INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH

2023, VOL. 33, NO. 1, 15–53

https://doi.org/10.1080/09603123.2021.1998390

Nature-based interventions for vulnerable youth: a scoping

review
Tracey A. Overbeya, Florian Diekmann and Kristi S. Lekiesc
a
University Libraries, The Ohio State University, Columbus, Ohio, USA; cFood Agricultural, and Environmental
Sciences Library, The Ohio State University, Columbus, Ohio, USA; cSchool of Environment and Natural Resources,
The Ohio State University, Columbus, Ohio, USA

ABSTRACT ARTICLE HISTORY

Nature-based interventions hold promise for vulnerable youth experien­ Received 30 June 2021
cing mental, emotional, developmental, behavioral, or social difficulties. Accepted 20 October 2021
This scoping review examined wilderness therapy, animal assisted ther­ KEYWORDS
apy, care farming, and gardening and horticultural therapy programs to Nature-based interventions;
raise awareness and guide future development of research and treatment green care; nature therapy;
options. Studies included in this review were identified through vulnerable youth; at-risk
a systematic search of the literature informed by a scoping review frame­ youth; scoping review
work. Studies were examined by design, sample, intervention, and key
findings. The majority of studies were quantitative using repeated mea­
sures designs and were conducted primarily in the United States. Sample
sizes were generally small. Interventions were residential and community
based with varying degrees of duration. Outcomes were largely positive
across a wide range of psychosocial and behavioral measures and often
maintained post-treatment. We emphasize the importance of robust
empirical designs, comprehensive description of the interventions and
surrounding therapies, and identification of target groups.

Introduction
Contact with nature and the utilization of natural environments have been recognized to contribute
to improving and promoting human health and well-being across the life span (Finlay et al. 2015;
Cox et al. 2017; Frumkin et al. 2017; Aerts et al. 2018; Vanaken and Danckaerts 2018; Engemann
et al. 2019; Mygind et al. 2019; Richardson et al. 2021). Researchers have investigated the relation­
ships between natural elements, green spaces, landscapes, and outdoor activities and identified
a diverse range of positive outcomes that include benefits for physical health, mental health,
cognitive development, and social interactions (e.g. Abraham et al. 2010; Annerstedt and
Währborg 2011; Bratman et al. 2012; Cox et al. 2017; Vanaken and Danckaerts 2018; Richardson
et al. 2021). The increasing number of meta-analyses, scoping reviews, systematic reviews, and other
research summaries in recent years has helped to synthesize the body of literature across outcome
variables or specific populations as well as identify areas for future research (e.g. Frumkin et al.
2017; Vanaken and Danckaerts 2018; Mygind et al. 2019; Shanahan et al. 2019; Richardson et al.
2021). As the evidence base continues to grow, so has the need to identify consistencies in research
findings, methodological approaches, and gaps in knowledge (Frumkin et al. 2017; Aerts et al. 2018;
Vanaken and Danckaerts 2018; Richardson et al. 2021).

CONTACT Florian Diekmann diekmann.4@osu.edu Food, Agricultural, and Environmental Sciences Library, The Ohio
State University, Columbus, OH
This article has been corrected with minor changes. These changes do not impact the academic content of the article.
© 2021 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.
0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
16 T. A. OVERBEY ET AL.

In this paper, we focus on nature-based interventions, sometimes collectively denoted as green

care activities, for vulnerable adolescents and young adults experiencing mental, emotional,
developmental, behavioral, or social difficulties. Nature-based interventions and green care
activities consist of a diverse range of programs and services that utilize plants, animals, and/or
landscapes to create therapeutic and treatment interventions designed to address health and care
needs of general populations as well as specific population groups (Sempik and Bragg 2013).
A broad range of organizations have developed and employed a variety of nature-based services
and therapeutic interventions to promote health and well-being in specific populations. Similarly,
the diversity of target groups and the variety of behavioral, clinical and non-clinical problems is
extensive. While many of the studies deal with children and young people with a mental health
diagnosis, there are studies that target educational and social benefits. The latter are excluded
from the present research, which focuses on therapeutic benefits rather than skill building
exercises.
Increasingly, concerns have been raised about high levels of adolescents and young adults
struggling with mental health problems, adjustment difficulties, problem behavior, disengage­
ment, or disaffection (e.g. Olfson et al. 2015; Coley et al. 2018; Keyes et al. 2019; Murray et al.
2019; Mojtabai and Olfson 2020; Cybulski et al. 2021). The severity of needs, gaps in existing
services, and service provision challenges have generated interest in effective treatment
approaches (McGorry et al. 2013; Vyas et al. 2015; De Vries and Wolbink 2018), which include
nature-based interventions. The interventions are diverse not only in their targeted groups but
vary also greatly in their design and setting (Annerstedt and Währborg 2011; Moeller et al. 2018;
Shanahan et al. 2019). Based on the literature, the main types of nature-based interventions can
be categorized broadly into wilderness therapy (Wilson and Lipsey 2000), animal-assisted
therapy (Lentini and Knox 2015; May et al. 2016; Hoagwood et al. 2017), care or social farming
(Murray et al. 2019), and gardening and horticultural interventions (Sempik et al. 2014; Park
et al. 2016).
Although these programs are receiving attention in the academic literature, only a small number
of evidence reviews have focused on nature-based interventions solely targeting vulnerable or at-
risk youth populations (e.g. Wilson and Lipsey 2000; Lentini and Knox 2015). More often, youth-
focused interventions are addressed as a specific subgroup in evidence reviews on nature-based
interventions across age groups (e.g. Murray et al. 2019; Shanahan et al. 2019) or based on specific
conditions, such as attention deficit hyperactivity disorder (Faber Taylor et al. 2001; Faber Taylor
and Kuo 2009). Furthermore, the studies can be found in a variety of disciplines, thereby limiting
awareness by the larger body of literature to the community of scholars and practitioners (Harper
2017). The growing concern for adolescent and young adult populations point to the need to
examine nature-based interventions and services across intervention types. Mapping the existing
literature helps guide further development and application of interventions for this population and
can point to areas of future research needs.

The present study

The current evidence review fills a void by summarizing the literature on nature-based interven­
tions for a youth population that is considered vulnerable or at-risk of significant mental, emo­
tional, developmental, behavioral, or social difficulties, or placed in out-of-home institutional care.
Our specific objective is to present a summary of methodological designs, samples, interventions
characteristics, and key findings of the studies on wilderness-therapy, animal-assisted therapy, care
farming, and horticultural-based interventions for adolescents and young adults. We permit both
quantitative and qualitative research methodologies. While the strength of quantitative methods is
the empirical support for theoretical advances, qualitative studies situate the interventions in their
environment which can provide a rich contextual understanding of their impacts (Deighton et al.
2010). By examining studies across different types of interventions, our study summarizes the
 INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH 17

current knowledge on interventions and points to ways in which these interventions can be
beneficial for vulnerable youth, and provides direction to researchers and practitioners who seek
to advance the evidence base on this topic.

Materials and methods

Our study was informed by a scoping review framework identified as the most suitable approach to
determine the extent and nature of the broad and diverse literature on the topic and to identify key
areas for future research and scholarly engagement by identifying gaps in the literature (Arksey and
O’Malley 2005; Levac et al. 2010).

Study eligibility criteria

Our review focused on studies targeting children, adolescents, and young adults between the ages of
10 and 24 years and who could be considered vulnerable and at-risk for poor psychosocial outcomes
due to mental health diagnoses, inpatient hospitalizations, involvement in child welfare and juvenile
justice systems, substance abuse, family issues, trauma, school and community difficulties, and
other emotional, developmental, or behavioral concerns (Sanders and Munford 2014). We con­
sidered studies investigating a wide range of interventions aiming to utilize nature to improve and
promote quality of life, human health, and wellbeing of eligible populations. With no restrictions on
modes of delivery, intervention type or durations, the review included the breath and diversity of
nature-based interventions. The review considered studies presenting primary data (original
research) regardless of methodology, study design, publication date, or geography. Evidence-
syntheses (literature reviews, meta-analyses, systematic reviews, etc.) were also eligible. If
a primary data study was also included in an evidence-syntheses study, we indicated the overlap
in the table that lists the evidence-synthesis studies (Table 5). Only peer-reviewed studies published
in scholarly journals in English were considered. Studies without outcomes measures related to
broadly defined quality of life, human health, and wellbeing categories were excluded from this
review. This included studies focused primarily on educational or vocational activities, including
academic instruction and learning. Likewise, studies that focused on everyday life activities or
casual encounters with nature (e.g. private gardening, animal-assisted recreation, or outdoor
recreational activities, such as walking, running, or cycling in nature) were excluded.

