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Developing a Theory-of-Change linking Nature-based Therapies and Mental Health and Wellbeing Equity: An eDelphi Study

This eDelphi study engaged diverse Global North stakeholders to develop a consensus-based Theory-of-Change outlining how nature-based therapies can improve mental health equity, while identifying critical pathways and systemic barriers—such as funding, accessibility, and professional recognition—that currently limit their equitable impact.

Original authors: Helen V. S. Cole, Michelle Howarth, Penny A. Cook, Anna Åshage, Virginia Cioncoloni, Jesus Montero-Marin, Anna María Pálsdóttir, Petra Ellora Cau Wetterholm, Andrea Pistillo, Eli Zachary Epperson, Mar

Published 2026-08-07

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CC BY 4.0

Original authors: Helen V. S. Cole, Michelle Howarth, Penny A. Cook, Anna Åshage, Virginia Cioncoloni, Jesus Montero-Marin, Anna María Pálsdóttir, Petra Ellora Cau Wetterholm, Andrea Pistillo, Eli Zachary Epperson, Margarita Triguero-Mas

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine your mind is a garden. Sometimes, it gets overgrown with weeds of worry, or the soil feels too dry and hard to grow anything happy. For a long time, scientists have known that stepping outside, breathing fresh air, and touching the earth can help water that garden and make it bloom again. This idea is called "nature-based therapy." It's not just about taking a walk; it's about using the natural world—like forests, gardens, or even the ocean—as a tool to heal our minds. But here's the tricky part: not everyone has a garden in their backyard, and not everyone knows how to get to the nearest forest. Some people face big walls like lack of money, bad weather, or even doctors who don't believe nature can actually help. This paper asks a big question: How can we make sure that the healing power of nature is available to everyone, not just the lucky few who live near a park?

To answer this, a team of experts from all over Europe and beyond decided to hold a giant, digital meeting. They didn't just guess; they used a special method called an "eDelphi study." Think of this like a high-stakes game of "telephone" where, instead of messages getting lost, they get clearer. In the first round, experts wrote down everything they thought about how nature therapy works and what stops it from helping everyone. Then, in the second round, they looked at all those ideas and voted on which ones were the most important and true. They wanted to build a "Theory of Change." Imagine this as a treasure map. A normal map shows you where the treasure is, but a Theory of Change map shows you exactly how to get there: what tools you need (inputs), what steps to take (activities), and what signs you'll see along the way (outcomes) to know you're on the right path to the treasure of better mental health for everyone.

The team focused on three main types of nature therapy: gardening (working with plants), forest therapy (walking in the woods), and blue therapy (being near water). They gathered 25 experts for the first round of voting. These weren't just random people; they were mostly women, many with advanced degrees, and most had spent years working in research or running these nature programs. When they got to the second round, 19 of them came back to vote again, but this time, they only voted on the gardening ideas because there weren't enough experts in the other two categories to reach a clear agreement yet.

Here is what their map looks like. The experts agreed that nature therapy isn't just "going outside." To really work, it needs a trained guide, like a coach or a teacher, who knows how to help people connect with nature. It can happen indoors or outdoors, and it's not just about staring at a tree; it involves doing things like planting seeds, watering, or walking. The map shows that when people do these activities, they start to feel less stressed, get more exercise, and feel more connected to other people. Over time, this can lead to bigger changes, like people feeling more confident in society and even helping to fix the gaps in our healthcare system.

However, the map also highlights some huge roadblocks. The experts voted that the biggest things stopping people from getting this help are money (lack of funding), not having a place to go (inadequate space), and people not believing it works (misconceptions). They found that if a therapy is too expensive, or if a person doesn't have a bus to get to the forest, the magic doesn't happen. They also noted that if doctors don't recognize nature therapy as a real medical treatment, they won't prescribe it, and people won't get the help they need.

The paper suggests that for nature therapy to truly fix mental health inequality, we can't just plant a few trees and hope for the best. We need a system-wide plan. This means making sure the programs are free or cheap, that they are located near where people live, and that doctors and the government actually trust and support them. The authors are careful to say that while this map looks promising, it hasn't been tested in the real world yet. They suggest that we need to try these ideas out to see if they really work. But the consensus is clear: nature has the power to heal, but only if we build the bridges that let everyone cross over to it. Without fixing the access issues, the garden remains a secret club, and the mental health gap stays wide.

Technical Summary: Developing a Theory-of-Change Linking Nature-based Therapies and Mental Health and Wellbeing Equity

Problem Statement
Mental health disorders disproportionately affect marginalized groups, leading to significant health inequities. While a growing body of evidence suggests that Nature-based Therapies (NBTs) can improve adult mental health and wellbeing, there is a critical gap in understanding how these interventions impact health equity at the population level. Current literature often focuses on individual-level efficacy without explicitly mapping the mechanisms, contextual factors, and structural determinants that shape whether NBTs can deliver equitable benefits across diverse populations. Furthermore, the field lacks a unified definition of NBTs and a structured framework to guide their integration into mainstream healthcare systems in a way that addresses barriers to access.

