Rachel RY OH ^1,2* Andres Felipe Suarez Castro ³ Richard A. Fuller ⁴ Michael Tervo ⁵ Kevin Rozario ^1,2,6,7 Birte Peters ^1,2 Shawan Chowdhury ^1,2,6 Julia von Gönner ^1,2,6 Martin Friedrichs-Manthey ^1,2,6 Ambros Berger ⁸ Tracy Schultz ⁵ Angela J Dean ^4,9 Ayesha Tulloch ¹⁰ Aletta Bonn ^1,2,6

• ¹ German Centre for Integrative Biodiversity Research (iDiv), Leipzig, Lower Saxony, Germany
• ² Department of Ecosystem Services, Helmholtz Centre for Environmental Research, Helmholtz Association of German Research Centres (HZ), Leipzig, Lower Saxony, Germany
• ³ Griffith University, Nathan, Queensland, Australia
• ⁴ School of the Environment, The University of Queensland, Brisbane, Queensland, Australia
• ⁵ The University of Queensland, Brisbane, Queensland, Australia
• ⁶ Friedrich Schiller University Jena, Jena, Thuringia, Germany
• ⁷ Leipzig University, Leipzig, Lower Saxony, Germany
• ⁸ University of Natural Resources and Life Sciences Vienna, Vienna, Vienna, Austria
• ⁹ School of Agriculture and Food Sciences, Faculty of Science, The University of Queensland, Gatton, Queensland, Australia
• ¹⁰ School of Biology and Environmental Science, Faculty of Science, Queensland University of Technology, Brisbane, Queensland, Australia

The global rise in mental health issues underscores the critical importance of assessing the mental health benefits of engaging with nature. Beyond their primary aim of involving citizens in scientific data collection, nature-based citizen science initiatives offer significant potential for enhancing conservation (e.g. connection to nature) and human health and wellbeing (e.g. emotions, depression, stress, anxiety) outcomes. However, the effectiveness of various types of initiatives in achieving specific health outcomes remain unclear. This study evaluates changes in eight nature connection and health and wellbeing outcomes before and after participation in five such initiatives, specifically three dimensions of connection to nature (Self, Experience and Perspective) measured by the Nature Relatedness scale), and mental health outcomes-depression, stress and anxiety-measured by the DASS-21 scale; along with positive and negative emotions assessed using the Scale of Positive and Negative Experience (SPANE). We found that participants generally reported improvements across all outcomes, but only positive emotions and reduced anxiety and stress symptoms were significantly enhanced. This suggests that short-term nature-based interventions are effective in boosting emotions and alleviating anxiety and stress, though significant changes in nature connection and depression may require prolonged or more intensive engagement. We also found that the Queensland Trust for Nature initiative, characterized by its extended duration and social interactions, emerged as a particularly effective model in achieving synergies between biodiversity and human health goals. Consequently, we advocate for the reimagining of these nature-based initiatives as integral components of broader health-promoting strategies. By aligning citizen science efforts with health promotion frameworks, we can amplify the utility and impact of nature-based citizen science initiatives, enhancing their contributions to scientific knowledge, nature conservation and human health.