Shinrin-Yoku (Forest Bathing) and Nature Therapy: A State-of-the-Art Review

International Journal of
Environmental Research
and Public Health
Review
Shinrin-Yoku (Forest Bathing) and Nature Therapy:
A State-of-the-Art Review
Margaret M. Hansen *, Reo Jones and Kirsten Tocchini
School of Nursing and Health Professions, University of San Francisco, 2130 Fulton Street, San Francisco,
CA 94901, USA; rjjones2@usfca.edu (R.J.); kntocchini@usfca.edu (K.T.)
* Correspondence: mhansen@usfca.edu; Tel.: +1-014153787577
Academic Editors: Yoshifumi Miyazaki, Hiromitsu Kobayashi, Sin-Ae Park and Chorong Song
Received: 11 June 2017; Accepted: 21 July 2017; Published: 28 July 2017
Abstract: Background: Current literature supports the comprehensive health benefits of exposure
to nature and green environments on human systems. The aim of this state-of-the-art review is to
elucidate empirical research conducted on the physiological and psychological effects of Shinrin-Yoku
(or Forest Bathing) in transcontinental Japan and China. Furthermore, we aim to encourage healthcare
professionals to conduct longitudinal research in Western cultures regarding the clinically therapeutic
effects of Shinrin-Yoku and, for healthcare providers/students to consider practicing Shinrin-Yoku to
decrease undue stress and potential burnout. Methods: A thorough review was conducted to identify
research published with an initial open date range and then narrowing the collection to include
papers published from 2007 to 2017. Electronic databases (PubMed, PubMed Central, CINAHL,
PsycINFO and Scopus) and snowball references were used to cull papers that evaluated the use of
Shinrin-Yoku for various populations in diverse settings. Results: From the 127 papers initially culled
using the Boolean phrases: “Shinrin-yoku” AND/OR “forest bathing” AND/OR “nature therapy”,
64 studies met the inclusion criteria and were included in this summary review and then divided into
“physiological,” “psychological,” “sensory metrics” and “frameworks” sub-groups. Conclusions:
Human health benefits associated with the immersion in nature continue to be currently researched.
Longitudinal research, conducted worldwide, is needed to produce new evidence of the relationships
associated with Shinrin-Yoku and clinical therapeutic effects. Nature therapy as a health-promotion
method and potential universal health model is implicated for the reduction of reported modern-day
“stress-state” and “technostress.”.
Keywords: Shinrin-Yoku; forest bathing; nature therapy; integrative medicine
1. Introduction
Research conducted in transcontinental Japan and China points to a plethora of positive health
benefits for the human physiological and psychological systems associated with the practice of
Shinrin-Yoku (SY), also known as Forest Bathing FB (FB) [1–3]. SY is a traditional Japanese practice
of immersing oneself in nature by mindfully using all five senses. During the 1980s, SY surfaced
in Japan as a pivotal part of preventive health care and healing in Japanese medicine [4]. The
reported research findings associated with the healing components of SY specifically hones in on
the therapeutic effects on: (1) the immune system function (increase in natural killer cells/cancer
prevention); (2) cardiovascular system (hypertension/coronary artery disease); (3) the respiratory
system (allergies and respiratory disease); (4) depression and anxiety (mood disorders and stress);
(5) mental relaxation (Attention Deficit/Hyperactivity Disorder) and; (6) human feelings of “awe”
(increase in gratitude and selflessness) [5]. Moreover, various contemporary hypotheses, such as:
Kaplan’s Attention Restorative Hypothesis [6]; Ulrich’s Stress Reduction Hypothesis [7]; and Kellert
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Int. J. Environ. Res. Public Health 2017, 14, 851 2 of 48
and Wilson’s Biophilia Hypothesis [8] provide support and a lens for the practice of SY and other
forms of nature engagement.
Furthermore, SY may be considered a form of Nature Therapy (NT). Song, Ikei and Miyazaki’s
present day model: Concept
Concept of Nature Therapy
Therapy (CNT)
(CNT) [9] clearly
clearly defines NT as “a set of practices
aimed at achieving ‘preventive medical effects’ through
at achieving ‘preventive medical effects’ through exposure exposure to natural
to naturalstimuli that that
stimuli render a state
render a
of physiological
state relaxation
of physiological and boost
relaxation the weakened
and boost the weakened immune
immune functions to prevent
functions diseases”
to prevent [9]. The
diseases” [9].
conceptual
The model
conceptual of NT
model starts
of NT with
starts a “stressed
with a “stressedstate” atat
state” the
thetop
topand
andthen
thenpoints
pointsto to the
the “restorative
effects” of nature (forests, flowers, etc.) where there is a hypothesis of improvementimprovement in “physiological
relaxation” and
relaxation” and“immune
“immune function recovery”
function responses
recovery” (individual
responses differences
(individual noted). These
differences responses
noted). These
to nature are then incorporated in the Evidence Based Medicine (EBM)
responses to nature are then incorporated in the Evidence Based Medicine (EBM) model and is model and is illustrated
by an arrow
illustrated byleading
an arrow to leading
the “preventive medical effect.”
to the “preventive medicalThis clearThis
effect.” model supports
clear Song, IkeiSong,
model supports and
Miyazaki’s [9] review of some medically proven outcomes. Kaplan
Ikei and Miyazaki’s [9] review of some medically proven outcomes. Kaplan and Kaplan [6] and Kaplan [6] associated
with exposure
exposure toto naturally
naturallyoccurring
occurringstimuli
stimuli(all
(all5 senses)
5 senses) that
that hashas a direct
a direct effect
effect on increasing
on increasing the
the parasympathetic
parasympathetic nervous
nervous system
system andand a heightened
a heightened awareness
awareness thatleads
that leadstotoaastate
state of
of relaxation
(Figure 1).
Figure
Figure 1.
1. Concept
Concept of
of nature
nature therapy
therapy [9].
[9]. Permission
Permission to
to publish
publish from
from Yoshifumi Miyasaki.
Yoshifumi Miyasaki.
Individuals living and interacting in green spaces (GS) report being more energetic, in good
Individuals living and interacting in green spaces (GS) report being more energetic, in good
overall health and, have more of a sense of meaningful purpose in life [10]. Current scientific findings
overall health and, have more of a sense of meaningful purpose in life [10]. Current scientific findings
are illuminating what humans intuitively know: nature has great benefits for the human brain and
are illuminating what humans intuitively know: nature has great benefits for the human brain and this
this is shown through increased happiness, health/well-being and cognition [5]. Historically
is shown through increased happiness, health/well-being and cognition [5]. Historically speaking,
speaking, Cyrus the Great intuitively built lush green gardens in the crowded urban capital of Persia
Cyrus the Great intuitively built lush green gardens in the crowded urban capital of Persia 2500
2500 years ago to increase human health and promote a sense of “calm” in a busy city. The 16th
years ago to increase human health and promote a sense of “calm” in a busy city. The 16th Century
Century Swiss-German physician, Paracelsus, declared: “The art of healing comes from nature, not
Swiss-German physician, Paracelsus, declared: “The art of healing comes from nature, not from the
from the physician” [5]. These insights have lead SY researchers to investigate the modern health
physician” [5]. These insights have lead SY researchers to investigate the modern health benefits of
benefits of humans being exposed to nature or GS.
humans being exposed to nature or GS.
Several studies explored the therapeutic benefits of SY in Asian countries [2,3,9,11].
Several studies explored the therapeutic benefits of SY in Asian countries [2,3,9,11]. Physiological
Physiological and psychological differences between participants in a “forest therapy (FT)” program
and psychological differences between participants in a “forest therapy (FT)” program and a control
and a control were examined in the Seoul Metropolitan area with findings of a significant reduction
were examined in the Seoul Metropolitan area with findings of a significant reduction in chronic
in chronic widespread pain and depression [3]. Song and colleagues [9] demonstrated how male
widespread pain and depression [3]. Song and colleagues [9] demonstrated how male Japanese
Japanese students who walked 15-min in an urban park during the autumn season had decreased
students who walked 15-min in an urban park during the autumn season had decreased stress and
stress and heart rates. By using several valid psychological tests, researchers demonstrated the
heart rates. By using several valid psychological tests, researchers demonstrated the positive effects of
positive effects of FT on individuals coping with chronic side effects of a cerebral vascular accident -
FT on individuals coping with chronic side effects of a cerebral vascular accident - specifically anxiety
specifically anxiety and depression [2]. At the Center for Environment, Health, and Field Sciences,
Chiba University, Japan, researchers measured oxyhemoglobin levels in the pre-frontal cortexes of
research participants while the participants observed three dracaena plants [11]. Results indicated a
and depression [2]. At the Center for Environment, Health, and Field Sciences, Chiba University,
Japan, researchers measured oxyhemoglobin levels in the pre-frontal cortexes of research participants
while the participants observed three dracaena plants [11]. Results indicated a significant increase in
participants’ oxyhemoglobin levels for urban, domestic and workplace foliage effects which directly
demonstrates the health-promotion effects associated with indoor foliage plants on humans [11].
While exploring recent research about the health benefits associated with SY a dearth of scientific
research conducted in Western populations was determined. Therefore, the increasing interest and the
current published significant research findings surrounding the healing benefits related to SY, GS and
the wilderness offers healthcare professionals an opportunity to delve deeper into this complementary
modality for the prevention of disease and to assist with the potential healing of certain existing
conditions in Western cultures. Revealing current research methods and subsequent research outcomes
associated with SY practices may provide researchers, clinicians and students with an intervention that
assists with preventative medicine and evidence-based practice (EBP). Therefore, the aim of this paper
is to offer: (a) an in-depth inquiry of the current literature, (b) invite researchers residing in Western
cultures to design and conduct empirical research regarding the therapeutic benefits associated with
SY and, (c) to encourage healthcare providers/students to consider practicing SY to decrease undue
stress and potential disconnection.
2. Materials and Methods
Review Method
The terms of this comprehensive review were to emphasize the core elements of the research
proposition. The initial literature search was conducted with the intention of identifying publications
that offered significant historic relevance to the practice of SY, included various populations, sample
sizes and geographic locales, utilized evidence-based practices, illustrated measurable physiological
and psychological effect parameters, expounded upon practical frameworks and methodologies for the
practice of SY, explicated unique measurable criteria for the application of SY and deduced limitations
of previous research.
Search Method
The electronic databases searched included PubMed Central, PubMed, CINAHL, Scopus, and
PsycINFO (Figure 2). Hand searched bibliographies and reference lists from seminal researchers of
SY were also applied to the initial culling of publications. PubMed Central was searched to ensure
the incorporation of relevant publications not indexed in PubMed. Keywords were used for each
database and during snowball searches. All titles and abstracts were searched with the following
terms: “shinrin-yoku,” “forest bathing,” and “nature therapy.” These searches were combined with the
Boolean operators AND/OR. These terms were chosen from careful analyses of supporting literature.
For example, the aforementioned terms “nature therapy”, “shinrin-yoku”, and “forest therapy” are
used in conjunction with one another in the most recent scholarly literature review of NT in Japan [9].
To remain prescient, the reference range utilized in this review included literature published
between the years 2007 and 2017. Therefore, the inclusion criteria allowed for publications that were
available in English, dated from 2007 to 2017, incorporated transparent evidence based practices in
reviews or trials, included robust quantitative and/or qualitative data, offered unique frameworks
and theories, and explored current trends in research. Studies not meeting the tenets of this criteria,
specifically those that pertained to physical exercise, fitness, landscape architecture, and laboratory, or
animal studies were withdrawn from considerations.
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Int. J. Environ. Res.
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Public Health
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37
Figure 2.
Figure Literature search
2. Literature search process.
process.
3. Results
The findings of allall relevant
relevant studies
studies were
were synthesized
synthesized (Table
(Table 1).
1). The initial literature search
revealed a series of topical themes apropos of the research aim. Articles were grouped into categories
reflecting upon their most
most pertinent
pertinent features. These categories
features. These categories include Background information,
Frameworks, Physiological
Physiological and
and Psychological
Psychological effects,
effects, Sensory
Sensory Metrics,
Metrics, and
and Limitations
Limitations to
to findings.
findings.
Previous Systematic Reviews and Literature Reviews were identified. Characteristics of publications
specific
specific to
to the
the themes
themes of
of Physiological
PhysiologicalandandPsychological
PsychologicalEffects
Effects(PP),
(PP),Sensory
SensoryMetrics
Metrics(SM),
(SM),which
whichis is
a
subtopic
a subtopicofof
PP, and
PP, Frameworks
and Frameworks (F)(F)
areare
delineated, anan
delineated, explicated within
explicated thethe
within key in in
key Table 1. 1.
Table
3.1. Physiological and Psychological (PP) Effects

Livni [12] published an editorial on the health benefits of SY and described the historic trends in
biophysical and psychosocial research. While news of the beneficial elements of SY has been
gathering momentum in popular lexicon, it has been the robustness of pioneering research, largely
from Japanese scholars, that illuminates empirical links between the PP effects of SY. Tsunetsugu,
Park and Miyazaki [13] conducted a novel review representing a didactic integration of various
parameters specific to central nervous system (CNS) activity biomarkers; heart-rate variability
(HRV), salivary cortisol levels (SCL), immunoglobulin A (IgA) and sense-specific metrics.
Of the studies included within the PP section, and irrespective of study aims, there was a trend
towards small sample sizes, gender and age homogeneity, and skewed ratios of females to males/vice
versa, which by either methods of convenience, purpose and/or imparted bias to the research. An
overwhelming number of studies included homogenous gender sampling [14–27]. Population
demographics specific to gender were unreported in [28–30]. Proportionately skewed ratios of male
Table 1. Characteristics of selected studies and supporting evidence.
Study Country Population Sample Setting Aim & Design Findings

