Abstract
Forests can foster mental health and well-being. Yet, the contribution of forest biodiversity remains unclear, and experimental research is needed to unravel pathways of biodiversity-health linkages. Here, we assess the role of tree species richness, both actual and perceived, and how stress reduction and attention restoration can serve as potential mediating pathways to achieve positive mental health and well-being outcomes.We conducted an experimental, multicentric field study in three peri-urban forests in Europe, employing a mixed design with 223 participants, that comprised 20-min stays in forests with either low, medium or high tree species richness or a built control. Participants' short-term mental health and well-being and saliva cortisol as a biomarker of stress were measured before and after the intervention.Forest visits for 20 min were found to be beneficial for participants' short-term mental health, short-term mental well-being, subjective stress, subjective directed attention and perceived restorativeness compared with a built environment. No differences were found for the physiological stress indicator saliva cortisol, which decreased in both the forest and the built environments.Increased perceived biodiversity-possibly linked to structural forest attributes-was significantly associated with well-being outcomes, while no association was found for differences in actual tree species richness. Structural equation modelling indicates that higher levels of perceived biodiversity had an indirect effect on short-term mental health and well-being through enhancing perceived restorativeness.While we found no evidence of actual tree species richness effects, perceived biodiversity was associated with positive short-term mental health and well-being outcomes. Understanding these biodiversity-health linkages can inform conservation management and help develop effective nature-based interventions for promoting public health through nature visits.