A Quantitative Literature Review on Forest-Based Practices for Human Well-Being

Abstract

Over the last decade, the scientific community has increasingly focused on forest-based practices for human well-being (FBPW), a term that includes all forest activities (e.g., forest bathing, forest therapy, social outdoor initiatives) important for improving people’s health and emotional status. This paper aims to develop a quantitative literature review on FBPW based on big data analysis (text mining on Scopus title and abstract) and PRISMA evaluation. The two techniques facilitate investigations across different geographic areas (major areas and geographical regions) and allow a focus on various topics. The results of text mining highlight the prominence of publications on FBPW for the improvement of human health in East Asia (e.g., Japan and South Korea). Furthermore, some specific themes developed by the literature for each geographical area emerge: urban green areas, cities, and parks in Africa; sustainable forest management and planning in the Americas; empirical studies on physiological and psychological effects of FBPW in Asia; and forest management and FBPW in Europe. PRISMA indicates a gap in studies focused on the reciprocal influences of forest variables and well-being responses. An investigation of the main physiological indicators applied in the scientific literature for the theme is also developed. The main strengths and weaknesses of the method are discussed, with suggestions for potential future lines of research.

1. Introduction

Since the early years of the last century, the importance of forests for improving psycho-physical well-being has been empirically demonstrated. Forests supply several ecosystem services—e.g., mitigate floods and droughts, improve the quality of drinking water, and protect soil fertility—that support the creation of healthy living environments. In particular, forests promote humans’ mental and physical health, thanks to the positive changes in human physiology caused by “immersion” in a forest and the reduction in stress and anxiety. However, only recently, the relationship between forests and human health has received increasing global attention in people’s daily practices and in the political agenda following crisis events such as the COVID-19 pandemic.

In the international literature, the author of a pioneering manuscript on the role of forests and human health [1] affirmed that “so great is the value of national forest area for recreation, an so certain is this value to increase with the growth of the count and the shrinkage of the wilderness, that even if the forest resources of wood and water were not to be required by the civilization of the future, many of the forests ought certainly to be preserved, in the interest of national health and well-being, for recreation”. Since then, many projects, publications, and forest management practices have been developed to analyze, investigate, and implement the subject [2].

In recent decades, the scientific community has also focused on the effects of forests on people’s psycho-physical well-being. In the early 1980s, the Japanese Forest Agency and the Ministry of Health, Labor, and Welfare of Japan established forest bathing (FB) (or “Shinrin-yoku”) as a practice to promote relaxation and relieve stress and anxiety of the urban population through an immersion in the forest environment [3]. Afterward, FB was established as a national health program in Japan to encourage people to spend time in forests for health and well-being reasons [4]. In the first conceptualization, FB was defined as a walk in a forest with mindful awareness, engaging the five senses (sight, sound, hearing, touch, and smell), and contemplating the surrounding natural environment [5]. Since the early 2000s, the Japanese Society of Forest Medicine and the Nippon Medical School have undertaken a series of research activities on the positive effects of forest therapy (FT)—defined as a set of practices aimed at achieving “preventive medical effects”—on human health. Among these studies, many studies began to empirically demonstrate the positive physical (e.g., increasing the number of Natural Killer (NK) cells and intracellular levels of anti-cancer proteins) and psychological (e.g., attention restoration as well as reducing stress and anxiety) effects of FB/FT on human well-being and health [6,7,8,9]. This practice then began to spread beyond Japan, first to other Eastern Asian countries (e.g., China, Taiwan, and South Korea) and later to Western countries (e.g., Europe, Canada, and the USA), combining forest visits with health and well-being-oriented tourism [10]. With the spread of FB worldwide, scientific publications and literature reviews on this topic have increased rapidly [11].

FB and FT are often treated synonymously in academic papers. Still, gray literature distinguishes these terms: FB refers to nature-based practice developed in forest areas from overall well-being improvement, while FT involves structured practices promoted by practitioners trained to work at a therapeutic level, thanks to the inclusion. A more precise definition was provided in [12]. The authors reported that “the term “forest bathing” […] is defined as being in a forest environment to restore balance psychologically and physiologically and absorb its atmosphere”, while “forest therapy” […] is the medically proven health effects of exposure to forest environment”. In the present study, the general term “forest-based practices for human well-being (FBPW)” was proposed to identify the beneficial effects of forests on people from physiological and psychological viewpoints due to (i) the lack of a unique definition and categorization of FB and FT recognized at the international level and (ii) the presence of paper focused on the well-being effects of forest examined within a general lemma in addition to FB/FT terms (e.g., nature therapy, Shinrin-yoku, forest medicine, healing forest [13]). Furthermore, activities in urban green areas and effects on social relationships are also included in the evaluation.

