Inter- and transdisciplinary knowledge is critical for nature-based solutions to contribute to just urban transformations

Abstract

Nature-based solutions (NBS) are used to transform existing unsustainable and undesirable path dependencies in cities. For NBS to contribute to just urban transformations, a stronger inter- and transdisciplinary knowledge base is needed. This knowledge base is essential to engage with six complex yet crucial questions about NBS, including “for what?,” “which nature?,” “where?,” “how?,” “when,” and “for whom?.” To address these questions, we identify two critical opportunities to advance the knowledge of NBS. First, we argue for solidifying interdisciplinary approaches to examine how NBS can be designed, planned, and implemented for multifunctionality. Second, we argue that researchers need to work transdisciplinarily with diverse stakeholders to ensure the design, siting, and planning of NBS are appropriate to the context. In both critical opportunities, justice should be a core guiding principle from the beginning of planning the NBS, starting with the foundational understanding that NBS are not inherently just or unjust. Instead, their value depends on a holistic examination of the context in which they operate and the institutional logic that guides their planning. To center justice in the inter- and transdisciplinary research and practice of NBS, a knowledge shift from epistemological injustice to epistemological inclusivity is a critical way forward.

Nature-based solutions (NBS) can be understood as actions inspired or supported by nature to address social, economic, and environmental challenges (1, 2). NBS are often defined as “actions to protect, sustainably manage, and restore natural and modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits” (3). NBS are adopted in cities around the globe to mitigate and adapt to challenges like climate change, to support human health and well-being, and to improve sustainability and resilience. Research on the effectiveness of NBS in addressing the adverse consequences of challenges such as droughts, heat waves, and flooding has increased in recent years (4–6), showing NBS impact on urban heat stress (7) through the implementation of widespread tree planting campaigns to provide cooling; on decreasing flooding by unsealing soils and implementing retention areas (8); and as means to restore urban ecosystems benefiting people and nature in multiple ways (9, 10). The introduction of certain NBS in urban settings is also linked to physical and mental health benefits (11–13). These studies demonstrate the benefits of NBS and provide arguments to justify more consideration of NBS in urban planning.

Yet, the actual adoption of NBS is also linked to urban development agendas and discussions about gentrification that create or reinforce social inequalities, cause displacement, and support neoliberal agendas by increasing rent or real estate values due to environmental quality improvements (14, 15). The related criticisms of the ways NBS are adopted raise concerns about the possibility that NBS are used as a means for profit accumulation or value increase that fail to address the problems of a growth-based economic and planning paradigm (16–18) and potentially further exclude historically marginalized groups (19, 20). The possibility of NBS simultaneously providing important benefits to some city dwellers while leading to burdens for others has led to research examining the justice and equity dimensions of NBS design and implementation (21–23). While what can be considered just or unjust is context-specific, typically justice concerns can be understood as asking about fairness in i) the distribution of burdens and benefits among social groups, ii) opportunities for participation in decision-making, and iii) recognition and valuation of different identities involved (24–26).

How do NBS allow for or hinder justice in urban settings? We contend that NBS are not intrinsically just or unjust, but instead that their ability to deliver or erode justice dimensions depends on how NBS are designed, planned, sited, managed, and governed. Research on and with NBS, therefore, needs to be approached in a way that centers justice dimensions of urban planning and decision-making from inception rather than treating justice as an afterthought or as irrelevant (27). To achieve this, reflection on NBS knowledge-making practices is needed, since how research is done fundamentally shapes the insights and recommendations about NBS and their role in delivering or hindering justice.

We argue that a strengthened inter- and transdisciplinary organization of knowledge is needed for a deeper examination and understanding of how NBS can be employed and planned to contribute to just urban places for people and nature. Such an interdisciplinary and transdisciplinary knowledge base examining short-, medium-, and long-term outcomes related to urban NBS and the many drivers of potential injustices is needed to better equip urban planning with a holistic understanding of NBS benefits and the potential trade-offs of creating or reinforcing inequalities.