Articles were culled from
PubMed, EMBASE, CINAHL, Article total = 25. Studies that
PsycINFO, Web of Science, met the review inclusion Systematic review to collate
SPORTDiscus, ASSIA, HMIC criteria included crossover or and synthesize the findings of
Data, LILACS, UK Natl. controlled trials, which studies that compare
Research Register archives, investigated the effects of Centre for Evidence-Based measurements of health or
The studies suggested that
TRIP database, UK Natl. Lib. short-term exposure to each Conservation at the School of well-being in natural and
natural environments may
for Health, Index to Theses environment during a walk or the Environment and Natural synthetic environments. Effect
Bowler [1] UK have direct and positive
Online, Directory of Open run. Including ‘natural’ Resources, Bangor University, sizes of the differences between
impacts on several aspects of
Access Journals, Economic and environments, such as public Bangor, Gwynedd, United environments were calculated
health and well-being.
Social Data Service, Database parks and green university Kingdom. and meta-analysis used to
of Promoting Health campuses, and synthetic synthesize data from studies
Effectiveness Reviews, Trials environments, such as indoor measuring similar outcomes.
Register of Promoting Health and outdoor built PP
Interventions, Cochrane environments.
Collab., Campbell Collab.
Assessment of forest therapy
effectiveness for treating
depression and anxiety in
Forest groups had BDI,
patients with chronic stroke by
HAm-D17 and STAI scores
using psychological tests. This
were significantly lower
study measured reactive
following treatment. BAPs
oxygen metabolite (d-ROM)
were significantly higher than
Chronic stroke patients levels and biological
Settings included a recreational baseline. Urban group STI
recruited from a stroke welfare antioxidant (BAPs) potentials
forest area in Gyenggi-do, scores were significantly higher
center in the Republic of Korea. N = 59; 40 men, 19 women; 60.8 associated with psychological
Republic of Korea. The urban following treatment. Forest
Chun [2] Korea Of those included: 31 patients ± 9.1 years of age with an age stress. Patients were randomly
group stayed in a hotel therapy is beneficial for
had a history of cerebral range of 36–79 years. assigned to a forest group
Gyenggi-do in the Republic of treating depression and anxiety
infarcts, and 28 with a history (recreational forest site) or
Korea. symptoms in patients with
of intracerebral hemorrhage. urban group (staying in an
chronic stroke and may be
urban hotel). Scores on Beck’s
useful in patients who can’t be
Depression Inventory,
treated by standard
Hamilton Depression Scale,
pharmacological or
and the Spielberger State Trait
electroconvulsive therapies.
Anxiety Inventory were
analyzed.
PP
Table 1. Cont.

To explore the effects of a 2-day
Forest therapy intervention forest therapy program on
Employees of a public took place at a campsite at the those with chronic widespread Forest therapy participants
organization providing N = 61; 35 females and 26 Saneum Natural Recreation pain. reported significant decreases
building and facilities males; randomly assigned to Forest in Yangpyeong county Measures assessed included in pain, depression and
Han [3] Korea management services in Seoul the either the experimental of Gyeonggi Province. the following: pre- post heart increased QOL. Forest therapy
Metro area, all of whom were forest therapy group (n = 33), Additional assessments were rate variability, natural killer is an effective intervention to
diagnosed with Chronic or the control group (n = 28). taken at the Inje University cell, self-reported pain, relieve psychological and
Widespread Pain (CWP). Seoul Paik Hospital in the depression level and health physiological pain.
urban environment. related quality of life.
PP
Shinrin Yoku. A website
Anonymous describing the practice of SY
Supporting material NA NA NA
[4] and programs offered for forest
guide training.
An article presented in the
Williams [5] Supporting material NA NA National Geographic magazine NA
about the effects of NT.
A book about Kaplan’s
Kaplan [6] Supporting material NA NA Attention Restorative NA
Hypothesis.
An article about Ulrich’s Stress
Ulrich [7] Supporting material NA NA NA
Reduction Hypothesis.
A book explaining the
Kellert [8] Supporting material NA NA NA
Biophilia Hypothesis.
Researchers elucidated various
Literature review aimed to scientific data, which assessed
objectively demonstrate the physiological indicators, such
physiological effects of NT. as brain activity, autonomic
Researchers culled articles Reviewed research findings in nervous activity, endocrine
Song [9] Japan from the Pubmed database Article total: 52 NA Japan related to the green activity, immune activity are
using various keywords. space, plants and wooden accumulating from the field
material and the analysis of and lab experiments. NT will
differences that arise therein. play a significant role in
PP preventative medicine in
the future.
Table 1. Cont.

A Time magazine article about
the effects of living and
interacting in green spaces.
Results indicate people are
Sifferlin [10] Supporting material NA NA NA
more energetic, in good overall
health and have more of a
sense of meaningful purpose
in life.
Quantitative study was to
determine if images of natural
objects elicited similar neural
responses (activation of the
prefrontal cortex) as those Subjects viewing actual live
brought about with the plants had significantly
interaction of real objects. increased oxy-hemoglobin
Physiological measurements concentrations in the prefrontal
Artificial climate chamber in a were performed in an artificial cortex. Subjective ratings of
Female students from the
N = 18; adult female university laboratory of the Center for climate chamber maintained at “comfortable vs.
University of Chiba, Japan,
Igarashi [11] Japan students with a mean age of Environment, Health, and 25 ◦ C with 50% relative uncomfortable” and “relaxed
deemed healthy at the time of
21.6 ± 1.5 years. Field Sciences, Chiba humidity and 300 lux vs. awakening” were similar
the study.
University, Japan. illumination. For foliage plants for both live and artificial
three dracaena plants (Dracaena plants. Results were significant
deremensis) were used. for the benefits for urban,
Oxy-hemoglobin domestic and
concentrations in the prefrontal workplace foliage.
cortex were assessed with
time-resolved near-infrared
spectroscopy.
SM
The Japanese practice of ‘Forest
Livni [12] Supporting material NA NA Bathing’ as scientifically NA
proven to improve your health.
Table 1. Cont.

To investigate the physiological
effects of Shinrin-yoku
according to specific themes
centered on the health
Author-researchers culled applications of FB. The authors
articles for this literature reviewed previous
review from a studies rooted in physiological experiments with Author-researchers
physiological data, data trials in forests and laboratory summarized the separate
collected from field settings, to determine the elements of forests in terms of
Tsunetsugu experiments in forest settings, physiological effects on the five senses, and provide
Japan N/A N/A
[13] laboratory settings, and studies individuals from exposure to contribution to effects of
categorized into sub-themes forests and elements of forest Shinrin-yoku within the
specific to the five-senses. settings. Metrics investigated framework of the “Therapeutic
Exact literature search included: physiological Effects of Forests” project.
methodology and total number measurements of central
of articles culled unknown. nervous activity, autonomic
nervous activity, and
biomarkers reflecting stress
response.
PP
Quantitative. Controlled trial
without randomization. The
aim of this study was to
elucidate how floral fragrance
could impact human health;
specifically, the
psycho-physiological
Participants comprised responses to the floral scent of Sensory stimuli from plants
Japanese male graduate and Chiba University in a screened the Japanese plum blossom. may reduce stress and provide
N = 26; males aged early to
undergraduate students at room, such that the Changes in cerebral activity a general sense of wellbeing
Jo [14] Japan mid- twenties mean age 24 ±
Chiba University, recruited participants were blinded to were measured by among this population.
1.8 years.
from landscape and the observers. multichannel near-infrared Hypothesis was supported by
horticulture programs. spectroscopy. Pulse rate, the data.
heart-rate variability and
arterial blood pressure were
taken. The brief-form Japanese
version Profile of Mood States
questionnaire (POMS) tested
for psychological stress.
SM
Table 1. Cont.

Physiological and
psychological relaxation effects
of viewing kiwifruit orchard
landscapes in summertime in
Japan were investigated.
Seventeen Japanese adult Quantitative, randomized Significant increase in PNS
females were recruited from a controlled trial wherein activity and marginally
Kiwifruit orchard adjacent to
population living within the N = 17; Adult Japanese females subjects viewed a kiwifruit significant decrease in HR and
the Center for Environment,
Igarashi [15] Japan urban suburbs of Kashiwa in with a mean age of 46.1 ± 8.2 orchard landscape or a an increase in comfortable,
Health and Field Sciences,
the Chiba Prefecture of Japan. years. building site (control) for 10 relaxed and natural feelings
Chiba University, Japan.
All were deemed healthy prior min. Intervals. HRV and HR and a significant improvement
to the experiment. were measured continuously. in mood states.
Modified semantic differential
method and short-form Profile
of Mood States (POMS) were
determined.
SM
Quantitative controlled trial
without randomization was to
determine the effects of Olfactory stimulation by
olfactory-stimulation of the a-pinene significantly
alpha-pinene (a volatile increased the High Frequency
Female students from the compound in Japanese cedar measure of HRV, which is
N = 13; adult female university Center for Environment,
University of Chiba, Japan, wood) on autonomic and associated with
Ikei [16] Japan students with a mean age of Health and Field Sciences,
deemed healthy at the time of parasympathetic nervous parasympathetic nervous
21.5 ± 1.0 years. Chiba University, Japan.
the study. system activity. Measures were activity, and decreased HR
taken at 30 s before and 90 s overall—these are signs of
during/after smell admin. increased physiologic
HRV and HR were measured. relaxation.
HR
SM
Table 1. Cont.

To deduce and present the
“normative values,” or
“reference” range of heart rate
variability (measured in 417
young male students), and
salivary alpha-amylase in 430
“healthy” male students from Results suggested a relatively
Experimental design and Chiba University with an small correlation between HRV
The study consisted of 456 procedures took place at the emphasis on the distribution and salivary alpha-amylase.
Japanese male students at the N = 456; Males aged 20 to 29 Forestry and Forest Products and reproducibility of the This study is mostly indicative
Kobayashi
Japan University of Chiba, Japan, years old (mean, Research Institute and Center values. Measures within this of intra-individual variability
[17]
deemed healthy at the time of 21.9 ± 1.6 years). for Environment, Health and quantitative study included: in measures. Provides example
the study. Field Sciences, Chiba short-term HRV; beat to beat of metrics we can use in our
University, Japan. HR recorded at 2 min intervals study as well as
with portable/wearable HR “normative” values.
monitor Salivary
alpha-amylase measurements
taken before breakfast (6:30 to
7:30 a.m.) after subjects sat
“resting” 1 min.
PP
Quantitative study aimed to
specify the normal salivary
cortisol levels, and reference
ranges in subjects at University
of Chiba, as a relatively
innocuous biomarker for stress
levels during the mornings on
two consecutive days, which
Consistency and reliability
The population consisted of in Chiba University’s research were analyzed by
(“distribution characteristics”)
267 male students from The labs and additional laboratory radioimmunoassay.
Kobayashi N = 267: Males with a mean of salivary cortisol measures
Japan University of Chiba, Japan, studies performed at the Quantitative. Saliva collected
[18] age of 21.7 ± 1.5 years. were reported to be steadier in
deemed healthy at the time of laboratories of SRL Inc. in before breakfast, appx.
the morning samples
the study. Tokyo, Japan. 20–40 min after awakening
~30–45 min after waking.
(6:30–7:30 a.m.) and again
before participants brushed
teeth. Each subject rested for
1 min in a sitting position
before saliva collection.
Measures were repeated the
following day.
PP
Table 1. Cont.

Quasi-experimental study was
to gauge the feeling elicited by
(with eyes closed), touching
four different “tactile” samples:
a plate of aluminum, a piece of
velveteen, leaf of natural
Epipremnum aureum, and an
artificial resin-made leaf, for
about ~120 s. Measures
Participants successfully
included pre and posttest
Japanese male students from reported feeling a measurable
N = 14; Males with an age Laboratory rooms at The psychological and
Koga [19] Japan The University of Chiba were sense of “calm” when touching
range of 21–27 years. University of Chiba, Japan. physiological indices, Cerebral
recruited for this study. natural plant material, as
Blood Flow (hemodynamics)
opposed to the other materials
measured via near infrared
spectroscopy (NIRS; NIRO-300;
Hamamatsu Photonics,
JAPAN); measured pre and
post stimulus. Psychological
data were acquired using a
semantic differential
questionnaire.
SM
To examine the psychological Feelings during the
and physiological benefits of transplanting task were
interaction with indoor plants different from that during the
vs. computer tasks. computer task. Feeling more
Researchers implemented a comfortable, soothed, and
Settings included laboratory
Male students from the N = 24; Japanese males with a quantitative crossover natural after the transplanting
Lee [20] Japan rooms at The University of
University of Chiba, Japan. mean age of 24.9 ± 2.1. experimental design. task Sympathetic activity
Chiba, Japan.
Participants were randomly increased over time during the
distributed into 2 groups computer task but decreased at
(n = 12 plants; n = 12 the end of the transplanting
computer task). task. Diastolic BP lower after
PP transplanting task.
Table 1. Cont.