Methodology
This study employed a two-stage electronic Delphi (eDelphi) approach to develop a Theory of Change (ToC) for NBTs. The process involved a diverse panel of 25 experts from the Global North (primarily Europe), including researchers, NBT practitioners, and policymakers, affiliated with the Horizon Europe GreenME project and related initiatives.

Round 1: Participants responded to open-ended questions structured around standard ToC components (context, inputs, activities, outputs, outcomes, impact) and specific questions regarding enablers and challenges to health equity. They also provided feedback on the initial definitions of NBTs and their intended impacts.
Round 2: Unique statements generated in Round 1 were compiled into a survey. Participants rated each statement for importance and relevance on a 5-point scale.
Analysis: Consensus was determined using a composite score formula: $Composite = (Importance \times 0.6) + (Relevance \times 0.4)$ . Items were considered agreed upon if the mean composite score was $\geq 3.5$ and the coefficient of variance (CV) was $< 0.25$ . Items with a CV $> 0.45$ indicated strong disagreement.
Scope: Due to low response numbers for specific modalities, the final quantitative ToC was primarily built on "gardening-related" NBTs. However, qualitative data from forest-related and blue-space-related NBTs were reviewed and integrated where substantial overlap existed, resulting in a unified framework with specific specifications for different modalities.

Key Contributions
The study produces a structured, stakeholder-informed Theory of Change that moves beyond efficacy to explain how and under what conditions NBTs contribute to mental health equity. Key contributions include:

Refined Definitions: A consensus definition of NBTs that specifies the role of a trained facilitator, allows for both indoor and outdoor settings, and targets both physical and mental health.
Expanded Impact Scope: A redefinition of NBT impact to include not only individual mental health but also environmental health, conservation, resilience, and community/social cohesion.
Equity-Focused Pathways: Identification of specific enablers (e.g., funding, accessibility, professional recognition) and challenges (e.g., misconceptions, lack of integration) that determine whether NBTs reach marginalized populations.
Multi-Level Framework: A ToC that explicitly links individual mechanisms (e.g., stress reduction, physical activity) to community and system-level outcomes (e.g., reduced demand on primary care, improved health equity).

Results
The eDelphi process yielded strong agreement on several critical components of the NBT ToC:

Definition and Impact: Experts agreed that NBTs must be directed by trained facilitators and can occur indoors or outdoors. The intended impact was expanded to include contributions to environmental health, resilience, and social cohesion alongside individual mental health equity.
Contextual Factors: High agreement was found on the importance of facilitator training, public funding, healthcare integration, and the recognition of NBTs as legitimate healthcare. Conversely, there was disagreement regarding whether NBTs must be conducted outdoors or involve physical changes to the setting.
Activities: Consensus supported activities involving person-plant interactions (sowing, watering), group work, and supervised, goal-oriented tasks. There was disagreement on the necessity of specific mindfulness activities like meditation or breathing exercises within the core definition.
Inputs (Resources): Critical resources identified include ongoing funding, health and safety policies, mental health first aid training, and dedicated physical spaces.
Outputs and Outcomes: Measurable outputs include increased participation and self-reported mental health improvements. Long-term outcomes include increased nature connectedness, pro-environmental behaviors, reduced health inequalities, and decreased demand for other healthcare services.
Equity Enablers and Challenges:
- Enablers: Access to transportation, low/no cost, integration into publicly funded institutions, and the absence of age/health restrictions.
- Challenges: Lack of funding, inadequate space, cultural norms, misconceptions by healthcare providers and the public, and lack of trained facilitators.

Significance and Claims
The authors claim that this study provides one of the first structured ToCs linking NBTs explicitly to mental health equity at the population level. The significance of the work lies in its ability to:

Clarify the mechanisms by which NBTs operate across individual, community, and system levels.
Identify specific barriers (such as lack of professional recognition and funding) that prevent equitable access.
Offer a framework for designing interventions that are inclusive and responsive to marginalized populations.

The paper concludes that while NBTs hold significant potential to reduce mental health inequities, this impact is not automatic. Realizing this potential requires deliberate design, system-level integration, and the addressing of structural barriers. The authors note that the proposed ToC has not yet been empirically tested in real-world implementation and serves as a foundation for future evaluation studies. The study acknowledges limitations, including the lack of direct input from NBT beneficiaries and a sample primarily drawn from the Global North, which may limit the transferability of findings to other global contexts.

Technical Summary: Developing a Theory-of-Change Linking Nature-based Therapies and Mental Health and Wellbeing Equity

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