Interdisciplinary and Transdisciplinary Needs for NBS

NBS require interdisciplinary and transdisciplinary knowledge and collaboration so their design and siting can consider ecological challenges and social concerns simultaneously and with due recognition of local and regional context. Knowledge generated from interdisciplinary research is emitting from the integration of different disciplinary scientific knowledge to advance understanding or to work toward solutions that are beyond the scope of a single discipline (28, 29). Knowledge from transdisciplinary research is generated within reflexive and integrative approaches that combine knowledge from scientific actors of various disciplines, as well as nonscientific actors (such as urban planners, NGOs, community groups, Indigenous knowledge holders, government agencies), together aiming to coproduce solution-oriented, transferable knowledge, that is applicable to societal challenges and related scientific questions (30).

If fair distribution, process, and recognition to advance inclusion and justice in NBS design and implementation is to be prioritized, then six key questions should be given explicit consideration in NBS research and practice. These questions are

• •“for what?” (what challenges are NBS a response to?),
• •“Which nature?” (which ecological and biodiversity features are NBS composed of?),
• •“Where?” (where should NBS be sited to consider multiple spatial contexts to make them effective, desirable, and equitable?),
• •“How?” (how should social or technical dimensions be involved in their design and maintenance?),
• •“When” (when should NBS be introduced or implemented to increase the likelihood of just outcomes?), and
• •“For Whom?” (who will benefit—or not—from NBS introduction and implementation?).

The answers to these questions need to be informed by different pieces of knowledge, so as to avoid tunnel vision and exclusions, thus requiring knowledge collaborations in research and practice. We identify two main opportunities to include different pieces of knowledge for urban NBS through interdisciplinary and transdisciplinary research.

First, interdisciplinary research is required to design and evaluate the multifunctionality of NBS and understand how potential benefits and burdens are negotiated, recognized, distributed, and appreciated to inform urban planning and governance. While disciplinary knowledge provides needed NBS knowledge (for example, on water retention capabilities), a more holistic view is required if we are to understand NBS in its full context, i.e., the diversity of benefits and potential trade-offs coming with NBS implementation. Interdisciplinary knowledge in NBS needs to consider expertise in urban ecology, sociology, urban planning, urban design and architecture, governance, public health, political science, and many more fields—all related to potential outcomes of NBS and bringing different insights about social and ecological limitations and possibilities (31). Working across disciplines is critical when knowledge practices are geared toward understanding and solving societal challenges such as climate change adaptation and urban regeneration and, as such, are beyond the scope of a single discipline or field of expertise. By integrating and interrogating not only information and data but also tools and techniques, as well as theories, frameworks, and concepts, an interdisciplinary mode of research can lead to a more comprehensive perspective and understanding of the issues at hand, thus providing a more holistic understanding for centering issues of justice.

Through interactions and exchange between researchers from different disciplinary backgrounds, a more reflexive attitude can be stimulated, one that questions commonly held disciplinary assumptions (including ontological, epistemological, methodological, and ethical assumptions) and interrogates prevailing concepts (disciplines frequently use the same concept but with different definitions). This, in turn, can lead to a reinterpretation of problems as well as appropriate ways to address them. For example, in NBS research, disciplinary differences exist over what is considered a benefit and why (32). In considering NBS as urban shoreline features, for instance, ecologists may see an increase in biodiversity as a benefit, engineers instead value structural integrity, while social scientists potentially emphasize benefits like recreational value, quality of life, and equitable access to nature (33). Interdisciplinary thinking helps us understand that NBS can deliver different kinds of benefits (which might happen simultaneously or exist as trade-offs), meanwhile changing the understanding of the core problem: How to introduce ecological benefits for social and ecological good while curtailing social risk. We are then stimulated to dive into the contextual drivers that often determine the NBS planning approach (34, 35), including their ecological appropriateness (36). The challenge for NBS planning and governance, then, is how to stimulate NBS investments without becoming a means of increasing social inequality.

The conceptualization of justice (and associated concepts like equity or fairness) in NBS research is often implicit, and an interdisciplinary interrogation can help in explicating the different meanings and operationalizations of the concept of justice and how these, in turn, influence our knowledge practices (37, 38). While some understand justice as a universally equitable distribution of multiple ecosystem services from NBS (i.e., ref. 39), others see it as a qualitative matter of how communities perceive and experience the distribution of benefits from NBS and, respectively, how such understandings are examined and theorized. For example, Wijsman and Berbes-Blazquez (23) maintain that such differences in understanding the concept of justice lead to differences in the knowledge created about justice and, therefore, urge NBS scholars to be explicit about how they understand the reasons, recipients, and operation of justice. Such a process of explicating diverse meanings of and assumptions about justice in NBS work helps us understand why conflicting assessments about the appropriateness of NBS emerge and can reveal points of similarity (or difference) in terms of how NBS can be a means and an end for just urban futures (23, 40).