Results of each indicator were
Twelve young Japanese male
To provide scientific evidence compared against each
adults were recruited from
Field experiments were supporting the efficacy of FB as environmental stimulus. HF
local universities. At the
performed at two different a natural therapy by power analysis, which reflects
recruitment stage, those who
sites (forest and urban) in investigating its physiological the activity of the
had past or current mental
Hokkaido Prefecture, Japan. benefits using biological parasympathetic nervous
disorders, and those with
The forest site was indicators in outdoor settings. system, significantly higher
cardiovascular or allergic N = 12; Japanese males with a
Lee [21] Japan characterized by broad-leaved 3 days 2-night study. values were obtained for forest
diseases were screened. Those mean age of 21.
deciduous trees and was Physiological responses as well stimuli than urban stimuli.
who were habituated to
located in Tsurui Village. The as self-reported psychological Additionally, LF/HF ratio
smoking or drinking were
urban site was a typical responses to forest and urban values of HRV, which mediate
excluded. The adults who
commercial area situated in the environmental stimuli were the activity of the sympathetic
participated in the study had a
town of Kushiro. measured in real settings. nervous system, were
mean age of 21.2 years
PP significantly lower in the forest
[standard deviation (SD) 0.9].
than at the urban site.
Quasi-experimental study
aimed to compare the effects of
a forest walking therapy
program with an Urban
walking program over 2
consecutive days to determine
Field experiments were the cardiovascular relaxation
performed at four different indices. Walks included Cardiovascular relaxation was
sites in Japan including: 12–15 min of self-paced noted with the forest walking
Male students ages 21–22 at
Yoshino Town in Nara walking in forest (4 sites therapy program, but not as
Chiba University in Japan were
Prefecture, Akiota Town in selected throughout Japan) and with the urban control
recruited to participate in the N = Japanese males with a
Lee [22] Japan Hiroshima Prefecture, urban (the control) -specifically the differences in
walking programs. All were mean age of 21.1 ± 1.2 years.
Kamiichi Town in Toyama environments. HRV measured HRV and BP within the two
deemed healthy at the outset of
Prefecture, and Oita City in with a portable ECG w/in exposures. Psychological tests
the trials.
Oita Prefecture. Data analysis 1 min intervals. 4 psychological are concurrent with these
performed at The University of questionnaires delivered: findings.
Chiba, Japan. semantic differential (SD)
techniques. Japanese version of
the Profile of Mood States
(POMS). Anxiety levels studies
with Spielberger State-Trait
Anxiety Inventory (STAI).
PP
Table 1. Cont.

To study NK activity in both
forest and urban environments.
Twelve healthy male subjects,
age 35–56 years, experienced a
three-day/two-night trip to
forest fields and to a city, in
which activity levels during
both trips were matched. On
Phytoncide concentrations in
day 1, subjects walked for two
forest and city air were
hours in the afternoon in a
measured. The FB trip
forest field; and on day 2, they
significantly increased NK
walked for two hours in the
activity and the numbers of
Male adult subjects were Various forested and urban morning and afternoon,
NK, perforin, granulysin, and
selected from four large locations across Japan. respectively, in two different
granzyme AlB-expressing cells
companies in Tokyo, Japan. Specifically, the FB groups forest fields; and on day 3, the
and significantly decreased the
Subjects having infectious experienced three different subjects finished the trip and
concentration of adrenaline in
disease, utilizing N = 12; Males aged 35–56 years, forest areas in Agematsu town returned to Tokyo after
Li [23] Japan urine. The increased NK
immunosuppressive drugs with a mean age of 45.1 ± 6.7. in Nagano prefecture of drawing blood samples and
activity lasted for more than 7
and/or other relevant northwest Japan. Whereas the completing the questionnaire.
days after the trip. In contrast,
medications were ruled out. city group experienced Nagoya Blood and urine were sampled
a city tourist visit did not
Subjects were deemed healthy city located in Aichi prefecture on the second and third days
increase NK activity, numbers
at the time of the trial. in the center of Japan. during the trips, and on days 7
of NK cells, nor the expression
and 30 after the trip, and NK
of selected intracellular
activity, numbers of NK and T
anti-cancer proteins, and did
cells, and granulysin, perforin,
not decrease the concentration
and granzymes A/B
of adrenaline in urine.
expressing lymphocytes in the
blood samples, and the
concentration of adrenaline in
urine were measured. Similar
measurements were made
before the trips on a normal
working day as the control.
PP
Table 1. Cont.

Quantitative randomized
controlled trial was to measure
the effects of forest-bathing for
short periods of time on overall
human health using a variety
of metrics. To investigate
potentially positive effects of
Data supported the hypothesis
Male University students FB on the subject’s health from
Locations included the Wuchao that several physiological and
deemed healthy at the time of the standpoint of
Mountain Forest in Hangzhou, psychological metrics were
the trials without documented N = 20; Male age pathophysiological metrics.
Mao [24] China Zhejiang, China and the urban, presented in accordance with a
history of physiological or 20.79 ± 0.54 years. Subjects were randomly
downtown district of decrease in overall stress and
psychiatric disease and/or divided into two groups.
Hangzhou, China. subsequent toxic physiologic
disorder. Forest site and city site.
effects of stress.
Measures included:
malondialdehyde (MDA)
concentrations, cytokine
production, serum cortisol,
testosterone assay, lymphocyte
assay, POMS evaluations.
PP
Pulse rate, salivary cortisol
levels were significantly lower
than baseline indicating a
physiological relaxed state.
Reported significantly more
To assess the psychological and
comfortable, relaxed and
Participants included those Forest therapy phase was physiological effects of a forest
natural according to the
recruited from the Health conducted in Akasawa Shizen therapy program on middle
semantic differential. POMS
Promotion Center in Kyuyourin, Akasawa Natural age adult women. Measures
negative mood subscale for
Agematsu, Nagano Prefecture. N = 17 Female adults with an Recreation Forest, Agematsu, included pulse rate, salivary
Ochiai [25] Japan tension and anxiety was
All participants needed to be average age of 62.2 ± 9.4 years. Nagano Prefecture. Additional cortisol levels and
significantly lower while the
Inclusion aged 40 years or assessment took place at the psychological indices were
“vigor” was significantly
older and deemed healthy at nearby health promotion taken the day before and the
higher following forest therapy.
the time of the study. center. day of forest therapy.
A significant decrease in pulse,
PP
decrease in salivary cortisol
levels, increase in positive
feelings, decrease in negative
feelings. Substantial benefit to
middle age females.
Table 1. Cont.

To investigate the relationships
between psychological Researchers found that
responses and either an urban descriptions of the forest area
or a forest setting. Using both using the SD method were
Participants included young the SD method and POMS more “enjoyable, friendly,
N = 168 Male (100%), mean age 14 forests and 14 urban areas
Park [26] Japan male Japanese university questionnaire, comparisons natural, and sacred”. There
20.4 ± 4.1 years across Japan
students. were made for both the were also significant
walking and viewing phases differences among POMS
within each area of results for both the city and
accommodation. forest areas.
PP
To investigate the physiological
effects of Shinrin-yoku using
salivary cortisol and cerebral
activity as indicators. On the
first day of the experiment, one
group of 6 subjects was sent to Results indicated that cerebral
a forest area, the other 6 were activity in the prefrontal area of
sent to a city area. On the the forest area group was
second day, each group was significantly lower than that of
sent to the opposite area for a the group in the city area after
cross check. In the morning, walking; the concentration of
The experimental trials took the subjects were asked to walk salivary cortisol in the forest
Male University students
N = 12; Males with an average place in a Seiwa Prefectural around their location for 20 area group was significantly
Park [27] Japan recruited from Chiba
age of 22.8 ± 1.4 years. Forest Park in Chiba Prefecture, min. In the afternoon, they lower than that of the group in
University, Japan.
Japan. were asked to sit on chairs and the city area before and after
watch the landscapes of their watching each landscape. The
set locale for 20 min. Prefrontal results of the physiological
cortical cerebral activity and measurements show that
salivary cortisol were Shinrin-yoku can effectively
measured before and after relax both people’s body and
walking in the forest, or city spirit.
locations and before and after
watching the landscapes in the
afternoon in the forest and city
areas.
PP
Table 1. Cont.

Determine if forest
environments have
physiological and
psychological relaxing effects
Total hgb and oxyhemoglobin
by viewing a forest area
concentrations were
compared with viewing an
Forested-region located in significantly lower in their
Eight Korean university urban area from the roof of an
Dowon-ri, Toseong-myun, forest area than the urban area.
students participated in this urban building without being
N = 8; Participants had an age Goseong-gun, Gangwon-do, Comfortable, natural, and
study. The subjects were watched by others.
Joung [28] Korea range of 22.0 ± 2.2 years. Korea. The contrasting urban soothed were significantly
deemed physically and Near-infrared spectroscopy
Gender undocumented. area was in Yuseong-gu, higher in the forest vs. urban
mentally healthy prior to the measurement was performed
Daejeon Metropolitan City, area.
initiation of this study. on subjects while they viewed
Korea. For mood states, the forest
scenery for 15 min. At each
group had significantly lower
experimental site (forest and
negative emotions.
urban) Total hgb and
oxyhemoglobin concentrations
were measured.
SM
controlled trial was to provide
scientific evidence to support
the use and efficacy of SY as a
practical application for
Results of this study
treating, or ameliorating
demonstrated that there is
essential hypertension in the
direct evidence to support the
elderly. Patients with essential
application of SY for the
Broad-leaved evergreen forest hypertension were randomly
amelioration of essential
Subjects included patients “White Horse Mountain divided into a field study
hypertension in the population
diagnosed with essential National Forest Park” in group and a control group of
N = 24; Adults, aged from 60 to studied. Data indicates that SY
hypertension in stable Suichang, County, Zhejiang 12 persons each. The
Mao [29] China 75 years, specific practices contribute to the
condition at the time of the Province, China. For intervention (field study)
demographics unknown. inhibition of the
study. All were being treated in comparison, the control city group went to a broad-leaved
renin–angiotensin system and
Hangzhou, China. was an urban area in evergreen forest to experience
inflammation, thereby
Hangzhou, China. a 7-day/7-night trip, and the
reducing cardiac workload and
control group experienced a
further stress on the heart
city area in Hangzhou for
when compared with the urban
control. Measurements of the
control.
following were collected:
blood pressure indicators,
cardiovascular disease-related
pathological factors including
endothelin-1,
Table 1. Cont.

homocysteine, renin,
angiotensinogen, angiotensin
II, angiotensin II type 1
receptor, angiotensin II type 2
receptor, inflammatory
cytokines interleukin-6 and
tumor necrosis factor were
detected. The profile of mood
states (POMS) was used for
psychological indicators.
PP
To determine the effects of
garden walking on depression
in older adults. Participants
were asked to complete 12 two-
hour garden walks during a
3-month period. Throughout
the walks, they were asked to Mean scores on the Geriatric
Participants included older N = 40 (mean age = 71.3 years)
McCaffrey read a descriptive paragraph Depression Scale decreased
USA adults over the age of 65 with with depression diagnosed by Morikami Gardens, Florida
[30] and journal upon reaching from 13 to 9.4 after completion
depression. a physician.
specified locations within the of the 12 forest walks.
gardens. Pictures of these
locations were also provided so
that journaling could continue
when the participants were
away from the gardens as well.
PP
Table 1. Cont.

To test the effect of cognitive
behavior therapy (CBT)-based
psychotherapy applied in a
forest environment on major
depressive disorder. Tests used
included the Hamilton Rating
Scales for Depression (HRSD)
scores of the forest group were CBT-based psychotherapy
significantly decreased after 4 applied in the forest
Patients recruited for this study Settings were the following;
sessions compared with environment was helpful in the
were among a population N = 63 males and females; 23 in the forest program took place
controls. Montgomery-Asberg achievement of depression
diagnosed with major the forest group, 19 in the at the Hong-Reung arboretum,
Kim [31] Korea Depression Rating Scales remission, and its effect was
depressive disorder at one hospital group, and 21 in the while the hospital program
(MADRS) scores of the forest superior to that of
university hospital located in control group. took place at the Seoul Paik
group were significantly psychotherapy performed in
Seoul, Republic of Korea. Hospital.
decreased compared with both the hospital and the usual
the hospital group and the outpatient management.
controls. The remission rate (7
and below in HRSD) of the
forest group was 61% (14/23),
significantly higher than both
the hospital group (21%, 4/19)
and the controls (5%, 1/21).
PP
Pre and posttest study was to
evaluate the immediate effects
of forest walking in a
community-based population
with sleep complaints.
Ryukoku Forest of Ryukoku Results indicated that 2 h of
Two-hour forest-walking
University in Shiga Prefecture, forest walking improved sleep
71 healthy adult volunteers sessions were conducted on 8
N = 71; 43 males and located in the western region of characteristics; impacting
Morita [32] Japan participated in this study. Ages different weekend days. Sleep
28 females. Honshu, Japan. Data analysis actual sleep time, immobile
ranged from teens to late 70s. conditions were compared
took place at the University of minutes, self-rated depth of
between the nights before and
Shiga, Japan. sleep, and sleep quality.
after walking in a forest by
self-administered
questionnaire and actigraphy
data.
PP
Table 1. Cont.