Literature search process

A comprehensive search strategy was developed and searches for relevant literature in both generic
and subject-specific bibliographic databases were conducted, including Web of Science Core
Collection, Scopus, CAB Abstracts and Global Health (via Web of Science), CINAHL Plus (via
EBSCOhost), ERIC (via EBSCOhost), PsycINFO (via EBSCOhost), and SocINDEX (via
EBSCOhost). We searched MEDLINE via the Scopus interface. Search terms were derived from
initial scoping searches and reviewing the literature. The search strategy intentionally considered
a broad range of nature-based interventions and was piloted to check the appropriateness of
selected databases and search terms. The search string used in all databases was as follows:
(“green care“ OR “care farm*“ OR “social farm*“ OR “community farm*“ OR “therap* farm*“
OR “prison farm*“ OR “social horticult*“ OR “sensory garden*“ OR “healing garden*“ OR
“rehabilitation garden*“ OR “school garden*“ OR “community garden*“ OR “horticultural therap*“
OR ”therap* horticult*” OR ”garden therap*” OR ”therap* garden*” OR ”forest* therap*” OR
ecotherap* OR ”eco therap*” OR ”nature therap*” OR ”nature assisted therap*” OR ”nature
intervention*” OR ”animal assisted therap*” OR ”animal assisted activit*” OR ”wilderness therap*”
OR ”nature rehabilitation” OR ”nature based rehabilitation”) AND (child* OR adolesc* OR youth*
OR young* OR juvenile* OR teen*).
18 T. A. OVERBEY ET AL.

Figure 1. Study selection flow chart.

Database searches were conducted on 17 December 2018. The search was repeated on 8 July 2020
to identify studies published since the original search date. Search results were de-duplicated to
remove redundant citations identified from multiple sources. All records were reviewed at the title
and abstract level for studies that potentially met the a priori inclusion criteria. In the next step, full-
texts of all records were obtained and assessed by two independent reviewers for eligibility.
Potential discrepancies in screening were resolved by consensus. Following full-article screening,
standardized descriptive data such as bibliographic information and descriptive study metadata,
including sample populations, study type, intervention characteristics, outcome measures, and
narratively summarized key findings were documented for each study. The final analysis consisted
of tabulating and grouping the studies by intervention types. Because of the wide range of
interventions and the variety of methods and study designs considered, study validity assessment
(critical appraisal) was outside the scope of the review. Figure 1 summarizes the study selection
process and indicates the number of articles excluded at each phase of screening.
 INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH 19

Results
Studies on wilderness-therapy interventions
Wilderness therapy programs, also referred to as outdoor behavioral healthcare, utilize the natural
environment, generally in remote areas, as the setting for an intensive therapeutic process under the
direction of skilled leaders. These programs consist primarily of residential programs ranging in
length from a few weeks to several months or longer but also can include shorter intensive periods
of three to 10 days that are incorporated into in-patient hospital, outpatient mental health,
traditional residential treatment, or specialized treatment programs. Components include learning
outdoor skills, hiking extensive distances, overnight camping, being away in remote areas, and
individual and group therapy sessions. There may also be a family component, in which parents
participate in therapy while their child is in care separately or as part of the wilderness therapy
program. Additionally, parents may participate in outdoor activities with their child for a short
period of time. Youth are placed in small groups with 6–8 other youth, with group process, trust,
and cooperation essential components. Programs serve youth with severe mental health, behavioral,
and social difficulties, including substance dependence or abuse. Prior to placement, youth typically
have participated in other types of treatment modalities such as outpatient or inpatient mental
health services which were unsuccessful in remedying the underlying issues (Russell 2001, 2003;
Bettmann et al. 2016; Fernee et al. 2017).
A total of 35 studies of wilderness therapy were identified which included 31 original studies and
four evidence-synthesis reviews. Of the 31 original studies, 18 used quantitative methods, one used
mixed methods, and 12 used qualitative methods (Tables 1 and Table 5). Samples ranged from 14 to
816 in the original quantitative studies and from four to 148 in the original qualitative studies. The
sample of the original mixed methods study was 32 adolescents. In addition to the original
intervention studies, four evidence-synthesis studies met inclusion criteria and consisted of two
meta-analyses (Bettmann et al. 2016; Gillis et al. 2016), one scoping review (Harper 2017), and one
qualitative review (Fernee et al. 2017). The two meta-analyses included 2,399 and 2,667 participants.
The review of qualitative studies examined a total of 102 adolescents.
Ages of youth in the treatment programs ranged from 12 to 34 years of age. In the 31 original
studies, data were obtained from youth in treatment programs (N = 29), parents or caregivers
(N = 9), and/or staff members (N = 3) (Table 1). Most of the studies examined youth in programs
that served males and females, but five studies examined programs exclusively for males (Lambie
et al. 2000; Russell 2000; Gillespie and Allen-Craig 2009; Somervell and Lambie 2009; Margalit and
Ben-Ari 2014) and two studies examined programs exclusively for females (Caulkins et al. 2006;
Pryor et al. 2006). Almost all programs indicated they served youth with severe mental health,
behavioral, and social difficulties, including substance abuse and dependence or focused on specific
groups such as youth who have committed sex offenses or delinquent acts, or experienced trauma.
The original studies took place primarily in the United States (N = 19, Table 1) with other
locations including Australia (N = 3, Pryor et al. 2006; Gillespie and Allen-Craig 2009; McIver et al.
2018), Norway (N = 3, Gabrielsen et al. 2019a, 2019b; Fernee et al. 2020), New Zealand (N = 2,
Lambie et al. 2000; Somervell and Lambie 2009), Canada (N = 1, Harper et al. 2019), Israel (N = 1,
Margalit and Ben-Ari 2014), Ireland (N = 1, Conlon et al. 2018), and the United Kingdom (N = 1,
Paquette and Vitaro 2014). The two quantitative meta-analyses (Bettmann et al. 2016; Gillis et al.
2016) and scoping review (Harper 2017) examined studies exclusively or predominantly from the
United States; the qualitative review article included only studies from the United States (Fernee
et al. 2017) (Table 5).
The majority of the 31 original intervention studies examined stand-alone wilderness therapy
programs (N = 18) that lasted between three and 22 weeks (Table 1). Other studies examined
hiking, camping, or other wilderness components that were integrated into inpatient hospital,
specialized mental health care, or drug treatment programs (N = 5, Berman and Anton 1988; Pryor
et al. 2006; Harper 2017; Gabrielsen et al. 2019a, 2019b; Fernee et al. 2020), residential treatment
 20

Table 1. Original intervention studies on wilderness therapy.

Reference Population Participants Age Country Study design Intervention Outcome measures Results
Quantitative studies
Bandoroff Adolescents with 66 (27 13–18 USA One group repeated 21-day (3-week) Overall program At post-test and 6-weeks
and substance abuse, participating measures (pre, post, wilderness therapy satisfaction, family post, family functioning
Scherer behavioral problems, and 39 non- 6 week post treatment) program followed by functioning, moved from clinical to
(1994) poor school participating with comparison group 4-day wilderness family delinquency, within normal range;
T. A. OVERBEY ET AL.

performance, and families in of nonparticipating therapy program problem behavior, ratings of delinquency
delinquent activity and family therapy families self-concept and problem behavior
their parents component, decreased; and self
65% male, concept improved for
35% female, both groups
90% White)
Berman Adolescents in acute 14 (57% male, 13–17 USA One group pre-post test 1 backpacking trip of 7 or Behavioral, Improvement in locus of
and psychiatric hospitals 43% female) plus some measures at 9 days into wilderness mental well-being, control, treatment plan
Anton with symptoms of discharge from hospital areas locus of control objectives, peer
(1988) impulsive, acting out interaction, behavior,
behaviors, or and mental health
withdrawn, inhibited indicators noted across
behaviors; two groups measures, particularly
of youth appropriate for youth not engaging
for wilderness therapy in aggressive or highly
and experimental distractible behaviors
group with more
severe difficulties
Bettmann Young adults with 157 (65% male, 18–28 USA One group pre-post test 8-week wilderness Attachment, global Improvements across
et al. mental health, 35% female, therapy program, mental health almost all measures
(2017) substances use 95% White) average of 63.5 days, functioning, related to mental
disorder, and multiple range of 28–106 days psychological health, attachment
diagnoses individuation with parents,
interpersonal
relationships, and
symptom distress with
medium to large effect
sizes; many
improvements clinically
significant
(Continued)
Table 1. (Continued).
Reference Population Participants Age Country Study design Intervention Outcome measures Results
Bettmann Adolescents with 41 (34% male, Average: USA One group repeated 8-week wilderness Intrapersonal distress, Improvement in
et al. substance use 66% female, 15.8 measures (pre-post test therapy program with somatic distress, psychological, social,
(2013) disorders, mental 82% White) and 6 month post strong family interpersonal and behavioral
health, and behavioral treatment) component relations, critical functioning with
diagnoses items, social medium to large effect
problems, behavioral sizes; gains maintained
dysfunction or improved at
6-month follow up
social functioning;
reduction in symptoms
Bettmann Adolescents with 96 (62% male, 14–17 USA One group pre-post test 7-week wilderness Attachment Study examined
and oppositional 38% female, therapy program attachment to parents
Tucker defiant disorder, 90% White, 3% including family and peers; mixed
(2011) depression, substance Hispanic, 2% component findings related to
use disorder, Native attachment to parents;
attention-deficit American, 1% differences noted by
/hyperactivity Asian, 4% age and diagnosis
disorder, anxiety Other)
Clark et al. Adolescents with severe 109 (62% male, 13–18 USA One group pre-post test 21-day (3 week) Defense styles, Treatment had impacts on
(2004) mental health and 38% female) (youth pre and post wilderness therapy personality patterns, all dysfunctional
behavioral problems treatment; parents pre program expressed concerns, personality patterns
comparable to those in and 2 months after clinical syndromes, and clinical syndromes
psychiatric hospitals treatment) behavior scales, many with
medium to large effects
Combs Adolescents with 659 (71% male, Average: 16 USA One group repeated 7-week wilderness Interpersonal distress, Youth made
et al. significant levels of 29% female) measures (pre, weeks 3 therapy program somatic symptoms, improvements
(2016) emotional and and 5, and post interpersonal throughout treatment
behavioral treatment and at 6 and relations, critical and were discharged at
dysfunction, especially 18 month post- items, social normal level of
mood, substance treatment) problems, and functioning on
abuse, and anxiety behavioral measures of
disorders dysfunction psychological, social,
and behavioral
functioning;
improvements
maintained at 6 and
INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH

18 months; some
differences noted by
gender
(Continued)
21
 22

Table 1. (Continued).
Reference Population Participants Age Country Study design Intervention Outcome measures Results
Davis- Adolescents in outpatient 23 (65% male, 13–18 USA One group pre-post test 1.5–2 week backpacking Locus of control, self- Improvements in all
T. A. OVERBEY ET AL.

