Forest Exposure Lowers Physiological Stress Markers: Exploring the Role of Forest Type and Environmental Factors

More than half of the global population resides in urban areas. While offering numerous benefits, urbanisation is also associated with an increased prevalence of chronic stress, causing systemic health issues. A growing body of evidence suggests that spending time in forests, compared to urban environments, lowers physiological stress biomarkers. However, the effects of different forest types and underlying mechanistic interactions remain poorly understood. We conducted a randomised controlled trial to investigate the physiological effects of a three-hour guided hike in either a deciduous forest (Sihlwald, near Zurich), a coniferous forest (Parc Jura Vaudois, near Lausanne) or an urban environment (Zürich City). A range of stress biomarkers (heart rate (HR), heart rate variability (HRV), systolic and diastolic blood pressure (SBP and DBP) and salivary cortisol) was assessed pre- and post-intervention in 161 participants. Environmental parameters (meteorological, acoustic, visual, air pollution, air chemical composition and radiation) were continuously monitored throughout each intervention. Exposure to forest environments significantly reduced HR, HRV and DBP compared to the urban environment, while SBP and cortisol were not significantly affected. No significant physiological differences were observed between the coniferous and deciduous groups. Initial analyses indicate potential links between stress markers and environmental factors including temperature, airborne ultrafine particles and acoustic indices. Our results build upon previous research by providing evidence that different types of forests may offer similar stress-reducing benefits while also highlighting environmental factors that might influence physiological stress. These findings underscore the sensitivity of human physiology to environmental conditions and emphasise the importance of accessible green spaces and intact natural ecosystems for public health.