To explore the impacts of
spiritual care and integration
of the natural environments in
terms of its’ impact on 22
cancer patients. Specifically,
the integrative treatment
Patients were recruited from a
protocol consisted of forest
pool of cancer patients,
therapy, horticultural therapy, There were dramatic shifts pre
specifically those with breast Within the Kyoto prefecture of
yoga meditation, and support and post intervention to
cancer, or lung cancer of Japan, sites included: The
group therapy sessions were support the hypothesis
various stages. For all N = 22; Men and women with Japan World Exposition 70
conducted once a week for 12 aforementioned. Emotional
participants, one month passed a mean age of 58.1 years +/10.8 Commemorative Park (Suita,
weeks. The spirituality (the and spiritual health improved
after they had undergone years. Participants included 4 Osaka Pref, Japan), parks,
Nakau [33] Japan Functional Assessment of for all participants. This study
surgery, chemotherapy, or males with an average age of forests, and gardens within the
Chronic Illness helps to delineate what is
radiation and were in stable 65.3 and 18 females with an park, horticultural settings,
Therapy-Spiritual well-being), meant by “spiritual well-being”
condition at the time of study. average age of 56.6 years. participants’ homes, and a
quality of life (Short Form-36 with specific questionnaires
All participants resided in local day treatment facility.
Health Survey Questionnaire), from which we can glean much
urban areas and lacked access While watching a yoga video.
fatigue (Cancer Fatigue Scale), in terms of semantics.
to green, outdoor
psychological state (Profile of
environments.
Mood States, short form, and
State-Trait Anxiety Inventory)
and natural killer cell activity
were metrics assessed before
and after the sessions.
PP
Researchers culled their
participants from a sample of Quantitative longitudinal
patients being treated for Type study aimed to address the
II Diabetes with an age range effects of Shinrin-Yoku on
of 60–83, mean height 154.0 cm blood glucose levels in patients Results demonstrated that
± 1.3, and mean body mass with Type II Diabetes. In an Shinrin-yoku and a decrease in
index (BMI) of 23.6 ± 0.4 effort to summarize data from blood glucose are significantly
Research facility and nearby
kg/m2 . Additionally, N = 48 (16 males and 32 female) future studies, the author of correlated. However, due to
recreational areas in connection
Ohtsuka [34] Japan researchers incorporated data Type 2 Diabetic patients with a this article noted that an the additional longitudinal
with Hokkaido University,
from longitudinal studies mean age of 66.8 years. additional sample of 116 participant sample being
Japan.
addressing Type II Diabetic persons, organized into 25 reported in the data, the
patients over a period of 6 paired groups were specificities of the total
years. This increased the incorporated. Available data population are unclear.
sample to 116 persons, from reflects these additional
which 25 paired samples were participants.
studied. Healthy subjects were Of the initial sample (N = 48),
used as a control.
Table 1. Cont.

11 participants experienced
only dietary and exercise
therapy, 27 were given oral
medication, and 10 were being
treated with insulin
administration at the time of,
and during the study.
Pre and posttest measures of
blood glucose were taken at
specific timed intervals during
the intervention process.
Participants were assessed after
morning meals at the research
hospital. Peripheral venous
blood samples were collected
for glucose levels. Participants
were divided into two
forest-walking groups. Glucose
samples were drawn again
post Shinrin-yoku treatment.
PP
Quantitative
case-control/cohort study with
pretest vs. posttest assessments.
Subjects were assessed over
Subjects were adult males and Alcoholics with higher pre-test
9-day while in a forest healing
females diagnosed with depression levels improved on
camp in Saneum Recreational
alcoholism and coming from the BDI post-test scores upon
Forest, in Kyungggi Province,
treatment at the Korean completion of the forest
Saneum Recreational Forest, in South Korea, for the
Alcohol Research Center, N = 92; Adults 84 males, 8 program more than
Shin [35] Korea Kyungggi Province, determining this therapy’s
Chungbuk Province, South females, aged ~44–49 yeas. participants with lower pre-test
South Korea. potential treatment of
Korea. The Korean Alcohol depression levels. Education
depression for alcoholics.
Research Center is a national level and marital status of
Measures included The Beck
inpatient alcohol participants did not
Depression Inventory (BDI),
rehabilitation facility. significantly influence results.
and a self-reported survey of
21 items relating to personal
variables and lifestyle metrics.
PP
Table 1. Cont.

Case study of pre-existing data.
The aim of this study was to Results of this study
research and determine the demonstrate that Danish
relevant associations between individuals living more than 1
access to green-space, health, km from green-space reported
health-related quality of life lower satisfaction of perceived
Initial sampling of data from indicators, and stress. Data health and quality of life than
21,832 adults from Denmark was collected from respondents those living less than 1 km to
was used for this study. The following up of a 2005 Danish accessible green-space.
sample came from a 2005 Utilized data from a previous Health Interview Survey. The Additionally, persons living
nationally administered health study taking place across data was collected from less than 1 km from a
N = 10,250; Adult Danes aged
Stigsdotter interview survey employing various regions of Denmark by face-to-face interviews and green-space experienced less
Denmark 16–75 years, 5802 men and
[36] region-stratified random The Danish National Institute self-administered stress than respondents living
5448 women.
sampling from the Danish Civil of Public Health, University of questionnaires. Measures farther from green-space.
Registration Southern Denmark. analyzed included: the SF-36, Respondents who didn’t report
System. 10,250 individuals (measuring eight dimensions stress were reported to be more
responded and their data of health) and the Perceived likely to visit green-spaces than
recorded for this study. Stress Scale. Multiple logistic respondents reporting stress.
regression analyses were used Overall, there was a viable
to determine the association association between distance to
between distance to green green-spaces and the health-
space and self-perceptions oriented variables in the
stress. research question.
PP
controlled trial forest recreation
and its effects on the
autonomic nervous system
Pulse rate, diastolic blood
were assessed. By random
pressure and LF/(LF + HF)
assignment, two groups were
(LF—low frequency, HF—high
formed into forest-area and
frequency) components of HRV
urban-area groups. Measures
Conifer forest in Hinokage were significantly lower in the
Male students from the Chiba N = 12; Male (100%), mean age included heart rate and
Park [37] Japan Town , and Hyuga City in forest area than in the city area.
University, Japan. 21.8 ± 0.8 heart-rate variability. The R-R
Miyazaki Prefecture, Japan HF components of HRV tended
interval of the
to be higher in the forest than
electrocardiogram was used to
in the city. Forest recreation is
analyze how aspects of HRV
effective for relaxation of both
reflect the parasympathetic
the mind and body.
nervous activity sympathetic
nervous activity respectively.
Pulse rate a blood pressure
were also measured. PP
Table 1. Cont.

To determine the physiological
effects of SY. Day one of the
experiment required that six
subjects went to the forest area,
and the other six went to a city
area. On the second day,
subjects went to the opposite of
their previously assigned areas. Researchers found that HRV of
During the morning and subjects in the forest area was
evening within the area of significantly higher than that of
Participants included young Areas of study included accommodation, heart rate subjects in the city area. On the
N = 12; Male (100%), mean age
Park [38] Japan male Japanese university Shinano town and Nagano city variability (HRV), salivary other hand, both pulse rate and
21.3 ± 1.1
students. in Nagano Prefecture. cortisol and pulse rate were salivary cortisol concentration
measured, In the afternoon, of subjects in the forest area
they were seated on chairs was significantly lower than
watching the landscapes of that of subjects in the city area.
their given area for 15 min. The
aforementioned physiological
indices were again measured
before and after watching the
landscapes in the given field
areas.
PP
Quantitative. Non-randomized
controlled trial, within-subjects
design. The aim of this study
was to demonstrate how the
The walk in the park enhanced
intervention of walking in
relaxation in the participants
urban parks during the fall
via parasympathetic nervous
Kashiwa-no-ha Park in season impacted participants’
system stimulation, while
Kashiwa City, Chiba Prefecture, heart-rate and stress levels.
Male students from the Chiba N = 23; Male (100%), mean age sympathetic nervous system
Song [39] Japan Japan, with a nearby city area Students walked 15 min each
University, Japan. 22.3 ± 1.2 stimulation was decreased.
denoted as the urban control on specific trails in a park and
Heart-rate lowered overall.
site. in a nearby urban area (the
Suggests the effectiveness of
control). HR, HRV, the State
even “small” green areas on
Trait Anxiety Inventory, and
heart-rate variability.
POMS, were measured to
assess the difference outcomes
between walk-sites.
PP
Table 1. Cont.

To study the physiological
effects of SY were examined by
investigating blood pressure,
pulse rate, heart rate variability
(HRV), salivary cortisol
concentration, and
immunoglobulin A Data of the study revealed that
concentration in saliva. blood pressure and pulse rate
Subjective feelings of being were significantly lower, and
“comfortable”, “calm”, and that the power of the HF
Male university students were “refreshed” were also assessed component of the HRV tended
Conducted in a broadleaf
Tsunetsugu recruited for this study. All N = 12; Males aged 21 to 23 by questionnaire. Physiological to be higher and LF/(LF + HF)
Japan forest mainly Nukumidaira,
[40] were deemed healthy at the (mean ± SD: 22.0 ± 1.0). measurements were conducted tended to be lower. Salivary
Oguni, Yamagata, Japan.
time of the trial. six times, i.e., in the morning cortisol concentration was
and evening before meals at significantly lower in the forest
the place of accommodation, area, and feelings of comfort
before and after the subjects were significantly higher in the
walked a predetermined forest area.
course in the forest and city
areas for 15 min, and before
and after they sat still on a
chair watching the scenery in
the respective areas for 15 min.
PP
To look at the effects of forest HR significantly lower and
walking on the autonomic high frequency component of
nervous system in middle aged HRV was significantly higher.
hypertensive adults. Subjects Questionnaire results indicate
Participants recruited for this Akasawa Shizen Kyuyourin;
were instructed to walk after walking in the forest the
study were adult male Akasawa natural recreation
predetermined courses in feelings were increased around
Japanese citizens with a history forest within Agematsu town
N = 20; Adult men with a mean forest and urban (control). The comfortable, relaxed, natural,
Song [41] Japan of prehypertension and/or of Nagano Prefecture in central
age of 58.0 ± 10.6 years. course length was 17-min. vigorous, decreased tension
current hypertension deemed Japan. The control was a city
Walk walking speed and and anxiety, depression,
in suitable physical condition area within A City of Nagano
energy expenditure were equal anxiety hostility, fatigue and
to participate in this study. Prefecture, Japan.
between both groups. HRV confusion. A brief walk in the
and HR were used to quantify forest elicited psychological
physiological responses. relaxation and physiological
PP calm on the subjects.
Table 1. Cont.

Having 10 or more trees in a
Multivariate study combining
city block improves health
high-resolution satellite
perception in a way that is like
imagery and individual tree
an increase in annual personal
data from Toronto with
Large urban population in Tree lined streets in urban The study was conducted in salary of $10,000. And, having
Kardan [42] Canada self-reports of general health
Toronto, Canada. neighborhoods. Toronto, Canada. 11 more trees in a city block
perception, cardio-metabolic
decreased cardio-metabolic
conditions and mental illness
conditions in ways compared
derived from the Ontario
to an increase in an annual
Health Study.
personal income of $20,000.
Quantitative Randomized
Controlled Trial was to study
the impact of forest-walking on
patients being treated for CAD.
Participants were randomly
assigned to either green or
urban exposure groups and
20 male and female residents of The study was conducted in
walked in these different
Kaunas, Lithuania each with a Kaunas. The urban exposure
environments for 30 min on 7 Walking in a park had a more
diagnosis of Coronary Artery area was a street near the
N = 20; Male and female consecutive days. Researchers positive effect on overall
Grazuleviciene Disease and cardiac Hospital of Lithuanian U.
Lithuania participants with a mean age of aimed to determine how the cardiac function in patients
[43] comorbidities being treated at Cardiology Clinic. The green
62.3 ± 12.6 years. different environments than walking in urban
the Cardiologic Clinic of the exposure region was a pine
impacted patients’ environments.
Hospital of Lithuanian tree park located near the
hemodynamics and state of
University of Health Sciences. Cardiology Clinic.
their CAD diagnoses. Testing
involved pretest phenotype
questionnaires, various health
assessment tools including:
SBP, DBP, HR, PWV, ECG, W
(workload), Spiroergometry.
PP
Table 1. Cont.