Berman mental health 35% female) trip efficacy, self-esteem, outcome measures
and counseling, with behavior symptoms
Berman family, relationship
(1989) problems,
depression,
anger and impulse
control difficulties
Gabrielsen Adolescents in 33 (30% male, 16–18 Norway One group repeated Half day, full day, and 3– State anxiety Decrease in state anxiety
et al. specialized mental 70% female) measures (data 7 day trips for a total of for majority of
(2019b) health care program collected each day of either 12 or 18 days of participants with
with severe mental final 6–7 day trip) wilderness trips medium effect size; as
health concerns demands of program
including social increased, anxiety
anxiety, depression, levels remained stable
behavioral disorders,
adjustment disorders
and fatigue
Gillespie Adolescents experiencing 19 (100% male) 14–16 Australia One group repeated 5-week program that Resilience Participants’ resilience
and psychosocial and measures (pre, post included simple and 6 of 10 protective
Allen- family difficulties and and during the pioneer living, factors increased with
Craig at risk of significant program) community moderate to large
(2009) mental health involvement, activities, effect sizes
problems and a 10-day
wilderness experience
followed by 2-year
mentoring program
(Continued)
Table 1. (Continued).
Reference Population Participants Age Country Study design Intervention Outcome measures Results
Harper Adolescents with 221 (62% male, 13–18 USA One group repeated 21-day wilderness therapy Family functioning, Improvements in
et al. emotional, behavioral, 38% female, measures (pre, program behavior, mental behavior, mental
(2007) and substance abuse 92% White) 2 months post, and health, school health, social
problems and parents and 124 12 months post) success, social engagement, and
parents engagement school performance;
some decreases in
family functioning
particularly from pre to
2 months post;
medium to large effect
sizes; most changes
maintained at
12 months; some
gender differences
Hoag et al. Young adults with 297 (73% male, 18–34 USA One group repeated Wilderness therapy Subjective discomfort, Improvements in mood,
(2013) substance abuse, 27% female, measures (pre, weeks 3, program of at least interpersonal interpersonal
mood, and other 88% White) 5, and post, with 6 and 5 weeks; average of relationships, social relationships, social
personal difficulties 12 month follow-up) 9.8 weeks role performance, and life skills, and
life skills, cognitive behavioral difficulties
distortions from intake to
discharge and
throughout the
program; large effect
sizes
Johnson Adolescents with trauma 816 (69.2% 13–17 USA One group repeated Trauma-informed Psychological Improvements in family
et al. and stressor-related White, 5.0% measures (pre-post, wilderness therapy functioning, family functioning and
(2020) disorders, reactive African 6 month and 1 year program 10–12 weeks, functioning, psychological
attachment, American, post-treatment) average of 80 days Psychophysiological functioning with large
depressive, and 7.6% Asian, functioning effect sizes at
anxiety disorders; 8.6% Hispanic/ discharge; mixed
substance use; or Latinx, 1.0% results at 6 and
disruptive behavior Native 12 months;
American, improvement in
8.6% other) psychophysiological
and 189 functioning pre to post
INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH

caregivers with small to moderate

effect size
(Continued)
23
 24

Table 1. (Continued).
Reference Population Participants Age Country Study design Intervention Outcome measures Results
Margalit Adolescents from low- 93 (100% male, in 14–16 Israel Non-randomized 12 group sessions that Cognitive autonomy, Improvements in
and income families boarding repeated measures included 10 prep self-efficacy cognitive autonomy
Ben-Ari experiencing behavior, school for design with 3 groups: sessions on outdoor and self-efficacy
(2014) social educational 1.5 years) full program, partial skills, a 4-day compared to controls;
difficulties program, and control backpacking trip, and 2 gains persisted at
group (pre, post, and closure meetings (full 5 months
5 month follow up) program) or
T. A. OVERBEY ET AL.

participation in prep
sessions only (partial
program)
Paquette Adolescents and young 220 (87% male, 16–30 UK One group repeated Wilderness therapy Antisociality, Improvements in
and adults on probation or 13% female) (majority measures (pre-post 3 program of either 8– interpersonal skills, behavior and socio-
Vitaro ordered to do under and 6 months after 10 days or 17–20 days accomplishment professional status
(2014) community service 25 years of treatment) motivation, socio- (employment, school
work age) professional status attendance, or
volunteering),
interpersonal skills with
larger effect size for
longer program. Gains
maintained or
improved 3–6 months
post treatment;
improvements in
interpersonal skills and
achievement
motivation from pre to
post with larger effect
size for longer program
Roberts Young adults with mood 186 (82% male, 18–32 USA One group repeated Outdoor behavioral Psychosocial Improvements in overall
et al. disorders, substance 18% female) (majority measures (pre, weeks 3 health program functioning, psychosocial
(2017) use disorder, anxiety 18–23) and 5 during the between 5 and symptom distress, functioning, symptom
disorder, pervasive program, post, and 6 22 weeks with an interpersonal distress, interpersonal
development, and 18 months post- average of 10 weeks relationships, social relationships, and
behavior and treatment) role performance social role performance
attachment disorders from pre to post with
gains maintained at 6
and 18 months post-
treatment
(Continued)
Table 1. (Continued).
Reference Population Participants Age Country Study design Intervention Outcome measures Results
Russell Adolescents with 523 (69% male, 16–18 USA One group repeated 7 outdoor behavioral Interpersonal distress, Improvements in
(2003) a variety of disorders 31% female), measures (pre, post, health programs somatic symptoms, psychological, social,
including oppositional 372 parents and 12-month post 3 weeks, 6 weeks, interpersonal and behavioral
defiant, substance use, treatment) 8 weeks, or 24 weeks; relations, critical functioning; outcomes
and depression average of 45 days items, social maintained or
problems, and improved at
behavioral 12 months;
dysfunction improvements across
all groups and
treatment lengths
particularly for longer
treatment program;
some differences based
on age of youth
Tucker Adolescents with mental 516 (70% male, 13–18 USA One group pre-post test Wilderness therapy Interpersonal distress, Improvements in healthy
et al. health, substance 30% female, program average of somatic symptoms, weight, body mass, and
(2016) abuse, and behavioral 79% White, 7% 79.8 days interpersonal psychological, social,
disorders Hispanic, 2% relations, critical and behavioral
Asian, 1% items, social functioning
African problems, and
American, 1% behavioral
Native dysfunction, body
American, 10% mass index
Other)
Mixed-methods studies
Gabrielsen Adolescents participating 32 (34% male, 16–18 Norway One group repeated Eight single days and 2 State anxiety Few changes on
et al. in a specialized mental 66% female) measures (pre-post and overnight trips of 3 and numerous mental
(2019a) health care program 12-month post 6 days within an 8–10- health measures pre to
diagnosed with treatment); participant week period post but more
depression, social observation and semi- differences from pre to
anxiety, behavioral structured interviews 12 months follow up.
disturbance, with participants within Participants reported
adjustment disorders, 6 weeks post treatment varying degrees of
mental fatigue or at 12 month follow change; benefits were
up not immediately
apparent to
INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH

participants and may

take time to process
Qualitative studies
(Continued)
25
 26

Table 1. (Continued).
Reference Population Participants Age Country Study design Intervention Outcome measures Results
Caulkins Adolescents with a range 6 (100% female) 15–16 USA Participant observation, 6–12-week wilderness General impacts Study examined impacts
et al. of psychological document analysis, and therapy program (reflection, perceived of backpacking
(2006) symptoms including semi-structured competence, component which
clinical depression, interviews with accomplishment), included reflection,
T. A. OVERBEY ET AL.

