The Impact of Forest Therapy Programs on Stress Reduction: A Systematic Review

Round 1

Reviewer 1 Report

There seems to be an issue with the inclusion/exclusion criteria based on what was stated in the introduction. What was the reason for excluding 8 studies that only reported on forest walking, siting, or forest bathing without structured activities and CBT? The need for structured activities and CBT was not well described in the introduction or with a rationale in the materials and selection section. There could also be more detail in the inclusion/exclusion section pertaining to the selection of the criteria and specifically of studies without structured activities and CBT.

Were the studies "manual inspected" or "manually inspected?"

The description of the studies included for analysis was well described. However, the review did not control for the type of scheduled activities or the use of know interventions that would affect stress reduction. This is a limitation of the review to be able to include only studies that compared forest therapy with the limitation of no additional interventions, like schedule activities or CBT. Therefore, reading at this point in the paper there seems to be confounders for any outcome that could be described from this review.

In the Results section, POMS and PANAS and the emotional elements that they measures was introduced. This was new information that was not introduced earlier in the paper where the concepts were being introduced. This is a shortcoming in the preparation of the paper and needs to be corrected. Also, the introduction of self-report measures should also be included earlier in the paper. Similarly, the EQ-VAS and the SVS were not introduced earlier as concepts of interest. Burnout was described well in this section.

In the Discussion section, what does "participants were instructed to make essential oils before the post-test measurement?" There was also a statement of concern that the rest period was not long, and the effect of the activities might influence the post-test. The authors included many limitations of the individual research papers, which was a strength of this section. 

The Limitations section did not include some of the issues with how the studies were included or not. They did make a mention publication bias and the limitation to including English language papers only.

The conclusions were acceptable. Please consider stating that forest therapy programs are in their infancy and at this time there are two few studies with similar designs to make comparisons that were attempted in this paper. The paper really showed off this aspect and perhaps in the introduction this type of statement could be used. The review was exploratory as to the type of forest therapy interventions were being conducted.

there are only a few misspellings and one noted item noted that the authors refer to the "Republic of Korea" and since it starts the sentence and is not a concept noun, should be "The Republic of Korea."

Author Response

Dear editor and reviewer,

The authors would like to thank the editor and reviewer for the kind and constructive comments and feel that they have strengthened the manuscript. Responses to the editor and reviewer's comment are listed below:

 To the editor,

Comment (1)

We have detected that our self-citation is much higher than the threshold of this category, which may bring negative results. We would like to inform you that it will be necessary to remove or replace some references published by Forests during the revision process of your manuscript. We suggest keeping at most 1 reference published by Forests. Thank you very much for your kind understanding and cooperation.

Reply:

    Thank you for your suggestion. We have attempted to remove or replace some references published by Forests. There were three references found in this study that were published by Forests. However, since these studies were three of the 17 that met the inclusion and exclusion criteria, and since they served as the analysis material for this review, they may not be able to be removed or replaced. Forests is one of the best journals for forest research. A systematic review is unlikely to surpass this journal in terms of quality. Thanks for your kind understanding. Below are three references:

60. Chen, H.-T.; Yu, C.-P.; Lee, H.-Y. The Effects of Forest Bathing on Stress Recovery: Evidence from Middle-Aged Females of Taiwan. Forests 2018, 9, 403.
61. Bielinis, E.; Bielinis, L.; Krupinska-Szeluga, S.; Lukowski, A.; Takayama, N. The Effects of a Short Forest Recreation Program on Physiological and Psychological Relaxation in Young Polish Adults. Forests 2019, 10, 34.
62. Cvikl, D.; Avgustin, C.; Kreft, S. The Physiological and Psychological Effects Benefits of Forest Therapy (FT) on Tourists in the Kranjska Gora Destination. Forests 2022, 13, 1670.

To the Reviewer,

Comment (1):

There seems to be an issue with the inclusion/exclusion criteria based on what was stated in the introduction. What was the reason for excluding 8 studies that only reported on forest walking, siting, or forest bathing without structured activities and CBT? The need for structured activities and CBT was not well described in the introduction or with a rationale in the materials and selection section. There could also be more detail in the inclusion/exclusion section pertaining to the selection of the criteria and specifically of studies without structured activities and CBT.