Within the forest group, there
Elucidate health effects of a FB was a significant decrease of
trip on elderly patients with perforin and granzyme B
chronic obstructive pulmonary expressions, accompanied by
Adult patients diagnosed with disease (COPD). decreased levels of
Chronic Obstructive Subjects were randomly pro-inflammatory cytokines
N = 20; male and female adult
Pulmonary Disease, from the divided into two groups. One and stress hormones.
Jia [44] China participants aged 60 to Hangzhou, China
region of Hangzhou, China, group was sent to forest, and Meanwhile, the scores in the
79 years.
with no exacerbations of COPD the other was sent to an urban negative subscales of POMS
within 6 weeks of the trial. area as control. Flow cytometry, decreased after FB trip. These
ELISA, and profile of mood results indicate that FB trip has
states (POMS) were evaluated. health effect on elderly COPD
PP patients by reducing
inflammation and stress level.
Quantitative longitudinal
study aimed to address the
effects of Shinrin-Yoku on
blood glucose levels in patients
with Type II Diabetes. In an
Researchers culled their effort to summarize data from
participants from a sample of future studies, the author of
patients being treated for Type this article noted that an
II Diabetes with an age range additional sample of 116
of 60–83, mean height persons, organized into 25
154.0 ± 1.3 cm, and mean body paired groups were
mass index (BMI) of incorporated. Available data
23.6 ± 0.4 kg/m2 . Research facility and nearby reflects these additional
N = 48 (16 males and 32 female)
Additionally, researchers recreational areas in connection participants.
Ohtsuka [45] Japan Type 2 Diabetic patients with a NA
incorporated data from with Hokkaido University, Of the initial sample (n = 48),
mean age of 66.8 years.
longitudinal studies Japan. 11 participants experienced
addressing Type II Diabetic only dietary and exercise
patients over a period of 6 therapy, 27 were given oral
years. This increased the medication, and 10 were being
sample to 116 persons, from treated with insulin
which 25 paired samples were administration at the time of,
studied. Healthy subjects were and during the study.
used as a control. Pre and posttest measures of
blood glucose were taken at
specific timed intervals during
the intervention process.
Participants were assessed after
morning meals at the research
Table 1. Cont.

hospital. Peripheral venous
blood samples were collected
for glucose levels. Participants
were divided into two
forest-walking groups. Glucose
samples were drawn again
post Shinrin-yoku treatment.
PP
Pre and posttest study was to
evaluate the immediate effects
of forest walking in a
community-based population
with sleep complaints.
Ryukoku Forest of Ryukoku Results indicated that 2 h of
Two-hour forest-walking
University in Shiga Prefecture, forest walking improved sleep
71 healthy adult volunteers sessions were conducted on 8
N = 71; 43 males and located in the western region of characteristics; impacting
Morita [46] Japan participated in this study. Ages different weekend days. Sleep
28 females. Honshu, Japan. Data analysis actual sleep time, immobile
ranged from teens to late 70s. conditions were compared
took place at the University of minutes, self-rated depth of
between the nights before and
Shiga, Japan. sleep, and sleep quality.
after walking in a forest by
self-administered
questionnaire and actigraphy
data.
PP
To study the effects of a Forest
Therapy/CBT-based
community program on adult
patients with HTN, referred
from two local health centers in
Seoul, S. Korea. This study was
The forest group participated a controlled trial without true
Forest Therapy/CBT-based
at two recreation forest sites randomization. For an 8-week
community program may have
Recruitment included stable including Hoengseong and intervention duration of the
The initially reduced SBP measures,
patients with stage 1 HTN, N = 56; Males and females Saneum, in Kangwon-do, treatment protocol. Data
Sung [47] Republic of marked decrease in salivary
and/or patients who were on aged 63–73 years. Republic of Korea. The control included a comparison of pre
Korea cortisol levels, and
antihypertensive medication. group maintained regular and post intervention
improvement in A Qol
treatment at the treatment measures of: BP, A. Qol.
measures.
facility. (Quality of Life survey tool),
and salivary cortisol
measurements of control group
vs. Forest Therapy program
group, SBP and DBP manual
measurements.
PP
Table 1. Cont.

Quantitative study with a
N = 503. Office staff at a cross-sectional design.
southeastern university. Employed all web-based Significant, negative
Response rate (30%). Women questionnaires including (via association between nature
(92.9%) Caucasian (82.5%). email invitation); 16-item contact and stress and nature
Full-time, desk-bound, and
Mean age (42 years; SD 12 survey on workplace environs, contact and general health
otherwise sedentary office staff
Largo-Wight years) Appx. (47.5%) of all Workplace (office) environment the Nature Contact complaints. The results
USA (secretaries and clerks), at an
[48] participants attended college or at a southeastern university. Questionnaire (NCQ), The indicate that as workday
undisclosed southeastern
technical school. (49.5%) Perceived Stress Questionnaire nature contact increased,
university in Florida, USA.
reported annual income of (PSQ) and 13-item health perceived stress and
$25,001–$35,000 per year. behavior assessed dependent generalized health complaints
(54.4%) reported being variables and health outcomes. decreased.
married. web-based survey design.
PP
To test the beneficial health
effects of walking in forests
against urban environs in 45 Hypothesis was supported—in
total respondents. Four nature that- compared with the urban
Forested and urban sites (8 walking sites and an urban control, overall psychological
Participants were recruited
total)), were used in this study. control were used as the field well-being improved more in
from four prefectures in Japan.
Takayama N = 45; Adult males aged All sites located in, or near to sites. This quantitative study forest environments. Subjects
Japan All participants were male
[49] 19–22 years. the towns of Yoshino, Akiota included the following noted that the forest walking
university students deemed
and Kamiichi and the city of psychological assessment tools: program induced feelings of
healthy at the time of the study.
Oita, Japan. Profile of Mood States (POMS) relief and revitalization,
indexes, Restorative Outcome whereas the urban walks did
Scale (ROS) and Subjective not.
Vitality Scale (SVS).
PP
Table 1. Cont.

To compare the pain-reducing
effect of FB alone vs. FB in
combination with stretching
and strengthening exercises in
patients with chronic posterior
neck pain. Participants were
randomly divided into FB
Participants for this study were Alone (FBA: n = 32) and FB
recruited from the Department Experimental trials took place Exercise (FBE: n = 32). The The number of TRPs were
of Rehabilitation Medicine of at the Department of Visual Analog Scale, neck significantly reduced in the
Hanyang University Medical N = 64; 11 males and Rehabilitation Medicine of disability index (NDI), FBE group compared with the
Kang [50] Korea
Center, where they were being 53 females. Hanyang University Medical Euro-Qual 5D-3L VAS (EQ FBA group (p = 0.013). The
treated with posterior neck Center and undisclosed nearby VAS) and index (EQ index). other scales used showed no
pain for a period of 3 months forested area. McGill pain questionnaire difference.
or greater. (MPQ), number of trigger
points in posterior neck region
(TRPs) and ROM of cervical
spine were evaluated on the
first and last day of the
program and compared
between groups.
PP
Measures of adult pain: Visual
Analog Scale for Pain (VAS
Pain), Numeric Rating Scale for
Pain (NRS Pain), McGill Pain
Questionnaire (MPQ),
Short-Form McGill Pain
Visual Analog Scale reliability
Hawker [51] NA NA Questionnaire (SF-MPQ), NA
and validity
Chronic Pain Grade Scale
(CPGS), Short Form-36 Bodily
Pain Scale (SF-36 BPS), and
Measure of Intermittent and
Constant Osteoarthritis Pain
(ICOAP)
Table 1. Cont.

Quantitative, randomized
controlled trial with pre- and
post-test design. Participants
were exposed to urban and
natural forested environmental Participants experienced less
settings respectively for 20 min physiological & psychological
at a time. Salivary amylase and stress from exposure to the
subjective measures of stress natural environments versus
N = 15; 15 (8 males, 7 female), Urban and natural outdoor were taken before and after built environs as measured by
Participants included residents
Beil [52] USA aged 20–61 years with an settings (4 total) within 15 km each exposure. Testing pre- and post-intervention
of Portland, Oregon.
average age of 42.3. of research lab. methods included web-based changes in salivary amylase
survey analyses via the and self-reported stress. The
Subjective Stress Scale (Stress), greatest decrease in stress was
Environmental Identity (EID) noted in females in natural
Scale Perceived Stress Scale settings.
(PSS) Perceived Restrictiveness
Scale (PRS) [post-test only],
Saliva (sCort and sAA).
PP
To expose Japanese students at
the Chiba University to urban
and forest environments
respectively—in order to
ascertain relevant effects on
autonomic nervous system
function. This quantitative
RCT included 57 Forest and 57 Demonstrated a roughly 80%
Urban sites selected across increase in the
Japan. Participants sat for 15 parasympathetic indicators of
The study consisted of 625
min while viewing either HRV with a decrease in
male Japanese students at the
Kobayashi N = 625; Males with a mean Forested areas (57), and urban setting. Measures included sympathetic indicators of
Japan University of Chiba, Japan,
[53] age of 21.6 years +/1.6 years. areas (57) within Japan. HRV, which was monitored HRV—physiologically
deemed healthy at the time of
continuously. The experiment demonstrating that
the study.
was performed over 2 forest-viewing was more
consecutive days at each site. effective in reducing indicators
Measures of HRV were of stress than the urban areas.
conducted between 13:30 and
15:30 for 15 min at a time.
These were RCTs; one group
was exposed to the forest site
prior to the urban site & vice
versa.
PP
Table 1. Cont.

Investigation into the
cross-correlation of salivary
Engert [54] Supporting material NA NA cortisol and alpha-amylase NA
responses to
psychological stress.
A Conversation with
Fisher [55] Supporting material NA NA NA
David Milarch
Clarification on the
physiological and
Exposure to real pansies
psychological effects on HS
increased the activity of the
students viewing real vs.
Students (male and female), Parasympathetic Nervous
N = 48; 19 high school males artificial pansies. Participants
from the Chiba Prefectural Chiba Prefectural System (PNS). Viewing real
mean age 16.2 ± 0.7 years, and were exposed to yellow fresh
Igarashi [56] Japan Kashiwanoha Senior School, Kashiwanoha Senior High flowers resulted in comfortable
21 high school females mean pansies for 3 min each.
deemed in good health prior to School lab rooms. relaxed and natural feelings.
age 16.6 ± 0.9 years. Artificial pansies in a planter
the orientation of the study. Visual stimulation with real
were used as a control. Heart
flowers induced psychological
rate variability (HRV) was
relaxation effects HS students
tested.
SM
To determine whether
stimulation by viewing an
individual preferred video of
sea or forest has an effect on
relaxation. Participants were
Decreased HR, increase in high
divided into two groups based
frequency and sustained
on their preference for sea or
arousal level were observed
forest scenery. By using a
while viewing the preferred
Participants included young Studies completed in visual analog scale the
Tsutsumi N = 12; Males, with a mean age video. The viewing of the
Japan male Japanese adults deemed laboratory settings at the participants watched 90 min.
[57] of 22.2 ± 1.7 years. preferred video had a positive
healthy at the time of study. research center. DVDs of the sea with natural
relaxation effect. Individual
sounds and forest with natural
preferences should be honored
sounds while HR variability
when initiating video
and Bispectral Index System
relaxation therapy.
value were measured using
MemCalc/Tawara and
Bispectral Index System
monitor.
SM
Table 1. Cont.

The physiological effects of
Shinrin-yoku (taking in the
forest atmosphere or forest
Park [58] Supporting material NA NA NA
bathing): Evidence from field
experiments in 24 forests
across Japan.
Literature review is based
upon 30 years of available
research demonstrating the
potential healing properties of
nature on mental and physical Research culled demonstrated
well-being under the premise that “nature” exposure is
of nature’s healing power beneficial to the mind in terms
Logan [59] USA Supporting material NA NA coined by Sir. J. Arthur of relaxation and feelings of
Thomson. The authors propose connectedness - as are viewed
a philosophical and by the tenets of this paper to be
psychological framework from “beneficial.”
which to conceive of the
potential for forest-therapy and
forest-bathing programs
F
The Science of Nature’s
Selhub [60] Supporting material NA NA NA
Influence on Your Health
Describes a creative framework
in which nature is incorporated
into therapy with older adults.
Using a practical example, this This framework highlighted a
study illustrated how the way in which the connection
integration of concepts from a between the personal story and
narrative approach and the the natural, cosmic story could
innovative nature-therapy enhance the participants’ sense
Berger [61] USA Supporting material NA NA
framework could aid a geriatric of completion within
population in expanding themselves and their
personal perspectives, surroundings, which may be
strengths, and coping further implemented into
strategies, while gaining a holistic nursing.
wider sense of acceptance and
completion in life.
F
Zdravkovic Nature and forest therapy
Supporting material NA NA NA
[62] workshops offered online.
Table 1. Cont.

Qualitative study employed a
phenomenological approach in
an effort to understand and
elucidate the effects of
Nature-Based Therapy (NBT),
Researchers generated three
on the well-being of the
key themes from analysis of
subjects. The design of the
The population addressed the interviews. These included:
study was based on a previous
were soldiers and veterans taking nature in, Nature-Based
University of Copenhagen case study from China
from the Danish military association as an initiation to
forest therapy garden addressing similar questions.
Poulsen [63] Denmark rehabilitation unit who had N = 8; Males aged 26–47 years. therapeutic processes, and
“Nacadia,” which is located in In this study the participants
served in war and were nature seen as a part of
Hørsholm arboretum. PTSD is the concern, the
diagnosed with some degree of everyday life. Participants
context is the forest therapy
Post-Traumatic Stress Disorder. reported a sense of refuge,
garden and the phenomenon is
safety, calmness, and general
the participant’s experience of
wellbeing.
NBT from 10 consecutive
weeks of treatment. Interviews
were conducted at four stages
of the program.
PP
Perceived level and sources of
Beck [64] Supporting material NA NA stress in baccalaureate nursing NA
students.
Perceived stress and social
support in undergraduate
Reeve [65] Supporting material NA NA NA
nursing students’ educational
experiences.
Integrative nursing:
Kreitzer [66] Supporting material NA NA Application of principles NA
across clinical settings.
The core concepts of Jean
Watson [67] Supporting material NA NA Watson’s Theory of Human NA
Caring and Caring Science.
Table 1. Cont.

Qualitative interview based
study was to determine and
Results of these interviews
report on how persons
reflected that subjects
diagnosed with dementia
unanimously experiences a
Population criteria included reflect on what it’s like for
sense of well-being and
males and females from a them when experience an
self-worth regarding
region in Sweden diagnosed outdoor setting. Purposive
Interviews in this study took independent outdoor activity.
with early-stage dementia of sampling was used to obtain
N = 11; Aged between 52 to 81 place in the participant’s Furthermore, interviewees
Olsson [68] Sweden various ages, who were able to this cohort. As part of a larger
years, 5 women and 6 men. homes; indoors and outdoors reported the outdoor setting as
speak. Sampling included study focusing on dementia,
at the homes. complementary to a sense of
persons who had an expressed qualitative content analysis
well-being. Potential
desire to be alone outdoors and was used to categorize the
challenges and adaptive
were living at home. interview results into core
strategies were addressed
themes based upon
when navigating outdoor
interviewee’s experiences and
settings.
discussion.
PP
To determine the effects of FB
on the autonomic nervous
HF HRV was increased while
system. Participants were
viewing a forest landscape,
asked to sit in both urban and
while heart rate was decreased
Middle-age hypertensive men, forest areas for 10 min in each
Akasawa natural recreation in comparison to the urban
that had never taken N = 20; Male (100%, )mean age location and Heart Rate were
Song [69] Japan forest near the Agematsu town setting viewings. Additionally,
medication for HTN, HLD, or 58.0 ± 10.6 years both measured. Questionnaires
of Nagano Prefecture participants felt more
DM were also given to participants
“comfortable,” “relaxed,” and
to collect data on emotional
“natural” after viewing the
condition while viewing both
forest.
settings.
PP
Proposed an application of NT
The innovative approach
for the treatment of emotional
offered in this article was
and psychiatric issues. This
supported by background
expository piece provided a
research in relevant expressive
framework based upon
Berger [70] USA Supporting material N/A N/A arts therapies. It inferred that
previous applications of NT in
NT enables persons to feel
two anecdotal examples from
relief from stress in addition to
Israel: “The Healing Sand” and
increased social
“The Enchanting Forest.”
conscientiousness.
F
Table 1. Cont.