suicidal, received participants and staff substantive impacts perceived competence,

treatment previously shortly before end of (self-efficacy, sense of
program awareness, accomplishment, and
timelessness) an increase in self-
efficacy, and awareness
of self, others, and
surroundings
Conlon Adolescents in foster care 11 (90% male, 12.7–18.4 Ireland Semi-structured Wilderness experiences Social skills, self Participants reported
et al. and referred from the 10% female) interviews with incorporated into other development, anger increases in social skills,
(2018) care system, participants at end of therapeutic management, trust, self-esteem, self-
immediate residential program programming; 1 life changes efficacy, anger
care, or mental health full day per week of management, and
professionals and not outdoor activities and more positive world
experiencing overnight camping views
substance abuse trips every other week;
problems participation ranged
from 3 days to
10 months with an
average of 5.3 months
Fernee Adolescents with mental 10 (60% female, 16–18 Norway Semi-structured 10-week program that Mood, emotional Participants continued to
et al. health diagnoses that 40% male) interviews with included 8 single day regulation, self- use nature as a remedy
(2020) included anxiety, participants 12 months and two overnight trips acceptance, self- and reported
depression, post- post treatment of 3 and 6 days confidence, and improvements in
traumatic stress duration incorporated social interaction mood, emotional
disorder, and chronic into hospital outpatient regulation, self-
fatigue and had one or mental health program acceptance, self-
more adverse confidence, and social
childhood experiences interaction
(Continued)
Table 1. (Continued).
Reference Population Participants Age Country Study design Intervention Outcome measures Results
Harper Adolescents in residential 148 (67% male, 13–19 Canada Analysis of written Wilderness therapy Psychosocial skills, hard Youth perceived
et al. treatment with 33% female) surveys completed by component of 6– skills, self-efficacy, improvement in
(2019) addictive behavior, participants after 9 weeks followed by perspective, self- psychosocial well-
mental health issues, wilderness experience 8 months in residential esteem, Physical and being, communication,
and behavioral treatment program mental leadership, emotional
difficulties improvements regulation, physical
health, sobriety,
outdoor skills, and
increases in self-esteem
and self-efficacy
Lambie Adolescents who had 14 (100% male) 13–19 New Semi-structured 1–2 year community Social relationships; Youth reported the ability
et al. committed sexual and 12 parents Zealand interviews after treatment program empathy; cognitive to avoid high-risk
(2000) offenses completion of program with 3 wilderness distortions, safety situations, taking
with participants and experiences of 10 days plans, coping with responsibility for
parents; examination of total throughout the high-risk situations, behavior, victim
child protective service program; family offending cycle empathy, appropriate
records therapy and follow up behavior, perceived social relationships,
therapy for up to level of risk, and improvement in
18 months post intimacy, sexual self-esteem; none had
treatment relationships reoffended two years
post-treatment
Liermann Adolescents with poor 9 (primarily Not USA Pre and post 28-day wilderness Communication, trust, Reported improvement in
and family relationships White) provided questionnaires program and 3-day course components family relationships,
Norton and high-risk (1 month prior and parent/guardian communication, and
(2016) behaviors 1 week and 6 months seminar at the end trust
post treatment) and
telephone interviews
with parents 3 months
post treatment
McIver Young adults recovering 19 and 9 staff 18–25 Australia Semi-structured 9–11 wilderness program Relationship to staff, Youth reported an
et al. from significant members (58% interviews with sessions including self, nature, peers increased awareness of
(2018) mental health female, 42% participants and staff 3-day trip for youth in self and peers, self-
conditions male) 10 days after final 12-month residential confidence, self-
session treatment and esteem, healthier
INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH

community program behaviors

(Continued)
27
 28

Table 1. (Continued).
Reference Population Participants Age Country Study design Intervention Outcome measures Results
Pryor et al. Young adults in a drug 7 (100% female) 17–24 Australia Semi-structured 6-week program with 12- Contextual issues, Participants reported
(2006) treatment intervention interviews with day wilderness trip physical health, improvements in
program and who had participants pre and drug/alcohol misuse, physical and mental
experienced adverse post wilderness trip, mental health, social health, social
childhood events, self- and at end of 6-week connection, relationships, social
harm, and mental program economic skills, economic
T. A. OVERBEY ET AL.

health difficulties participation participation, more

positive body image,
greater resiliency, less
risk taking, less drug
and alcohol abuse and
better stability of
treatment; better
management of mental
health symptoms
Russell Adolescents with 4 (100% male) Not USA Client case studies 4 different wilderness Family relationships, Participants reported
(2000) substance use and their provided consisting of therapy programs abstinence, better relationships
dependency and parents participant ranging from 21– academic with family, abstinence
mental health observation, interviews 52 days achievements from alcohol and drugs,
disorders and focus groups with and desire to complete
staff, interviews with school; Some relapse
participants was noted at 4 months
immediately after
treatment and
interviews with
participants and
parents at 4 months
post treatment
Russell Adolescents with 47 (67% male, 16–18 USA Semi-structured 7 outdoor behavioral Well-being, program Almost all felt the
(2005) a variety of disorders 33% female) interviews with health programs effectiveness, family program was effective;
including oppositional and 88 parents participants and 3 weeks, 6, weeks, communication, the majority of youth
defiant, substance use, parents 24 months post 8 weeks, or 180 days; school were doing well but
and depression treatment average of 45 days had transitional
difficulties post-
treatment especially
with friends and
substance abuse
(Continued)
Table 1. (Continued).
Reference Population Participants Age Country Study design Intervention Outcome measures Results
Russell and Adolescents with severe 12 and parents 13–17 USA Client case studies 4 wilderness therapy Relationships with Participants reported
Phillips- behavioral problems and staff consisting of programs, average of counselors, peer program was effective
Miller participant observation 38 days dynamic, facilitated in helping to motivate
(2002) and interviews post- reflection on life, behavioral change,
treatment challenge and desire to abstain from
structure of process, substance use, and self-
behavioral improvement; increase
awareness, in self-confidence and
abstinence, self esteem
becoming better
person
Somervell Adolescents from various 7 (100% male) 13–18 Not Participant observation, Wilderness therapy Enhanced relationships, Participants reported
and cultural backgrounds and 4 provided semi-structured experience of 4–6 days view of self, intensity enhanced relationships
Lambie who have committed therapists interviews on 2–3 occasions of the experience, with peers and a more
(2009) sexual offenses and incorporated into 12– disclosure positive view of self
were living with 24-month community-
family/whānau, in based sexual offender
foster care, or in program
residential treatment
INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH
29
30 T. A. OVERBEY ET AL.

programs (N = 3, Gillespie and Allen-Craig 2009; McIver et al. 2018; Harper et al. 2019), outpatient
counseling (N = 1, Davis-Berman and Berman 1989), boarding schools (N = 1, Margalit and Ben-
Ari 2014), or foster care, community-based treatment programs or other types of therapeutic care
(N = 3, Lambie et al. 2000; Somervell and Lambie 2009; Conlon et al. 2018). These experiences
lasted a total of four to 20 days over an extended period of time.
The 18 original quantitative (Table 1) and one original mixed methods studies (Gabrielsen et al.
2019a) used well-established measures and repeated measures designs to assess psychological,
social, and behavioral functioning from pre to post treatment, as well as family functioning
(N = 5, Bandoroff and Scherer 1994; Russell 2000, 2005; Harper et al. 2007; Johnson et al. 2020),
attachment to parents (N = 2, Bettmann and Tucker 2011; Bettmann et al. 2017) and body mass
index and weight (N = 1, Tucker et al. 2016). Measures such as the Youth Outcome Questionnaire
or Youth Outcome Questionnaire-Self Report (Burlingame et al. 2004) have indicators of clinical
significance that allow for differentiating clinical and non-clinical samples. Thus, clinical as well as
statistical significance was often reported.
Overall, positive change was indicated across studies on a broad range of measures from pre to
post treatment that included symptom distress, self-esteem, self-efficacy, locus of control, pro­
blem behaviors, substance use, social interaction, school attendance, recidivism, and other
psychosocial and well-being indicators, often with medium to large effect sizes (Table 1).
Additionally, positive change was maintained upon completion of treatment to later follow up
periods ranging from six weeks to 18 months later (N = 12, Bandoroff and Scherer 1994; Russell
2003; Clark et al. 2004; Harper et al. 2007; Bettmann et al. 2013; Hoag et al. 2013; Margalit and
Ben-Ari 2014; Paquette and Vitaro 2014; Combs et al. 2016; Roberts et al. 2017; Gabrielsen et al.
2019a; Johnson et al. 2020). Change was often noted by t-tests with more recent use of regression
analysis and hierarchical linear modeling (Paquette and Vitaro 2014; Combs et al. 2016; Bettmann
et al. 2017; Roberts et al. 2017; Johnson et al. 2020). Some studies included analyses by gender,
age, or diagnosis with mixed program impact findings based on subgroup (Berman and Anton
1988; Russell 2003; Harper et al. 2007; Bettmann and Tucker 2011; Combs et al. 2016). Findings
were also mixed on measures of family functioning or attachment to parents (Harper et al. 2007;
Bettmann and Tucker 2011).
The 12 qualitative studies (Table 1) all utilized interviews with participants with the exception of
one study that analyzed open-ended survey responses (Harper et al. 2019) and one study that
interviewed parents only (Liermann and Norton 2016). Additionally, five studies used participant
observation, focus groups, and document analysis along with interviews (Lambie et al. 2000; Russell
2000; Russell and Phillips-Miller 2002; Caulkins et al. 2006; Somervell and Lambie 2009). These
methods were used to gain greater insights into the treatment process, including beneficial
components, allowing youth a greater voice in outcomes assessment, and gaining multiple per­
spectives from youth, parents, and staff. Four studies included interviews with parents (Lambie et al.
2000; Russell 2000, 2005; Liermann and Norton 2016) and three studies included interviews with
staff (Russell 2000; Caulkins et al. 2006; McIver et al. 2018).
Most interviews were done immediately at post-treatment with five studies conducting inter­
views at three to 24 months post-treatment (Russell 2000, 2005; Pryor et al. 2006; Liermann and
Norton 2016; Fernee et al. 2020). The studies examined impacts from participation in the wilderness
therapy program as a whole, although one study specifically examined the family therapy compo­
nent (Liermann and Norton 2016) and one study examined the backpacking component (Caulkins
et al. 2006).
Confirming the quantitative studies, the qualitative research noted positive impacts on a range of
psychological, social, and behavioral outcomes, as well as relationships with parents and peers. Most
gains were maintained post treatment. Going beyond the insights gained from quantitative studies,
two qualitative studies, and the qualitative component of the mixed methods study (Gabrielsen et al.
2019a) noted transition difficulties after treatment and youth needing more time to process the
changes that occurred through treatment (Russell 2000, 2005). Also unique to qualitative research,
 INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH 31

most of these studies included discussion of key components of wilderness therapy that contributed
to positive outcomes, such as the role of nature, peer and staff relationships, being in a new
environment, physical rigors, and other challenges.

