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Short-Term Effects of Forest Therapy on Mood States: A Pilot Study

International Journal of

Environmental Research

and Public Health

Article

Short-Term Effects of Forest Therapy on Mood States:

A Pilot Study

Francesco Meneguzzo 1,2,* , Lorenzo Albanese 1, Michele Antonelli 3 , Rita Baraldi 4,

Francesco Riccardo Becheri 5, Francesco Centritto 6, Davide Donelli 3, Franco Finelli 2, Fabio Firenzuoli 7 ,

Giovanni Margheritini 2, Valentina Maggini 7 , Sara Nardini 8 , Marta Regina 9, Federica Zabini 1,*

and Luisa Neri 4

Citation: Meneguzzo, F.; Albanese, L.;

Antonelli, M.; Baraldi, R.; Becheri, F.R.;

Centritto, F.; Donelli, D.; Finelli, F.;

Firenzuoli, F.; Margheritini, G.; et al.

Short-Term Effects of Forest Therapy

on Mood States: A Pilot Study. Int. J.

Environ. Res. Public Health 2021, 18,

9509. https://doi.org/10.3390/

ijerph18189509

Academic Editor: Pier Mannuccio

Mannucci

Received: 24 August 2021

Accepted: 7 September 2021

Published: 9 September 2021

Corrected: 4 March 2022

Publisher’s Note: MDPI stays neutral

with regard to jurisdictional claims in

published maps and institutional afﬁl-

iations.

1 Institute of Bioeconomy, National Research Council, 10 Via Madonna del Piano, I-50019 Sesto Fiorentino, Italy;

lorenzo.albanese@cnr.it

2 Italian Alpine Club, 19 Via E. Petrella, I-20124 Milano, Italy; franco.ﬁnelli55@libero.it (F.F.);

giomarghe@yahoo.com (G.M.)

3 Local Public Health Authority, AUSL- IRCCS, I-42122 Reggio Emilia, Italy; michele.antonelli@ausl.re.it (M.A.);

davide.donelli@ausl.re.it (D.D.)

4 Institute of Bioeconomy, National Research Council, 101 Via Gobetti, I-40129 Bologna, Italy;

rita.baraldi@cnr.it (R.B.); luisa.neri@ibe.cnr.it (L.N.)

5 Pian dei Termini Forest Therapy Station, 2311 Via Pratorsi, I-51028 San Marcello Piteglio, Italy;

ricerca@terapiaforestale.it

6 “Cesare Alﬁeri” Political Science School, University of Florence, 60 Via Vittorio Locchi, I-50141 Firenze, Italy;

francescocentritto08@gmail.com

7 CERFIT, Careggi University Hospital, I-50134 Florence, Italy; fabio.ﬁrenzuoli@uniﬁ.it (F.F.);

valentina.maggini@uniﬁ.it (V.M.)

8 A.M.I.S.I. Italian Medical Association for the Study of Hypnosis, 28 Via Paisiello, I-20131 Milano, Italy;

nardini_s@libero.it

9 Mindfulness Association UK, Edinburgh EH9 1AR, UK; marta@martaregina.com

* Correspondence: francesco.meneguzzo@cnr.it (F.M.); federica.zabini@cnr.it (F.Z.);

Tel.: +39-392-985-0002 (F.M.); +39-333-379-2947 (F.Z.)

Abstract: Immersion in forest environments was shown to produce beneﬁcial effects to human

health, in particular psychophysical relaxation, leading to its growing recognition as a form of

integrative medicine. However, limited evidence exists about the statistical signiﬁcance of the effects

and their association with external and environmental variables and personal characteristics. This

experimental study aimed to substantiate the very concept of forest therapy by means of the analysis

of the signiﬁcance of its effects on the mood states of anxiety, depression, anger and confusion.

Seven forest therapy sessions were performed in remote areas and a control one in an urban park,

with participants allowed to attend only one session, resulting in 162 psychological self-assessment

questionnaires administered before and after each session. Meteorological comfort, the concentration

of volatile organic compounds in the forest atmosphere and environmental coherence were identiﬁed

as likely important external and environmental variables. Under certain conditions, forest therapy

sessions performed in remote sites were shown to outperform the control session, at least for anxiety,

anger and confusion. A quantitative analysis of the association of the outcomes with personal

sociodemographic characteristics revealed that only sporting habits and age were signiﬁcantly

associated with the outcomes for certain psychological domains.

Licensee MDPI, Basel, Switzerland.

This article is an open access article

distributed under the terms and

conditions of the Creative Commons

Attribution (CC BY) license (https://

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4.0/).

Keywords: anger; anxiety; confusion; depression; forest therapy; mental health; volatile organic

compounds

1. Introduction

The direct exposure to forest environments was attributed a wide range of straight

benefits to human health. Such benefits cover primarily the psychological sphere (mental

processes, stress, anxiety and emotions), cognitive processes, social life (skills, interactions,

Int. J. Environ. Res. Public Health 2021, 18, 9509. https://doi.org/10.3390/ijerph18189509

https://www.mdpi.com/journal/ijerph

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behavior and lifestyle) and spiritual wellbeing [1–4]. On the physiological side, significant

effects emerged with regards to the improvement of the cardiovascular functions and the

hemodynamic, neuroendocrine, metabolic, immune, inflammatory and oxidative indices [5,6].

As pointed out by a recent comprehensive review, the impact on the psychophysical

well-being of humans by immersion in forest environments was by far the most studied and

revealed statistically signiﬁcant and sometimes intense results [7]. However, in the same

review, the results of experiences with patients affected by various diseases and addictions

were reported, such as improving sleep quality in patients with gastrointestinal cancers [8].

In addition, in-patients with affective and psychotic disorders received signiﬁcant beneﬁts

to their mental health from forest therapy programs, with the type and extent of the

improvements related to the characteristics of the given disorder [9].

Individual benefits can turn into benefits for the society as a whole due to cost savings

for healthcare systems, insurance and safety, as well as gains in productivity. A recent study

showed that the economic value of natural protected areas, assessed on the basis of the

mental health of visitors, amounts to about 8% of the global gross domestic product, i.e.,

around USD 6 trillion [10]. Such an amount, being 100 to 1000 times greater than the budget

of the agencies managing the natural protected areas, could justify any scientifically based

effort aimed at increasing the efficiency and expanding the functions and ecosystem services

of the natural and protected areas towards human mental and physiological health [10].

The preventive and healing effects directly delivered by forest environments have

been widely documented in the scientiﬁc literature, and, in most cases, concern experiences

of free walking or meditation in the absence of appreciable physical exercise [11]. The

beneﬁcial effects towards the psychological and physiological aspects of human health

are often signiﬁcant, dose-dependent (e.g., duration and frequency of the experiences and

concentration of airborne bioactive substances), related to the structure and tree species

composition of the forest and to the season and time of the day [11]. Personal characteristics

such as gender, age, psychological traits and physical health contribute to modulating the

extent of beneﬁcial effects of the forest immersion. In particular, a recent study performed

in Hungary showed that walking in the forest for 2 h, with minimal guidance and aimed at

maintaining a slow pace, resting, observation, breathing and touching the wood produced

a signiﬁcant decrease of systolic blood pressure both in late spring and winter [12]. As well,

a signiﬁcant stimulation of NKbright cells and activation of various immune cell subsets was

observed in late spring, while a slight activating and a balancing effect regarding TIM-3,

an inhibitory immune checkpoint molecule, were observed in winter, thus suggesting

positive forest healing effects throughout the year [12].

The forest healing effects can be wide-spectrum, such as in the case of the immune

system [13], long-lasting and devoid of undesirable side effects. Just 15–20 min of forest

immersion are enough to convey, at least, signiﬁcant psychological beneﬁts, two hours

(even not continuously) allow enhanced wellbeing for a week, irrespective of individual

characteristics such as age and presence of chronic diseases [14]. Three or more days of

forest immersion can reinforce the immune defense system for a month [15].

