valuing the full range of these approaches’ social, economic and environmental benefits over time is challenging and requires capacity; thus, benefits are often undervalued. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| Methodologies for estimating blue carbon are far behind those for estimating in land forest-based carbon, so investment in mangrove forests for their carbon sequestration value is lagging. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| Evaluating the progress and effectiveness of adaptation measures is hampered by a lack of long-term monitoring mechanisms and institutions, including long-term research stations, such as for mountainous and high-elevation grasslands and rangelands. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| There is also a lack of clearinghouse mechanisms and open access to data, limiting empirical research. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| Sufficient evidence of the cost-effectiveness of EbA is currently lacking, hampering the uptake of such approaches across sectors. Related challenges include establishing accepted methodologies for valuing ecosystem services, including the recognition of non-monetary ecosystem service values, and understanding the ways in which long-term finance can aid in achieving adaptation, mitigation, livelihood, biodiversity and other benefits. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| Key challenges associated with adaptation governance knowledge gaps include governing at multiple scales, given that climate change impacts occur at various scales and ecosystem governance occurs within a complex web of stakeholders operating at different levels; governing across different sectors; and governing under uncertainties regarding the sensitivity of the climate system, regional climate change impacts and the consequences for socialecological systems. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| Mechanisms for the effective transdisciplinary governance of adaptation strategies are needed, including large-scale, landscape-level planning that integrates ecosystems across political boundaries. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| Developing mechanisms for regional and subregional cooperation and transboundary and multi-stakeholder collaboration. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| Defining criteria for going beyond incremental adaptation and achieving transformational adaptation. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| Synergies among adaptation, mitigation and biodiversity are often assumed, but caution must be applied to avoid downplaying trade-offs, including livelihood resilience, for local people. There is a need to critically assess the assumptions underlying synergies using empirical research. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| Conservation restrictions preserving ecosystem integrity versus rights of local communities to access resources that may strengthen resilience. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| Strengthened forest management due to external intervention versus local power and control over forest resources. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| There is a need to develop scientific and policy frameworks that navigate trade-offs, explicitly listing existing trade-offs at the local, national and international level and underlining clear strategies for maximizing synergies. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| The development of inclusive approaches may be hampered by limited methodologies or lack of capacity for bottom-up community participation in adaptation strategies. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| Gender-specific data and guidelines for NbS and EbA {Ecosystem-based Adaptation} initiatives that include baselines and gender assessments beyond simple sex-disaggregated data so as to account for both tangible and intangible gender dimensions – including intersecting categories of, for example, ethnicity, class and age – are needed to address the gender gaps at the interface of gender, biodiversity and climate change. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| EbA {Ecosystem-based Adaptation} and NbS need to address the root causes of vulnerability to avoid exacerbating rather than reducing existing injustices while leaving challenges of climate change unaddressed. | Desk Study | Grey literature | UNFCCC (2021) Scoping paper on knowledge gaps in integrating forest and grassland biodiversity and ecosystems into adaptation strategies. 100 pp. Bonn. |
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| Development of governance-related information, including legislative measures that are most relevant for decent work in NbS. | Desk Study | Grey literature | ILO, UNEP and IUCN. 2022. Decent Work in Nature-based Solutions 2022. Geneva. Licence: CC BY-NC-SA 3.0 IGO |
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| Developing information sources and methods concerning finance and investment for decent work in NbS related to demand, supply and use of funds; types of NbS activities financed, geographical distribution; the cost of funds; financing conditions; and impacts of the funds. | Desk Study | Grey literature | ILO, UNEP and IUCN. 2022. Decent Work in Nature-based Solutions 2022. Geneva. Licence: CC BY-NC-SA 3.0 IGO |
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| In the specific context of decent work, detailed statistics on NbS could inform the design of complementary environmental and labour market policies to support the creation of decent work in NbS through a just transition. | Desk Study | Grey literature | ILO, UNEP and IUCN. 2022. Decent Work in Nature-based Solutions 2022. Geneva. Licence: CC BY-NC-SA 3.0 IGO |