Reply:

Thank you for your suggestion. We have now clarified the reason and explained with more details as requested. We have now added “As for eligibility criteria, we distinguished between forest therapy programs, forest exposure, forest exercise, and forest therapy. The term forest exposure refers to being in a forest in some way, such as breathing or sitting in a forest. Forest exercise involves exercising in a forest, which can include walking. Forest exposure or forest exercise can be considered a form of forest therapy[48]. We operationalized the forest therapy program to include a combination of other structured activities and cognitive-behavioral therapy to improve one's health and well-being. Therefore, forest-based exposure and/or exercise, combined with other structured activities and cognitive-behavioral therapy (e.g. meditation, experiencing the forest through the senses), meet our definition of forest therapy program. Nonetheless, simply being in a forest or exercising in a forest was not sufficient to qualify as a forest therapy program.” in the “2.1. Inclusion and Exclusion Criteria” section in the manuscript.

 

Comment (2):

Were the studies "manual inspected" or "manually inspected?"
Reply:

Thank you for your suggestion. It has now been corrected as you suggested and "manual inspected" has been replaced with "manually inspected". We have now stated “References of the retrieved relevant review studies were manually inspected for additional manuscripts on forest therapy programs and stress reduction (Supplementary Table 8).” in the “2.2. Study Selection Process” section in the manuscript.

 

Comment (3):

The description of the studies included for analysis was well described. However, the review did not control for the type of scheduled activities or the use of know interventions that would affect stress reduction. This is a limitation of the review to be able to include only studies that compared forest therapy with the limitation of no additional interventions, like schedule activities or CBT. Therefore, reading at this point in the paper there seems to be confounders for any outcome that could be described from this review. 
Reply:

Thank you for your suggestion. A description and discussion of duration control of scheduled activities has now been added to the manuscript. We have now added “3.4. Duration of Forest Therapy Programs and Stress Reduction  Among the seven studies that finished forest therapy programs within 1 day, one study [68] reported significant reductions in salivary cortisol levels, another study [54] reported significant reductions in serum cortisol levels, two [63,64] showed significant reductions in pulse rate, three [34,62,64] revealed significant reductions in DBP, and four [34,62-64] exhibited significant reductions in SBP. Two studies [34,62] did not show a significant reduction in pulse rate, one [63] did not find a significant reduction in DBP, and one [64] did not find a significant reduction in salivary cortisol levels. All salivary cortisol levels [52,56] and serum cortisol levels [58] were significantly reduced in studies in which forest therapy programs ranged from more than one day to less than one week. In the studies with a duration ranging from more than one day to less than one week, one [60] showed a significant reduction in SBP, but no significant reduction in pulse rate or DBP. In light of the above results, interventions that last two to six days appear to be more physiologically effective than those that last one day when it comes to salivary cortisol levels. There were no physiological outcomes tested in studies in which the duration of forest therapy programs ranged from 8 weeks to more than 8 weeks. In all 17 studies, psychological stress was reduced significantly regardless of the length of the programs.” in the “Results: 3.4. Duration of Forest Therapy Programs and Stress Reduction” section in the manuscript and “Forest therapy programs lasting between two and six days appear to be physiologically more effective than interventions lasting less than one day in terms of stress reduction, when it comes to salivary cortisol levels. It has been proposed by Christup[78] that long-term interventions produce more significant changes than short-term interventions. The study confirmed the results of the previous study to some extent. It should be noted, however, that there are only a few related studies in this review, which could result in inaccurate results. Further, based on the review, there have been no studies analyzing the physiological and psychological stress reduction effects of forest therapy programs with intervention durations of 1 to 7 weeks, as well as the physiological stress reduction effects of forest therapy programs with intervention durations of 8 weeks or more. In light of this, there is a lack of empirical research data regarding the evaluation of stress reduction effects and the duration of forest therapy programs. It is therefore not possible to examine in depth the relationship between stress reduction and the duration of the intervention. For a better understanding of the relationship, more empirical research is required.” in the “Discussion: 4.1. Health Benefits of Forest Therapy Programs” section in the manuscript, and “The optimal period of intervention exposure for forest-based stress therapy programs remains unknown. In order to examine the dose-response relationship, varying the duration (e.g., one versus two versus three weeks) and frequency (e.g., once per week versus twice per week versus three times per week) is recommended.” in the “Discussion: 4.2 Future Studies” section in the manuscript,