Studies on animal-assisted interventions

Animal-assisted interventions represent a broad category of structured interventions that include or
incorporate animals in health, education and human services with the goal of reaching therapeutic
gains in humans (IAHAIO 2018). Animal-assistant interventions are aimed at improving beha­
vioral, social, emotional, cognitive or physical functioning and typically include defined goals and
measured outcomes (Maber-Aleksandrowicz et al. 2016). Of the 37 studies on animal-assisted
therapy, 29 are original intervention studies with 15 quantitative, five mixed-methods, and nine
qualitative designs (Table 2). An additional eight studies present evidence-synthesis studies,
including four systematic reviews (Maber-Aleksandrowicz et al. 2016; Hoagwood et al. 2017;
Jones et al. 2019; White et al. 2020), two literature reviews (Lentini and Knox 2015; May et al.
2016), one meta-analysis (Wilkie et al. 2016) and one systematic map (McDaniel Peters and Wood
2017) (Table 5).
The sample ranged from 29 to 138 participants in the 15 original quantitative studies (Table
2); the one meta-analysis examined 377 children and adolescents. The sample of the original
mixed methods studies ranged from seven to 28 study participants and the sample size of the
qualitative studies ranged from five to 80 children and adolescents. Ages of study participants
ranged from two to 22 years of age. Most of the 37 studies on animal-assisted therapy examined
male and female participants; four studies focused on males (Mallon 1994; Conniff et al. 2005;
Williams and Metz 2014; Boshoff et al. 2015; Hemingway et al. 2015) and three studies focused
on female children and adolescents (Conniff et al. 2005; Carlsson et al. 2015; Carlsson 2018;
Naste et al. 2018). Overall, the majority of this literature examined youth with mental health
difficulties, including several studies that focus on populations with specific conditions, such as
autism, post-traumatic stress syndrome, and attention deficit hyperactivity disorder. Many of the
37 studies targeted specific samples, such as children and adolescents in foster care, adolescents
living in residential care, incarcerated adolescents, and hospitalized children and adolescents.
The majority of the 37 studies examined equine-facilitated interventions (N = 23), followed by
canine-facilitated interventions (N = 11) involving trained therapy dogs and pets or shelter animals.
Three studies involved farm animals. The activities consisted of structured sessions offered over
period of nine to 12 weeks with weekly sessions between 60 and 180 minutes with few original
studies describing interventions with durations longer than three months (N = 3, Burgon 2011,
2013; Bachi et al. 2012). Six evidence-based synthesis studies include interventions longer than three
months with the longest being 18 months (Maujean et al. 2013; Kemp et al. 2014; Saggers and
Strachan 2016; Tsantefski et al. 2017; Dunlop and Tsantefski 2018). Studies are located primarily in
the USA (N = 14), Australia (N = 5, Maujean et al. 2013; Kemp et al. 2014; Saggers and Strachan
2016; Tsantefski et al. 2017; Dunlop and Tsantefski 2018), and European countries (N = 8, Burgon
2011, 2013; Balluerka et al. 2014, 2015; Carlsson et al. 2015; Hemingway et al. 2015; Stefanini et al.
2015, 2016; Muela et al. 2017; Carlsson 2018).
Key findings of the 37 studies addressed psychological, social, and behavioral outcomes. Studies
that examined psychological outcomes addressed these at different levels. The literature indicated
the associations of animal-assisted interventions with global psychological measures, especially
stronger psychological well-being, better internal regulation and cognitive functioning, higher
emotional states, fewer emotional problems, and lower levels of post-traumatic stress disorders.
With regard to individual differences measures, animal-assisted interventions were associated with
several personality measures, including higher levels of self-image, self-control, trust, self-
confidence, self-esteem and self-efficacy, as well as measures of life satisfaction, calmness, and
32 T. A. OVERBEY ET AL.

feeling of safety. Additionally, the studies documented the association of animal-assisted interven­
tions with lower levels of mental health disorders, such as irritability, self-stigmatization, anxiety,
and depression, as well as better management of emotions, especially anger and fear.
Social outcome measures that were found to be related to animal-assisted interventions included
global measures of better overall social functioning and higher levels of social cognition. In
addition, the research documented the association of animal-assisted interventions with interper­
sonal skills in social interaction, including empathy, respect, humor, and patience in treating others.
Studies also reported higher engagement, bonding, attachment formation, helping others, and steps
toward taking leadership. A number of studies pointed to communication-related outcomes, such
as use of communication strategies and better coping with teasing and bullying.
Behavior-related outcome measures that were found to be related to animal-assisted interven­
tions included global constructs of a lower number of negative, disruptive, and difficult behaviors,
lesser behavioral dysregulation and hyperactivity. A positive association of animal-assisted inter­
ventions and attendance of school and treatment sessions was also reported.

Studies on care farming interventions

Care farming interventions, also described in the literature as social farming or green care farming
interventions, are provided primarily through agricultural farms and landscapes. They utilize
structured programs of farming-related activities to deliver health, social, and educational services
to adolescents and young adults (Sempik and Bragg 2013; Murray et al. 2019). Care farms typically
complement traditional social support services. Well established in many European countries
(Hassink and Van Dijk 2006; Hassink et al. 2014), adolescent-focused care farming interventions
vary markedly based on the type of farming enterprise, farming activities involved, support services
provided, service user groups engaged, and other factors (for examples of care farming programs,
see Murray et al. 2019). While overlapping in some aspects, the farming component of care farms
typically involves a broader range of activities than the more narrowly focused horticultural- and
animal-based therapy interventions (Murray et al. 2019), distinguishing care farming interventions
and characterizes the related literature.
Four studies in the final dataset investigate adolescent-focused care farming interventions based
on our inclusion criteria. Three studies are original research located in Europe (Kogstad et al. 2014;
Schreuder et al. 2014; Leck et al. 2015, Table 3). Of those three studies, two studies employed
a qualitative, semi-structured interview methodology to retrospectively analyze experiences and
observations and semi-structured interviews (Kogstad et al. 2014; Schreuder et al. 2014). The third
study used a mixed-method design included 216 baseline and 137 follow-up survey responses as
well as 33 semi-structured interviews with a subsample of survey respondents (Leck et al. 2015).
Adolescents struggling in mainstream education comprised the principal subpopulation (N = 30).
In addition to the three original intervention studies, the fourth study in this sample was
a systematic review, which assessed studies based on a logic model that examined the studies’
settings, intervention components, mechanisms linked to theoretical concepts, proximal outcomes,
and outcomes (Murray et al. 2019, Table 5). Four studies on disaffected adolescents were included
in the systematic review, including the above three studies.
The two qualitative studies had nine and 11 study participants (Kogstad et al. 2014; Schreuder
et al. 2014), the mixed methods study had 30 study participants (Leck et al. 2015), and the
systematic review included studies with a total of 112 children and adolescents (Murray et al.
2019). The care farming interventions with residential programs varied in length from about three
months to over a year, where this information is provided.
Key findings across the three original intervention studies point to three main components of
successful care farming. The first component is the farm setting, the farmer, and the farming
environment that is conducive to recovery. The second effective component is the variety of tasks
and the environmental engagement that allow for a gradual increase in adolescents’ self-efficacy.
Table 2. Original intervention studies on animal-assisted interventions.
Reference Population Participants Age Country Study design Intervention Outcome measures Results
Quantitative studies
Bachi et al. (2012) Adolescents with severe 29 14–18 Israel Controlled trial, pre- Equine-facilitated Self-image, self-control, Data indicate no significant
personal and post test, one year psychotherapy, weekly trust, life satisfaction effects but showed trends of
adaptive needs in follow up sessions (50 min) for positive effects on all
residential treatment 7 months (14–26 sessions outcome measures
facility in total)
Balluerka et al. Adolesents with 46 (30% female, 12–17 Spain Controlled trial, pre- Animal-assisted Attachment (secure, Data indicate increase in secure
(2014) childhood trauma 70% male) post test psychotherapy with dogs preoccupied, avoidant, attachment and decrease in
and mental health and horses at a local farm, disorganized preoccupied attachment
problems additional guided attachment), family (high effect sizes) but no
(behavioral, interactions with cats and functioning significant differences in
depressive, anxiety other farm animals, 2 other attachment
disorders) in consequtive days with dimensions
residential care overnight stay for
12 weeks (34 sessions in
total)
Balluerka et al. Adolesents with 63 (38% female, 12–17 Spain Controlled trial, pre- Animal-assisted Psychosocial adaptation Data indicate increase in school
(2015) childhood trauma 62% male, post test psychotherapy with dogs (clinical symptoms, adjustment and
and mental health 68% from and horses at a local farm, personal adjustment, improvement of social skills
problems (behavioral Basque additional guided adaptive skills, and and leadership, decrease in
and anxiety Country, 32% interactions with cats and school adjustment) hyperactive behavior and
disorders) in migrants other farm animals, 2 less attention problems but
residential care from consequtive days with no significant differences in
Northern overnight stay for other clinical symptoms or
Africa) 12 weeks (34 sessions in personal adjustment scores
total)
Boshoff et al. (2015) Adolesents in treatment 39 (100% male, 14–18 South Controlled trial, pre- Equine-assisted therapy, 8 Subjective well-being, Data show modest
at youth care facility 69% Black, Africa post test sessions in total, no coping (problem improvements in
for problem 31% White) further details reported focused, emotion psychological wellbeing,
behaviour focused, dysfunctional including improved
coping) subjective wellbeing,
problem-focused and socio-
emotion-focused coping
but no effect on
dysfunctional coping
INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH

(Continued)
33
 34

Table 2. (Continued).
Reference Population Participants Age Country Study design Intervention Outcome measures Results
Gabriels et al. (2015) Children and adolesents 116 (87% male, 6–16 USA Randomized Therapeutic horseback Irritability, hyperactivity, Data indicate significant
with Autism 13% female, controlled trial, riding, weekly sessions (45 social cognition, social improvements in all
Spectrum Disorder 18% Hispanic pre-post test + min) for 10 weeks communication measures
79% White,
3%
Indigenous,
3% Asian, 1%
T. A. OVERBEY ET AL.

