Here are a few research articles I put together for you:
Nature Connection
Human–Nature Connection: a Multidisciplinary Review
Nature Connection and Happiness: a Meta-Analysis
Happiness and Feeling Connected
Overall Health Benefits of Nature and Forest Therapy
Review: Health Benefits of Forest Bathing
Nature Contact and Human Health
Green Perspectives on Public Health
Acute Effects of Walking in the Forest
Forest Therapy on Cardiovascular Relaxation
Nature and Mental Wellbeing
Benefits: Mental wellbeing and cognitive functioning
Nature and Mental Health: Ecosystem Perspective
Nature Connection and Pro-Environmental Behaviour
Is a Green Identity associated with Green Living?
Reconnecting with Nature for Sustainability
The Effects of Nature Attachment on our Environmental Behaviour
Effects of Nature Experiences on our Beliefs and Behaviour towards Nature
Natural Place Attachment and Conservation of Native Vegetation