Abstract
In recent decades, forests have expanded from natural resources for conservation and production to health-promoting resources. With the growing body of evidence supporting the therapeutic effects of forests, the number of investigations on the relationship between forest characteristics and therapeutic effects have increased. However, quantitative synthesis of primary studies has rarely been conducted due to a limited number of health studies including forest description and high heterogeneity of forest variables. In this study, we conducted a systematic review and meta-analysis to evaluate the relationship between the forest structure and the therapeutic effect. We systematically searched the studies examining the therapeutic effects of forests with different stand density and canopy density and synthesized the results. As a result of subgroup analysis, we found that stand density modifies the therapeutic effects. Emotional and cognitive restoration showed greatest improvement in low-density forests with a stand density of less than 500/ha and the therapeutic effects diminish as the stand density increases. The impact of canopy density was not found due to a lack of studies reporting canopy density. Although some limitations remain, the findings in this study have great significance in providing the basis for establishing management strategies of forests for therapeutic use.
Highlights
Human use of nature to promote mental and physical health has a long history and continues accumulating plenty of empirical evidence
Anger state significantly relieved in the forest environment (SMD −0.35; 95% confidence intervals (CIs) −0.58 to −0.12; p = 0.0026; I2 = 73%; 106 participants)
Vigor significantly improved in the forest environment (SMD 0.23; 95% CI 0.07 to 0.39; p = 0.0041; I2 = 84%; 300 participants)
Summary
Human use of nature to promote mental and physical health has a long history and continues accumulating plenty of empirical evidence. One is the attention restoration theory (ART) which suggests cognitive recovery through experience in nature. Viewing natural scenery arouses positive emotions, limits negative thoughts, and alters the autonomic nervous system activity towards being parasympathetic-dominant, leading to more relaxed states [5,6,7,8]. In addition to these two approaches, several health-promoting pathways in the natural environment have been proposed, such as promoting physical activity and social contact, providing a quality environment for improving mental health [9,10]
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