Study of the Vertical Structures, Thermal Comfort, Negative Air Ions, and Human Physiological Stress of Forest Walking Spaces in Summer

Abstract

Forest walking is a popular, healthy, and light outdoor activity. The potential comprehensive relationships between the vertical structures, thermal comfort, negative air ions (NAI), and human physiological stress in forest walking spaces have not been determined. We performed an experiment in the Baishuihe National Nature Reserve, Sichuan Province, China. Thirty-two college students recruited as subjects completed a forest walk (approximately one kilometer) on the same trail divided into three vertical structure type subsections, namely: A (dense herb and shrub layers with a sparse tree layer), B (dense tree, herb and shrub layers), and C (dense tree and herb layers with a sparse shrub layer). When the subjects passed preset environmental measurement points, staff measured climatic indexes (air temperature, relative humidity, wind velocity, surface temperature and global radiation) and NAI levels, and these data were input into the Rayman model to form a comprehensive thermal comfort index, the physiologically equivalent temperature (PET). PET and NAI differences and dynamic data among the subsections were analyzed. The subjects’ brain waves, heart rates (HRs), and walking speed (S) were digitally recorded. We selected brain wave θ, γ and β-high/α rates, neuroemotional indexes (stress and relaxation) and HR as physiological indicators, and S as an auxiliary indicator. The correlations between PET and NAI with physiological and auxiliary indexes were analyzed. Forest type C showed the lowest PETs and highest NAIs along with the most stable dynamic changes. PET was negatively correlated with HR and positively correlated with γ (12 channels). NAI was positively correlated with S and relaxation and negatively correlated with γ (two channels) and the β-high/α ratio (five channels). These comprehensive relationships suggest that dense tree, sparse shrub, and high-coverage herb layers combined with optimal temporal conditions (before noon or after a light rain) form the best thermal comfort and NAI conditions conducive to reducing human physiological pressures during summer daytime forest walking. These results provide theoretical references for forest walking and spatial regulation.

Key Characteristics of Forest Therapy Trails: A Guided, Integrative Approach

“…Human thermal comfort and recreation climatology [79,80], "biophobia"-fear of nature and insects [81,82] Accessibility-getting to and using the site Proximity Distance/travel time from "home" or population centers "Develop trails close to where people live for easier access" (5). "For a lot of people it is an edge to come out on one of these walks and .…”

“…In our previous review of the forest therapy literature [22], the few studies examining microclimatic factors generally found that measures such as high air temperatures and relative humidity can negatively impact physiological and psychological health outcomes [171][172][173]. Notably, Lin et al [80] developed a thermal comfort model to identify the optimal structural conditions and times of day for forest walks. A growing focus of recreation climatology has examined the impact of climate change on nature-based activities [174][175][176], including those dependent on a narrow range of environmental conditions such as snow for skiing [177,178], as well as how increased pollinosis [179,180], the spread of disease-transmitting insects [181][182][183], and other concerns can pose challenges for people seeking a comfortable experience in nature.…”

Forest Therapy Trails: A Conceptual Framework and Scoping Review of Research

“…Additionally, with respect to location, studies were set in rural (n = 105, 45.1%) [83,139], urban (n = 89, 38.2%) [84,140], mixed rural-urban (n = 25, 10.7%) [141,142], or were virtual studies without a specified location (n = 14, 6.0%) [143,144]. Along with these broad categorizations, the settings of 54 studies were identified as designated forest bathing or forest therapy sites, mainly in Japan [145,146], South Korea [108,111], and China [63,147].…”

Relative Humidity Dominances in Negative Air Ion Concentration: Insights from One–Year Measurements of Urban Forests and Natural Forests

“…NAIs offer various psychological and physiological benefits to the human body, including stress reduction [3], enhancement of cardiovascular function [4], and improvement of cognitive abilities [5]. Animal experiments [6,7] and human studies investigating both physiological and psychological health [3,8] have confirmed NAIs' effectiveness as supplementary treatment methods for a wide range of diseases. Furthermore, NAIs contribute to air purification and dust adsorption, playing a crucial role in maintaining environmental cleanliness levels [9][10][11].…”

“…They are specifically called negative oxygen ions due to oxygen's exceptional ability to capture free electrons and its inherent inclination to acquire them [1,2]. NAIs offer various psychological and physiological benefits to the human body, including stress reduction [3], enhancement of cardiovascular function [4], and improvement of cognitive abilities [5]. Animal experiments [6,7] and human studies investigating both physiological and psychological health [3,8] have confirmed NAIs' effectiveness as supplementary treatment methods for a wide range of diseases.…”