An additive effect (constantly growing beneﬁts) deriving from the regular repetition

of sessions was observed, which was larger in the case of subjects with depressive tenden-

cies [16]. A recent study, consisting of free forest immersion sessions (four weekly sessions

each lasting four hours), suggests the persistence of psychological beneﬁts (indicators of

stress, wellbeing and positive emotions) up to a month after the end of the sessions, con-

trary to virtual immersion experiences [17]. Indeed, virtual experiences showed signiﬁcant

psychological effects but only in the short term [18].

Forest experiences, where professionals assist participants according to structured pro-

tocols, often based on psychotherapy, meditation and mindfulness practices [19], showed

signiﬁcant and remarkable therapeutic superiority over both similar activities carried out

in non-forested environments and free immersion in forest, for example, in the treatment

of depressive symptoms [11,20]. The actual forest therapy foresees not only the individual

free immersion in a forest environment, often called forest bathing, but also the guidance by

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suitable professionals, such as psychologists and psychotherapists, according to protocols

aimed at boosting the health outcomes [11,20]. Indeed, the very possibility of issuing

green prescriptions in the frame of medical phytotherapy protocols was conditioned on the

availability of forest therapy providers [21].

The benefits of forest immersion are mediated by all human senses. Viewing repetitive

natural structures (fractals), such as trees, and hearing the typical sounds of forests convey the

perception of a relaxing and unchallenging environment, in which it is much easier to adapt

and increase one’s own perceptive fluidity [22,23], even in virtual experiences [18]. Touching

the wood of the trees induces significant physiological and psychological relaxation [24].

Smell plays a key role through the inhalation of biogenic volatile organic compounds

(BVOC) emitted by plants and soil in the forest atmosphere, in particular, certain terpenes

endowed with antioxidant and anti-inflammatory activities, as well as beneficial to psycholog-

ical and cognitive processes [25]. First of all, the concentration and type of such substances in

the forest atmosphere depends on the emission rate by plants and thus on the tree species [26]

and their vegetative status (thus, the season) [27]. At any forest site and in any season (es-

pecially during the warm season), the time of the day plays a very important role due to

changing atmospheric conditions (temperature, solar irradiance and surface stability), leading

to distinct and regular peaks and troughs in the total BVOC concentration levels [28,29].

The beneﬁts and potential of forest therapy were ofﬁcially recognized by the United

Nations in the framework of the green recovery from the COVID-19 pandemic [30]. The

main challenges were identiﬁed in informing, educating and persuading healthcare systems

and professionals and citizens with regard to green prescriptions, for example, based on

those that have been issued for years in Japan and South Korea [5,31,32]. In those countries,

as well as in Taiwan and China, green prescriptions have been framed into preventive

medicine, as a means to improve physiological health and ease stress levels [33]. Another

urgent challenge was identiﬁed in the certiﬁcation of professional providers of services

related to forest therapy meant to effectively enable green prescriptions and allow interested

people to access a widespread and high quality offer [21,34].

Despite the growing scientiﬁc evidence, many countries, especially in the Western

world, lag behind in the rigorous identiﬁcation of sites and trails for forest therapy practices,

including preliminary selection and qualiﬁcation based on actual functionality (observed

psychological and physiological beneﬁts) according to structured programs of activities.

First, the following consolidated evidence was seldom incorporated: while exposure to

most greenspaces allows for improvements in mood and wellbeing, speciﬁc and signiﬁcant

preventive effects with regard to the risk of depression were attributed only to natural

environments, in particular forested ones, remote from urban areas [35,36]. This is par-

ticularly important because depression is a pandemic illness, especially in the developed

world [35], with immense human, social and economic costs [36]. Thus, natural remedies

such as forest therapy performed in suitable locations can lead to substantial savings for

healthcare and welfare systems and gains in terms of productivity [34].

Second, especially in the Western world, forest therapy experiences in remote forest

areas involving large numbers of participants, according to structured and repeatable

programs and including control sessions in urban settings, were seldom performed, let alone

the search for the main determinants of health outcomes that would allow the generalization

of qualification criteria. Despite recent improvements in the methodological rigor, the

recommendations issued in a comprehensive review published in 2017 are still relevant [37].

The main motivation of this study was to quantitatively assess the effectiveness of

a few forest therapy sessions performed in remote areas on the improvement of certain

mood states, i.e., anxiety, depression, anger and confusion, compared with a control session,

thus substantiating the very concept of forest therapy. Another aim was to contribute to the

preliminary identiﬁcation of the main determinants of the outcomes of forest therapy ses-

sions, taking advantage of the different environments involved, the relatively large number

of participants and the representativeness in terms of sociodemographic characteristics.

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The main hypotheses of this study were: (1) forest therapy carried out in remote forest

areas is more effective than in urban parks; (2) forest therapy (professionally guided) is more

effective than forest bathing (free); (3) different environmental conditions, either structural

or variable, and personal characteristics, affect the outcome of forest therapy sessions.

2. Materials and Methods

2.1. Forest Therapy Sessions: Basic Features and Measures

The Italian Alpine Club and the Institute of Bioeconomy of the National Research

Council arranged seven forest therapy sessions from August to October 2020. All sessions,

named FTS1 to FTS7, were performed in Italy at remote forest areas (at least 20 km from

the nearest town with more than 10,000 inhabitants or trafﬁcked road). All sessions had

a duration of 3.5 ± 0.5 h, along paths with total lengths not exceeding 4 km and uphill

gradients smaller than 150 m.

A further control session, named FTSC, was performed in June 2021, in an urban park

with an area of about 4 hectares, located downtown in the city of Florence, Italy (about

400,000 inhabitants) and surrounded by buildings and trafﬁcked roads.

Figure 1 shows the location of the forest therapy sites in central and northern Italy.

Figure 1. Locations of forest therapy sessions (FTS1 to FTS7 and FTSC) in central and northern Italy.

During each session, the concentration of total volatile organic compounds (TVOCs)

was continuously collected by means of a portable (0.72 kg) photoionization detector (PID,

model Tiger VOC detector, Ion Science Ltd., Fowlmere, Royston, UK), with detection limits

from 1 µg/m3 to 20,000 µg/m3. The PID was equipped with a pump, sucking in ambient air

at a rate of 220 mL/min, and an ultraviolet, 10.6 eV lamp, allowing the ionization of organic

substances present in the sampled air, including all the monoterpenes (MTs) found in

biogenic VOCs (BVOCs). The resulting electric current ﬂowing between two electrodes was

measured, ampliﬁed and transformed into a concentration level of the ionized substance

or group of substances. TVOC concentration could be considered representative for BVOC

concentration, although clearly higher due to the presence of VOCs other than MTs, at

least at forest sites far from anthropogenic pollution sources where the change in TVOC

concentration is mainly driven by plants’ emissions, as explained in a previous study [28].

Finally, the average temperature during each session was assessed based on data collected

at nearby weather stations.

The ﬁrst session (FTS1), which can be classiﬁable as forest bathing, was performed

without professional guidance, suggesting to participants to relax in the woods during

two stops lasting between 20 and 30 min each, and providing scientiﬁc information about

the surrounding environment (botany and geology) and the sessions meaning for one’s

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own health. All the other sessions were performed with professional guidance, according

to the method of conducting illustrated in Section 2.2. However, the control session FTSC,

which was performed in an urban park downtown the city of Florence, Italy, although

including professional guidance, was carried out according to a method of conducting that

was different and substantially simpliﬁed in comparison with the method illustrated in

Section 2.2, in particular based on the immersion in nature with mindful use of the senses

of sight, hearing, touch and smell.