1.1. Literature Review on Forest Bathing and Forest Therapy

In 2017, the first literature review article on FBPW was published in [14] to track the state of the art on this topic. The authors identified 127 papers from five databases (PubMed Central, PubMed, CINAHL, Scopus, and PsycINFO) over 12 years (2007–2017) and categorized them into four sub-groups with these themes: “physiological,” “psychological,” “sensory metrics,” and “frameworks.” Two years later, ref. [15] conducted a systematic review of the effects of gardens and gardening on the emotional and social health of people with dementia, analyzing 18 papers published before 2017. These first two literature reviews contextualize the positive effects of FBPW both in more natural environments (natural and semi-natural forests) and in less natural ones (gardens and urban green areas).

From 2017 to 2024, 34 literature reviews were carried out internationally, corresponding to an average of 4.3 ± 3.2 peer-review publications per year and an average of 6.4 ± 1.3 per year over the last 5 years (2020–2024). Since 2020, the year of the spread of the COVID-19 pandemic worldwide, literature review articles on the effects of forests and green areas on human well-being and health have grown exponentially, as shown in Figure 1.

The literature reviews published from 2017 to 2024 are shown in Supplementary Materials S1.

Analyzing these 34 publications makes it possible to highlight the trends and patterns in the international literature on this topic in English.

First, it is important to distinguish publications that focus exclusively on literature reviews about different aspects of forests’ positive effects on human well-being from those that use literature reviews as introductory frameworks for broader purposes (e.g., empirical studies, preparation of protocols, and recommendations). Among the latter, ref. [16] conducted a systematic review to analyze the status and level of evidence of forest healing programs in South Korea, while [17] adopted a summative review of existing published systematic reviews and meta-analyses to provide recommendations for practice and research within the field of outdoor therapies. Ref. [18] implemented a literature review aimed at developing a certification standard for recreational and therapeutic forests, while [19] analyzed 9 key articles related to nature-based interventions and treatment of pain to develop a theoretical framework on nature-based interventions and pain.

Second, literature reviews can be distinguished into those focused on a specific issue (physical health, psychological/mental health, or both) from systematic reviews of other literature reviews.

In the first group, several publications focused on the positive effects of FBPW on physical health. In particular, ref. [20] compared 13 studies on the impact of an FBPW program on adults’ immune function using PICO-SD (participants, interventions, comparisons, outcomes, study design), while [21] investigated through 14 papers the physiological and psychological benefits of FBPW for adults suffering from pre-hypertension or hypertension. Ref. [22] explored through a literature review the harmful health effects of air pollution (i.e., particulate matter) in urban environments, while [16] investigated the effectiveness of forest healing programs through a systematic literature review using four electronic databases and the timeframe 2000–2021. Ref. [23] studied the effects of forest VOCs (volatile organic compounds) on human health through an analysis of over 140 articles. Ref. [24] assessed 33 papers focused on the immunomodulatory effects of nature exposure by inhalation of natural substances, while [25] focused on the role of FBPW as a preventive measure against the onslaught of COVID-19. Ref. [26] investigated the literature about the effects of nature-based interventions on 2786 cancer survivors who participated in 12 studies.

Other publications have considered the effects of FBPW on psychosocial and psychological health. Among these, ref. [27] focused on the literature about the impact of mindfulness and Shinrin-yoku on emotional response, neuroendocrine response, and neurobiological response, while [28] analyzed the scientific literature (32 studies published from 1991 to 2019) about the relationship between forests, stress relief, and relaxation. Then, ref. [29] analyzed publications on empirical research conducted from 2000 to 2022 on the effects of FBPW on mental health (i.e., better management of stress and emotions, reduction in indicators of depression and anxiety), while [30] identified a set of indicators to analyze the psychosocial and physiological effects of FBWP through a systematic literature review of 29 papers published from 2010 to 2021. More recently, ref. [31] investigated psychological outcomes due to an FBPW session with a special focus on Europe, while [32] implemented a systematic literature review to analyze studies that investigate the multi-sensory stimulation of FBPW. Ref. [33] examined the effectiveness of mental health interventions on children and adolescents in residential youth care through a systematic literature review. Ref. [34] used a systematic literature review to explore the effects of FBPW on self-criticism, self-compassion, and self-protection.