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| Another key barrier that is often seen as one of the most challenging at a project level is the lack of data and the lack of monitoring, reporting and verification processes. | Desk Study | Grey literature | Hudson, G., Hart, S., Verbeek, A. (2023). Investing in nature-based solutions. European Investment Bank. 144p. https://www.eib.org/en/publications/20230095-investing-in-nature-based-… |
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| Another risk is the lack of understanding of IPLCs {Indigenous People and Local Communities} traditions and knowledge, which may lead to top-down, inadequate climate change responses, thus affecting the well-being of these peoples. | Desk Study | Grey literature | Vidal, A., Martinez, G., Drion, B., Gladstone, J., Andrade, A. & Vasseur, L. (2023). Nature-based Solutions for corporate climate targets. Views regarding the corporate use of Nature-based Solutions to meet net-zero goals. Gland, Switzerland: IUCN. https://portals.iucn.org/library/sites/library/files/documents/2023-032… |
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| Most of the nature-based solutions included, and most of the mitigation estimated, are terrestrial. All syntheses included conservation and restoration of some coastal ecosystems, but there is substantially more terrestrial than marine research on the potential scale of nature-based solutions, their benefits and risks, and related uncertainties. | Desk Study | Grey literature | United Nations Environment Programme and International Union for Conservation of Nature (2021). Nature-based solutions for climate change mitigation. Nairobi and Gland. |
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| The lack of information on the implications of NbS translated into monetary figures remains a major gap. | Desk Study | Grey literature | BirdLife International, IUCN, Vertigo Lab, MAVA Foundation. (2022). The economics of Nature-based Solutions. Opportunities for Mediterranean coastal wetlands. https://www.birdlife.org/wp-content/uploads/2022/06/Economics-of-NbS-Gu… |
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| Design support tools to encourage willing stakeholders to implement NbS are still lacking on the ground. | Desk Study | Grey literature | BirdLife International, IUCN, Vertigo Lab, MAVA Foundation. (2022). The economics of Nature-based Solutions. Opportunities for Mediterranean coastal wetlands. https://www.birdlife.org/wp-content/uploads/2022/06/Economics-of-NbS-Gu… |
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| NbS studies frequently focus on coastal ecosystems, but there is still a lack of quantified data to be robust, and thus shared and reused by the interested stakeholders. | Desk Study | Grey literature | BirdLife International, IUCN, Vertigo Lab, MAVA Foundation. (2022). The economics of Nature-based Solutions. Opportunities for Mediterranean coastal wetlands. https://www.birdlife.org/wp-content/uploads/2022/06/Economics-of-NbS-Gu… |
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| Whilst there is a growing literature and evidence base for NbS across Europe, further effort is needed to package the information in ways that are meaningful to the economic sectors and their objectives. For example, converting environmental data into financial planning metrics such as return on investment, or risk reductions. | Desk Study | Grey literature | Bérczi-Siket A., Blackstock K., Carmen E., Ebeltoft M., Gruber T., Hernandez Herrero E., Hougee M., Ibrahim A., le Clech S., Lopez-Gunn E., Manzon V., Nauta S., Nyírő F., Pokrajac S., Saliasi V., Samu A., Vion Loisel A. and Vítková J., 2023. Mainstreaming aquatic restoration using Nature-based Solutions. EU H2020 research and innovation project MERLIN deliverable 4.1. 63 pp. https://project-merlin.eu/outcomes/deliverables.html |
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| Limited data on river flows, as well as evidence on the value of freshwater and terrestrial ecosystems brings a lack of knowledge on the costs and benefits, technologies, markets, and financial products associated with NBS. | Desk Study | Grey literature | Bérczi-Siket A., Blackstock K., Carmen E., Ebeltoft M., Gruber T., Hernandez Herrero E., Hougee M., Ibrahim A., le Clech S., Lopez-Gunn E., Manzon V., Nauta S., Nyírő F., Pokrajac S., Saliasi V., Samu A., Vion Loisel A. and Vítková J., 2023. Mainstreaming aquatic restoration using Nature-based Solutions. EU H2020 research and innovation project MERLIN deliverable 4.1. 63 pp. https://project-merlin.eu/outcomes/deliverables.html |
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| Human wellbeing considerations of ecosystem restorations are often overlooked. | Desk Study | Grey literature | Bérczi-Siket A., Blackstock K., Carmen E., Ebeltoft M., Gruber T., Hernandez Herrero E., Hougee M., Ibrahim A., le Clech S., Lopez-Gunn E., Manzon V., Nauta S., Nyírő F., Pokrajac S., Saliasi V., Samu A., Vion Loisel A. and Vítková J., 2023. Mainstreaming aquatic restoration using Nature-based Solutions. EU H2020 research and innovation project MERLIN deliverable 4.1. 63 pp. https://project-merlin.eu/outcomes/deliverables.html |
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| The lack of strong freshwater indicators beyond the WFD {Water Framework Directive} could be problematic for mainstreaming NbS. | Desk Study | Grey literature | Blackstock K., Baffert C., Bérczi-Siket A., Carmen E., England M., Gray R., Gruber T., Hernandez-Herrero E., Ibrahim A., Le Clech S., Matthews K., Nyírő F., Rouillard J., Schultz L., Vion Loisel A. and Waylen K., 2023. Briefing on policy opportunities for mainstreaming freshwater nature-based solutions. EU H2020 research and innovation project MERLIN deliverable 4.3. 52 pp. https://project-merlin.eu/outcomes/deliverables.html |