Volunteer participants were enrolled and insured by local sections of the Italian Alpine

Club following information spread by means of standard channels (newsletters, social

media, etc.). No selection was applied except for age (>18 years) and the requirement of

being healthy. Participants were allowed to attend only one session, to prevent any contri-

bution from the possible persistence of the effects. Overall, 207 participants were recruited,

returning 162 valid self-assessment questionnaires, the nature of which is described below

in Section 2.1. Table 1 shows the basic information about forest therapy sessions.

Table 1. Basic features of forest therapy sessions performed in Italy.

Session

Place, Municipality/Date/

Initial Time 1

Lat/

Lon/

Altitude

Weather, Temperature/

Tree Species/

Water Bodies—Streams

TVOC

Average (Peak)

Unit: µg/m3

Participants/

Valid Question-

naires 2/Gender 3

FTS1

Torre dei Sogni, Empoli and

Montespertoli (FI)

22 August 2020

14:30

43◦41 11.77 N

11◦0 0.69 E

100–200 m

Sunny, weak wind, 30 ◦C

Cypress, maritime pine,

holm oak, lentisk

68 (120)

M: 11; F: 13

FTS2

Monte Duro, Vezzano sul

Crostolo (RE)

6 September 2020

08:30

44◦32 34.49 N

10◦32 26.49 E

500–600 m

Sunny, calm, 23 ◦C

Scots pine, ﬁeld maple,

black and white hornbeam,

elderberry, dogwood

27 (50)

M: 8; F: 13

FTS3

Parco del Respiro, Fai della

Paganella (TN)

11 September 2020

13:30

46◦10 33.25 N

11◦4 39.98 E

900–1000 m

Sunny, calm, 22 ◦C

Spruce, beech

Water streams, waterfalls

38 (108)

M: 8; F: 25

FTS4

Parco del Respiro, Fai della

Paganella (TN)

12 September 2020

08:30

46◦10 33.25 N

11◦4 39.98 E

900–1000 m

Sunny, calm, 17 ◦C

Spruce, beech

Water streams, waterfalls

28 (65)

M: 5; F: 12

FTS5

Battisti Refuge, Ligonchio

(RE)

27 September 2020

08:00

44◦15 42.24 N

10◦24 45.58 E

1750 m

Cloudy, windy, 4 ◦C

Beech, silver ﬁr, mountain

pine

10 (20)

M: 5; F: 3

FTS6

Torre dei Sogni, Empoli and

Montespertoli (FI)

17 October 2020

14:00

43◦41 11.77 N

11◦0 0.69 E

100–200 m

Partly cloudy, weak wind,

15 ◦C

Cypress, maritime pine,

holm oak, lentisk

50 (90)

M: 11; F: 13

FTS7

Fonte del Borbotto, San

Godenzo (FI)

18 October 2020

09:00

43◦52 57.78 N

11◦41 10.65 E

1250–1350 m

Sunny to cloudy, calm, 7 ◦C

Beech, scattered silver ﬁr

Water streams, pond

15 (30)

M: 12; F: 17

FTSC

Villa Vogel urban park,

Firenze (FI)

23 June 2021

09:00

43◦46 33.54 N

11◦12 23.89 E

39 m

Sunny, calm, 28 ◦C

Holm oak, stone pine and

other species

Water pond

15 (56) 4

M: 8; F: 4

1 Local solar time. 2 Number of self-assessment questionnaires further considered for analysis. 3 Data referred to valid questionnaires

(M: male; F: female). 4 Urban park surrounded by buildings and trafﬁcked roads. TVOC levels could not be considered representative of

plant emissions.

′″

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Figure 2a–f shows representative pictures of forest therapy sites.

6 of 21

(a)

(b)

(c)

(d)

(e)

(f)

Figure 2. Representative pictures of forest therapy sites: (a) FTS1 and FTS6; (b) FTS2; (c) FTS3 and FTS4; (d) FTS5; (e) FTS7;

(f) FTSC.

Limited to participants that returned valid questionnaires and relevant demographic

data, there were more female (84) than male (50) participants, the age group 41–60 was the

most represented for both genders (almost half of total) and the place of residence of more

than 59% of participants was outside towns with more than 40,000 inhabitants. Figure 3a,b

shows the basic demographic features of participants to forest therapy sessions.

Ryan–Joiner test for normality was performed for height and weight variables for the

entire study population, resulting in a non-normal distribution (height: p = 0.044; weight:

p < 0.01). Moreover, chi-square test matrix for homogeneity among categorical variables

was performed for the entire study population for sex, study degree, job, smoking and

residence variables, resulting in homogeneity only for sex variable (p = 0.182). Table 2

shows the data about age, height and weight for each forest therapy session.

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(a)

(b)

Figure 3. Basic demographic features of participants to forest therapy sessions: (a) Distribution by age group and gender;

(b) Distribution by residence and gender.

Table 2. Data about age, height and weight of participants to each forest therapy session.

Variable

Age

Height

Weight

Session

FTS1

FTS2

FTS3

FTS4

FTS5

FTS6

FTS7

FTSC

FTS1

FTS2

FTS3

FTS4

FTS5

FTS6

FTS7

FTSC

FTS1

FTS2

FTS3

FTS4

FTS5

FTS6

FTS7

FTSC

Number of Available Data

Mean ± Standard Deviation

52.42 ± 10.32

52.86 ± 9.89

45.58 ± 16.84

44.94 ± 15.15

64.38 ± 7.89

50.76 ± 14.37

51.83 ± 11.69

57.67 ± 15.74

170.74 ± 9.25

170.67 ± 9.03

165.36 ± 8.22

164.13 ± 7.45

166.25 ± 8.46

170.29 ± 11.54

170.28 ± 11.32

170.92 ± 8.84

69.04 ± 10.59

70.52 ±13.24

58.97 ± 15.36

57.56 ± 6.46

71.13 ± 11.43

70.06 ± 13.98

69.62 ± 19.47

72.08 ± 16.75

Participants reached the forest therapy site by car, and the informed consent was

collected on site and in written form from every participant before each session. Overall,

at least half an hour, and up to one hour, elapsed before participants started the forest

therapy session, during which every participant was presented also with a reduced Proﬁle

of Mood States (POMS) questionnaire and listened to a short speech. Such time could

have helped relieving transport-related stress. The POMS questionnaire was completely

anonymous and included information about gender, age, place of residence, job and habits

such as smoking and sports. The POMS questionnaire consisted of 34 questions about

moods perceived at that precise moment, recommended for the analysis of psychological

outcomes of forest therapy sessions [38] and derived from previous studies on sport

psychology [39]. The same questionnaire was recently used in an investigation of stress

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reduction of healthcare staff after a short break in nature [40]. However, since no validation

study could be found regarding the speciﬁc subset of POMS items, it was decided to limit

the analysis to the psychological domains for which all the items were also included in the

originally validated questionnaire [39]. Thus, the considered domains were the mood states

of anxiety (also called tension in the original version), depression, anger and confusion

according to the recommended classiﬁcation [39]. The POMS questionnaire was ﬁlled

immediately before and after the session. For each questionnaire, single answers to any of

the items were grouped to provide the above-mentioned synthetic indices. Only completely

ﬁlled questionnaires were considered for further analyses.

2.2. The Method of Conducting the Forest Therapy Sessions

Except for session FTS1, and for session FTSC that was carried out according to

a different and simpliﬁed method of conducting referred to in Section 2.1, a professional

psychologist or psychotherapist took part in each of the other forest therapy sessions,

according to a program named Forestfulness®, partly based on mindfulness practices, in

particular on the Mindfulness-Based Stress Reduction (MBSR) program developed since

1982 [19]. Mindfulness-based meditation is a way to pay attention to the present moment

by observing and accepting whatever experience is occurring.