Finally, some publications have included both physical and psychological benefits. Ref. [35] summarized FBPW’s effects on cardiovascular health (10 papers), the immune system (6), the neuroendocrine system (3), and mental health (11) through a literature analysis. Similarly, ref. [22] analyzed the main physiological (i.e., cardiovascular, cerebrovascular, respiratory) and psychological health effects associated with exposure to forests through a literature review of 11 papers. Ref. [36] implemented a literature review identifying 93 papers regarding the psychological, physiological, and social well-being effects related to FBPW. In the same direction, ref. [37] classified the benefits of FBPW in three categories (physiological, psychological, environmental) to spread this practice in Canada. Ref. [38] evaluated forest-based interventions’ therapeutic psychological and physical effects through 11 systematic reviews covering 131 different primary intervention studies. The authors highlighted that forest-based interventions are beneficial to the cardiovascular system, immune system, and mental health. Ref. [39] applied a meta-analysis, meta-regression, and systematic review to explore the forest effects on human well-being by examining psychological scores and biomarkers, while [40] implemented a systematic literature review focused on forest therapeutic tourism and well-being forest tourism using three databases distinguishing three categories of papers: those of literature reviews (7), those focused on medical findings of psychological and physiological effects on human well-being (9), and those focusing on the explicit relationship between forest well-being effect and tourism activity (13). Ref. [41] analyzed 21 studies focused on the impacts of FBPW on the physical and mental health of college students through a systematic literature review, while [42] investigated the importance of beneficial forest elements for human well-being through 31 studies. Ref. [43] explored the physiological and psychological benefits of different forest therapies for healthy and pathological elderly people (more than 60 years) using a systematic literature review.

In the second group (systematic reviews of other literature reviews), four literature review publications were identified concerning the following issues: (i) the preventive and therapeutic psychological and physical effects of forest-based interventions [38], (ii) the respiratory benefits of biogenic organic compounds (BVOCs) during FBPW [44], (iii) the theories explaining nature’s role in outdoor therapies [17], and (iv) the benefits of FBPW for the promotion of individual well-being [45].

1.2. Motivations and Aims of the Study

The prominent increase in papers and reviews concerning FBPW registered in the last years highlights the need for advanced techniques for literature review. Big data analysis is a relatively recent and straightforward approach that facilitates categorizing scientific production in numerical terms [46,47]. Among big data analyses, text mining allows for reducing and managing information in large texts, resulting in automated quantitative and statistical outputs [48].

Based on the authors’ knowledge, a global geographic-based text mining approach has never been applied to analyze the scientific literature concerning FBPW. In addition, the scientific summary reported in Section 1 shows how a focus on forest typologies and characteristics, as well as recent and specific analysis of methods and tools applied to investigate the physiological impact of FBPW, is rarely introduced in literature reviews.

Based on these premises, the aim of the paper is to develop a quantitative literature review on FBPW by comparing it with existing literature reviews. The quantitative literature review focused on two topics: (i) a worldwide geographic-based text mining focused on FBPW and (ii) a quantitative review on forest characteristics combined with techniques to evaluate physiological responses due to FBPW. To this end, these are the research questions: (1) How did the concept of FBPW spread in the scientific literature at the geographical level? (2) What are the key forest variables of FBPW according to scientific studies? (3) What are the physiological measurements related to FBPW considered in the scientific literature?