In this way, interdisciplinary research has the potential to become a vehicle to question dominant understandings of NBS and their relation to justice and to create space for more radical understandings and agendas; ones that aim for transformations rather than maintenance of the status quo (41). This approach is needed if sustainability science and research on NBS is to deliver action rather than pay lip service to social justice (38, 42). Interdisciplinary examination of the multifunctional design of NBS and identification of beneficiaries of their functioning is increasingly advocated (36, 43, 44), and deliberation on multifunctionality meaning is therefore needed.

Many NBS justice studies focus on the distributional justice effects of NBS, mapping how different NBS features such as tree plantings or bioswales are sited over space and social groups (45–47). Yet, increasingly, dimensions of procedure and recognition are acknowledged as key to understanding the longer-term justice implications of NBS (48), requiring a broadening of the kinds of expertise and methodological approaches used in NBS research. For example, Mihaere et al. (49) bring to the forefront the importance of recognizing local Indigenous concepts and knowledge of well-being in urban NBS to be socially just for Oceania, explicating the different ways “nature” is understood in Indigenous communities.

One way to think about and design for justice in varied ways is through multifunctional planning, which explicitly combines ecological and social considerations by balancing the needs of humans with those of animals and plants in regenerating and restoration efforts such as in the examples of restoring urban landfills into urban parks (36). This approach can also make explicit trade-offs between NBS rectifying past injustices or focusing on future needs (23, 50, 51). Rodgers et al. (52) present how planting native species in urban greening programs in Aotearoa, New Zealand, contributes to “righting injustices of the past” (p. 3) and contributes to urban justice for Indigenous Peoples.

Strategic urban planning has, thus, a pivotal role in identifying priority areas to improve the quality and interconnectedness of existing NBS before extending to plan for new ones that incorporate and prioritize justice. Still, bridging justice-informed objectives to policy and planning actions remains challenging, especially for considering and delivering on justice outcomes (53, 54), further showing the pressing need for a science and policy collaboration to bridge this gap. Kato-Huerta and Geneletti (55) exemplify this by showing how urban climate action plans in Latin American metropolitan areas increasingly mention environmental justice concerns but do not relate them to policy or planning actions. Assessing the different needs (or required benefits) based on social and ecological insights and linking these needs to availability, access, and quality of urban green space can aid the selection of NBS type and inform just planning of it (56, 57). For example, in the Overvecht neighborhood in Utrecht, the Netherlands, the local government has several funding mechanisms and supportive urban programs that enable community-led initiatives for greening (58). This case is an example of how strategic urban planning can contribute to recognition and procedural justice in place.

Second, transdisciplinary modes of knowledge creation for NBS are important to ensure that the design, siting, and planning of NBS are appropriate to the context, which must be understood in biophysical, socioeconomic, and historical registers simultaneously (59, 60). Transdisciplinary knowledge extends expertise from interdisciplinary academics to diverse knowledge actors, including decision-makers, city practitioners (including advocacy groups), local or Indigenous communities, and citizens in partnerships (particularly those affected by interventions and who are historically marginalized in decision-making processes (61); together ensuring local relevancy, acceptance (62), and embeddedness. Torres et al. (63) argue that for Brazilian cities, the shift from citizens participation to be about “giving voice and interest representation” to codesigning NBS projects with citizens, practitioners, and experts served as a way forward to improve environmental justice. In another example, in the city of Katowice (Poland), a collaborative effort of urban planners and academics engaged with neighborhood groups and women's associations on how to rethink a local urban park as a community space. This transdisciplinary effort resulted in a new action plan that included new trails for walking that are safe during rainy days, rethinking the access to the park (that was previously fenced off) and opened the discussion about the social and ecological benefits of the space beyond the need for market activities that dominated previous planning. The community members stressed the importance of accessibility and the value of the park for the children to play and meet (34). It is the knowledge and voicing of the social needs as well as the place-specific knowledge that community groups brought into the cocreation of the action plans for the neighborhood that made the regeneration of the urban park inclusive and its results more equitable, specifically improving procedural and recognition justice dimensions.