Mindfulness was shown to reduce pain in a wide range of clinical and non-clinical

problems [41], improve immune functions [42], improve mental health in breast cancer

patients [43], create a higher subjective wellbeing and attenuate emotive reactivity [44],

reduce relapses in depression and blood pressure [45], reduce anxiety and improve mood

state [46]. Mindfulness practiced in forest environments showed signiﬁcant and remarkable

therapeutic superiority over similar activities carried out in non-forested environments, for

example, in the treatment of depressive symptoms [20].

In the forest environment, mindfulness can be practiced by means of walking mind-

fully, using breathing as the center of attention, observing the surrounding environment

with acceptance and creating a deep connection with nature using the ﬁve senses. Walking

meditation is one of MBSR’s main practices, while walking in forests can lower blood

pressure and reduce the concentration level of cortisol (also named the stress hormone),

resulting in relaxation [47,48]. Walking meditation is performed by bringing the attention

to the physical sensations coming from breathing and walking. Although this exercise

could produce good results also indoor or in urban environments, higher beneﬁts were

observed in the woods, including improvement in mood state [49].

Conscious and focused use of all human senses—sight, hearing, smell, touch and

taste—is another milestone of the MBSR program as a means to increase the awareness of

the experience and amplify the effects of forest immersion. Through the perception of the

surroundings, senses provide orientation, rooting into the present an interpretation of our

experiences [50,51]. Indeed, beneﬁts for health from the exposure to forest environments

are effectively conveyed by the mediation of all human senses [33,52,53], which further

motivates the conscious focusing on human senses during forest therapy sessions.

Moreover, in the conduction of the forest therapy sessions, a method of communication

was adopted, which alternated metaphorical speeches with literal verbalizations in order to

stimulate increased emotional involvement in the participants [54]. In the past, the use of

metaphor was considered more an art than a scientiﬁc instrument [55], although one with

therapeutic value [56]. However, more recently, this classiﬁcation has been questioned,

with interesting practical implications. For example, it was established that the educational

metaphors are useful for simplifying difﬁcult concepts during class lessons [57]; in the

clinical ﬁeld, metaphors help in understanding delicate health conditions [58] and can

be useful for developing scientiﬁc theories [59]. In everyday life, metaphorical language

is a tool that is able to promote and guide thought processes and to activate cognitive

maps for problem solving [60]. From a therapeutic point of view, metaphorical discourses

represent a cornerstone of Ericksonian and Neo-Ericksonian Hypnotic Psychotherapy;

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for example, a recent study demonstrated the effectiveness of Mindful Hypnotherapy to

reduce stress and create mindfulness [61].

In the context of forest therapy sessions, the attention of the participants to the present

moment was stimulated in order to promote a more effective immersion, in addition

through the conscious use of the ﬁve senses, the breath and the movement, looking for

the deep connection with the surrounding environment. Both mindfulness practices and

metaphorical discourses contributed to this purpose, as they could anticipate or deepen

the proposed experience at an imaginative and evocative level and prepare neural maps

for what will be physically practiced. Some neuroimaging studies showed that metaphors

activated cortical areas corresponding to the suggested action; for example, the expression

“she grabbed the idea” could activate the motor cortex [62].

During the structured forest therapy sessions (FTS2 to FTS7 listed in Table 1), in order to

stimulate the sensory activities, the participants were invited to “savor the experience”, to

“touch with the eyes the surrounding environment” and to “listen to their emotions”, to name

a few. The words chosen in these verbalizations aimed at several purposes:

• Generating a sensation of coherence between the internal dimension (feeling) and

the external dimension (acting calmly). The sense of coherence (internal–external),

in accordance with temperament and emotional intelligence, seems predictive of the

individual’s ability to cope with stressful situations [63];

• Facilitating processes of introspection and decoding of the feelings and emotions of

the participants to feed a condition of conscious presence;

• Promoting processes of identiﬁcation with the elements of nature, which are in dy-

namic balance and can offer more effective learning and working models [64];

• Stimulating the transformative activity of any dysfunctional aspects detected [65].

The method of conducting the forest therapy sessions was structured in six main

steps, brieﬂy:

1. Right attitude and entrance into the woods: Leave behind challenging thoughts, and

smile as if meeting with an old friend;

2. Wearing the most beautiful dress: Embrace the silence, leave behind planning and

commitments, gain space for the emergence of one’s own best part;

3. Walking mindfully: Involves bringing attention to any sensation coming from the feet

in order to keep the wandering mind anchored;

4. Breathing in the woods: By observing the breathing, it is possible to tune in with the

environment and to be aware of the state of mind and body as well; consequently, let

it all go, such as tensions, thoughts and feelings;

5. Using the senses: Intentionally looking at the surrounding environment or a natural

object that is found to be relaxing, recognizing wood fragrances during breathing,

concentrating on typical forest soundscape (birds, wind through the trees, crunch of

branches and leaves underfoot, etc.), touching wood and trees and, when possible,

tasting products of the undergrowth;

6. Meditating with the trees: Choosing a speciﬁc tree as the most faithful mirror of

oneself and approaching it with the right attitude and intentions, towards the identiﬁ-

cation with the tree and its qualities such as resilience, vitality and projection towards

the sky and the light.

2.3. Data Analysis

Data reported on the reduced POMS questionnaires described in Section 2.1 were

transferred to Microsoft Excel worksheets. Psychological indices were obtained from the

questionnaires’ data by adding the values of the corresponding items according to the

recommended classiﬁcation [39]. In addition, the TVOC data collected from the PID were

transferred from the proprietary software of the instrument to Microsoft Excel, and average

and peak concentration levels along the forest therapy paths were computed.

Pre-post average percentage differences of the outcomes for each considered mood

state were computed for each session based on data stored in Microsoft Excel worksheets.

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Domain

Anxiety

Depression

Anger

Confusion

Then, Minitab 19 was used for further statistical analyses. One-way ANOVA was preferred

since the samples were small in number and with quasi-normal distributions. For non-

normal samples, the Mann–Whitney test was used. The Ryan–Joiner test was used to

test for normality of continuous variables, while the chi-square test was used to test

for homogeneity among categorical variables. An ANOVA mixed-effects model was

used to test for associations between pre and post changes of each POMS domain and

sociodemographic features.

3. Results

3.1. Overall Psychological Outcomes

In order to ensure that the comparison among different sessions would not be affected

by statistically signiﬁcant differences in initial mood states (i.e., baseline), a one-way

ANOVA test was performed on the pre-intervention POMS questionnaires [39] across

all forest therapy sessions including the control session (FTSC). The results showed no

statistically signiﬁcant differences among groups in terms of pre-intervention scores for

all mood states: anxiety (DF = 7; DF error = 154; F = 1.59; p = 0.141), depression (DF = 7;

DF error = 154; F =1.66; p = 0.124), anger (DF = 7; DF error = 154; F = 0.64; p = 0.725) and

confusion (DF = 7; DF error = 154; F = 1.71; p = 0.111). Table 3 shows the relevant statistics.

Table 3. POMS pre-intervention domain scores.

