Mental health problems are associated with lower quality of life, increased unscheduled care, high economic and social cost, and increased mortality. Nature-based interventions (NBIs) that support people to engage with nature in a structured way are asset-based solutions to improve mental health for community based adults. However, it is unclear which NBIs are most effective, or what format and dose is most efficacious. We systematically reviewed the controlled and uncontrolled evidence for outdoor NBIs. The protocol was registered at PROSPERO (CRD42020163103). Studies that included adults (aged ≥18 years) in community-based settings with or without mental and/or physical health problems were eligible for inclusion. Eligible interventions were structured outdoor activities in green and/or blue space for health and wellbeing. We searched ASSIA, CENTRAL, Embase, Greenfile, MEDLINE, PsycINFO, and Web of Science in October 2019; the search was updated in September 2020. We screened 14,321 records and included 50 studies. Sixteen studies were randomised controlled trials (RCTs); 18 were controlled studies; and 16 were uncontrolled before and after studies. Risk of bias for RCTs was low to moderate; and moderate to high for controlled and uncontrolled studies. Random effects meta-analysis of RCTs showed that NBIs were effective for improving depressive mood −0.64 (95% CI: 1.05 to −0.23), reducing anxiety −0.94 (95% CI: 0.94 to −0.01), improving positive affect 0.95 (95% CI: 0.59 to 1.31), and reducing negative affect −0.52 (95% CI: 0.77 to −0.26). Results from controlled and uncontrolled studies largely reflected findings from RCTs. There was less evidence that NBIs improved physical health. The most effective interventions were offered for between 8 and 12 weeks, and the optimal dose ranged from 20 to 90 min. NBIs, specifically gardening, green exercise and nature-based therapy, are effective for improving mental health outcomes in adults, including those with pre-existing mental health problems.

Access and exposure to public green space might be critical to health promotion and prevention of mental ill health. However, it is uncertain if differential health and mental health benefits are associated with undertaking different activities in public green space. We evaluated the health and wellbeing benefits of different activities in different locations of public green spaces in urban and semi-urban areas. We used a mixed-methods before-and-after design. Volunteers at three conservation sites were recruited and took part in group guided walks, practical conservation tasks or citizen science. Repeated measures one-way ANOVAs with Bonferroni correction assessed the relationship between location and activity type on change in acute subjective mood from pre- to post-activity, measured with the UWIST Mood Adjective Checklist (UWIST-MACL). Qualitative semi-structured interviews were undertaken and analysed thematically to explore participants’ perceptions about the health and wellbeing benefits of activities in public green space. Forty-five participants were recruited, leading to 65 independent observations. Walking, conservation and citizen science in public green space were associated with improved mood. Across all participants acute subjective mood improved across all domains of the UWIST-MACL. There was a significant association between reduction in stress and location (p = 0.009). Qualitatively participants reported that conservation and citizen science conferred co-benefits to the environment and individual health and well-being and were perceived as purposeful. Undertaking purposeful activity in public green space has the potential to promote health and prevent mental ill health.

Progress towards the United Nations’ Sustainable Development Goals (SDGs) is monitored using a set of targets and indicators. Gaps in official datasets have led to calls for the inclusion of data generated through citizen science (CS) and allied approaches. Co-benefits of CS mean these approaches could also contribute to localising, defining, and achieving the SDGs. However, mapping of current and potential contributions is needed, as well as an understanding of the challenges these approaches present. We undertake a semi-systematic review of past and current CS projects and assess them against dimensions of CS—spatial, temporal, thematic, process, and management—and their value for the SDGs set out by Fritz et al. in 2019, focusing on low and middle income country (LMIC) cities as key environments in the battle for sustainability. We conduct interviews with project leaders to further understand the challenges for CS in these contexts. We find opportunities for projects to monitor and achieve a wide range of goals, targets, and indicators. However, we find fewer projects in low income countries when compared with middle income countries. Challenges include balancing local needs with national monitoring requirements and a lack of long-term funding. Support is needed for LMICs to achieve the potential of CS.

Citizen science has a problem with engaging diverse participants, with a growing number of studies showing those most marginalised in society, who could benefit most from citizen science activities, are the least likely to participate. The full implications of this lack of diversity for what citizen science can achieve remains unexplored. To do this, we reviewed the literature to create a comprehensive list of 70 proposed benefits, outcomes, and impacts of citizen science. We used this list to construct 9 pathways to impact, showing how short-term project outcomes under the themes of data, participant engagement and collaboration lead to a suite of medium- and long-term outcomes. We then explored how a lack of diversity in citizen science participants can cascade through these pathways, affecting the overall ability of citizen science to achieve its myriad potential impacts and further entrenching disparities in society. We advocate for project leaders to use a pathways to impact approach to explore how who they recruit will affect what their projects can achieve. We also call for greater imagination in exploring, testing, and sharing ways in which barriers to participation can be understood and overcome to open citizen science up to all and to achieve its potential.