Quantifying the Threshold Effects and Factors Impacting Physiological Health Benefits of Forest Exposure

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study is thought to be a reasonably interesting study that can reveal the mechanisms for forest exposure and health benefits. In particular, it is thought that setting a threshold model of physiological health effects and deriving the visual utilization and meteorological influencing factors can expand the view on forest exposure and health benefits.

However, I think this article needs some supplements before being published in this journal.

2.3. Case study

1) It is necessary to add information on the vegetation status and characteristics (tree species, average height, average diameter of breast height(DBH), average age, area, etc.) and altitude above sea level for the three representative forests (Caoyutang, Daji, and Meiqi) selected in this study. Also, please explain why you selected the three forests as representative forests.

2) Please attach the field photos of the three forests.

3) Is there any difference in the characteristics of the three representative forests?

3.2. Participants' basic information and meteorological data collection 

1) Please explain how to recruit candidates.

2) Please explain how 52 subjects were distributed to three forests and the number of subjects assigned to each site.

3. Result

1) Please deal with the interpretation of the results of this study in Discussion 4.1 and 4.2. I think it would be good to describe only objective results in the results.

This manuscript judges that the results have been interpreted based on the authors' thoughts. Please provide a reason for the results through consideration of previous studies.

For example, when both OE and BF group participants were exposed to the forest, the EEG index showed positive effects, but in the BF group, the relative α index and the relative (α+θ) index showed negative effects. Please present the difference between the OE and BF groups through comparison with the results of previous studies.

In addition, please present the results of previous studies on the factors affecting the threshold model of PHB.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

There is now a growing emphasis on learning about the mechanisms that lead to well-being through contact with the forest environment and the practice of mindfulness in the forest. I read the manuscript with interest. It is written intelligibly, interestingly and is polished in terms of graphics and style.

In the introduction, the abbreviations AUCg and AUCi appear, which are only explained later; they should already be explained here.

In the main part of the manuscript ( and not in the appendices ) should be the characteristics of natural forest areas in terms of landscape and stand (species, age, density, canopy) as well as urban green space. Also information that the people studied, are connected with nature- should be In the main part of the manuscript ( and not in the appendices.)

I have the most comments on the discussion. The discussion is more like an introduction than a discussion. It makes very few references to other studies.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

There are very few natural forests in the world, I think the authors mean managed or unmanaged forests. I suggest correcting the entire work and instead of writing natural forest, simply write forest.

Lines 39-41: it is better to number cited publications according to the rule: [1-4] not [1,2,3,4].

When writing about exposure to forests, the authors should also mention the threats resulting from staying in the forest, e.g. how safely allergy sufferers can take walks in the forest, whether the threat is the same in every high green area. It was found that the beech forest has a weaker actual impact from pollen allergens than the pine forest and that the risk of allergenic pollen is greater in a forest clearing than under a tree canopy (see: https://doi.org/10.1007/s10342-018-1144-x).

Moreover, in the introduction it should be added that empirical studies of the forest environment in terms of its impact on the health of forest visitors are carried out, where the qualitative and quantitative chemical composition of the air of various types of forest is determined, with the structure of terpenes probably responsible for the positive effect of the forest on health.

In the presented studies on forest exposure, certain differences were noticed in the body's physiological response to changing meteorological conditions: temperature, air humidity, wind. The same factors influence the concentration of terpenes in the forest air. This may be why almost all selected EEG indices showed a positive effect in both people with their eyes open and those with their eyes closed. This is further proof that breathing forest air rich in phytoncides has a positive effect on mental and physiological well-being. The authors see atmospheric volatile organic compounds (VOCs) as a factor that may influence the body's response (lines 399-400) and plan to include them in future research. It is even more worth extending the introduction to this issue.

To sum up, the model tested in this work is so valuable that research should be continued by adding further, important factors determining the impact of the forest environment on health, e.g. VOCs. The work complements and confirms the already known relationships related to the impact of forests on improving well-being and physiological parameters (EEG has also already been tested, e.g. Forests 2022, 13, 1668. https://doi.org/10.3390/f13101668; Forests 2021, 12, 1380 .https://doi.org/10.3390/f12101380). What is new in this study is the model used and its indication of clear differences between the impact of urban greenery and forests on health. Many publications have been written on this topic, of which I have proposed only a few additional ones for inclusion. However, they suggest expanding the literature review to include other items as well.

Taking into account the dynamics of development of research on the impact of forests on public health, I believe that this work may be of interest to a wide international opinion.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The authors could relate the study also to the biodiversity hypotheses on allergies and asthma (Hanski, von Hertzen, Fyhrqvist, Haahtela. Environemntal biodiversity, human microbiota and allergy are interrelated 2012; Haahtela: Biodiversity hypothesis. Allergy 2019, for example).

Also the description of the nature area and urban park area would make the differences between the two different experiment places. The exposure times in both cases were very short to have proper experiment. Also the regularity and sequence of visits to nature areas would increase the impact. To keep immunity, people in different ages need to be exposured continuously to nature to maintain the benefit.  Therefore, the age is an important variable. 

Author Response

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Author Response File: Author Response.pdf