Expositional case study, rooted
in grounded theory analysis,
qualitatively analyzed the This study demonstrated a
utilization of the NT successful protocol and
The population at the center of framework for children with application for nature -oriented
this study included students in Galim elementary school learning and behavioral therapeutic activities in a
N = 13; 9 boys and 2 girls aged
the elementary classroom of (Israel) for children with disabilities. Subjects engaged classroom setting for study
Berger [71] Israel 7–9, 2 female adults aged 42
Galim as well as their learning and behavioral in a NT program for 1 year. population and described how
and 33, respectively.
homeroom teacher and disabilities. Interviews and questionnaires NT can enhance, or support
therapist. provided data based upon pre-existing modalities for
analysis of the framework’s students with learning
role in education and scholastic disabilities.
development.
PP
NT created theories and
models to assist the therapist
working in nature to create a
therapeutically appealing
setting. From a psychological,
eco-social perspective, the
author surmised that
strengthening a relationship
with nature may reduce This framework showcased
Berger [72] USA Supporting material N/A N/A depression and anxiety and concepts from eco-psychology,
foster emotional continuity, drama and ritual.
happiness and wonder. The
purpose of this book chapter
(#2) was to illustrate a
framework for NT as a creative
therapeutic discipline via
active research and reflexive
process for the author’s PhD.
F
Key: PP: Psychological & Physiological. SM: Sense Metrics. F: Frameworks.
3.1. Physiological and Psychological (PP) Effects

Livni [12] published an editorial on the health benefits of SY and described the historic trends
in biophysical and psychosocial research. While news of the beneficial elements of SY has been
gathering momentum in popular lexicon, it has been the robustness of pioneering research, largely
from Japanese scholars, that illuminates empirical links between the PP effects of SY. Tsunetsugu, Park
and Miyazaki [13] conducted a novel review representing a didactic integration of various parameters
specific to central nervous system (CNS) activity biomarkers; heart-rate variability (HRV), salivary
cortisol levels (SCL), immunoglobulin A (IgA) and sense-specific metrics.
Of the studies included within the PP section, and irrespective of study aims, there was a
trend towards small sample sizes, gender and age homogeneity, and skewed ratios of females to
males/vice versa, which by either methods of convenience, purpose and/or imparted bias to the
research. An overwhelming number of studies included homogenous gender sampling [14–27].
Population demographics specific to gender were unreported in [28–30]. Proportionately skewed
ratios of male to females and vice versa were identified in these studies [31–36]. Studies may have
been limited to research participants specific to the student body of the courses and facilities within
which the research was designed. The aspects of cultural specificities and sensitivity in research
design must be considered when approaching a literature review from a global lens. The methods,
tests, and findings of 40 relevant publications expounding upon the PP indices are included in this
review. These publications are further assorted into Heart-rate Metrics; Disease States; Autonomic
Nervous System Effects; Endocrine Function; and Sense Metrics. The multitudinous reasons for natural
environs generating the aforementioned positive qualities have been systematically incorporated into
the investigation of the physiological and psychological effects of SY as follows.
3.2. Heart-Rate Metrics

As changes in cardiac function, revealed by cardiac monitoring, are correlational to the
physiological effects of stress regardless of environmental setting, it is coherently expected more
than one third of the articles reviewed observe not only standard vital signs, including heart rate (HR)
and pulse rate (PR), systolic and diastolic blood pressure (SBP/DBP) and ECG interpretation, but
also heart rate variability (HRV), as well as left ventricular function and right ventricular function
(LVF/RVF). While LVF is attributed to the ability of the left ventricle to perfuse the body, RVF is related
to pumping blood to the lungs. HRV is defined as the variation in the time interval between heartbeats
and is associated with the activation of the parasympathetic nervous system (PNS) through high
frequencies (HF) and the sympathetic nervous system (SNS) through low frequencies (LF).
The trends revealed by SY research over the past 10 years in relation to the cardiovascular
and autonomic nervous systems (ANS) appears to have started with basic cardiac monitoring then
shifted to the correlation of cardiac monitored data points with the PNS and SNS, and this started the
development of a more in-depth study design to research the effects of SY on specific disease states,
such as: hypertension (HTN), coronary artery disease (CAD), and chronic obstructive pulmonary
disease (COPD).
According to Kobayashi, Song, Ikei, Song, Kagawa and Miyazaki [18], 625 Japanese males situated
in 57 forest-sites and 57 urban-sites across Japan revealed an 80% increase in the parasympathetic
indicators of HRV while experiencing the forest setting—physiologically demonstrating forest-viewing
was more effective in reducing indicators of stress than in the urban participants. The methods and
findings of this large sample study are grounded in some of the earlier pilot studies culled for this
review. In Park et al. [37] quantitative study, the sample size was limited to 12 males; however, it was
one of the earliest studies to interpret the R-R intervals of the electrocardiogram analyzing pulse rate,
in addition to SBP/DBP and LF/HF) components of HRV. This study design [37] has been echoed
throughout multiple studies which limit physical activity levels to 20-min for each activity researched in
order to control for the cardiovascular effects of physical exertion on each participant [19,22,27,38–41].
Blood pressure and PR also decreased while in the forest settings compared to the urban settings.
In comparison to physical exercise tasks, Lee, Lee, Park and Miyazaki [20] measured HR and BP
in relation to synthetic versus organic stimulation. This study revealed both HR and BP decreased
in participants after they had completed a garden transplanting task compared with participants’
HR and BP gradual increase throughout a computer performance task. Similar to the findings of
Tsunetsugu et al. [40] consisting of 12 males, a study of 17 females over the age of 40 by Ochiai et al. [25]
revealed an overall decrease in HR after one day of a “forest-therapy program”. These studies
demonstrate cardiovascular benefits for both genders. After controlling for both demographic and
socioeconomic factors, Kardan et al. [42] conducted a correlation analyses of data acquired through the
Canadian Ontario Health Study. High resolution satellite imagery suggests residents of neighborhoods
with a higher density of trees on the streets report less ill cardio-metabolic conditions than do residents
of neighborhoods with less trees. Thematically, it is evident the cardiovascular (CV) benefits of
SY are apparent regardless of age, gender, socioeconomic background, or previous exposure to a
nature setting.
3.3. Physiological Disease States

Significant research has revealed the effects of SY and NT on specific physiological disease states,
including HTN, CAD, COPD, and Diabetes Mellitus Type II (DMII). In a randomized control trial
(RCT) of 24 adults with HTN, Mao et al. [29] found throughout a week-long trip to a nature setting, BP
indicators, and CV disease-related pathological factors decreased the activation of the renin-angiotensin
system, therefore reducing the workload of the heart and helping to manage the symptoms of HTN. In a
RCT of 20 Lithuanian adult patients with CAD, Grazuleviciene et al. [43] found after a week of 30-min
sessions in nature, the participants’ cardiac function improved overall. This is a groundbreaking
study in there has never been a study prior to their publication that addressed “cardiovascular
relaxation and recovery of homeostasis in CAD patients.” Jia et al. [44] found a decrease of perforin
and granzyme B expressions accompanied by decreased levels of pro-inflammatory cytokines and
stress hormones in 20 patients diagnosed with COPD indicating some of the potential health benefits
of SY for individuals living with COPD. Furthermore, in a longitudinal study of 48 adults diagnosed
with DMII, Ohtsuka [45] found blood glucose readings declined after multiple SY practice sessions,
therefore indicating a significant correlation between SY and the reduction of blood glucose levels.
This study is one of the few measuring the effects of SY over time, which indicates further research
may be conducted to confirm the long-term effects of SY, not only for its effects on patients with DMII,
but for patients with different disease states as well [23,29,43–45].
3.4. Psychological
Morita et al. [46] noted while SY has been popularized in Japan given the ease of access to
forested environments and its’ conscientious governmental recommendations, individuals globally
have reduced acute psychological distress from time spent in greenspace (Figure 3).
Furthermore, Morita et al. [46] investigated SY’s effect on 498 Japanese residents suffering from
acute and chronic stress. Of these research participants, those suffering from chronic stress states
reported the greatest reduction in subjective feelings of hostility, depression and anxiety as a direct
result of time spent in the forested environs. Additionally, a RCT reflecting this practice, Sung et al. [47]
developed a Cognitive Behavioral Therapy (CBT) based on a FT program, which included educational
sessions and guided FB activities for middle-aged men and women diagnosed with Stage I HTN in
South Korea. The CBT FT program incorporated elements of meditation and relaxation techniques
in chosen forested environments, as well as participant self-reflection and goal setting [47]. The
results of which demonstrated a significant decrease in the salivary cortisol (tested as a biomarker of
stress), increase in Quality of Life (via the QoL questionnaire) and a decrease in anxiety. However,
this study also gleaned a transient effect in the reduction of individual’s manual self-reported BP
measures. Self-reported manual BP reports are subject to reliability issues of measurement and bias.
3.4. Psychological
Moreover,
Moritathe
etlack of additional
al. [46] noted whileobjective
SY hasanalysis in the short-term
been popularized forest-environment
in Japan given the easeexposure
of accessare
to
identified confounding variables, as well as the fact the participants took prescribed antihypertensive
forested environments and its’ conscientious governmental recommendations, individuals globally
medications
have reducedthroughout the trials in
acute psychological the intervention
distress from time and control
spent groups respectively
in greenspace (Figure 3). [47].
Figure
Figure 3.
3. Walking in nature.
Walking in nature. Permission
Permission to
to publish
publish from
from CiCi
CiCi Lee.
Lee.
Furthermore, Morita et al. [46] investigated SY’s effect on 498 Japanese residents suffering from
A hallmark of SY research has been the investigation of its’ relaxation inducing properties and
acute and chronic stress. Of these research participants, those suffering from chronic stress states
application for ameliorating psychological distress. Within this review, 12 studies specifically addressed
reported the greatest reduction in subjective feelings of hostility, depression and anxiety as a direct
psychological disorders/disease states and relevant comorbid conditions with popular reference to
result of time spent in the forested environs. Additionally, a RCT reflecting this practice, Sung et al.
stress and stress related heart disease, emotional distress and chronic depression, alcoholism, sleep
[47] developed a Cognitive Behavioral Therapy (CBT) based on a FT program, which included
disorders, and pain [5,6,26,30–33,47–51]. Takayama et al. [49] noted the impetus for their SY research
educational sessions and guided FB activities for middle-aged men and women diagnosed with Stage
stemmed from a growing concern for overworked urban dwellers’ chronic stressors. The results of
I HTN in South Korea. The CBT FT program incorporated elements of meditation and relaxation
this comparative study, while limited by sampling bias regarding the subject population consisting
techniques in chosen forested environments, as well as participant self-reflection and goal setting
entirely of males, indicated a unanimous preference for forest walks versus urban walks based upon
[47]. The results of which demonstrated a significant decrease in the salivary cortisol (tested as a
data synthesized from participants’ responses to the Profile of Mood States (POMS), Restorative
biomarker of stress), increase in Quality of Life (via the QoL questionnaire) and a decrease in anxiety.
Outcome Scale (ROS) and Subjective Vitality Scale (SVS) pre- and post-intervention. Stress from urban
However, this study also gleaned a transient effect in the reduction of individual’s manual self-
environments caused by surmounting noise and environmental pollution, commuter traffic, financial
reported BP measures. Self-reported manual BP reports are subject to reliability issues of
expenses, increasing tasks, and lack of proximity to FB environs/attributes motivated Park et al. [26]
measurement and bias. Moreover, the lack of additional objective analysis in the short-term forest-
to investigate the connection between psychological distress and greenspace accessibility. This study
environment exposure are identified confounding variables, as well as the fact the participants took
which included a large, single-sex sample of 168 males between the ages of to 20 to 24 years of age,
prescribed antihypertensive medications throughout the trials in the intervention and control groups
demonstrated subjects’ preferences for forested environments, specifically in relation to temperature,
respectively [47].
as demonstrated by participants’ reported lower Predicted Percentage Dissatisfied (PPD) scores related
A hallmark of SY research has been the investigation of its’ relaxation inducing properties and
to summer climes within forested environs compared with higher air temperature and heat indexes in
application for ameliorating psychological distress. Within this review, 12 studies specifically
urban environments [26].
addressed psychological disorders/disease states and relevant comorbid conditions with popular
Citing the impact of chronic stress on growing populations with insomnia and poor sleep patterns
reference to stress and stress related heart disease, emotional distress and chronic depression,
in Japan, Morita et al. [32] studied forest-walking to induce relaxation and improve general sleep-wake
alcoholism, sleep disorders, and pain [5,6,26,30–33,47–51]. Takayama et al. [49] noted the impetus for
cycles in a population of 71 men and women over the course of three months. Participants reported a
their SY research stemmed from a growing concern for overworked urban dwellers’ chronic stressors.
statistically significant correlation between increased sleep time (from an average of 365.9 ± 89.4 min
The results of this comparative study, while limited by sampling bias regarding the subject
to 419.8 ± 128.7 min) post 2-h afternoon forest walks with decreased anxiety.
population consisting entirely of males, indicated a unanimous preference for forest walks versus
McCaffrey, Hansen and McCaffrey [30] investigated garden walking to reduce severity of signs
urban walks based upon data synthesized from participants’ responses to the Profile of Mood States
and symptoms of depression in older adults. Participants’ personal stories citing the emotionally
(POMS), Restorative Outcome Scale (ROS) and Subjective Vitality Scale (SVS) pre- and post-intervention.
healing attributes of the natural surroundings and garden walking paths at the Morikami Japanese
Stress from urban environments caused by surmounting noise and environmental pollution,
Museum and Gardens in Delray Beach Florida, USA inspired the aforementioned researchers. Similarly,
commuter traffic, financial expenses, increasing tasks, and lack of proximity to FB environs/attributes
Kim, Lim, Chung and Woo [31] investigated the application of a 4-week forest-walking based CBT
program for treating clinical depression. Research findings from Kim et al. [31] demonstrated a
significant remission rate in the forest walking group at 61% over the traditional psychotherapy
hospital-based group at 21%. Kim et al. [31] explicitly cited the work of Australian bush adventure
therapy researchers Pryor, Carpenter and Townsend [52] in their pioneering work regarding the
connection between time spent in nature and an increase in participants’ health, well-being and
emotional confidence. Kim et al. [31] employed a robust research design in so much as researchers
incorporated the comparisons of a forest-walking based CBT program (N = 23), a hospital based
treatment group (N = 19) and an outpatient control (N = 21). Yet, as with the Pryor et al. [52] research,
inherent to the research aim of investigating the previous successes of nature-based therapy [31] is an
implicit bias toward the functionality and reliable successes of the research outcomes.
Given SY practices are relatively innocuous when compared with other more invasive procedures,
Chun, Chang and Lee [2] studied FT for patients (N = 59) diagnosed with depression and anxiety
(roughly 60–80% of the participants), as well as oxidative stress (roughly 30–50% the participants) that
is associated with stroke susceptibility and a positive stroke history. The results of this study, indicated
the Beck Depression Inventory (BDI), Hamilton Depression Rating Scale (HAM-D17) and Spielberger
State-Trait Anxiety Inventory (STAI) indicate scores were lowered in the post FT intervention group
when compared with the control group scores. These results led researchers to recommend FT as a
medically viable intervention for the psychological distress associated with chronic illness [2]. Since
its’ inception in the 1970s, the STAI has been a hallmark test used to differentiate between participants’
state and trait anxiety, however, its’ brevity and pre-supposed delineation between anxiety-oriented
temperaments inspires cause for concern over its’ reliability [53].
Han et al. [3] and Kang et al. [50] focused on chronic widespread pain (CWP) and localized pain in
relation to the emotional distresses of coping with the side-effects of intractable pain. In Han et al. [3]
psychological indices were measured pre- and post- FT intervention with the BDI and the Visual
Analog Scale (VAS) to measure intensity and frequency of CWP. The results revealed statistically
significant decreases in pain and associated psychological distress as per the psychometric scales.
Whereas, Kang et al. [50] utilized the VAS and the neck disability index (NDI) for chronic neck pain
and the McGill pain questionnaire (MPQ) for localized pain, among other measures for physiological
indices. Kang et al. [50] measured incidents of painful trigger points in the posterior neck region (TRPs)
in the FB with exercise group compared with the FB without exercise, which resulted in reduction by
nearly 12 of TRPs in the FB plus exercise group. Widely utilized as a metric for measuring pain, Kang
et al. [50] noted the test’s functional role in objectively evaluating participants’ subjective experiences
of pain. Researchers noted the popularity of the VAS [51], but further investigation was warranted
to determine its’ reliability and validity. The VAS does have a reported test-retest reliability among
patients experiencing chronic pain (r = 0.94; p < 0.001) in a previous investigation [51], yet, given the
subjective nature of pain and uncertain unanimous consensus on pain metrics in international medical
literature, this study demonstrated a lack of criterion validity for the VAS.
With regards to human spirituality, Nakau et al. [33] noted in their pilot study involving 22 breast
or lung cancer patients, consisting of 4 males (with an average age of 65.3 ± 2.6 years) and 18 females
(with an average age of 56.6 ± 11.3 years), that FT can be viewed as an enhancement of spiritual health
in cancer patients. Patients in this study [33] were all participating one month or more after undergoing
surgery, chemotherapy, or radiation treatment. While patients were not considered to be at risk of
life-threatening conditions at the time of study [33], the stress of undergoing treatment for chronic
disease was implicated. All patients (N = 22), participated in the integrated FT, horticultural therapy,
yoga exercise, meditation and group therapy treatment intervention at the Japan World Exposition
(1970) Park in Suita, Osaka prefecture, Japan [33]. The results of this study indicated statistically
significant correlations pre- and post-intervention between green environments and individuals’
experiences of self-realization, increased emotional health and integrative well-being, as measured by
the Japanese version of the Functional Assessment of Chronic Illness Therapy-Spiritual Well-Being
Scale (FACIT-Sp), QoL questionnaire, Cancer Fatigue Scale, POMS and STAI, in addition to physiologic
measures of NK activity [33].
3.5. Autonomic Nervous System Effects

