A systematic review of the relationship between natural environments and physiological and mental health during different stages of the COVID-19 pandemic.

COVID-19 has altered how individuals interact with natural environments. Numerous studies have investigated the effects of such environments on health. However, how natural environments influenced individuals' physiological and mental health during various stages of the COVID-19 pandemic remains unclear. Therefore, we conducted this study to investigate the effects of natural environments on individuals' physiological and mental health during different stages of the pandemic; we also identified factors that mediated these effects. Overall, we evaluated the importance of natural environments during challenging times. This study adhered to the Preferred Reporting Items for Systematic Review and Meta-Analysis guidelines. The pandemic period was divided into three stages on the basis of severity: pandemic (March 2020 - February 2022), easing (February 2022-September 2022), and post-acute COVID pandemic (September 2022 - present). An initial pool of 3018 studies was narrowed down to a final sample of 73 studies. During the pandemic stage, individuals frequenting public green spaces exhibited improved well-being, reduced stress levels, and a sense of nature deprivation. Private green spaces played crucial roles in maintaining health during the pandemic stage. Highquality window views were associated with improved well-being and reduced depression. During the easing stage, the environmental quality of public green spaces influenced individuals' perceived safety and sense of belonging. And coastal areas were the preferred natural destinations in this stage. During the post-acute COVID pandemic stage, individuals acknowledged the importance of natural environments in maintaining physiological and mental health as they gradually returned to prepandemic normalcy. In conclusion, the COVID-19 pandemic highlighted humanity's reliance on nature. Therefore, sufficient urban spaces should be dedicated to preservation of natural environments to mitigate negative emotions arising from prolonged indoor stays.