2. Materials and Methods

2.1. Text Mining

2.1.1. Implementation of Database

The Scopus database was used to download titles, abstracts, and keywords of interest to create a text corpus at the global, major area, and regional scales. Only the Scopus database was selected to avoid double accounting of scientific publications. The choice was based on both empirical tests and references that demonstrated a broader paper coverage for the forest sector compared with other databases (e.g., PubMed, Web of Science) [49]. Major areas and regions were identified with their respective names but also with the introduction of adjectival and demonymic forms [50]. This categorization provided five major areas (Africa, Americas, Asia, Europe, and Oceania) and 22 geographical regions (Eastern Africa, Western Africa, Southern Africa, Middle Africa, Northern Africa, Northern America, Southern America, Central America, Latin America and the Caribbean, Eastern Asia, Southern Asia, South-Eastern Asia, Western Asia, Central Asia, Northern Europe, Western Europe, Eastern Europe, Southern Europe, Australia and New Zealand, Melanesia, Polynesia, Micronesia). The Antarctic region was excluded due to the absence of interest in forests. Only English language publications were considered, covering the period up to 2025. The advanced query search is reported in Supplementary Materials S2 (for example, for Southern Europe; scripts for global analysis or other specific regions are available upon request to the authors).

2.1.2. Statistical Analysis of Corpus

Text mining was implemented through T-LAB Plus 2018 software (www.tlab.it). The corpus was imported as a .txt file and pre-processed through disambiguation of lexical units (expressions consisting of one or more words that behave as single terms), lemmatization, and lexicalization [51]. Lemmatization reduces the corpus words to their respective hardwords (i.e., lemmas). Lexicalization is a process through which a syntagm (a sequence of words) becomes a lexical unit. In T-LAB, the “basic” stop-word check was selected; in this case, the stop words (terms that on their own do not have any specific and/or significant content) were chosen from a set of predefined list (i.e., articles, adverbs, preposition, etc.). For the text segmentation, the elementary context for the computation of co-occurrences was the “chunk” option. The key-term selection method is automatically provided by software with selected maximum items set at 1000 key terms (medium-low option among available values, i.e., 500, 1000, 1500, 3000). The “basic” option was also applied to elaborate multi-words, a set of two or more words that stand for only one meaning. Multi-word categories include compound words, phrasal verbs, and idioms.

Clustering of the corpus was developed by a hierarchical method that computes an association index within the elementary contexts (i.e., sentences, fragments, paragraphs). In T-LAB, using different techniques, association indexes analyze the presence/absence of lexical units. Statistical analysis applied the cosine index to perform multidimensional scaling (MDS). MDS allows a graphical representation of relationships among lexical units through concept mapping within a space of reduced dimensions. MDS is based on Sammon’s algorithm [52,53] (see the T-LAB manual for more details; https://mytlab.com/Manual_en.pdf, accessed on 10 March 2025).

2.2. PRISMA

Literature Search and Eligibility of Criteria

The second step of the work—review of forest characteristics and techniques to evaluate physiological responses due to FBPW—was developed in the framework of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [54,55]. The search string included terms related to forest identification and FBPW. Using the software Covidence (https://www.covidence.org/, accessed 12 May 2025), a literature review was divided into three main phases: collecting and identifying papers, screening, and synthesizing data. Scientific works were selected following the inclusion criteria of (i) a clear definition of physiological analysis in terms of applied technique and/or instrument (e.g., measurement of salivary cortisol, heart rate variability, electroencephalography), (ii) a quantitative measurement of physiological responses to FBPW has to be reported in the paper, (iii) structured activities involving on-site exercise and/or exposure to a real or virtual forest environment according to the definition of FBPW reported in Chapter 1 and potentially influencing psycho-physiological or social responses of individuals, (iv) publication in English in peer-reviewed journals from the Scopus database, and (v) timeframe: 2000–2024. No limits were set on the country’s study or forests’ and participants’ characteristics.

The complete query search scripts applied for PRISMA are available in Supplementary Materials S3.

3. Results

3.1. Text Mining

3.1.1. Overall Analysis of Corpus

The total number of scientific papers on the topic has increased significantly over the period covered by the Scopus database (since 1910) (Figure 2), with a relevant growth starting from 2010.

The results for regions highlight a prominent dominance of Eastern Asia (901 papers), confirming the diffusion of FBPW for the improvement of human health in countries such as Japan and South Korea and, more recently, China (Figure 3a). Other regions with high levels of scientific production include Northern America and Northern Europe (743 and 727 papers, respectively). Central America, Africa, Central Asia, and regions of Oceania (apart from Australia and New Zealand) exhibit relatively low contributions to the overall scientific output.