Research on the cardiovascular effects of SY have precipitated a trend to discover how FB affects
the ANS. At the level of the central nervous system (CNS) alone, marked changes in cerebral activity
have been identified. Joung et al. [28] designed novel research to investigate identified specific
anatomical cortices within the brain that vary in stimulation to both forest and urban areas. Activity
in the prefrontal cortices of the forest-area group participants were significantly lower than that of
the city-area group participants in the “after walking” through their randomly assigned locations.
This decrease in activity suggests a strong correlation between nature settings and ANS activity [28].
Research has shown peak HF levels can be seen within 5–7 min of each nature experience, which
demonstrates not only will SY benefit the health of the ANS, but that positive HF components of HRV
are evident within minutes of forest immersion [9]. Regarding other physiologic indicators of stress,
Mao et al. [24] conducted a quantitative RCT that demonstrated after short periods of time in nature,
measures of malondialdehyde (MDA) concentrations, cytokine production, serum cortisol, testosterone,
and lymphocytes decreased. Universal findings revealed LF components were significantly lower in
the forest areas than in the city areas, while HF components of HRV tended to be higher in the forest
than in the city and therefore these research findings are important for further physiological research
and the effects of SY [17,18,20,23–25,27,52].
3.6. Endocrine Function

This section, a further investigation into the physiological and psychological effects of SY or
NT via the physiological metrics relevant to endocrine included 11 publications. These resources
specifically measured the effects of SY or NT on specific physiological and psychological indicators
of stress via measures of salivary cortisol (sCort), and/or emotional indicators of health and
well-being [1,17,24–27,34,36,40,47–49,52,53]. Kobayashi and Miyazaki [53] studied baseline cortisol
measures in 267 healthy male students from The University of Chiba, Japan, with the aim to compare
measures in future SY studies. In Largo-Wright et al. [48] researchers deduced a correlation between
increased contact with nature and decreased stress levels and generalized health complaints in office
workers at a Southeastern university in the U.S. via the Nature Contact Questionnaire (NCQ), The
Perceived Stress Questionnaire (PSQ), and a health behavior assessment derived from contact with the
outdoors, over other types of contact with nature, such as indoor plants [48]. Additionally, practices of
SY have demonstrated statistical significance in lowering blood-glucose. In a 2012 longitudinal trial,
researchers from Hokkaido University, Japan, demonstrated forest-walking reduced blood glucose
levels in 48 Type 2 diabetic patients [34]. A total of 48 participants, 16 males and 32 females, with a
mean age of 66.8 years and diagnosed with DMII, walked for distances of 3 to 6 km nine times per
week over a period of 6 years. There was no statistically significant difference between the subjects’
glucose levels, or HbA1c levels between the shorter and longer walks. However, averages of both
groups’ blood glucose levels pre and post-forest walks declined by 79 ± 10 mg/dL and 76 ± 7 mg/dL
respectively [34].
In the pilot study with a cross-over experimental design, investigators [52] addressed the impact
of participants (N = 15) exposure to four urban and natural environments on physiological and
psychological stress matrices. The study [52] utilized sCort and salivary amylase (sAA) as metrics,
which the authors note via the work of Engert et al. [54] have been significantly reliable physiological
biomarkers for stress. Additionally, Beil and Hanes [52] obtained data from questionnaires measuring
participants’ experience of stress via the Perceived Stress Scale (PSS), Perceived Restorativeness Scale
(PRS), Subjective Stress Scale (SSS) and susceptibility of affective connections to natural environments
via the Environmental Identity Scale (EID), pre- and post-intervention, which included a 20-min
exposure to 4 different environments ranging from the “mostly built” to the “mostly natural.” The
participants’ sAA and sCort levels respectively peaked after exposure to the urban environments, while
levels were within normal range post exposure to the natural environments, which also correlated
with participants’ subjective impressions of stress [52]. The EID, while relatively novel, was noted to
have been previously tested for its’ effectiveness in ascertaining subjects’ general health and welfare
status in response to the environment [52].
3.7. Sensory Metrics (SM)

Fisher [55] illuminated an emerging interest in FT practices for psychological and physiological
healing. By interviewing a proponent of FT, Fisher described the growing trend of individuals restoring
native tree habitats with the dual purpose of environmental stewardship and psychological welfare
of the persons involved in the process; paralleling the sentiments of many SY researchers [9] and
supporting the Biophilia hypothesis [8]. Furthermore, Stigsdotter [36] conducted a case-study that
followed up on survey driven data collected from a 2005 Danish Health Interview of 10,125 adult
males and females and, results revealed significant positive correlations between access to green-space
within 1 km, self-perceptions of stress and general health and well-being.
A subset of publications explicitly focused on sensorial stimuli, as a function of the effects of
SY, which included time spent in forested outdoor environments, interactions with elemental aspects
of natural environments and laboratory settings. Tsunetsugu et al. [13] synthesized evidence from
physiological and psychological indices into subcategories, which exemplified the biomechanics of
SY impact on the five senses. Eight key publications specific to SM were incorporated within this
review, including: the metrics of olfaction [14,16], tactile stimulation [19], and visual stimulation, or
neurological response [11,15,28,56,57].
Research included within the SM theme invariably measured nervous system activity and
emotional response of participants in relation to experiencing authentic aspects of forested
environments by comparative means. Igarashi et al. [56] studied participants’ HRV, as an indicator
of PNS activity in 48 high-school students viewing real vs. artificial pansies, the results of which
illustrated a stronger correlation between relaxation with the real pansies versus the silk flowers.
This was represented by a significant decrease in the ratio of LF/HF HRV, and subjective analysis
of students’ self-perception of relaxation indicating preference towards real flowers. Furthermore,
Igarashi et al. [11] analyzed right and left prefrontal cortical activity in terms of cerebral blood-flow, and
hemoglobin concentration changes via Near Infrared Time Resolved Spectroscopy (NIRS), which was
measured in units of micro-meters (µM), according to the wavelengths observed. This was performed
before and after participants were subjected to four visual conditions (real dracaena plants, images of
dracaena plants, cardboard boxes and images of cardboard boxes) for timed intervals of 0–3 min each.
Notably, µM concentrations were higher in participants viewing the actual dracaena plant stimulus
for 3 min versus the pictorial sample for the same amount of time in right and left prefrontal cortical
areas respectively [11]. Joung et al. [28] also utilized NIRS to determine µM levels pre-posttest
upon participants viewing actual forested versus urban areas. Counter to the aforementioned
Igarashi et al. [11] study, participants demonstrated increased subjective measurements of relaxation
correlated with decreased µM concentrations and prefrontal cortical activity, and increased feelings
of calmness from the forested site vs. urban site [28]. This may indicate not only are aspects of the
natural environment optically stimulating as illustrated by Igarashi et al. [11] but they may also require
less executive functioning as demonstrated by Joung et al. [28]. Mutual feelings of “calmness” were
derived from each study.
Igarashi et al. [15] looked at comparisons between participants viewing images of kiwifruit
orchards and specific urban areas in Japan. The POMS and HRV were used to evaluate participants’
responses, which demonstrated moderate increases in PNS activity and feelings of “relaxation and
calmness” when viewing the orchard versus an urban setting. Subjective measures of stress reduction
have been consistently apparent in the studies focused on visual stimulation regardless of physiological
indices. In Tsutsumi et al. [57], researchers aimed to investigate and compare participants’ relaxation
states before and after viewing visual footage of forested landscapes, and comparatively, seascapes.
Measures of HRV, results from POMS questionnaires, and Bispectral Index System analysis (measured
brain activity via electrode placement) allowed researchers to determine participants’ sleep-wake
states while comparing brain wave activity. Findings indicated significant decreases in HR, greater
relaxation in post-intervention analysis in both groups, with the forest-viewing group demonstrating
the greatest difference in relaxation-states across all measures [57]. These studies give statistically
significant credence to the notion visual stimulation by aspects of forested environments reduces stress
and increases a general sense of well-being in various study populations. Furthermore, these studies
serve as templates to be integrated into therapeutic practices as suggested by Tsutsumi, et al. [57].
Koga and Iwasaki [19] investigated the potential for foliage-based tactile stimuli to induce relaxing
effects that have been demonstrated via SY based field experiments. These researchers [19] utilized
NIRS to detect cerebral blood-flow and the Semantic Differential (SD) model to determine emotional
responses in participants’ experiences with touching leaves versus other non-natural substances,
such as plates of metal and fabrics. As noted by Park et al. [58], laboratory-based research on the
physiological and psychological effects of SY has been paramount. Furthermore, the Koga and
Iwasaki [19] study revealed statistically significant correlations between touching natural substances,
such as tree-bark, and incidents of decreased blood pressure. Moreover, these findings are associated
with an increase in participants’ subjective feelings of calmness. However, despite the clarity in
exposition, researchers didn’t identify the reliability and validity of the SD method utilized in the
study. As with several SY studies, specific to psychological indices, self-reported measures in the form
of questionnaires, such as the SD method, provided a bulk of the data. Therefore, leaving a question
about the consistency, validity and reliability of the reported psychological outcomes.
Previous research regarding the effects of SY explored elements of olfaction as a sense metric
relevant to the biological effects of experiencing forested environments. Tsunetsugu et al. [13] noted
in their review, phytoncides, or volatile organic chemical compounds released from plants and trees
have previously been associated with the effects of SY. Furthermore, Li et al. [63] described how the
scent derived from phytoncides of 13 different tree species (phytoncides are unique to each specie and
serve as a critical communication pathway between trees classified under the same genus) increased
human Natural Killer Cell activity and decreased adrenaline in the FT intervention group of the study
comparing urban and forested environments on human immune and stress function. Ikei et al. [16]
studied the impact of α-pinene, a phytoncide from Japanese cedar wood (which is notably ubiquitous
in forested areas of Japan) on ANS function via HRV indexes and the SD method. The results of which
indicated an increase in PNS activity and a decrease in heart rate [16].
Jo et al. [14] focused research efforts on “floral scent”, specifically Japanese plum blossoms,
utilizing NIRS, HRV, POMS, and the SD as the physiological and psychological indices. Researchers
created a unique apparatus for metering the floral and control scents, which involved a polypropylene
pressurized bag with a constant flow of controlled air to be inhaled by participants. This novel approach
controlled for many potential confounding factors given the ubiquity of various scents in laboratory
settings. Utilizing multichannel NIRS enabled researchers to investigate the effects of olfactory
stimulation on 47 localized neurological regions corresponding to areas noted for emotional, judgement,
motor control, memory, somatosensory, cognitive, visual, auditory, and speech functions [14]. The
literature expounding upon sense-metrics pertaining to the effects of SY illuminates a thorough pursuit
of specificity and ingenuity.
Following a systematic review of 25 articles from databases including, but not limited to PubMed,
EMBASE, CINAHL, and PsychINFO, Bowler [1] found each study suggested natural environments
may have direct and positive impacts on humans’ overall well-being. Bowler recognizes it is difficult to
truly separate the raw effects of experiencing nature from confounding factors, such as physical activity
performed, previous exposure to nature, as well as an optimal time frame for these effects. However,
Bowler and every author mentioned throughout this literature review stress the aim to encourage
research on the health benefits associated with the practice of SY. While research in primarily Japan
and China has shown a positive impact of SY on both the physiological and psychological structures
throughout the human body, it also calls for Western cultures to incorporate elements of the SY practice,
so as to demonstrate compatible results world-wide for both patients and their healthcare providers [1].
3.8. Conceptual Frameworks
3.8.1. Nature Therapy