Black, 10%
Multiracial
and other)
Hartwig (2017) Children and adolesents 29 (55% female, 10–18 USA Randomized Canine-assisted therapy, Anxiety, depression, Data indicate significant
in treatment at 45% male; controlled trial, weekly sessions (50 min) disruptive behavior, self- decrease in anxiety,
community 45% White, pre-post test for 10 weeks (10 sessions concept, anger depression, and disruptive
counseling clinic for 38% in total) behavior for both treatment
grief, loss, anxiety, Hispanic, 7% and comparison groups but
depression, and self- African- no significant change in
concept issues American, self-concept and anger
10% Other)
Kemp et al. (2014) Children and adolesents 30 (80% female, 8–17 Australia Controlled trial, pre- Equine facilitated therapy, Trauma symptoms, Data showed improved state of
experiencing sexual- 20% male, post test weekly sessions (90 min) psychopathology, psychological distress and
and/or physical 27% for 9–10 weeks depression, behavior, depression for all gender
abuse Indigenous, anxiety and age groups
63% Non-
indigenous)
Muela et al. (2017) Adolescents with 87 (39% female, 12–17 Spain Randomized Equine-facilitated Clinical symptoms, personal Data suggests improvements
mental health 41% male) controlled trial, psychotherapy, 34 adjustment, and in depression and sense of
problems and pre-post test sessions, no further details adaptive skills inadequacy but
childhood trauma in provided improvements in social skills
residental care and positive attitides
toward teachers were not
significant
Mueller and Children and adolesents 54 (83% male, 10–18 USA Randomized Equine-facilitated Intrusion, avoidance, Findings indicate that
McCullough with post-traumatic 17% female) controlled trial, psychotherapy, weekly arousal symptoms intervention may be an
(2017) stress syndroms pre-post test sessions (120 min) for associated with post- effective additional
10 weeks traumatic stress, human- treatment modality but not
animal bonding significant more effective
than traditional therapeutic
services
(Continued)
Table 2. (Continued).
Reference Population Participants Age Country Study design Intervention Outcome measures Results
Seivert et al. (2018) Incarcerated youth with 138 (70% male, 13–18 USA Randomized Animal-assisted therapy as Internalizing (depression, No significant increase in
psychological 30% female; controlled trial, experiental learning with anxiety, and empathy, impact on
disorders and 46% White, pre-post test shelter dogs in detention somatization), behavioral problems was
psychiatric 44% Black, facility, twice weekly externalizing inconslusive
diagnoses 4% Hispanic, sessions (120 min) for (aggression, conduct
6% Other) 10 weeks problems, and
hyperactivity/
impulsivity) behaviors,
emphathy
Stefanini et al. Children and adolesents 34 (53% male, 11–17 Italy Randomized Animal-assisted therapy with Global functioning, hospital Results show significant
(2015) hospitalized with 47% female) controlled trial, dogs, conducted in care format, school improvements in global
acute mental pre-post test hospital garden, weekly attendance, observation functioning, reduction in
disorders sessions (45 min) for of animal-assisted hospital care format, and
3 months (10 sessions in therapy increase in school
total) attendance
Stefanini et al. Children and adolesents 40 (45% male, 11–17 Italy Randomized Animal-assisted therapy with Global functioning, Results indicate decrease in
(2016) hospitalized with 55% female) controlled trial, dogs, conducted in tnternalizing and internalizing symptoms and
acute mental pre-post test hospital garden, weekly externalizing behavior increase in total
disorders sessions (45 min) for competence, and
3 months (10 sessions in improvements in global
total) functioning
Trotter et al. (2008) Children with high risk 164 (67% male, Grades 3–8 USA Non-randomized trial, Equine-assisted counselling Global functioning, Results indicate significant
for academic and/or 33% female, pre-post test at a horse ranch, weekly psychosocial behavior improvements, with
social failure 83% White, sessions (120 min) for increases in positive
7% African- 12 weeks behaviors and decreases in
American, 7% negative behaviors
Hispanic, 3%
Others)
Trujillo et al. (2020) Adolesents with 31 (65% male, 12–17 USA Quasi-experimental Animal-assisted therapy with Treatment participation, Data indicate intervention
psychiatric and 35% female, design, pre-post therapy dogs, weekly clinical outcomes (overall increased attendance of
substance use 94% test sessions for 12 weeks well-being, school substance use treatment
disorders Hispanic, 3% engagement), sobriety sessions and overall
Black, 3% wellbeing
White)
Tsantefski et al. Children exposed to 41 (58% female, 7–13 Australia Non-randomized trial, Equine-assisted therapy, Child behavior (prosocial, Data indicate a significant
(2017) parental substance 42% male) pre-post test, weekly sessions (120 min) hyperactivity, conduct decrease in difficult
abuse survey for 12 weeks disorder, emotional behaviors, emotional
INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH

sensitivity, peer problem problems, and hyperactivity

behaviour)
Mixed-methods studies
(Continued)
35
 36

Table 2. (Continued).
Reference Population Participants Age Country Study design Intervention Outcome measures Results
Conniff et al. (2005) Adolesents with 23 (100% 13–17 USA Randomized Unstructured animal-assisted Global behavior (anxiety, No significant differences on
conduct disorders at female, 48% controlled trial, activies (pet visitation depression, somatic behavior or emotional state
medium secure White, 35% pre-post test, program) within complaints, social but positive evaluation of
residential facility African survey (qualitative) residential facility, weekly problems, thought program by participants
American, sessions (60 min) for problems, attention
17% Other) 8 weeks problems, rule-breaking
T. A. OVERBEY ET AL.

behavior, aggressive
behavior
Ewing et al. (2007) Youth with emotional 28 10–13 USA Pre-post test, case Equine-facilitated Self-esteem, Quantitative results indicate no
disorders, behavioral study psychotherapy, twice empathy, locus of control, significant effects on self-
conduct disorders, weekly sessions (120 min) depression, loneliness estem, empathy, internal
learning disabilities for 9 weeks locus of control, and
feelings of depression and
loneliness but case studies
results indicate positive
changes
Hanselman (2001) Adolescents with 7 (100% White) 14–17 USA Pre-post test, Pet therapy with dogs, State and trait of anger, Data indicate significant
emotional, observational weekly sessions for human-animal bonding, decrease in state and trait of
behavioral disorders study 12 weeks mood, depression anger, increase in animal
bonding, tension, confusion,
anger and depression;
observations indicate
significant positive
behavioral change and
acceleration in therapy
Naste et al. (2018) Youth with complex 3 (100% female) 10–13 USA Empirically-driven Equine-facilitated Biological regulation, affect Study results indicate evidence
trauma exposure clinical case study psychotherapy for regulation, dissociation, of reduced internalizing
(observational complex trauma, varied behavioral control, problems, improved
study), length of times cognition, self-concept, interpersonal skills,
longitudinal data attachment, post- communication strategies,
traumatic stress and overall social
symptoms, functioning, also improved
dysregulation, internal regulation and
depression, somatic organization, cognitive
awareness, alexithymia functioning, development
of positive coping skills
(Continued)
Table 2. (Continued).
Reference Population Participants Age Country Study design Intervention Outcome measures Results
Perkins (2018) Adolesents in foster 7 (86% female, No information USA Pre-post test, Equine-assisted learning, Engagement, confidence, Results suggests
care, living in 14% male; provided observational data weekly sessions (45 min) respect, communication, improvements in emotional
a group home 86% White, for 8 weeks work ethic regulation, communication,
14% African- confidence, and respect,
American) indicating intervention
contributes to development
of specific life skills
Qualitative studies
Burgon (2011, 2013) Adolesents and young 7 11–21 UK Ethnographic case Equine-assisted therapy and Confidence and self-esteem, Results indicate psychosocial
adults displaying study, semi- learning, participants sense of mastery and benefits, including
complex social, structured and enroll into program for self-efficacy, empathy, improvements in
emotional, and unstructured open periods up to 2 years with opportunities confidence, self-esteem,
behavioural coping interviews weekly or bi-weekly self-efficacy, emphathy, and
strategies, including sessions opening of positive
attention deficit, opportunities
hyperactivity, autistic
spectrum diagnosis
Carlsson et al. Adolesents and young 9 (100% female) 15–21 Sweden Observational case Equine-assisted social work, Doing & performing and Data suggests positive effects
(2015); Carlsson adults in residential study, semi- weekly sessions (40– being & feeling with the in countering self-
(2018) care, self-harming structured 90 min), no further details horse as an object/ stigmatisation and lowering
interviews provided subject barriers to change
Dunlop and Children experiencing 33 (55% female, 7–13 Australia Semi-structured Equine-assisted group Safety and security, Results suggests that
Tsantefski (2018) problematic parental 45% male) interviews at therapy, weekly sessions personal and social participants experience
substance use and conclusion of (120 min) for 9 weeks development a sense of safety, feeling
adverse family program understood, and having
events a sense of the horses’
behaviour as predictable
and therefore manageable;
participants also reported
developing mastery over
fears, feeling good about
their new ways of treating
others.
Hemingway et al. Young adults 20 (100% male) 18–21 UK Semi-structured Equine-facilitated learning, 7 Calm assertivness, Results indicate that
(2015) incarcerated with interviews, sessions (150 min) over confidence, focus, participants felt that they
disruptive behavior observational a 4-day period practicality, facilitation developed and increased
and disengaged study (start and confidence, control of body
INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH

end sessions) language, and

communication with horses
(Continued)
37
Table 2. (Continued).
38

Reference Population Participants Age Country Study design Intervention Outcome measures Results
Lange et al. (2007) Adolescents 5 13–16 USA Explorative study, Animal-assisted therarpy Calming, humor relief, Results indicate beneficial
participaing in anger semi-structured with a dog, no further safety, empathy effects, including calming
management group interviews details provided state, humor relief, feelings
of safety, experiencing
empathy, and motivation to
complete program
Mallon (1994) Children and adolesents 80 (mostly male) 7–16 USA Exploratory study Animal-assisted therarpy Healing and therapetic Results indicate that
with behavioral, with farm animals effects, animals as intervention has positive
emotional and metapher, comfort/ impact on behavioral and
T. A. OVERBEY ET AL.

academic difficulties nurturing responses, emotional state

in residental communication, abuse/
treatment center aggression
(farm)
Maujean et al. Disengaged children 16 (69% male, 12–22 Australia Pilot study, semi- Equine-facilitated Enjoyment, psychological Results indicate positive
(2013) and adolescents 31% female) structured psychotherapy, weekly and social benefits, improvements in
interviews, pre- sessions for 10 weeks engagement, psychosocial outcomes,
post transferable skills, including developing of life
mechanisms of change skills, confidence and
engagement, suggesting
that treatment may provide
alternative to traditional
interventions
Saggers and Primary school students 11 (55% female, 10–13 Australia Explorative study, Equine-facilitated social- Horsemanship, developing Results suggests positive
Strachan (2016) at risk of school 45% male) semi-structured emotional learning, resilience impact on improving social-
failure interviews, pre- weekly sessions for emotional wellbeing and
post 8 weeks developing resilience,
including gaining
confidence, developing
communication skills,
coping with teasing and
bullying, learning to relax
and manage stress, and
developing attending skills
and task perseverance
Williams and Metz Adolescents in 5 (100% male) 15–17 USA Photovoice study, Animal-assistant intervention Gaining patience, Results suggest possible
(2014) residential care semi-structured involving training rescue attachment, wanting to therapeutic benefits; six
interviews and dogs, twice-weekly better themselves, themes emerged, inlcuding
focus groups (120 min) seesions for helping others, teaching, gaining patience, forming
12 weeks relating to the animal an attachment, wanting to
better themselves, helping
others, teaching, and
relating to the animal
 INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH 39

Experiences with farm animals provide comfort for adolescents lacking trust in people and life in
nature to recover a positive sense of self. The role of routine in farming provides structure to the
recovery of adolescents. Third, successful interventions provide opportunity for personal develop­
ment and the development of social interactions to improve physical and mental health and well-
being. The systematic review pointed specifically to the findings that care farming increased the
quality of life and decreased depression and anxiety for disaffected youth (Murray et al. 2019). The
three original studies and the single evidence-synthesis study indicate weak associations between
mechanism and outcomes and point to the need for robust analysis of the pathways through which
care farming interventions affect the proposed outcomes.

Studies on gardening and horticulture-based interventions

Gardening and horticulture-based interventions examine whether programs that teach gardening
and horticulture skills, for example, how to grow and maintain a community garden, are associated
with youth’s mental, psychological, and behavioral health. We identified six studies, including five
original intervention studies (Table 4) and one literature review (Table 5). Three of the original
studies used mixed-method approaches (Twill et al. 2011; Sonti et al. 2016; Chiumento et al. 2018)
and two used qualitative designs (Allen et al. 2008; Delia and Krasny 2018). The sample sizes in the
mixed-methods studies ranged from nine to 50 study participants. The samples in these studies
included males and females, where reported. The ages ranged from six to 25 years, with four of the
studies focusing on specific age groups, including age ranges of up to seven years. The single
evidence-synthesis study was a literature review that summarized 133 studies, but did not list
sample sizes of the individual studies; demographic information is provided in summary statistics
(Park et al. 2016, Table 5).
All interventions were based on community gardening, including specializations such as urban
farming (N = 2, Allen et al. 2008; Delia and Krasny 2018), school gardening (N = 1, Chiumento et al.
2018), neighborhood beautification (N = 1, Allen et al. 2008), and gardening in juvenile rehabilita­
tion (N = 1, Twill et al. 2011). The literature review study further identified interventions that
included indoor planting, craft-making, and flower arrangements (Park et al. 2016). The interven­
tions ranged from three to nine months, typically spanning the growing season; intervention hours
were not reported.
The three mixed-methods studies provided mixed findings about the role of horticulture-based
interventions for youth mental health (Twill et al. 2011; Sonti et al. 2016; Chiumento et al. 2018).
For example, one set of findings did not support a relationship between the intervention and self-
concept, emotional, and behavioral management (Twill et al. 2011). Another set of findings pointed
to positive associations with food, health, and environmental behaviors (short-term) and commu­
nication and decision-making skills (longer-term) (Sonti et al. 2016). One study did not provide
statistical analysis (Chiumento et al. 2018). The two qualitative studies emphasized the association
of horticulture-based interventions with social and leadership skills (Allen et al. 2008; Delia and
Krasny 2018), thus providing additional perspective to the empirical findings. Finally, the literature
review indicated that the relationship of intervention and outcome is dependent on the type of
mental disorder of the targeted youth (Park et al. 2016).

Discussion
This study contributes a summary of the literature for the specific population of vulnerable youth
experiencing mental, emotional, developmental, behavioral, or social difficulties across four types of
nature-related interventions: wilderness-therapy interventions, animal-assisted interventions, care-
farming interventions, and gardening and horticulture-based interventions. The literature includes
quantitative, qualitative and mixed-methods study designs, with the majority being quantitative
studies. Commonly used methodological approaches are repeated measures, control or comparison
 40

Table 3. Original intervention studies on care farming.

Reference Population Participants Age Country Study design Intervention duration Outcome measure Key findings
Mixed-methods studies
Leck et al. (2015) Adolescents 30 (14% of No information UK Survey of Care farming, adolescents Positive experience, Results indicate that intervention had
T. A. OVERBEY ET AL.

struggling total provided standardized working at 13 different personal development, positive effects on farm experience,
in sample) health and farm enterprises, varied environmental personal development,
mainstream wellbeing length of stay (<3 months engagement, social environmental engagement,
education measures, to >1 year), clients interaction, physical development of social interactions,
semi- worked 1 day, 2 days or health and well-being, improved physical and mental
structured 5 days per week mental health and well- health and well-being; effects were
interviews being positively associated with duration
of intervention
Qualitative studies
Kogstad et al. (2014) Young adults 9 17–27 Norway Observational Care farming, adolescents Leader and the group Data indicate that intervention can be
at-risk for study, semi- working full-time at 3 atmosphere, building of considered supplemental; effective
school- structured mixed-farm enterprises self-efficacy through factors were supportive group
dropouts, interviews, offering employment individually-adapted atmosphere, diversity of tasks
substance- 2–4 scheme, duration not meaningful tasks, increasing self-efficacy, farm animals
abuse, self- interviews, reported animals and nature providing comfort, nature helping
destructive conducted recovering a positive sense of self
behavior over 2-year
period
Schreuder et al. Young adults 11 (82% 17–22 The Netherlands Semi-structured Care farming as experiential Comprehensibility, Results showed that richness and
(2014) with severe male; interviews outdoor education, manageability, diversity of the farm setting was
social and 18% 6 months stay meaningfulness conducive to learning: factors were
mental female) ease of comprehending farm
health environment, ability to manage
problems resources, and a high level of
meaning assigned to farm
environment
Table 4. Original intervention studies on gardening and horticultural therapy interventions.
Reference Population Participants Age Country Study design Intervention duration Outcome measures Key findings
Mixed-methods studies
Chiumento et al. Children with 32 (61% male, 67%) 9–14 UK Qualitative 2-hour session per month, for Mental well-being Quantitative results scores
(2018) behavioral, assessment via 6 months; social and therapeutic (enhancing worsened post intervention
emotional and a mental horticulture to explore the control, increasing for 5 of 7 items (statistical
social difficulties wellbeing natural environment resilience and means difference tests not
impact community assets, calculated), qualitative
Assessment participation results indicate higher scores
toolkit; and social inclusion) for emotioal wellbeing and
quantitative self-help
pre-post
evaluation
Sonti et al. (2016) Young adults enrolled 50 (58% female, 42% 18–25 USA Online and mailed Internship of 3 to 9 months with Environment, self, Regression results indicate
in urban farming male, 56% Black, survey with training and work at urban farm, communication, association of curriculum
youth internship 20% mixed race, closed and community and backyard decision-making, with food, health, and
program 16% Latino, 8% open-ended gardens; 5 to 25 hrs./week community, environmental behaviors;
Asian) questions, learning and longer program
conducted experiences, participation with
1 years after perceived benefits communication and
completion of decision-making skills
intervention Qualitative responses indicate
learning by at least 50% of
respondents in gardening/
food and communication/
social skills
Twill et al. (2011) Adolescents in 19 (79% male, 21% 13–17 USA Two semi- Limited detail on intervention; Positive self-concept, Quantitative evaluations were
juvenile female, 79% White, structured focused on landscaping and emotional and similar in first and second
rehabilitation center 5% African- interviews at horticulture activities; duration behavioral interview; responses to open-
American, 16% week 8 and during growing season management ended questions indicate
other) week 17 of the positive self-concept,
intervention emotional and behavioral
management
Qualitative studies
(Continued)
INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH
41
 42
T. A. OVERBEY ET AL.