 

Comment (4)

In the Results section, POMS and PANAS and the emotional elements that they measures was introduced. This was new information that was not introduced earlier in the paper where the concepts were being introduced. This is a shortcoming in the preparation of the paper and needs to be corrected. Also, the introduction of self-report measures should also be included earlier in the paper. Similarly, the EQ-VAS and the SVS were not introduced earlier as concepts of interest. Burnout was described well in this section.

Reply:

Thank you for your suggestion. In response to the suggestion, we have added an introduction to these psychological measurement methods. In the manuscript, we have now stated as follows in the section entitled "Results: 3.3. Psychological Impact of Forest Therapy Programs on Stress Reduction"

“POMS usually contains six domains for identifying and assessing transient, fluctuating moods: tension, vigor, depression, fatigue, anger, and confusion [69]. Chinese revision of POMS by Chang and Lu (2001) added one domain: self-esteem [70].”

STAI-S measures state anxiety, which is anxiety induced by a specific situation [71]. In this review, studies utilizing the STAI-S examined how forest therapy programs affected subjects' levels of anxiety.

A total of 20 items are included in PANAS questionnaire, 10 of which address negative affect and 10 of which address positive affect. Negative affect symptoms include subjective distress and unsatisfactory engagement. The level of positive affect refers to how much pleasure an individual experiences as a result of his or her engagement with the environment [72].

Tools applied consisted of Stress Response Inventory (SRI)[31,51,55], Worker’s Stress Response Inventory Modified Form (WSRI-MF) [52], non-standard stress self-assessment surveys developed by Rajoo et al. research group [34,62], and Job-Seeking Stress Survey[61]. SRI [73] is one of the most important tools for assessing the effects of stress on mental health and physical health. This scale measures participants' levels of somatization, anger, and depression as a response to stress. WSRI-MF [73] is an adaptation of SRI, containing four additional items related to work. Non-standard stress self-assessment surveys developed by Rajoo et al. were used in the two studies [34,62] conducted by themselves. There was a slight difference between the two non-standard stress self-assessment surveys. One study [62] examined academic stress and the sources of stress, and the other [34] examined work stress and the sources of stress. In the Job-Seeking Stress Survey [74], four factors are considered: stress associated with studies, stress associated with personality, stress associated with college circumstances, and stress associated with family matters.

EQ-VAS [75] is a tool for assessing health-related quality of life that ranges from the worst possible health state to the best possible health state.

ROS [76] consists of six items, measuring human restoration in forests. SVS [76] was used to assess vitality and there were four common items chosen in this study: “I feel alive and vital”, “I don’t feel very energetic”, “I have energy and spirit”, and “I look forward to each new day”.

 

Comment (5)

In the Discussion section, what does "participants were instructed to make essential oils before the post-test measurement?" There was also a statement of concern that the rest period was not long, and the effect of the activities might influence the post-test. The authors included many limitations of the individual research papers, which was a strength of this section. 

Reply:

Thank you for your suggestion. According to your suggestions, we have revised these unclear sections of the manuscript. We have now stated “The arrangement of the activity may also be a contributing factor. As stated in one study in which a pulse rate decrease was not observed, participants were measured for their pulse rate right after making essential oil body wash. As participants made the essential oil body wash, they walked around the classroom, which could have affected their pulse rates [60]. Therefore, measuring physiological parameters immediately following an activity may result in inaccurate results.” in the “Discussion: 4.1. Health Benefits of Forest Therapy Programs” section in the manuscript.

 

Comment (6)

The Limitations section did not include some of the issues with how the studies were included or not. They did make a mention publication bias and the limitation to including English language papers only.