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| However, the lack of linkages in the literature between biodiversity and ecosystem approach/NBS reflects the difficulty observed during trials and the scoping literature searches in identifying studies exploring the role of biodiversity in NBS outcomes. | Desk Study | Grey literature | Akoumianaki, I., & Pakerman, P. (2021) D4.2 – Desk study on what is the state of knowledge on the role of biodiversity in the design, delivery, and benefits of Nature-Based Solutions? A scoping review. Biodiversa+ |
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| This gap suggests a bi-directional evidence gap and a need for deeper understanding of the role of biodiversity in NBS and the role of NBS in delivering biodiversity outcomes. | Desk Study | Grey literature | Akoumianaki, I., & Pakerman, P. (2021) D4.2 – Desk study on what is the state of knowledge on the role of biodiversity in the design, delivery, and benefits of Nature-Based Solutions? A scoping review. Biodiversa+ |
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| This is consistent with the finding of Key et al. (2022) that there is currently limited evidence for the biodiversity and ecosystem health outcomes of NBS, particularly in terms of the metrics and the taxa assessed. | Desk Study | Grey literature | Akoumianaki, I., & Pakerman, P. (2021) D4.2 – Desk study on what is the state of knowledge on the role of biodiversity in the design, delivery, and benefits of Nature-Based Solutions? A scoping review. Biodiversa+ |
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| Therefore, future research could further examine biodiversity metrics beyond species traits, species diversity, and ecosystem function and identify metrics in the context of “living nature” and NBS. This could help link living nature’s contributions to people with specific, local challenges and NBS projects to address them. This is akin to ongoing research on building ecosystem services frameworks, which however have been predominantly based on expert opinions and views and overlooked the effect of variation in perceptions and values of living nature. | Desk Study | Grey literature | Akoumianaki, I., & Pakerman, P. (2021) D4.2 – Desk study on what is the state of knowledge on the role of biodiversity in the design, delivery, and benefits of Nature-Based Solutions? A scoping review. Biodiversa+ |
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| This suggests further research is needed on the linkages between biodiversity and ecosystem services supply with NBS, including their synergies and trade-offs. | Desk Study | Grey literature | Akoumianaki, I., & Pakerman, P. (2021) D4.2 – Desk study on what is the state of knowledge on the role of biodiversity in the design, delivery, and benefits of Nature-Based Solutions? A scoping review. Biodiversa+ |
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| Potentially, there is a need to assess the linkages between existing ecosystem services frameworks with the IPBES framework on nature’s contributions to people (NCP) in the context of NBS. | Desk Study | Grey literature | Akoumianaki, I., & Pakerman, P. (2021) D4.2 – Desk study on what is the state of knowledge on the role of biodiversity in the design, delivery, and benefits of Nature-Based Solutions? A scoping review. Biodiversa+ |
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| Further, review articles identified the need to explore trade-offs and synergies between biodiversity and the ecosystem services supply-NBS nexus in urban systems. | Desk Study | Grey literature | Akoumianaki, I., & Pakerman, P. (2021) D4.2 – Desk study on what is the state of knowledge on the role of biodiversity in the design, delivery, and benefits of Nature-Based Solutions? A scoping review. Biodiversa+ |
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| Further research on the economics and governance aspects of embedding biodiversity in the outset of NBS projects could help better understand this evidence gap. | Desk Study | Grey literature | Akoumianaki, I., & Pakerman, P. (2021) D4.2 – Desk study on what is the state of knowledge on the role of biodiversity in the design, delivery, and benefits of Nature-Based Solutions? A scoping review. Biodiversa+ |
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| An additional problem is that studies on the BEF {Biodiversity Ecosystem Function} relationship have focused on the effects of biodiversity on ecosystem processes at relatively small spatial scales rather than on the impact of larger-scale biodiversity on ecosystem services. This lack of a mechanistic understanding on how biodiversity at larger spatial scales affects the delivery of multiple ecosystem services precludes the upscaling of biodiversity–ecosystem service relationships to the large spatial scales relevant to policy and management, and the implementation of NBS. It should be borne in mind that the IUCN Global Standard (2020) requires that NBS are implemented at landscape scale to enable delivery of benefits to humans. | Desk Study | Grey literature | Akoumianaki, I., & Pakerman, P. (2021) D4.2 – Desk study on what is the state of knowledge on the role of biodiversity in the design, delivery, and benefits of Nature-Based Solutions? A scoping review. Biodiversa+ |
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| Several authors have noted that there is a lack of understanding on how biodiversity and abiotic attributes of ecosystems at landscape scale influence the capacity of ecosystems to be multifunctional and supply multiple different services. | Desk Study | Grey literature | Akoumianaki, I., & Pakerman, P. (2021) D4.2 – Desk study on what is the state of knowledge on the role of biodiversity in the design, delivery, and benefits of Nature-Based Solutions? A scoping review. Biodiversa+ |