Bringing together people with different professional and personal backgrounds and experiences, transdisciplinary research is thus an explicit attempt to combine the theoretical and the practical, to value experience as a valid source of knowledge, and to acknowledge different ways of knowing as equally valuable. For example, in Sarajevo (Bosnia and Herzegovina), local community representatives that voluntarily participated in the cocreation of NBS in the city collaborated with academics and urban planners through a facilitated process (64) in which they contributed with histories of place, of nature, and of their relation with communities, with knowledge about the history and ecological memory of the place before embarking on envisioning and codesigning. The citizens involved brought in a novel perspective and knowledge of place that elucidated sociocultural paths and understandings of the past: Knowledge that is needed and can be tapped into for more inclusive NBS in the future, resulting in a new design of the green corridors’ plan and project. This transdisciplinary approach offers a way to understand and improve intergenerational justice issues in the cocreation of NBS.

Thus, a transdisciplinary approach to knowledge production can be a democratizing one that acknowledges the importance of local and cultural context to the way problems are defined, possible solutions come to be understood, and expectations and goals in projects take shape. For example, in the City of Unley in South Australia, the Green Verge program is an example of a city-citizens collaboration for urban greening that created an inclusive planning context. Upon the request of citizens, the city removed impermeable dolomite at no cost, enabling residents to plant vegetation in the area. The city provided a planting guide to citizens and was available for guidance and questions, creating a collaborative process. The Green Verge program resulted in a local street being a demonstration site for replicating other green verges. In addition to greening and aesthetic benefits, city officers noted from citizen surveys that residents of the street mentioned the health benefits, especially on mental health, increasing willingness to walk in the area, creating space and an environment for social encounters, and more. In this example, knowledge from citizens blends with the expertise of urban planners and created new possibilities and solutions for dealing with redistribution justice issues related to urban greening.

Additionally, transdisciplinary approaches also attempt to redefine problems, goals, and priorities (65, 66) and can contribute to the empowerment of stakeholders (67) by exchanging best practice examples or even failure so that stakeholders can learn from each other. For example, there is increasing interest in New York State in the United States to create nature-based shoreline features instead of hard gray infrastructures to deal with challenges of shoreline resilience. Yet, implementation lags due to a persistent regulatory norm that emphasizes engineering values and fails to capture ecological and social values in assessments of shoreline features. In the work on NBS shorelines in New York State, transdisciplinarity was crucial in creating a monitoring framework assessing NBS functioning that was scientifically rigorous but also locally relevant and pragmatically applicable (33). In a multiyear cocreative process, individuals from academia, government, industry, and nongovernmental organizations partnered to create a framework that would capture a wider spectrum of potential benefits delivered by shoreline features as a crucial step on the way to normalizing the permitting of NBS. In this process, the inclusion of local and regional partners was crucial to ensure relevance. In a state with approximately 2,600 miles of shoreline, there is a multiplicity of shoreline systems and governance arrangements. Practitioners from different backgrounds were crucial in prioritizing which potential NBS benefits to monitor from a seemingly endless possible parameters, indicators, and protocols the scientific community had come up with. A balance between credibility, legitimacy, and relevancy was made possible through the cocreative process that opened up participation in deciding what is valued most about NBS. What is more, the transdisciplinary setting foregrounded the necessity of deliberation on the one hand (participatory justice), and the social and changing nature of values on the other (recognitional justice). These local partners shaped the eventual framework in crucial ways, informing decisions on priorities and applicability that would have turned out differently if these partners were not included (33).

A way to progress toward more transdisciplinary knowledge production is by researching and cocreating institutional spaces for community engagement, activating the interface of science, policy, and community (68). An example of such an interface where pieces of knowledge from NBS experts, urban planners, and citizens (teachers and students) came together is from the city of Poznan, Poland. In Poznan, all schoolyards have been transformed into nature-based schoolyards through greening and removing impermeable surfaces initiative of the city, which included not only a series of dialogs and cocreation sessions but also activities with the aim of educating children and families about urban nature and its benefits. The schoolyards became the places where different visions for the public spaces were combined, and different knowledges were brought together to transform them from gray to green, that also expanded the green corridors and the network of the city (69).