Reply:

Thank you for your suggestion. In the limitations section, we have now included a description of the issues with how the studies were included or not. We have now stated “This review was based on empirical studies using quantitative methods. It is possible that there are additional studies that are valuable concerning this topic that fall outside this scope, such as those that use qualitative or mixed methods [79].” in the “4.3 Limitations of This Study” section in the manuscript.

 

Comment (7)

The conclusions were acceptable. Please consider stating that forest therapy programs are in their infancy and at this time there are too few studies with similar designs to make comparisons that were attempted in this paper. The paper really showed off this aspect and perhaps in the introduction this type of statement could be used. The review was exploratory as to the type of forest therapy interventions were being conducted.

Reply:

Thank you for your suggestion. In response to your suggestion, the content has been added to the introduction and conclusions sections. We now have added “In most countries, forest therapy programs are still relatively new, and only a few research studies have been conducted on them [31,34].” in the “1. Introduction” section in the manuscript, and “Forest therapy programs are still in their infancy, so there are only a few studies with similar designs that can be compared.” in the “5. Conclusions” section in the manuscript.

 

Comment (8)

There are only a few misspellings and one noted item noted that the authors refer to the "Republic of Korea" and since it starts the sentence and is not a concept noun, should be "The Republic of Korea."

Reply:

 Thank you for your suggestion. We now have corrected this grammatical error as you suggested and replaced "Republic of Korea" with "The Republic of Korea". We have now stated “The Republic of Korea had the highest number of included studies with nine, followed by Japan, Malaysia, Poland with two each, and China and Slovenia with one each.” in the “Results: 3.1. Study Characteristics” section in the manuscript.

 

Reviewer 2 Report

The manuscript has reviewed the studies on the impact of forest therapy on the stress and reported the results.

1. In the Introduction, ART also explained. ART is one of the critical theories directly on stress reduction.

2. The study deals with physiological aspects of the stress. So, in introduction or somewhere, the relationship between psychological-physiological aspect should be explained.

3. More detailed or specific strong and weak points of the previous studies should be discussed.

Author Response

Dear editor and reviewer,

The authors would like to thank the editor and reviewer for the kind and constructive comments and feel that they have strengthened the manuscript. Responses to the reviewer's comment are listed below:

Comment (1):

In the Introduction, ART also explained. ART is one of the critical theories directly on stress reduction.

Reply:

Thank you for your suggestion. Attention Restoration Theory（ART） has now been added to the manuscript as you suggested. We have now stated as follows “Attention Restoration Theory (ART) contends that prolonged use of directed attention fatigues neural mechanisms [28]. As suggested by ART, exposure to nature, such as forests, can reduce the feelings of fatigue or psychological stress. Certain key properties of settings enable the recovery of effective functioning, such as "being away", "extent", "fascination", and "comparability". These components refer to the key characteristics of forests that contribute to the experience of restorative wellness [29].” in the “Introduction” section in the manuscript.

Comment (2):

The study deals with physiological aspects of the stress. So, in introduction or somewhere, the relationship between psychological-physiological aspect should be explained.

Reply:

Thank you for your suggestion. As suggested, the relationship between psychological stress and physiological stress has been added to the manuscript. We have now stated “Psychological stress (measured by self-report methods) is the result of the evaluation of a stimulus in terms of its harmful and threatening potential [6]. Physiological stress response is characterized by a normal general, non-specific rise in arousal levels or activation levels [7]. It mobilizes biological resources, prepares the organism for a prompt response, and provides, in the long run, either a healthy adaptation or the accumulation of allostatic loads [8]. For many years, it has been assumed that there is a correlation between the different stress outcome systems, namely cognitive-emotional, physiological, and behavioral [9]. A cognitive evaluation of the significance of a stimulus and the available coping strategies is provided by the prefrontal cortex through the integration of sensory information. This subsequently leads to the formation of emotional responses through limbic connections, eventually leading to the activation of physiological systems such as HPA[10].” in the “Introduction” section in the manuscript.

Comment (3):

More detailed or specific strong and weak points of the previous studies should be discussed.