Session

FTS1

FTS2

FTS3

FTS4

FTS5

FTS6

FTS7

FTSC

FTS1

FTS2

FTS3

FTS4

FTS5

FTS6

FTS7

FTSC

FTS1

FTS2

FTS3

FTS4

FTS5

FTS6

FTS7

FTSC

FTS1

FTS2

FTS3

FTS4

FTS5

FTS6

FTS7

FTSC

Number of Available Data

Mean ± Standard Deviation

2.125 ± 3.687

2.714 ± 2.918

2.879 ± 2.955

4.180 ± 4.680

2.750 ± 2.605

3.833 ± 3.682

4.586 ± 4.280

1.750 ± 2.261

0.583 ± 1.886

1.000 ± 1.703

2.303 ± 3.127

2.353 ± 3.807

1.500 ± 2.268

2.500 ± 3.698

2.069 ± 2.434

0.750 ± 1.485

0.958 ± 2.579

1.000 ± 1.761

1.455 ± 1.922

1.529 ± 2.004

1.250 ± 1.753

1.500 ± 2.407

1.724 ± 1.869

0.583 ± 1.443

1.792 ± 2.604

1.905 ± 1.998

2.939 ± 2.487

2.882 ± 3.257

2.000 ± 2.070

3.889 ± 3.179

3.310 ± 3.547

1.500 ± 1.784

95% CI

(0.686; 3.564)

(1.176; 4.252)

(1.652; 4.106)

(2.47; 5.89)

(0.258; 5.242)

(2.172; 5.495)

(3.277; 5.895)

(−0.285; 3.785)

(−0.515; 1.682)

(−0.175; 2.175)

(1.366; 3.240)

(1.047; 3.658)

(−0.403; 3.403)

(1.231; 3.769)

(1.069; 3.068)

(−0.804; 2.304)

(0.138; 1.779)

(0.123; 1.877)

(0.755; 2.155)

(0.554; 2.505)

(−0.172; 2.672)

(0.552; 2.448)

(0.977; 2.471)

(−0.577; 1.744)

(0.670; 2.914)

(0.705; 3.104)

(1.982; 3896)

(1.549; 4216)

(0.057; 3.943)

(2.593; 5.185)

(2.290; 4.331)

(−0.087; 3.087)

The differences in scores for any mood states before and after forest therapy sessions

were tested; in particular, data were aggregated for intervention groups (FTS1 to FTS7),

while FTSC was tested separately. A one-way ANOVA was performed to test for pre–post

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differences in the aggregated intervention groups (FTS1 to FTS7) and in the control group

(FTSC), resulting in a statistically signiﬁcant reduction in each POMS domain score for

the aggregated intervention groups, while the control group resulted non-signiﬁcant for

each POMS domain. Table 4 shows the results, along with the respective F and p values.

The control group had a limited numerosity; thus, the observed trends toward a reduction

in any of the mood states might become statistically signiﬁcant with a larger sample,

especially for anxiety (p = 0.191).

Table 4. Statistical signiﬁcance of outcomes from forest therapy sessions aggregated intervention groups (FTS1 to FTS7) and

control group (FTSC).

Session

Intervention groups (FTS1 to FTS7)

Control group (FTSC)

Anxiety

↓

F = 59.62; p < 0.001

↔

F = 1.82; p = 0.191

Depression

↓

F = 24.64; p < 0.001

↔

F = 0.74; p = 0.399

Anger

↓

F27.48; p < 0.001

↔

F = 0.93; p = 0.345

Confusion

↓

F = 30.98; p < 0.001

↔

F = 0.43; p = 0.521

3.2. Speciﬁc Effects of Remote Forest Areas

The possible speciﬁc effects due to the remoteness of forest areas and the conditions

under which such effects could arise were investigated by means of the comparison of

outcomes (pre–post differences, i.e., change-from-baseline) of each intervention group

(FTS1 to FTS7) with the corresponding outcomes from the control group in the urban

park (FTSC).

First, Grubb’s test for outliers was performed on the changes-from-baseline for

all mood states derived from the answers to the POMS questionnaires [39] in order to

exclude potential outliers from the analysis (p < 0.05). For anxiety, only one outlier was

removed from session FTS7. For depression, one outlier was removed from each of the

following sessions: FTS1, FTS2 and FTS6. For anger, one outlier was removed from each of

the following sessions: FTS1, FTS2, FTS5, FTS6, FTS7 and FTSC. For confusion, only one

outlier was removed from session FTS1.

Next, a Ryan–Joiner test for normality was performed for the change-from-baseline of

each mood state derived from every forest therapy session. Table 5 shows the results of the

test, where only non-normal distributions are highlighted (p < 0.05).

Table 5. Results of the Ryan–Joiner test for normality of change-from-baseline for any mood state in

any forest therapy session. NN = non-normal; all other distributions were normal.

Session

FTS1

FTS2

FTS3

FTS4

FTS5

FTS6

FTS7

FTSC

Anxiety

Depression

Anger

Confusion

A one-way ANOVA test was applied for comparing normal samples, while a Mann–

Whitney test was applied when the comparison involved at least one non-normal sample.

Table 6 highlights the cases in which a forest therapy session performed in a remote forest

area resulted in improvements of mood states signiﬁcantly higher than in the FTSC (p < 0.05)

or close to signiﬁcantly (0.05 ≤ p < 0.10). The latter were added because the limited number

of participants to certain forest therapy sessions might have hindered the achievement of

statistical signiﬁcance.

Sessions FTS1, FTS2 and FTS5 showed no speciﬁc additional beneﬁt compared to

the control session FTSC. Session FTS3 showed an improvement in anger signiﬁcantly

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higher than FTSC and comparative improvements in depression and confusion close to

signiﬁcance. Session FTS4 again showed an improvement in anger signiﬁcantly higher

than FTSC and a comparative improvement in confusion close to signiﬁcance. Session

FTS6 showed improvements in anxiety and confusion signiﬁcantly higher than FTSC and

a comparative improvement in anger close to signiﬁcance. Finally, session FTS7 showed

an improvement in anxiety signiﬁcantly higher than FTSC and a comparative improvement

in anger close to signiﬁcance.

Table 6. Statistically significant differences between outcomes from each forest therapy sessions FTS1 to

FTS7 and outcomes from the control session FTSC. Green arrows: p < 0.05. Blue arrows: 0.05 ≤ p < 0.10

(close to significance).

Session

FTS1

FTS2

FTS3

FTS4

FTS5

FTS6

FTS7

Anxiety

Depression

Anger

Confusion

↓ (p = 0.027)

↓ (p = 0.042)

↓ (p = 0.084)

↓ (p = 0.023)

↓ (p = 0.028)

↓ (p = 0.088)

↓ (p = 0.072)

↓ (p = 0.082)

↓ (p = 0.093)

↓ (p = 0.024)

3.3. Association of Pshycological Outcomes with Sociodemographic Traits

A mixed model ANOVA was applied to check for any statistically signiﬁcant associa-

tion among the collected sociodemographic traits of the participants in the forest therapy

sessions, excluding the control session FTSC, and the respective changes-from-baseline for

any mood state. The variance estimation method was the restricted maximum likelihood

and the Kenward–Roger method was used for testing ﬁxed effects. In total, 128 question-

naires were considered, reporting complete sets of sociodemographic information. Table 7

shows the considered factors and their respective values.

Table 7. Factors and respective values used in the mixed model ANOVA for the assessment of the

association of forest therapy outcomes (sessions FTS1 to FTS7) with sociodemographic traits.

Factor

Values

Age

Height

Weight

Job

Education

Residence

Smoke

Sport 5

From 18 onwards (integer)

Any (integer)

IN; MA; RE; SO 1

SS; HS; UN 2

CI; VI 3

0; 1 4

0; 1; 2; 3 6

1 IN: intellectual worker; MA: manual worker; RE: retired; SO: social worker. 2 SS: secondary school; HS: high

school; UN: university and higher. 3 CI: city greater than 40,000 inhabitants; VI: village below 40,000 inhabitants.

4 0: not smoker; 1: smoker. 5 Sport is understood as a session of physical activity, indoor or outdoor, regardless

of the duration and intensity. 6 0: no sport; 1: 1 to 2 times a week; 2; 3 to 4 times a week; 3: more than 4 times

a week.