Centering Justice in the Science of NBS

Fairness in the distribution of benefits and burdens of NBS, the decision-making through participation about NBS and the recognition of different values and perceptions regarding NBS are all critical to interrogate with the six key questions we pose if NBS are to contribute to urban justice. While justice is increasingly becoming part of the sustainability science lexicon (20, 70–73), it remains challenging to put the three justice dimensions (distributive, procedural, and recognition) into practice through policy and planning actions (53, 55). We suggest that changing research practices in inter- and transdisciplinary ways is a crucial step in centering justice in the science and practice of NBS. However, these research approaches by themselves will not automatically lead to just NBS outcomes and processes, as inter- and transdisciplinarity processes are not without flaws in their realization. For that, we need to center justice in all our research on NBS from the inception, in terms of our research focus as well as how we conduct our research. Put differently, we need to rethink what epistemic justice means in the context of NBS.

By advocating for inter- and transdisciplinary research approaches for NBS, we recommend a way forward for centering justice in the science of NBS as one that shifts ways of knowing from an epistemic injustice perspective to epistemic inclusivity. Epistemic injustice refers to the exclusion of individuals or groups from knowledge projects on account of their identity (e.g., professional occupation, ethnicity, gender) or due to their knowledge not being seen as relevant or valid because of dominant standards of language or evidence (74). For example, an emphasis on quantified outcomes of NBS (75) sidelines qualitative approaches able to capture varying preferences and interpretations of NBS while risking turning numerical targets into an end themselves (23, 76, 77). The neglect of critical social science and humanities approaches in shaping research agendas leads to poor understandings and even misinterpretations of crucial concepts (like justice or intersectionality) and processes (like dominance or discrimination) and how they play out in NBS planning and governance (21, 78–80). It is thus imperative for NBS research to pay attention to "whose" knowledge and expertise are included and are dominating science-policy debates as well as any type of consultation (76). Increasingly, the importance of transdisciplinarity for NBS is advocated, including through the idea of cocreation (34, 81, 82), yet despite these calls, transdisciplinary approaches still remain marginal in both the knowledge production of NBS (6) and its application in urban planning. Shifting from epistemological injustice toward research practices fostering epistemological inclusivity is thus not simply a matter of merely adding more people and perspectives; instead, putting epistemological inclusivity into practice requires rethinking some of how research should be done. While this can be challenging, the consideration of epistemological inclusivity can ultimately result in more transparent, inclusive, and respectful science and practice for NBS (83, 84) and help to ensure that NBS do not become epistemologically hegemonic projects.

Conclusions

To center justice in the inter- and transdisciplinary research on NBS a knowledge shift from epistemological injustice to epistemological inclusivity is crucial. We argue for the need to include social sciences, arts, and humanities expertise in interdisciplinary NBS projects to critically interrogate who is involved, whose knowledge is considered in shaping decisions, who benefits from NBS, and how NBS are understood, appreciated, and “narrated” by communities (85–87). Importantly, we need to be cautious about how “community” is identified and understood to avoid reinforcing or generating inequalities (23) while critically examining justice considerations and equity opportunities (13). At the core of epistemic inclusivity in transdisciplinary settings is a discussion on what types of expertise are included (academic, Indigenous, traditional, practical, etc.), who is considered an expert, and how these experts are treated and included in planning and governance processes (42, 84, 88). Additionally, skill and capacity-building efforts need to build on justice literacy of urban planners and practitioners. These efforts should come hand-in-hand with a system’s thinking of NBS planning requiring multiple disciplines to work together interdisciplinary (89). This justice literacy can also be a policy lever to foreground broader protections against displacement in regenerating neighborhoods, ensuring that NBS as part of greening projects are not part of gentrification processes. NBS should be, thus, placed together with other efforts to address equity and justice such as programs on providing affordable housing and creating local jobs. In this way NBS can be part of a policy mix from climate and social welfare policy domains.

In the science and practice of NBS, it is paramount to strengthen the inter- and transdisciplinary knowledge base through disciplinary bridging, weaving, and cross-sectoral collaboration to achieve more just urban futures and to avoid reinforcing existing social injustices. The interdisciplinary and transdisciplinary journeys are simultaneously local and global projects. Including a justice perspective in the governance of NBS translocally while considering issues of epistemological inclusivity can help advance the science of NBS to contribute to more just urban futures.

Data, Materials, and Software Availability

All study data are included in the main text.