Reply:

Thank you for your suggestion. Following the suggestion, a description and discussion of specific strong and weak points of the previous studies has now been added to the manuscript. We have now added “3.4. Duration of Forest Therapy Programs and Stress Reduction Among the seven studies that finished forest therapy programs within 1 day, one study [75] reported significant reductions in salivary cortisol levels, another study [61] reported significant reductions in serum cortisol levels, two [70,71] showed significant reductions in pulse rate, three [41,69,71] revealed significant reductions in DBP, and four [41,69-71] exhibited significant reductions in SBP. Two studies [41,69] did not show a significant reduction in pulse rate, one [70] did not find a significant reduction in DBP, and one [71] did not find a significant reduction in salivary cortisol levels. All salivary cortisol levels [59,63] and serum cortisol levels [65] were significantly reduced in studies in which forest therapy programs ranged from more than one day to less than one week. In the studies with a duration ranging from more than one day to less than one week, one [67] showed a significant reduction in SBP, but no significant reduction in pulse rate or DBP. In light of the above results, interventions that last two to six days appear to be more physiologically effective than those that last one day when it comes to salivary cortisol levels. There were no physiological outcomes tested in studies in which the duration of forest therapy programs ranged from 8 weeks to more than 8 weeks. In all 17 studies, psychological stress was reduced significantly regardless of the length of the programs.” in the “Results: 3.4. Duration of Forest Therapy Programs and Stress Reduction” section in the manuscript and “Forest therapy programs lasting between two and six days appear to be physiologically more effective than interventions lasting less than one day in terms of stress reduction, when it comes to salivary cortisol levels. It has been proposed by Christup [85] that long-term interventions produce more significant changes than short-term interventions. The study confirmed the results of the previous study to some extent. It should be noted, however, that there are only a few related studies in this review, which could result in inaccurate results. Further, based on the review, there have been no studies analyzing the physiological and psychological stress reduction effects of forest therapy programs with intervention durations of 1 to 7 weeks, as well as the physiological stress reduction effects of forest therapy programs with intervention durations of 8 weeks or more. In light of this, there is a lack of empirical research data regarding the evaluation of stress reduction effects and the duration of forest therapy programs. It is therefore not possible to examine in depth the relationship between stress reduction and the duration of the intervention. For a better understanding of the relationship, more empirical research is required.” in the “Discussion: 4.1. Health Benefits of Forest Therapy Programs” section in the manuscript, and “The optimal period of intervention exposure for forest-based stress therapy programs remains unknown. In order to examine the dose-response relationship, varying the duration (e.g., one versus two versus three weeks) and frequency (e.g., once per week versus twice per week versus three times per week) is recommended.” in the “Discussion: 4.2 Future Studies” section in the manuscript.

 

Round 2

Reviewer 1 Report

There are still issues with the description of the exclusion of the 8 full-text articles. Please add one sentence to clarify this. I had to infer that the exclusion was related to the forest intervention type.

Please be explicit about the reason that participants were making forest oil body wash. Was this one of the "structured activities?"

Author Response

Dear editor and reviewer,

Thank you for your kind and constructive comments. The authors believe that the comments have made the manuscript stronger. Responses to the reviewer's comment are listed below:

To the Reviewer,

Comment (1):

There are still issues with the description of the exclusion of the 8 full-text articles. Please add one sentence to clarify this. I had to infer that the exclusion was related to the forest intervention type.

Reply:

Thank you for your suggestion. Following your suggestion, we have clarified the reason and provided more details. We have now added “8 articles were excluded for the following reasons: non-English articles (n=1), no forest therapy program intervention (n=7).” in the “2.2. Study Selection Process” section in the manuscript.

Comment (2):

Please be explicit about the reason that participants were making forest oil body wash. Was this one of the "structured activities?"
Reply:

Thank you for your suggestion. In response to your suggestion, it has now been added. We have now stated “As stated in one study in which a pulse rate decrease was not observed, participants were measured for their pulse rate right after making essential oil body wash, which was part of structured activities designed to stimulate the participants' senses.” in the “4.1. Health Benefits of Forest Therapy Programs” section in the manuscript.

Reviewer 2 Report

The authors revised their manuscript based on the reviewer's comments. 

Author Response

Dear reviewer,

Thank you very much for your positive feedback. I appreciate your constructive suggestions and valuable comments that helped me improve my paper.