Table 2.

Literature Matrix.

Article & Location	Sample	Design	Intervention	Cortisol Measures	Results
Horticulture Therapy (HT)
Detweiler, Self [36]   U.S.A	n = 24, n = 20 (HT), n = 18 (OT) Mean age 46.4 yrs. (SD 11.9) 0.03% female	Quasi-experimental, single arm	Setting(s): outdoor gardens (intervention), residential facility (control). Duration: 15, 60 min sessions over 3 weeks.	Salivary cortisol. Collected by research team. Time standardization. Measured at weeks 1, 2, and 3.	No between groups comparison due to sampling inaccuracy. Nonsignificant downward cortisol trend over time.
Han, Park [37]   South Korea	n = 28, n =14 Mean age 80.1 yrs. (SD 2.9) 8.6% female	Quasi-experimental, single arm	Setting(s): outdoor farm garden space (intervention), control setting unclear. Duration:10, 90 min sessions over 2 months.	Salivary cortisol Collected by research team Time standardized Measured at pre-test and post-test.	Significant cortisol decrease over time (M 7.56 - M 3.80 (p < 0.05). No significant cortisol change in control group. No significant between group difference.
Ng, Sia [38]   Singapore	n = 59, n =29 (treatment), n = 30 (waitlist control) Mean age 67.1 yrs. (SD 4.31) 78% female	Randomized wait-list controlled trial	Setting(s): outdoor parks, gardens, and nature reserves (intervention), waitlist (control) Duration: 15 hr. sessions for 3 months, repeated waitlist (6 months).	Plasma cortisol (fasting, venous blood). Collected by research team.Time standardized Measured at baseline, 3 months, and 6 months.	No significant effects of time, group, or time × group interactions on plasma cortisol.
Van Den Berg and Custers [39]   The Netherlands	n = 30, n = 14 (gardening condition), n = 16 (reading condition) Mean age 57.6 (38 – 79) yrs. 73.3% female	Quasi-experimental, single arm	Setting(s): personal outdoor and indoor gardens (intervention), reading (control) Duration: 30 min, “stressful task” for 25 additional minutes after baseline- before experimental activity.	Salivary cortisol. Collected by research team. Time not standardized. Measured at baseline, pre-stressful task, post- stressful task, during condition, postcondition over 2-weeks.	Stressful task non-significantly increased cortisol across both conditions compared to baseline. Significant decrease in cortisol post-stressor to post-condition in intervention (p < 0.001), and control group (p < 0.05). Significant condition to post-condition cortisol decrease in intervention group, (p < 0.05), but not control group.
Forest Bathing (FB) (Shinrin yoku) Active or Passive
Kobayashi, Song [40]   Japan	n = 74 Mean age 22.4 yrs. (SD. 1.8) 0% female	Quasi-experimental crossover	Active (walking) Settings(s): 7 forests and urban centers, ratio unclear. Duration: 25 min in an urban and forested site per participant (two site visits) over two days.	Salivary cortisol. Collector undisclosed. No time standardization Measured pre-test and post-test.	Significant interaction effect between setting X walking (p < 0.001). Significantly lower cortisol after walking in FB group than urban (p < 0.001). Significant pre-post decrease in cortisol (p < 0.001), but not urban walking.
Lee, Park [41]   Japan	n = 12 Mean age 21.2 yrs. (SD – 0.9) 0% female	Quasi experimental crossover	Passive (sitting) Setting(s): Forested region, urban street view Duration: 15 min at each site over two days.	Salivary cortisol. Collector undisclosed. Time standardization. Measured baseline, pre- and post.	Baseline cortisol significantly lower in FB group than urban (p < 0.05). Just before stimuli period, cortisol levels lower in the FB group than urban (p < 0.01). No significant differences in cortisol levels before and after stimuli period.
Mao, Lan [42]   China	n = 20, n = 10 Mean age 20.79 yrs. (SD = 0.54) 0% female	Randomized controlled trial	Active (walking). Setting(s): Forest site (intervention), city site (control). Duration: 1.5 h with 10 min rest twice a day for two days.	Serum cortisol. Collected by research team. Time standardization. Measured at baseline, pre-test and post-test.	Significantly lower cortisol in FB group than city-site post-intervention (p < 0.05). Exact levels for cortisol not reported.