The results showed a statistically signiﬁcant association of the change in anxiety with

sport activity (p = 0.035), in particular, the absence thereof (p = 0.020) with a negative coefﬁ-

cient, i.e., anxiety decreased signiﬁcantly for people who never played sports. Changes in

depression were signiﬁcantly associated with age (p = 0.031), with a positive coefﬁcient, as

well as with sport (0.038), in particular, the absence thereof (p = 0.041), with a negative coef-

ﬁcient. Changes in anger were signiﬁcantly associated with sports (p = 0.011), in particular,

the absence thereof (p = 0.002), with a negative coefﬁcient. Changes in confusion were not

signiﬁcantly associated with any considered factors, although the association with age was

close to signiﬁcance (p = 0.058) with a positive coefﬁcient.

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4. Discussion

4.1. Analysis of Presented Results

Based on the results shown in Table 4, the outcomes (i.e., change-from-baseline) from

the intervention groups altogether (forest therapy sessions FTS1 to FTS7, totaling 150 valid

questionnaires) were statistically signiﬁcant for any of the considered psychological do-

mains (anxiety, depression, anger and confusion). Thus, this study supports the hypothesis

that forest therapy sessions performed in remote forest areas are effective in improving the

considered psychological domains.

Conversely, none of the outcomes from the control group (session FTSC) were signiﬁ-

cant, suggesting that remote forests, where sessions FTS1 to FTS7 were performed, could

bring speciﬁc beneﬁts compared to urban forests. However, a main limitation of this study

was the small numerosity of the control group (12 valid questionnaires), which might have

hampered the signiﬁcance of the respective outcomes.

In order to try to overcome the above-mentioned limitation and provide further insight

into the factors affecting the outcomes of forest therapy sessions, the outcomes from each

of the intervention groups were separately compared with the corresponding outcomes

from the control group. As presented in Section 3.2 and shown in Table 6, few sessions

performed in remote forest areas resulted in speciﬁc and signiﬁcant beneﬁts for some

psychological domains, compared with the control session performed in an urban park. In

particular, both FTS6 and FTS7 signiﬁcantly outperformed FTSC for anxiety and close to

signiﬁcantly for anger, while FTS3 and FTS4 signiﬁcantly outperformed FTSC for anger and

close to signiﬁcantly for confusion. FTS3 also outperformed FTSC for depression, but only

close to signiﬁcantly. FTS6 showed the best results, also signiﬁcantly outperforming FTSC

for confusion. Sessions FTS1, FTS2 and FTS5 did not signiﬁcantly (or close to signiﬁcantly)

outperform FTSC. Overall, these results suggest that performing forest therapy sessions at

remote sites could help to enhance its effects compared to urban settings, but only under

certain circumstances.

Excluding FTS1, which was conducted non-professionally, and FTS5, which was

affected by a small numerosity and relatively harsh weather conditions, what peculiar

characteristics could underlie the additional and signiﬁcant beneﬁts deriving from certain

forest therapy sessions performed in remote sites?

Based on Table 1, FTS6, which was the highest performing session, enjoyed the highest

average concentration of TVOCs and was the only one performed in a Mediterranean

forest, without water bodies or water streams. On the other hand, FTS3 enjoyed the second

highest average concentration of TVOCs (and the highest among peak concentrations) and,

similar to FTS4 (performed on the same site as FTS3), included fascinating water streams

and small waterfalls. Notably, FTS4 enjoyed very good weather comfort, similar to FTS3,

but substantially lower average and peak concentration of TVOCs. FTS7 suffered from

less comfortable weather compared to all the other sessions, along with lower average

concentration of TVOC, but included water streams and a fascinating natural pond. Finally,

FTS2 enjoyed very comfortable weather, concentration levels of TVOCs only slightly lower

than FTS4 and higher than FTS7 and did not include water streams or water bodies.

Based on the available data, essentially on the performances of FTS6 compared with

all the other sessions and of FTS3 compared to FTS4, the hypothesis could be advanced that

the concentration of TVOCs is an effective factor affecting the performance of professionally

conducted forest therapy sessions in remote forests. This can be regarded as an original

experimental result of this study.

However, the matter is further complicated by partially contrasting results about the

systemic absorption of MTs, which represent most of the BVOCs emitted by plants, which,

in turn, are likely to contribute substantially to the observed concentration of TVOCs. To

the best knowledge of the authors, only two studies dealt with this important topic. In

2015, Japanese scholars found that the serum concentration of α-pinene, but not of other

monoterpenes, increased by several folds after walking in a conifer forest for one hour [66].

In 2021, Spanish scholars found that the blood concentration of α-pinene, but not of other

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monoterpenes, increased by a much slighter extent and only in subjects starting from the

lowest baselines levels after walking in an evergreen broadleaf forest (holm oak as the most

representative species) for two hours [67].

Although very important and innovative, both studies [66,67] were affected at least

by small sample sizes, by the unknown individual levels of metabolic transformation rates

and by the limited exposure time. Moreover, the health effects produced by MTs could

follow pathways other than by systemic absorption, such as direct effects on the upper

respiratory tract and on the central nervous system through brain absorption [25]. However,

due to the great importance of α-pinene as an anti-inﬂammatory, analgesic, antioxidant,

anxiolytic, antidepressant and sedative, as well as an antiproliferative agent [25], the

results obtained in this study, although quite limited, could point to some impact of

BVOC concentration on the psychological outcomes after forest therapy sessions lasting

about 3.5 h. Clearly, the detailed analysis of the relative and absolute concentration of

the different monoterpenes available in TVOCs during further forest therapy sessions

involving large numbers of participants will help clarify the possible impact of different

BVOCs on short-term psychological outcomes.

Despite lower levels of weather comfort and concentration of TVOCs, FTS7 generated

few signiﬁcant results compared with the control session FTSC. Conversely, a very good

weather comfort and concentration levels of TVOCs substantially higher than in FTS7 and

only slightly lower than in FTS4 did not allow session FTS2 to achieve any signiﬁcant

result in comparison to FTSC, underperforming in comparison to all the other sessions.

The hypothesis could be advanced that water streams and water bodies play an important

role, as already arisen in previous studies, for example, in a controlled experiment using

virtual reality [68]. However, considering that FTS6 lacked water bodies or water streams,

the matter could be more complicated.

It is further hypothesized that the presence of water streams or water bodies is very

important, but only if appropriate to the speciﬁc environment. In fact, FTS6 outperformed

all the other sessions even in the absence of those elements, but one could not expect

their presence in a typically dry Mediterranean forest. Conversely, FTS2 underperformed

all the other sessions, and one would expect to ﬁnd water streams in a mountainous

environment dominated by Scots pine. It remains unknown whether substantially higher

concentration levels of TVOCs at the site of FTS2 could compensate for a possibly less

efﬁcient environment: ongoing research at that site might help clarify the issue. Indeed,

FTS2 was performed in late summer, while, for Scots pine forests, it was found that young

sprouts in late spring and early summer emit far more BVOCs than mature needles in late

summer [27].

Overall, the coherence among the main natural elements, sometimes called environ-

mental coherence [69], could play a distinct role in boosting the performance of forest

therapy sessions. This coherence could also help explain why FTS7, carried out in a very

humid mountain environment, performed quite well despite low concentration levels of

TVOC and limited weather comfort. Moreover, it should be noted that FTS3 and FTS4,

despite the difference in the concentration of TVOCs, produced very similar results con-

cerning the psychological domains, i.e., signiﬁcantly better performances compared with

the control session for anger and close to signiﬁcance for confusion (as well as for depres-

sion, but only in FTS3). The speciﬁc and coherent environment characterizing FTS3 and

FTS4 could have been an effective driver for improvements at least in anger and, likely, in

confusion. The possible role of environmental coherence is another original experimental

result of this study, although it requires further research in order to elucidate its nature

and importance.

