The Forest as Therapist: What Meta-Analytic Evidence Says About Nature-Based Mental Health Interventions

The Japanese practice of shinrin-yoku—forest bathing, or immersive time spent among trees—has evolved from a cultural tradition into a growing evidence-based therapeutic modality. As urbanization concentrates more of the global population in environments stripped of natural elements, the question of whether nature exposure can serve as a clinical intervention has taken on practical urgency.

Siah, Goh, and Lee (2023) provide the most comprehensive meta-analytic assessment to date, synthesizing randomized and quasi-experimental studies of forest bathing's effects on psychological well-being. Their pooled estimates show statistically significant reductions in anxiety, depression, and perceived stress, with effect sizes in the small-to-moderate range. The intervention durations varied widely—from single two-hour walks to multi-day immersion programs—and longer exposures generally produced larger effects, though even brief sessions showed measurable benefits. Physiological markers corroborated the self-report data: cortisol levels decreased, heart rate variability improved, and blood pressure showed modest reductions. However, the authors note that study quality was uneven, with many trials lacking adequate blinding (participants obviously know whether they are in a forest or a control condition) and follow-up periods too short to assess durability.

Rodriguez-Redondo, Denche-Zamorano, and Muñoz-Bermejo (2023) map the broader research landscape through bibliometric analysis, identifying that nature-based therapy research showed exponential growth from 2006 to 2021, with the USA and South Korea being the countries with the highest scientific production. The analysis reveals a field in rapid expansion but with notable gaps: most studies involve healthy adult populations, relatively few examine clinical populations with diagnosed mental health conditions, and the intervention protocols are insufficiently standardized to support replication. The bibliometric data also show limited cross-pollination between the nature therapy literature and mainstream clinical psychology, suggesting that nature-based interventions remain on the periphery of evidence-based practice guidelines despite accumulating supportive data.

Eling and Cummins (2025) focus on an underexamined population—children and young people in educational settings. Their systematic review of green space interventions in schools finds promising but inconsistent effects on mental wellbeing. Programs that integrated nature exposure into the school day (outdoor classrooms, gardening curricula, regular access to natural play areas) showed more sustained benefits than one-off field trips. The review identifies a key moderating variable: the quality of the natural environment matters more than the quantity. A small but ecologically rich school garden produced larger wellbeing effects than a large but ecologically barren playing field, suggesting that biodiversity and sensory richness—not just "greenness"—drive the therapeutic mechanism.

The emerging consensus is that nature exposure has genuine mental health benefits, but the field faces several maturation challenges. Dose-response relationships are poorly characterized—how much nature, for how long, and in what form? The mechanisms are plausible but not fully established—candidates include attention restoration, stress physiology modulation, and microbial exposure via the "old friends" hypothesis. And the implementation pathway from research finding to clinical prescription remains unclear. Still, in a world where standard pharmacological and psychotherapeutic interventions reach only a fraction of those who need them, nature-based approaches offer a low-cost, low-risk complement that deserves serious clinical investigation.

The Japanese practice of shinrin-yoku—forest bathing, or immersive time spent among trees—has evolved from a cultural tradition into a growing evidence-based therapeutic modality. As urbanization concentrates more of the global population in environments stripped of natural elements, the question of whether nature exposure can serve as a clinical intervention has taken on practical urgency.

Siah, Goh, and Lee (2023) provide the most comprehensive meta-analytic assessment to date, synthesizing randomized and quasi-experimental studies of forest bathing's effects on psychological well-being. Their pooled estimates show statistically significant reductions in anxiety, depression, and perceived stress, with effect sizes in the small-to-moderate range. The intervention durations varied widely—from single two-hour walks to multi-day immersion programs—and longer exposures generally produced larger effects, though even brief sessions showed measurable benefits. Physiological markers corroborated the self-report data: cortisol levels decreased, heart rate variability improved, and blood pressure showed modest reductions. However, the authors note that study quality was uneven, with many trials lacking adequate blinding (participants obviously know whether they are in a forest or a control condition) and follow-up periods too short to assess durability.

Rodriguez-Redondo, Denche-Zamorano, and Muñoz-Bermejo (2023) map the broader research landscape through bibliometric analysis, identifying that nature-based therapy research showed exponential growth from 2006 to 2021, with the USA and South Korea being the countries with the highest scientific production. The analysis reveals a field in rapid expansion but with notable gaps: most studies involve healthy adult populations, relatively few examine clinical populations with diagnosed mental health conditions, and the intervention protocols are insufficiently standardized to support replication. The bibliometric data also show limited cross-pollination between the nature therapy literature and mainstream clinical psychology, suggesting that nature-based interventions remain on the periphery of evidence-based practice guidelines despite accumulating supportive data.

Eling and Cummins (2025) focus on an underexamined population—children and young people in educational settings. Their systematic review of green space interventions in schools finds promising but inconsistent effects on mental wellbeing. Programs that integrated nature exposure into the school day (outdoor classrooms, gardening curricula, regular access to natural play areas) showed more sustained benefits than one-off field trips. The review identifies a key moderating variable: the quality of the natural environment matters more than the quantity. A small but ecologically rich school garden produced larger wellbeing effects than a large but ecologically barren playing field, suggesting that biodiversity and sensory richness—not just "greenness"—drive the therapeutic mechanism.

The emerging consensus is that nature exposure has genuine mental health benefits, but the field faces several maturation challenges. Dose-response relationships are poorly characterized—how much nature, for how long, and in what form? The mechanisms are plausible but not fully established—candidates include attention restoration, stress physiology modulation, and microbial exposure via the "old friends" hypothesis. And the implementation pathway from research finding to clinical prescription remains unclear. Still, in a world where standard pharmacological and psychotherapeutic interventions reach only a fraction of those who need them, nature-based approaches offer a low-cost, low-risk complement that deserves serious clinical investigation.