Sung, Woo [43]   South Korea	n = 56, n = 28 Mean age 66 yrs. (SD 7) 0% female	Quasi experimental, single arm	Forest therapy program (FTP). Setting(s): two recreational forests. Duration: 3 days over 8 weeks.	Salivary cortisol. Researchers collected samples. Time standardization not reported. Measured at baseline and 8 weeks postexposure.	Significant pre to posttest difference, cortisol reduction larger in FB compared to the control group 0.03 (−0.02 to 0.08) vs. −0.03 (−0.11 to 0.01) μg/dL, (p < 0.05).
Greenspace Exposure (GE) Active or Passive
Beil and Hanes [44]   U.S.A.	n = 15 Mean age 42.3 (20 – 61) yrs. 46.7% female 100% Non- Hispanic White (NHW)	Quasi experimental, multi-arm, cross-over	Passive (sitting). Setting(s): Very Natural, Mostly Natural, Mostly Built, Very Built. Duration: 20 min. per setting, 120 min total over one month.	Salivary cortisol. Participants self-collected salivary. samples with oral swabs. Time standardized per setting. Measured pre-test and post-test.	Non-significant trend of decrease in cortisol post exposure in Very Natural and Mostly Natural settings, larger decreased in cortisol for the Mostly Built setting compared to the Very Built setting. No gender differences detected.
Grazuleviciene, Vencloviene [45]   Lithuania	n = 20, n = 10 Mean age 62.3 yrs. (SD – 12.6) 35% female	Randomized controlled trial	Active (outdoor walking). Setting(s): green, forested park (intervention), urban street (control). Duration: 30 min once a day for 7 days.	Salivary cortisol. Affect (PANAS). Collector undisclosed. Time standardized. Measured 3 times per day: baseline, immediately following the exposure (1 min after walking in either environment), 60 min after the exposure.	Significant correlation between negative affect (NA) and higher mean cortisol levels across all participants (p < 0.05). Cortisol levels not significantly correlated with positive affect (PA). SBP and cortisol negatively associated (p < 0.1). DBP and heart rate and cortisol slope over 7 days (p < 0.05). No significant between group differences.
Mokhtar, Abdul Aziz [46]   Malaysia	n = 20, Mean age 23.1 yrs. 0% female	Quasi-experimental, single arm crossover	Active (walking) Settings: Urban greenspace (UGS) (intervention), city center (control). Duration: 20 min, twice in one day.	Salivary cortisol. Collector undisclosed. No time standardization. Measured pre-test and post-test.	Significantly greater decrease in cortisol pre to post-test in UGS than city group, (UGS: 0.89 ± 0.55, city: 2.33 ± 1.04, p < 0.05). Significantly increased cortisol in city group from pre: 1.75 ± 1.00 μg/dl, to post 2.33 ± 1.04 μg/dl (p < 0.05).
Olafsdottir, Cloke [47]   Iceland	n = 67, n = 20 (nature setting), 30 (gym), 30 (TV) Mean age 24.4 yrs. (SD 2.61) 8.7% female	Mixed-method factorial-multi-arm design.	Active (walking, exercising). Setting(s): Spruce forest (nature group), indoor gym (treadmill group), indoor laboratory (video group). Duration: 40 min in each condition over 76 min of data collection over 2 months.	Salivary cortisol. Researcher collected. No time standardization.Measured pre- post intervention and after The Socially EvaluatedCold-Pressor Test (SECPT) was introduced.	Cortisol significantly decreased from pre to post all groups (p < 0.001), returned to baseline after SECPT (p < 0.001). Significantly lower cortisol in nature group compared to the video group post-intervention (p = 0.046). Exact cortisol values not reported.No gender differences reported.