Session FTS1, which produced no signiﬁcant outcome compared to FTSC, was per-

formed in the same site as FTS6, although with a remarkably lower level of weather comfort

(temperature of 30 ◦C compared to 15 ◦C in FTS6) and according to a non-professional

method. FTS1 enjoyed the highest average and peak concentration of TVOCs across all

forest therapy sessions. Although the comparison between FTS1 and FTS6 could lead to

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hypothesize an important role for the method of conducting forest therapy sessions, with

professional guidance more effective in producing signiﬁcant outcomes, the large difference

in weather comfort jeopardizes this hypothesis. Further experiments will be needed in

order to gain insight into this matter.

Based on Table 6, among the considered psychological domains, depression was the

least affected by the remoteness of the forest site, at least in comparison to anxiety, anger

and confusion. Possibly, items used to build the depression index would need longer forest

therapy sessions or regular repetitions for their effective marginal reduction in comparison

to sessions performed in urban settings.

The reasons why anxiety was signiﬁcantly only reduced in FTS6 and FTS7 in compari-

son to the control are hard to assess. Possibly, they have to do with the forest environments

characterizing FTS6 and FTS7 (distanced, mostly brightly colored trees and relatively low

beech trees), which could be regarded as more relaxing, or less aggressive, than in FTS3

and FTS4 (dense, dark-colored spruce trees), but further ongoing ﬁeld trials will hopefully

clarify this issue.

Overall, anger appears as the most affected psychological domain, having been signif-

icantly reduced in comparison to the control in FTS3 and FTS4 and close to signiﬁcantly in

FTS6 and FTS7. Possibly, items used to build the anger index were representative of acute

conditions and could have been more easily reduced by means of forest therapy sessions

performed at remote locations. Finally, confusion was signiﬁcantly reduced compared

to the control in FTS6 and close to signiﬁcantly in FTS3 and FTS4. Beyond environmen-

tal coherence, the concentration level of TVOCs, which was substantially lower in FTS7

compared to FTS3, FTS4 and FTS6, could have contributed to the result.

Concerning the association of the psychological outcomes from intervention sessions

(FTS1 to FTS7) with the sociodemographic traits presented in Section 3.3, sporting habits

showed the highest degree of association, in particular, the absence of sports. In fact, the

latter was signiﬁcantly and negatively associated with the size of reduction in anxiety,

depression and anger. The signiﬁcant association with the absence of sport could mitigate

the missing information on duration and intensity, according to the deﬁnition of sports

presented in Table 7. An important question arises as to whether such association means

that people never practicing sport receive substantial beneﬁts from simply walking, ir-

respective of the surrounding environment and method of conducting physical activity,

or the absence of sport is related to a reduced contact with nature and the immersion in

forest environments is the leading factor, irrespective of physical exercise. Further ﬁeld

experiments will help resolve this issue.

Age was the other trait showing some association in particular with depression

(signiﬁcant) and confusion (very close to signiﬁcant). The beneﬁts for depression and

confusion increased with age, which could be ascribed either to increasing trait levels of

such indices with age or to a greater sensitivity of older people to forest immersion. Again,

further research will help clarify this issue.

It is interesting to note that no other sociodemographic characteristics were significantly

associated with the results of this study: neither biometric features such as height and weight,

nor sex, job, education, residence and smoking habits. This evidence could mean that forest

therapy can be successfully applied to most people, irrespective of their conditions.

4.2. International Experiences

A recent systematic review on the effects of nature walks on states of anxiety and

depression evidenced clear and signiﬁcant effects on anxiety but somewhat inconclusive

effects on depression [70], in agreement with the results of this study. However, most of

previous studies dealing with the short-term effects of forest therapy sessions, in particular,

using POMS questionnaires, appear to lack a proper consideration of the nature of the

statistical distributions of the changes-from-baseline. Thus, comparisons with the results of

this study are difﬁcult to perform.

Research was performed in 2018 based on a 3-day structured forest therapy session

in a semitropical forest in Taiwan, mainly aimed at checking the effects on creativity and

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involving 21 participants (8 males, 13 females) across all age groups (52.0 ± 12.54 years,

from 25 to 70 years old) [71]. The analysis of POMS questionnaires returned only the

percentage changes from baseline, along with the Cohen’s d index for the assessment of the

size of the effect [72]. The following changes were presented: anxiety, −49%; depression,

−42%; anger, −38%; confusion, −33%. Based on the above-written, comparisons with this

study are worthless, let alone the fact that sessions considered in this study had much

shorter duration (around 3.5 h).

In a recent study performed in Italy over healthcare staff during the COVID-19 pan-

demic, 77 participants filled the same reduced POMS questionnaires used in this study, be-

fore and after short breaks (20–30 min) in nature (green areas nearby hospital facilities) [40].

The results showed improvements in all the psychological indices, which were greater

for staff directly involved in COVID-19 treatment areas, who were likely more stressed.

Throughout all participants, anxiety, depression and anger reduced by 60–66%, 53–56% and

47 to 84%, respectively, while confusion was reduced by 35–53%. Again, comparisons with

this study are hard to perform.

In a study performed in Taiwan, 128 middle-aged to elderly subjects were recruited

(43 males and 85 females, age range 45 to 86 years, on average 60.0 ± 7.44 years) to attend

structured forest therapy sessions focused on the activation of the senses [73]. Each session

included around 10 participants during 3 h, such duration being comparable to sessions

performed in this study, under conditions of high meteorological comfort. The analysis of

reduced POMS questionnaires returned the following changes: anxiety, −59%; depression,

−50%; anger, −55%; confusion, −44%.

A study was performed in Poland on young adults (21 participants, of which 12 were

males and 9 were females, with an age range between 21 and 29 years and an average age

23.86 ± 2.67 years) according to a forest therapy program structured over two days (indoor

and in forest) [74]. The analysis of reduced POMS questionnaires returned the following

changes: anxiety, −56%; depression, −54%; anger, −43%; confusion, −36%.

Another study was performed again in Poland on young adults based on structured

30-min walks [75]. The analysis of the reduced POMS questionnaires, referring to a conifer

forest, returned the following changes: anxiety, −53%; depression, −35%; anger, −34%;

confusion, −30%.

In a study performed in South Korea, 38 university students with a mean age of

around 22 years, with 24 males and 14 females, were assigned in equal numbers to a forest

therapy group or a control group [76]. The experimental group performed eight, one-hour-

long sessions once a week according to a structured program but without active guidance.

Reduced POMS questionnaires were presented to the participants at the beginning of the

ﬁrst session and the end of the last session. Except for anger, all other indices improved

substantially: anxiety (−34%), depression (−42%) and confusion (−31%).

In the opinion of the authors, it would be useful to re-examine some of the above-

cited studies based on appropriate and standardized statistical methods in order to build

a really useful international database concerning the performance of forest therapy and the

determinants of the respective outcomes.

4.3. Limitations and Preliminary Technical Guidelines

A few important limitations affected this study. All the forest therapy sessions lasted

3.5 ± 0.5 h, thus, the dose effect could not be investigated. All professionally conducted

forest therapy sessions in remote forest areas followed the same program, thus the effect

of different programs could not be investigated. In this respect, a recent Korean study

performed with elderly individuals showed that forest therapy programs focused on

Qigong or active walking produced speciﬁc neuropsychological and electrophysiological

beneﬁts, both beneﬁcial for preventing dementia and relieving related health problems [77].

Moreover, the single session performed without professional guidance (FTS1) was affected

by a low level of weather comfort, which could have played an important role in the

respective insigniﬁcant results.

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Participants in the forest therapy sessions discussed in this study were allowed to

attend only one session, thus the frequency effect could not be investigated. Neither

the psychological trait conditions nor the follow-up conditions of the participants were

collected; thus, the possible persistence of effects could not be investigated either. Another

limitation was that participants were not asked about their personal frequentation of forest

or green areas, even if the collected information about personal sporting habits might give

some clues to this effect. The latter limitation could have introduced a bias in terms of

persistence of effects for some sessions. Moreover, further information on the duration

and intensity of sport, understood here as a session of physical activity, would be useful to

reﬁne the analysis.