A preliminary analysis of scientific production in different regions seems to relate the total number of papers to the investment in different areas of research and development (R&D) [56]. Therefore, it is interesting to quantify the percentage of papers focusing on FBPW in the total scientific production (Figure 3b). Outputs stress higher FBPW papers for Eastern Europe, Western Europe, and South-Eastern Asia. Compared with the previous map, an increase in relative importance is noted for Middle Africa, Central Asia, and Central America; on the other hand, Northern America has a low relative importance on total publications.

3.1.2. Multidimensional Scaling

The MDS results for five major areas are shown in Figure 4. The degree of correspondence between (i) the distance among lemmas computed in MDS and (ii) the input matrix defined in the clustering procedure is measured by a stress function: the lesser the stress value, the better the performance of the obtained adjustment. The stress value described by Sammon’s algorithm highlights fair goodness for all maps; however, the results are acceptable due to the two-dimensional solution of MDS [57]. The obtained concept maps allow for interpreting the relationship (distance) between the lemmas (nodes), the importance (size) of each lemma in the corpus, and the dimensions that organize the space in which they are represented.

The main outputs from the MDS for Africa denote (in addition to the base lemma “forest”—second quadrant) an emphasis on the literature on urban green areas, cities, and parks (fourth quadrant). Methodological approaches seem to focus on evaluating the psychological and mental impact of urban forests and green infrastructures through perception analysis (fourth and third quadrants). The first quadrant suggests how attention is also paid to planning strategies for sustainable management of ecosystem services provided by trees and gardens (i.e., well-being and recreation). The general conservation of forest resources, tree species, water, and landscapes for environmental and economic purposes is stressed in the second quadrant. The MDS for Americas indicates that research on FBPW is concentrated on sustainable forest management and planning to take into account trade-offs among cultural (“recreation”) and provisioning (“timber”) services (first quadrant). Climate change seems to pose a risk to economic benefits also related to outdoor activities, with fires being a major contributing cause. In addition to psychological and mental outcomes in cities, parks, and urban green areas, the analysis also introduces the effects of FBPW on obesity, lifestyle, and social relationships (third and fourth quadrants). The methods applied in the Americas reveal the importance of spatial modeling. In the results for Asia, some specificities can be depicted with respect to previous MDS maps. In the second quadrant, the importance of tourism due to recreation is reported. The effect of air pollution is also examined. The in-depth analysis of FBPW is revealed in the third and fourth quadrants: lexical units such as “physical activity” and “blood pressure” as well as “control group,” “questionnaire,” and “survey” denote the amount of scientific production and structured approaches dedicated to the effects’ analysis of forest and urban green areas on the physiology and psychology of peoples. The typical term for Asia that confirms the above statement is “therapy,” introduced here first in the world. The MDS for Europe reports how forest management focused on FBPW should also consider biodiversity conservation for tourism valorization (fourth quadrant). Mental health and psychological well-being analyzed in green spaces have been intensely investigated here (first and second quadrants). Social benefits are related to modeling through surveys and questionnaires (third quadrant). Lastly, Oceania confirms the importance of topics reported also for other major areas. Some specificities are (i) the cross-sectional and longitudinal analysis for different ages of people (“adult,” “adolescent,” and “child” in the third and fourth quadrants) and (ii) social benefits and development of communities in the case of FBPW (first quadrant).

The MDS for the world merges the above maps with the importance of several nodes (correlated to the dimension of dots) due to the overall number of papers dedicated to each lexical unit.

3.2. PRISMA Outputs

PRISMA literature review identified 157 studies eligible for the analysis (Figure 5). The characteristics of papers focusing on the quantitative physiological responses of people in the case of FBPW are reported as follows.

Regarding forests, mainly natural ones were investigated (77.2%), followed by urban forests (22.8%). Several studies focused on the effects of a comparison between forests and artificial environments (43%). In these papers, real forests were mainly examined (69.6%) compared with virtual reality applications (14.5%). Photos and videos with forests were also used but in a more limited number of studies (

Table 1. Forest setting and variables analyzed in FBPW papers with a physiological focus.

