**5. Conclusions**

This study proposes forest SWB as a promising policy indicator based on measurement trials in Japan. Studies 1 and 2 suggest that there was variation in respondents' level of selfreported measures of forest SWB and forest SWB was significantly associated with some demographic variables and behaviors related to forest interactions. We further discussed the following rationales for using forest SWB as a policy indicator: (1) direct measurement of well-being—SWB is preferable to indirect measurements such as income levels; (2) wellbeing measures are influenced by respondents' interactions with forests; (3) inequalities among stakeholders can be identified; (4) SWB represents a holistic measurement.

Despite these novel findings and suggestions, challenges remain in establishing forest SWB as a policy indicator. Survey instruments for measuring forest SWB have not been standardized. Based on several measurement trials, we should ensure that survey instruments, especially survey questions, are valid and reliable. Efforts to improve the explanatory power of models explaining forest SWB should be increased. The mechanism for determining forest SWB should be further investigated. Although we attempted to control endogeneity by estimating the average treatment effect based on an endogenous treatment-regression model [36], other methods such as randomized controlled tests or the regression discontinuity design may provide more unbiased and efficient results. Measurements among different populations (e.g., different countries and regions) may reveal the generality or specificity of forest SWB and could contribute to revealing hidden mechanisms.

**Author Contributions:** All authors made contributions to the conception of this paper. T.T. and Y.U. designed the questionnaire instrument. T.T. led the questionnaire survey, data analysis and drafting, and Y.U., H.I. and N.O. critically reviewed drafts for intellectual content and revised them. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Research Institute for Humanity and Nature for the project, "Biodiversity-driven Nutrient Cycling and Human Well-being in Social-Ecological Systems (D06- 14200119)" and JSPS KAKENHI Grant-in-Aid for Scientific Research (B) 15H02871 and (B) 20H03090.

**Institutional Review Board Statement:** This statement is not applicable to the current review article.

**Informed Consent Statement:** This statement is not applicable to the current review article.

**Data Availability Statement:** Data available in a publicly accessible repository.

**Acknowledgments:** Kimberly Bowen provided valuable comments and suggestions to the manuscript. We would like to thank Editage for editing and reviewing this manuscript for English language.

**Conflicts of Interest:** The authors declare no conflict of interest.