During the review of the literature, existing conceptual frameworks emerged that may be applied
to SY practice and NT research. The first conceptual framework (CF) is Thomson’s “vis medicatrix
naturae,” otherwise known as, “the innate ability of the body to heal itself” as presented in Logan and
Selhub’s review of the effects nature has on the human brain [59]. Thomson posits the healing power
associated with nature is directly connected with an individual’s intentional contact with “animate
and inanimate” aspects of the outdoors, such as touching the bark of a tree. While recognizing today’s
citizens’ increased use of technology, exposure to air pollution and the associated increased stress
responses, Logan and Selhub [60] present questions based on Thomson’s framework. For example,
“What might be an appropriate “dose” (duration and frequency) of nature contact to reduce stress?”
“Are certain types of activities (e.g., gardening, walking in forest settings, contemplating in an urban
park) more effective than others?” [60] Future directions for research, global urban planning and
architecture, and policy making may be based on Thomson’s framework of “vis medicatrix naturae.”
Furthermore, the research conducted by Selhub and Logan directly points to the health benefits
associated with natural environments and may be parallel to the practice of SY and NT.
3.8.2. Psychological Underpinnings

The second CF is by Berger [61]. Berger presents a novel, autonomous and independent NT
framework that serves as a model to support art and drama therapy. Within this theoretical and
applied framework, which is considered “integrative” because it takes place in nature and serves as a
part of the human healing process is the self- “reflexive” process that includes personal experiences.
The NT model and theory are supported by past evidence derived from Gestalt psychology and the
narrative research approach mixed with traditional “ritual” foundations. This novel theory attempts to
put a spotlight on modern individuals’ detachment from nature, absence from community engagement
and spirituality through a psycho-eco-social lens. Berger purports individual’s personal estrangement
from nature, lack of involvement in community affairs and spirituality as being main factors influencing
the modern-day spread of loneliness, depression, anxiety, low self-esteem and detachment. SY practice
and NT research may be grounded in Berger’s CF that recognizes the healing natural forces, resilience
and recovery associated with nature.
The third CF is from a Threshold Concept and Transformational Learning perspective [62]. The
practice of SY assisted by trained nature and forest therapy guides leads individuals into a “liminal”
space. In this “liminal” space, also known as an “in-between” human state or “suspended state of
partial knowing,” the healing properties associated with SY are purportedly activated [62]. During
the “liminal” phase, a person integrates, discards and experiences an “ontological shift” and then
experiences “transformation” and a “changed discourse,” known as a “post-liminal phase.” The
individual may experience a “pre-liminal” space in nature and may vacillate between old and emergent
thoughts that may be disruptive. However, once in the “liminal” psychological space, the individual
experiences a sense of calm and mastery. The immersion into nature may lead to a transformative
way of knowing and understanding the self. These noteworthy concepts may serve as foundations for
future research studies.
3.9. Limitations
Limitations of this review include the biases among the authors of the studies and articles culled,
as well as the conceivable restrictions of SY as an evidence based practice within the traditional
principles of Western medicine. While search criteria for the articles remained consistent across all
database searches, publication bias must be acknowledged as most of the studies reviewed demonstrate
a positive correlation among SY practice and NT with favorable physiological and psychological
outcomes. In addition, original study sample sizes were often limited to less than 20 participants, with
the inclusion criteria of primarily of healthy, young, male university students, making results difficult
to generalize across entire populations. Other limitations within the studies include their inability to
distinguish physical and psychological effects purely based on the participants’ surroundings versus
the participants’ level of activity while present in either an urban or nature setting. Most studies offer
little distinction among senses used, and which, if any, have a greater influence on positive or negative
outcomes. While the current research has continued to trend toward the benefits of SY and NT on
specific disease states and diagnoses, it has primarily focused on the short-term effects of the practice
of SY and NT with little research to indicate the longevity of its benefits. This concept of permanence
relates not only to the amount of time spent in a nature setting for short-term optimal results within a
study timeframe, but the participants’ previous relationship with nature throughout their lifetime, and
how a priming bias may influence the amplitude and frequency of corporeal effects. SY as a therapeutic
practice to be exemplified by healthcare providers and recommended to their patients includes the
limitations of theoretically defining SY for clinical use, the social and economic determinants of health
which limit access to natural environments, and the correlation between the ever changing diversity of
nature itself and the unpredictable physiological and psychological responses it may induce within the
human body as noted by the Biophilia Hypothesis [8].
4. Discussion
4.1. Overview of Health Benefits of SY and NT

In general, from a physiological perspective, significant empirical research findings point to
a reduction in human heart rate and blood pressure and an increase in relaxation for participants
exposed to natural GS [13,40]. Even research involving the use of nature videos of the forest or the
ocean have the same physiological effects [60]. From a qualitative and psychological perspective,
Danish participants reported a sense of safety, calm and overall general wellbeing following exposure
or engagement with nature [63]. South Korean participants with a known alcohol addiction and high
pre-test scores of depression benefited more from the Forest Therapy Camp than participants with
lower pre-test scores of depression and alcohol abuse [35]. Differences in culture, gender, education,
marital or economic status were not associated confounding factors in many of the empirical studies.
Overall, our review of the literature, as illustrated in Table 1, points to positive health benefits associated
with SY and NT while confounding factors were clearly identified by the researchers.
4.2. Implications for Future Research

The aims of this state-of-the-art review are to showcase and elucidate the existing research
on the effects of the practice of SY and NT on human physiological and psychological systems,
existing frameworks and sense metrics in order to assist researchers in conducting future empirical
research to substantiate, gain a better insight and enrich the scholarly literature. Longitudinal
research is recommended to investigate the powers of nature as a healer and preventative element
in today’s modern/technological driven world over a long period of time. Proposed thoughtful and
well-designed research would include both quantitative and qualitative approaches to identify specific
SY and NT factors that influence disease and health promotion in Western Cultures. Furthermore, a
systematic review of the current literature would honor the scholarly work completed to date and
provide a higher level of evidence for the practitioner considering SY and NT as EBP interventions.
4.3. Implications for Future Healthcare Practice

This in-depth review illustrates, honors and supports the increased awareness of the positive
health-related effects (e.g., stress reduction and increased holistic well-being) associated with humans
spending time in nature, viewing nature scenes via video, being exposed to foliage and flowers indoors
and the development of urban green spaces in large metropolitan areas worldwide. Not only valid and
reliable psychometrics have been implemented, but valid and reliable physiological measurements
have been used to show significant and potentially healing and health promoting effects. Furthermore,
physiological and psychological research, based on sound NT frameworks and hypotheses is needed
in the areas of healthcare professional/student stress-reduction and life balance [64,65].
Healthcare professionals and educators may turn to the SY and NT literature for simple, affordable
and enjoyable complementary interventions to reduce stress, anxiety, and depression symptoms and
enhance joy, relaxation, overall sense of well-being and balance in life. The founder and faculty member
of the Association of Nature and Forest Therapy Guides and Programs, Amos Clifford, states the
organization’s mission is to integrate FT into healthcare systems [62]. Moreover, the profession of
nursing and medicine has moved toward an integrative approach to healthcare. The third integrative
nursing principle: “Nature has healing and restorative properties that contribute to health and
well-being” supports the health benefits associated with the practice of SY and NT and serves as
a part of the integrated healthcare model [66]. Furthermore, SY as a healing and restorative modality
may support the clinician’s and patient’s whole-being while promoting a sense of peace, dignity
and comfort. These ideas are supported by Watson’s Carative Processes [67], specifically Process
Eight: Creating healing environment at all levels, whereby wholeness, beauty, comfort, dignity, and peace are
potentiated.
5. Conclusions
Advancements in complementary and alternative medicine (CAM) are indicative of a time in
history when researchers and practitioners are willing to look at how humans evolved over the past
6- to 7-million years. When one ponders humans existing less than 0.01% of the species’ history in
modern surroundings and the other 99.99% of the time living in nature, it is no wonder some humans
yearn and are drawn back to where human physiological/psychological functions began and were
naturally supported. The Biophilia Hypothesis [8] supports SY and NT because it is steeped in the idea
humans have an inner biological attraction to nature and its importance in our human development.
Moreover, psychologically and spiritually speaking, humans intuitively know the relaxing, soothing
and “awe” effects of being in or viewing forests, plants, flowers, urban green spaces, parks and natural
wooden materials [68,69]. The mind-body-spirit experience associated with SY is for all humans and
may be accomplished in various documented ways as illustrated in the novel review. These methods
are supported by current scientific data, history and personal experiences reported over time. The
practice of SY and NT are ontological realism and offer humans an authentic way of healing and
health prevention for the mind, body and spirit [70–72]. How might we continue to encourage this
health-promotion method and demonstrate scientifically and intuitively in order to add to EBP and
global healthcare systems?
Acknowledgments: In great appreciation for the USF School of Nursing and Health Professions’ Faculty
Development Fund Committee for granting funds to publish in an Open Access journal. Claire Sharifi, Associate
Librarian: Liaison to the USF School of Nursing and Health Professions for her tireless support. CiCi Lee,
Independent Artist, thank you for contributing the nature photograph (Figure 3).
Author Contributions: Margaret M. Hansen led the research as Primary Investigator and contributed to the
writing/editing of the review. Reo Jones culled the research papers, organized and prepared the tables, literature
search figure, contributed to the writing/editing of the review and supervised Kirsten Tocchini. Kirsten Tocchini
organized the research papers and contributed to the writing/editing of the review.
Conflicts of Interest: The authors declare no conflict of interest.
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Keywords: Shinrin-Yoku; forest bathing; nature therapy; integrative medicine

2. Materials and Methods

3.1. Physiological and Psychological (PP) Effects

Table 1. Characteristics of selected studies and supporting evidence.

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

Study Country Population Sample Setting Aim & Design Findings

3.1. Physiological and Psychological (PP) Effects

3.2. Heart-Rate Metrics

3.3. Physiological Disease States

3.5. Autonomic Nervous System Effects

3.6. Endocrine Function

3.7. Sensory Metrics (SM)

3.8. Conceptual Frameworks

3.8.1. Nature Therapy

3.8.2. Psychological Underpinnings

4.1. Overview of Health Benefits of SY and NT

4.2. Implications for Future Research

4.3. Implications for Future Healthcare Practice

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