The administration of the POMS questionnaires to the participants allowed collecting

instantaneously perceived mood states, not corroborated by any measure on physiologi-

cal parameters. Only admittedly healthy participants were recruited, thus the effects on

individuals affected by psychological or physiological disorders could not be assessed.

Moreover, no health screening of participants was performed before the forest therapy

sessions, thus it cannot be excluded that some participants were affected at least by acute

physiological, psychological or psychiatric illnesses, or by alcohol and drug abuse.

Although representative enough of different outdoor forest environments in central

and northern Italy, the study sites could not be considered representative of all the pos-

sible environments; for example, chestnut forests, widespread in mid-mountain areas in

the Italian Apennines, were not investigated, along with coastal Mediterranean forests.

Moreover, elements other than forest species and few other natural features (e.g., water

streams or ponds) were not considered, such as artiﬁcial elements (fences, tables and chairs,

mountain retreats and their architecture, etc.). Although large enough in comparison

with other experiences reported in the literature, the investigated sample (sites, sessions

and number of participants) could not allow the disentangling of all the possible factors

affecting the considered psychological outcomes, as well as adequately representing all

the relevant age groups, genders and other sociodemographic characteristics. In particular,

the control session FTSC suffered from a relatively scarce number of participants. Finally,

only TVOCs concentration was measured, while individual monoterpenes are known to

potentially produce different and specialized health effects [25], which could be related to

the outcomes of forest therapy sessions.

It is planned to overcome most of the above-listed limitations in the ongoing research

across many other sites by using many more participants and including larger control

groups in urban settings across different seasons and performing more comprehensive

measures such as sociodemographic, psychological (trait and state) and physiological

measures, as well as measuring the relative and absolute concentrations of individual

BVOCs and MTs. In addition to extending the performance database, the continuation of

the study aims at more rigorously identifying the factors affecting the observed healing

effects and further linking the medical and forestry research, as recommended in a recent

study [11].

Another limitation concerns the considered health domains, which were focused only

on mood states. Within the psychological domain, for example, cognitive processes were

shown to receive distinct beneﬁts from forest therapy [25,71] and would be worth being

investigated, such as currently occurring in the frame of a large European project aimed

at fostering knowledge about the relationship between Information and Communication

Technologies and Public Spaces [78].

Based on the results obtained in this study and within its limitations, the following

preliminary guidelines concerning the short-term amelioration of psychological indices

can be advanced. Meteorological comfort, environmental coherence and concentration

levels of TVOCs appear quite important in the determination of the outcomes, especially

contributing to speciﬁc additional beneﬁts brought by forest therapy sessions performed

in remote forest areas. Contrary to anxiety, anger and confusion, the depression domain

seems not to receive speciﬁc beneﬁts from the remoteness of the forest site. Older people

Int. J. Environ. Res. Public Health 2021, 18, 9509

18 of 21

could beneﬁt more from forest therapy sessions, especially for depression and confusion.

People abstaining from sporting activities, and likely from regular contact with nature,

could beneﬁt more from forest therapy sessions, especially for anxiety, depression and

anger. These preliminary guidelines could help to optimize forest therapy sessions, as well

as to plan suitable sessions targeted to speciﬁc groups of participants, for example, those

belonging to a given age group or following certain habits, or aimed at improving speciﬁc

psychological indexes.

4.4. Policy Guidelines

The mobilization of ﬁnancial resources and the introduction of speciﬁc legislative

elements aimed at promoting, standardizing and regulating forest therapy programs

were deemed essential to the effective management of the forest ecosystems towards

human health [5]. More speciﬁcally, based on the evidence shown in this study, further

fundamental challenges consist in the information, education and motivation of health

facilities and professionals, as well as of citizens, towards green prescriptions, which have

been issued for years in countries such as Japan and South Korea [31].

Further important tasks concern the certiﬁcation of sites based on structural and

environmental characteristics and direct functionality (observation of health effects), as

well as the certiﬁcation of professional providers of services connected to forest therapy [34].

In the Western world, the Parks Prescription program introduced by the British Columbia

Parks Foundation in Canada aimed at the prescription of short and slow walks in protected

forest areas as a “superfood of exercise” could serve as a useful model [79].

5. Conclusions

The results achieved in this study conﬁrm, reinforce and expand the knowledge about

the healing effects of forests by means of structured forest therapy sessions. The short-term

reductions in the levels of anxiety, depression, anger and confusion were all signiﬁcant

for forest therapy sessions performed in remote areas and taken altogether, contrary to

a control forest therapy session performed in an urban park.

Speciﬁc effects of remoteness, in comparison to the control session, arose under certain

conditions with anxiety, anger and confusion but not for depression. Some characteristics

of the site appeared to affect the outcomes, especially the level of meteorological com-

fort, the concentration of TVOCs and the environmental coherence, as well as personal

characteristics of the participants, such as sporting habits and age.

Despite several limitations, a few preliminary technical guidelines were issued, which

could help to identify, design and optimize forest therapy stations and sessions also targeted

to speciﬁc groups of participants or improving speciﬁc psychological conditions.

Author Contributions: Conceptualization, M.A., R.B., F.R.B., D.D., F.F. (Fabio Firenzuoli), V.M., F.M.

and F.Z.; methodology, R.B., F.R.B., G.M., F.F. (Franco Finelli), F.M., S.N., L.N. and M.R.; software,

L.A. and F.M.; validation, M.A., R.B., F.R.B., F.C., D.D., F.F. (Franco Finelli), V.M., L.N. and F.F.

(Fabio Firenzuoli); formal analysis, R.B., F.M., F.F. (Fabio Firenzuoli) and F.Z.; investigation, L.A.,

F.C., F.M., S.N., M.R. and F.Z.; resources, G.M., F.M. and F.Z.; data curation, L.A., F.C. and F.M.;

writing—original draft preparation, F.M. and F.Z.; writing—review and editing, M.A., R.B., D.D., F.F.

(Fabio Firenzuoli), V.M., F.M., S.N., L.N., M.R. and F.Z.; visualization, L.A. and F.M.; supervision,

R.B., F.F. (Franco Finelli), F.F. (Fabio Firenzuoli), G.M., F.M., L.N. and F.Z.; project administration, F.F.

(Fabio Firenzuoli), G.M. and F.Z.; funding acquisition, F.R.B., F.F. (Franco Finelli), F.Z. and G.M. All

authors have read and agreed to the published version of the manuscript.

Funding: This research received no external funding.

Institutional Review Board Statement: The study was conducted according to the guidelines of

the Declaration of Helsinki and approved by the Institutional Review Board of National Research

Council and Italian Alpine Club (N.01/2021, 8 May 2021).

Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.

Data Availability Statement: All data are available by contacting the corresponding authors.

Int. J. Environ. Res. Public Health 2021, 18, 9509

19 of 21

Acknowledgments: The study could not have been performed without the invaluable support

of several Sections of the Italian Alpine Club, among which the Section of Reggio Emilia, the

Section of Firenze and the Section Valdarno Inferiore “Giacomo Toni”, as well as the Consorzio Fai

Vacanze (Fai della Paganella, Trento, Italy) and the Association Foresta Modello delle Montagne

Fiorentine (Florence, Italy). Giuliano Cervi, Sonia Cuseri and Giancarlo Tellini, as the president

of the Central Scientiﬁc Committee, president of the Tuscany Scientiﬁc Committee “Fiorenzo Gei”

and president of the Tuscany Regional Group of the Italian Alpine Club, respectively, are gratefully

acknowledged for their continuous support and advice. Finally, three anonymous Reviewers are

gratefully acknowledged for their careful and insightful comments and suggestions.

Conﬂicts of Interest: S.N. and M.R. are owners of the trademark Forestfulness®. The authors declare

no other conﬂict of interest.

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