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| Next is the assessment of benefits, internal and external. On the one hand there are the economic benefits, which ideally should be valued monetarily, on the other hand there are the social benefits and ecosystem services. The necessary research should adapt cost-benefit, cost-effectiveness and market-based analyses, using multi-criteria techniques, to the specific case of agricultural water management solutions. | Desk Study | Grey literature | EIP-AGRI Focus Group. (2022). Nature-based Solutions for water management under climate change. Final Report. https://ec.europa.eu/eip/agriculture/en/publications/eip-agri-workshop-… |
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| The first need is therefore for a common framework for qualification and assessment of NbS that are specific to agricultural water management. This framework could result from the adaptation of one of the existing generic frameworks for solutions to societal challenges, or from a development from scratch. | Desk Study | Grey literature | EIP-AGRI Focus Group. (2022). Nature-based Solutions for water management under climate change. Final Report. https://ec.europa.eu/eip/agriculture/en/publications/eip-agri-workshop-… |
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| Proposing new models of water governance adapted to the NbS is the role of interdisciplinary research. | Desk Study | Grey literature | EIP-AGRI Focus Group. (2022). Nature-based Solutions for water management under climate change. Final Report. https://ec.europa.eu/eip/agriculture/en/publications/eip-agri-workshop-… |
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| Mapping pedo-climatic and socio-economic conditions that favour the success of specific solutions (e.g. soil conservation practices). | Desk Study | Grey literature | EIP-AGRI Focus Group. (2022). Nature-based Solutions for water management under climate change. Final Report. https://ec.europa.eu/eip/agriculture/en/publications/eip-agri-workshop-… |
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| Catalogues of NbS for agricultural water management that collect evidence of their advantages and benchmarks and show their complementarity and synergies with conventional solutions | Desk Study | Grey literature | EIP-AGRI Focus Group. (2022). Nature-based Solutions for water management under climate change. Final Report. https://ec.europa.eu/eip/agriculture/en/publications/eip-agri-workshop-… |
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| In some countries, the quantification of ecosystem services is still the Achilles' heel that prevents from designing compensation mechanisms and proposing incentives to promote ecosystem services in forestry contexts. In those cases, more advanced research on the quantification of ecosystem services is needed. | Desk Study | Grey literature | SCAR SWG FOREST. (2021). European research priorities in the forest domain |
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| Trees outside forests (including farm trees, agroforestry systems and urbans trees) are an important field of research to develop. | Desk Study | Grey literature | SCAR SWG FOREST. (2021). European research priorities in the forest domain |
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| Research on forest bioeconomy is needed to improve knowledge of the forest heritage, increase awareness of good management of green infrastructure, and integrate the effects of forests on the quality of life and sustainability of the economy. For countries whose forest systems are vulnerable to global changes, research in forest management is considered essential to tackle this vulnerability, e.g. to reduce the forest fire risk. | Desk Study | Grey literature | SCAR SWG FOREST. (2021). European research priorities in the forest domain |
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| Differences in European forest ecosystems call for different approaches vis-à-vis biodiversity. Some biomes are more vulnerable, such as Mediterranean forests that are highly fragile to global change and forest fires. For European countries that have a relatively low forest cover (e.g. Ireland with 11% of forest cover), interactions between forests and other land sectors (e.g. agriculture) are more relevant for biodiversity than the bulk of forests. In countries that have a relatively high forest cover (like Finland, Latvia) improved understanding of habitat requirements of protected forest species and management approaches to maintain favourable conditions for these species over space and time, while combining it with forest production aspect are essential. | Desk Study | Grey literature | SCAR SWG FOREST. (2021). European research priorities in the forest domain |
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| Novel approaches combining, not contradicting production and protection aspects of forests have to be developed, and promoted, and social sciences needs to be involved in this research. | Desk Study | Grey literature | SCAR SWG FOREST. (2021). European research priorities in the forest domain |
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| The provision of biodiversity protection and other ecosystem services requires further research on appropriate management techniques and active implementation of appropriate measures to satisfy expectations of society. | Desk Study | Grey literature | SCAR SWG FOREST. (2021). European research priorities in the forest domain |
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