There is evidence for positive associations between species diversity and well-being (psychological and physical) and between ecosystem diversity and immune system regulation.
Aerts, Honnay and Van Nieuwenhuyse
British Medical Bulletin, 127(1), Sept 2018, pp. 5–22
Limited number of studies that relate measured biodiversity to human health. There is more evidence for self-reported psychological well-being than for well-defined clinical outcomes.