Forest biodiversity and structure modulate human health benefits and risks

Forest risks and benefits to human health are widely recognised. Yet, variation across forest types and their ecological characteristics driving health effects remain underexplored. Based on empirical data from an interdisciplinary European forest network, we developed a Bayesian Belief Network to quantify seven causal pathways relating different forest types to physical and mental health. Results show that forests always generate net health benefits regardless of their ecological characteristics. Forest canopy density and tree species diversity emerge as key drivers, but their effect size and directionality are strongly pathway-dependent. Changes in forest canopy density can generate trade-offs. For example, forests optimised for heat buffering and air pollution mitigation may compromise medicinal plant yield and enhance Lyme disease prevalence. Tree diversity effects were weaker but more consistently positive. Forest management should therefore account for such trade-offs to tailor forest biodiversity and functioning to local public health needs of priority.