Forest Setting		Forest Variable
Real forest	69.6%	Tree species	40.9%
VR forest	14.5%	Density/coverage	10.1%
Photo with forest	9.0%	Age	8.1%
Video with forest	3.4%	Diameter/height	2.0%
Only audio	2.1%	Leaf typology	0.7%
Essential oils	1.4%
Total	100.0%		61.8%

).

In 61.8% of the papers, one or more forest variables were explicated (Table 1); tree species is the most represented. Density or canopy coverage was also analyzed: when investigated, half of the papers compared different degrees of density (low/high or low/medium/high). Additional variables (e.g., degree of lightness) were applied. Some papers introduced age, diameter, height, or leaf typology. Age is usually assessed considering a single age (e.g., a stand of 30 years), single classes (e.g., 40–90 years), or generic categorization (e.g., young stand, old growth). A similar consideration can be given for diameter/height or additional dendrometric parameters (i.e., basal area). A few research studies focus on leaf typology (small, thin, or broad leaf). In 63.6% of the cases, comparisons among seasonal effects were developed, mainly evaluating different forest habitus due to deciduous species (

Table 2. Seasons or seasons’ combination analyzed in FBPW papers with a physiological focus.

Season or Season Combination	Percentage
Summer	23.8%
Autumn	15.9%
Spring/Autumn/Winter	6.6%
Winter	6.0%
All	2.6%
Summer/Autumn	2.0%
Summer/Winter	2.0%
Spring/Summer/Autumn	2.0%
Spring/Summer	1.3%
Autumn/Winter	0.7%
Spring/Winter	0.7%
Total	63.6%

).

Summer and autumn habitus were mainly evaluated, followed by winter (23.8%, 15.9%, and 6.0% in total, respectively). Combinations of seasons were also applied (17.9%).

Partitioning of the analyzed plant genus is expressed in Figure 6. Rarely, differences among physiological responses with separate species/genera is investigated [58]. Pinus and Quercus are the preponderant genera used for FBPW analysis. Similar considerations can be brought for the presence of deadwood and clean open areas, rarely examined in the literature [59].

Output from physiological measurement categories is shown in

Table 3. The physiological measurement category was analyzed in FBPW papers (the sum of papers and the sum of percentages are not n.157 and 100%, respectively, because one or more categories can be considered simultaneously in a paper).

Physiological Measurement Category	Number of Paper	Percentage
Cardiovascular	121	77.6%
Biochemical	35	22.4%
Neurological	29	18.6%
Skin conductance	13	8.3%
Immunological	6	3.8%
Metabolic Systems	2	1.3%
Eyes movements	2	1.3%
Respiratory	1	0.6%

.

Cardiovascular quantifications are the most applied physiological measurements, followed by biochemical ones. Neurological trends have also been investigated in several papers (18.6%).

Among the cardiovascular impacts of FBPW, heart rate (HR), heart rate variability (HRV), blood pressure, and pulse rate (PR) are often used as health indicators. The widespread application is mainly due to the availability of instruments and tools that are easily wearable both on-site and in laboratory settings. Output from these approaches is quite clearly interpretable by non-medical experts. Biochemical analysis involves more technical measurements. Salivary cortisol and amylase, urine, and blood analyses (evaluating adrenaline, noradrenaline, dopamine, and other components) are applied for biochemical studies.

In recent decades, brain activity has been further investigated in relation to FBPW. Electroencephalography is the most commonly applied technique, mainly through the measurement of alpha and beta waves, functional Magnetic Resonance Imaging (fMRI), and Near-Infrared Spectroscopy (NIRS), following previous techniques in terms of several research applications. A few brain analyses involve electromyography (EMG) and Transcranial Magnetic Stimulation (TMS).

Other techniques used in health analysis include skin conductance (Electrodermal Activity (EDA)) and immunological assessment (primarily through Natural Killer (NK) cell quantification). Rarely were metabolic studies, eye movements (eye-tracking tools), and respiratory experiments conducted.

4. Discussion and Conclusion

The substantial increase in interest in FBPW has led to a growth in scientific production on the topic. The complex interactions among forest variables, socio-economic factors, and individual characteristics affecting psycho-physiological conditions require instruments to manage the vast amount of information furnished by research.

Quantitative literature reviews, based on text mining and PRISMA, are a promising approach to examining geographic peculiarities and isolating the influence of environmental factors on individuals’ well-being.