Razani, Morshed [48]   U.S.A.	n= 154 (78 dyads), n = 50 (supported group), Parent mean age, 38.95 yrs. Child mean age 8.8 yrs. Parent 87% female Child 49% female 5% NHW	Quasi- experimental	Active (play), Setting(s): regional green park (supported park prescription group), no setting disclosed for independent park prescription group. Duration: 1–3 park outings once a month for 3 months.	Salivary cortisol. Study staff collected samples. No time standardization. Measured baseline, 1 month and 3 months post intervention.	Cortisol decreased significantly from baseline M = 0.18, SD = 0.13, to 3 months, M = 0.12, SD = 0.07, (p = 0.0241), CI = 0.05, 0.65. All other analyses were non-significant.
Tyrväinen, Ojala [49]   Finland	n = 77, Mean age 47.64 yrs. (SD 8.68) 92.2% Female.	Quasi-experimental, multi-arm crossover	Active (walking) and passive (sitting). Setting(s): urban park, large urban woodland (interventions), city center (control). Duration: roughly 3-h per month over 10 months.	Salivary cortisol. Collector undisclosed. No time standardization. Measured pre, during, and post-intervention.	Significant decrease in cortisol between pre and post exposure (p < 0.01) in all groups. No significant between groups differences.
Calogiuri, Evensen [50]   Norway	n = 14, n = 6 (green exercise), n = 7 (gym). Mean age 49 years (SD – 8) Female 50%	Quasi-experimental single arm crossover	Setting(s): Indoor gym (indoor group, control) and an outdoor forested park (outdoor group, intervention). Duration: 3 days over two-weeks with longitudinal follow-up at week 10.	Serum cortisol. Time standardized: participants self-collected saliva forCAR upon awakening, 15 min, 30 min.Nurses collected serum samples for CAR post exposure in the AM.Measured pre, post, 3 time points: baseline, afternoon and evening for 3 days.	Significantly lower postexposure cortisol for intervention group compared to control (p = 0.04). No significant differences between groups found for CAR AUCG and serum cortisol. Non-significant higher AM cortisol levels and more rapid decrease 30 min. post AM than control.
Outdoor Activity Programming (OAP)
Chang, Davidson [51]   U.S.A.	n = 33, n = 3 (kayaking), n = 3 (backpacking), n = 4 (canoeing) Mean age 20.67 yrs. (SD 1.45) 66.7% female	Quasi experimental non-equivalent groups mixedmodel	Settings(s): field trip courses in three independent groups: canoeing (n = 9), backpacking (n = 16) kayaking (n = 8). Duration: 3 days over 2 weeks.	Salivary cortisol. Collected by research team. Not time standardized. Measured baseline, pretest and post-test.	Nonsignificant trend of decreasing cortisol over time in all groups. Significant decrease in cortisol from pre to posttest in all groups (p < 0.05) No significant interaction or main effect of sex and time, or activity and time on cortisol.
Dettweiler, Becker [52]   Germany	n = 48 Mean age 11.6 yrs. 38% female (forest) 36% female(control)	Quasi-experimental Prospective longitudinal single-arm	Setting(s): forested park (outdoor learning intervention) and indoor classroom (control) Duration: 1 day each week for 9 months.	Salivary cortisol. Collector undisclosed. Time standardized. Measured at 8:30, 10:30 AM, and 12:30 PM, intervention day, 1 day per week, during school year	Intervention group significant greater overall decline of cortisol than controls, (p < 0.01). Nonsignificant trend of intervention group lower cortisol levels in spring compared to other seasons (p = 0.05).
Niedermeier, Grafetstätter [53]   Austria	n = 42, Mean age: 32 yrs. (SD 12). 48% Female.	Quasi experimental multi-arm crossover	Setting(s): Mountain region in a forest, indoor treadmill walking in a gym (interventions), computer room at a local University (control). Duration: 3 h in each condition over 14 days.	Salivary cortisol. Collector undisclosed. No time standardization. Measured pre-test and post-test.	Cortisol decreased significantly in all conditions over time (p < 0.001). Cortisol decreased more pre to post test in both intervention groups compared to control (p < 0.05). No significant difference between intervention groups.