The applied MDS approach highlights the specific analysis of FBPW at the regional and global levels. Some regions (e.g., Eastern Asia) are more advanced in investigating the topic and are also introducing it at the therapeutic level. It is important to underline that these countries are also the ones where FBPW was conceptualized and consequently spread first both at the scientific and practical levels. In Japan were developed the first studies on the positive impacts of forest bathing activities on the human immune system [3,7] and people’s well-being in terms of relaxation, sleep quality, reduction in anxiety, and stress [60,61,62]. Still referring to the East Asian context, some authors in South Korea and China have developed empirical studies in order to evaluate the positive effects of FBPW on different target people, such as adults with depressive symptoms [63], patients with chronic stroke [64], and elderly patients with chronic obstructive pulmonary disease [65]. In other geographical contexts, the topic is also treated in light of potential trade-offs with other ecosystem services, such as provisioning services, touristic and inner area valorization, biodiversity conservation, and the risk posed by climatic and global socio-economic changes. In Europe, some authors emphasized the role of the season, site, and stand characteristics of forests in the positive effects of FBPW on people [36,59,66]. In particular, these studies highlighted the importance of forest management practices in order to shape the forest site in terms of stem density, tree species composition, and horizontal and vertical stand structure. Other European authors have emphasized more the relationship between ecosystem services provided by forests and the provision of multiple ecosystem services useful for human well-being and health [67]. The ratio between the number of FBPW papers and total scientific production indicates the areas where the cultural service provided by forests could be considered a lever for developing marginal and mountainous areas. The effectiveness of FBPW in furnishing opportunities for eco-wellness tourism and ecotherapy activities is outlined by the literature review [40]. Due to the demonstrated therapeutic effects of forests through sensory stimuli (touch, sounds, smells, view), some authors investigated the “Certified Forest Bathing Guides and Practitioners” framework suggesting the inclusion of seven eco-wellness factors in guided forest therapy [68].

Big data analysis was based on extracting information from Scopus titles and abstracts: this may lead to the underestimation of the total number of papers due to the adjectival and demonymic forms of country names that do not consider sub-regional levels (i.e., NUTS-2 or NUTS-3 Eurostat classification). However, international manuscripts rarely do not have an explicit country of investigation. Gray literature was not introduced in the elaboration to maintain a standardized procedure in the paper collection and allow future analysis replication.

PRISMA shows that the majority of studies are developed in real forests. Virtual reality is also applied to examine forest variables in a controlled environment. This kind of technology can favor investigating the reciprocal influence of vegetation and environmental factors on human well-being. It should be applied in-depth to provide information to forest owners and managers for planning forest areas. As a matter of fact—as a result of PRISMA—the impact of tree species, dendrometric variables, or forest environmental and logistics aspects, as well as their reciprocal influence, is rarely taken into account to quantify and plan the suitability of the area for FBPW. As mentioned, some variables highlight a particular interest in the scientific literature (i.e., seasonality or comparison among urban/artificial and natural/semi-natural environments). However, there is a knowledge gap in the international literature regarding the direct relationship between key site characteristics (e.g., tree species composition, stand structure, age, density) and the effects of FBPW on participants’ psycho-physical health.

Even if psychological aspects are the most investigated in terms of well-being impact, the quantitative literature review reveals how physiological responses are also evaluated, mainly through cardiovascular measurements (e.g., blood pressure and heart rate). Biochemical reactions, skin conductance, and additional output demonstrated a particular interest in the literature. Neurological evaluation is a promising line of research to investigate further. Techniques based on electrical activity or brain oxygenation reveal pros and cons; electroencephalography (EEG) allows for precise measures from a time point of view but with a fewer spatial resolution; on the contrary, neuronal oxygenation (NIRS, fMRI, etc.) facilitates a more comprehensive spatial analysis of the brain but with a certain latency from a temporal perspective (magnitude of a few seconds). Future neuroscientific analysis should focus on emotional responses due to forest stimuli. In this sense, the magnitude and area of brain activation can give objective information about emotional reactions, furnishing additional output with respect to one elicited using interviews.

However, a combination of psychological and physiological responses can promote a holistic investigation of human well-being, giving deeper insights into the complexity of people’s health status in forest immersion and/or visualization.