Table 4. (Continued).
Reference Population Participants Age Country Study design Intervention duration Outcome measures Key findings
Allen et al. (2008) Children and 16 (100% African- 6–16 USA Case studies Work in community gardens, Constructive activity, Work was perceived as
adolescents in American) including including clearing lots, removing community constructive activity, positive
neighborhood- observations, trash, planting, weeding, contributions, contribution to community,
based community photography, watering, harvesting, mowing relationships/ relationship and
garden program semi-structured lawns and planting flowers in interpersonal interpersonal skills, informal
interviews the neighborhood, street skills, social social control, cognitive and
cleaning; about 9-month control, cognitive behavioral competencies,
duration from growing season and behavioral nutrition knowledge
to the end of the year competencies
Delia and Krasny Adolescents from 9 (88% female, 22% 15–18 USA One-on-one Internship program at urban farm Belonging, Results indicate that
(2018) under-resourced male, White, interviews; including growing and selling expectations, intervention contributes to
communities African and appreciative food, environmental education, complexity, positive youth development,
African-American; inquiry process and team leadership; about leadership authentic career settings,
Hispanic) 9-month duration from March to practice, critical consciousness and
November becoming self leadership, change agents
Table 5. Evidence-synthesis studies.
Reference Intervention Study type Number of studies Age Intervention details Outcome measures Results
Wilderness therapy interventions
Bettmann et al. Wilderness therapy Meta-analysis 36(a) Average 17.4 2399 private-pay Self-esteem, locus of control, Improvements across all areas,
(2016) adolescents behavioral observations, medium effect sizes
receiving personal effectiveness, clinical
treatment, 1982– measures, and interpersonal
2004, 1 week to measures
2 years of
treatment, average
of 7.04 weeks
Fernee et al. (2017) Wilderness therapy Qualitative review 7(b) 12–18 102 adolescents Wilderness therapy outcomes and Positive impacts including increase
programs study (realist receiving processes related to in self-confidence, self-esteem,
synthesis) treatment, 2000– psychosocial outcomes and self-awareness; sense of
2014, 10 days to accomplishment, social skills, and
1 year trust; emotional control; desire to
change including finishing school
and improving relationships with
family; few or no negative
findings noted
Gillis et al. (2016) Wilderness therapy Meta-analysis 21(c) Average 15.62 1458 participants, Interpersonal distress, somatic Large effect sizes for treatment
(residential, inpatient, 1998–2013, symptoms, interpersonal outcomes; effect sizes higher for
and outpatient average age relations, critical items, social Y-OQ in wilderness programs and
programs) 14.34 years problems, and behavioral lower for Y-OQ-SR in non-
dysfunction wilderness therapy programs
Harper (2017) Wilderness therapy, Scoping review 63(d) Not provided January 1997-March Wilderness and adventure Strong support for wilderness
therapeutic camping, 2017 (20 years) therapy, therapeutic camping, therapy as a treatment for youth
and adventure adventure education & with mental health and
education physical activity behavioral issues
Animal-assisted interventions
Hoagwood et al. Animal-assistet therapy Systematic review 24(e) 3–20 1,308 children and Emotional and behavioral issues, Results indicate that animal assistat
(2017) adolescents with trauma and post traumatic therapies can provide
mental health stress disorder, autism a complementary and integrative
problems ages 3– spectrum disorder, attention approach; scientific evidence
20 years, weekly deficit hyperactivity disorder base is limited but growing
sessions (10–
180 min) for 8–
INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH

26 weeks
(Continued)
43
 44

Table 5. (Continued).
Reference Intervention Study type Number of studies Age Intervention details Outcome measures Results
Jones et al. (2019) Canine-assisted Systematic review 7(f) 10–19 134 adolescents with Post-traumatic stress disorder, Results indicate positive impacts for
psychotherapy mental health depression, anxiety and internalising disorders, post-
problems, weekly internalising problems, anger traumatic stress disorders and
sessions (45– and externalising problems, equivalents effects for anxiery,
180 min) for 10– Engagement, socialisation & anger, and externalising
T. A. OVERBEY ET AL.

12 weeks connection disorders; also positive impact on

engagement and socialization
behaviors and reductions in
disruptive behaviors within
treatment sessions
Lentini and Knox Equine-assisted Literature review 66(g) 3–22 672+ at-risk children Quantitative review (at-risk youth, Results indicate that evidence base
(2015) psychotherapy and adolecents autism spectrum disorder), for equine-assisted
receiving mental qualitative review, psychotherapy for children and
health treatments, conceptional and theoretical adolescents is increasing,
mostly weekly review particular for at-risk youth with
sessions (30– ASD, overall positive effects for
120 min) for 3– assessed constructs
12 months
Maber- Animal-assisted therapy Systematic review 10 6–19 Most (= 9) studies Social, cognitive, emotional, Positive improvement reported
Aleksandrowicz targeting mostly behavior outcomes from studies for all assessesed
et al. (2016) male children and psychosocial outcomes but only
adolescents ages some reaching statistical
with intellectual significance
disabilities, mostly
weekly sessions
(20–240 min) for
2–18 months
May et al. (2016) Animal-assisted therapy Literature review 45(h) 1,694 youth with Study design, procedures, Data indicate that research on
focusing on physical and assessment and measures, animal-assisted therapy is guided
empirical mental health outcome analysis by principles of evidence-based
methodology concerns, age not practices (study quality average:
reported, 1–116 1.04/2.00); study quality is found
sessions to be moderately and positively
correlated with study date
(Continued)
Table 5. (Continued).
Reference Intervention Study type Number of studies Age Intervention details Outcome measures Results
McDaniel Peters and Equine-assisted Systematic map 33(i) 2–16 633 children and autism spectrum, post-traumatic Data indicate improvements in
Wood (2017) interventions adolescents with stress and attention deficit behavior, social interaction,
Autism spectrum disorder, equine-assisted communication, motor control
disorder, 1– interventions characteristics and self-care, 45% of outcomes
30 weeks (15– and components, therapeutic were statistically significant, 22%
120 min), 1–40 goals and measured outcomes, positive, 33% negative
sessions in total state of scientific development
Wilkie et al. (2016) Equine therapy Meta-analysis 7(j) 8–19 377 at-risk children Only studies with quantitative Study finds medium effect sizes and
and adolesents, data amendable to meta- indicates that intervention is
treatment 5– analysis considered, study uses a viable alternative to
26 weeks random effects model conventional strategies among
at-risk youth
White et al. (2020) Equine-assisted therapy Systematic review 10 6–14 118 children and Behavioral symptoms, Data suggests positive trends in
adolesents with psychological symptoms, behavioral, psychological, and
attention deficit/ physical symptoms, body of physical outcomes for children
hyperactivity evidence framework with attention deficit/
diagnosis, 1–3 hyperactivity, but few studies
weekly sessions with significant results
(45–90 min) for 4–
32 weeks
Care farming interventions
Murray et al. (2019) Care farming Systematic review 31 (4 in target 9–27 4 studies with 112 Quality of life, depression, anxiety Results suggests that care farming
population)(k) disaffected/ increased quality of life,
excluded youth, decreased depression and
varied length of anxiety for disaffected youth
stay
Gardening and horticultural therapy interventions
(Continued)
INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH
45
 46

Table 5. (Continued).
Reference Intervention Study type Number of studies Age Intervention details Outcome measures Results
Park et al. (2016) Horticultural activity Literature review 207 (133 studies with Children age 8 to 13; Varying length (under Psychological, emotional, social, Interventions for general population
interventions for youth children, 74 studies adolescents age 14 10 to more than 31 behavioral, cognitive, children and adolescents were
from general with adolescents) to 19 sessions, duration educational factors related to physical,
T. A. OVERBEY ET AL.

populations, with 30–120 min) and psychological/emotional,

developmental group sizes (less cognitive, social, educational,
disorders, emotional than 11 to more and behavioral outcomes;
and behavioral than 30), Activities: interventions for adolescents
disorders, and mental gardening with developmental disorders
illnesses outdoors, planting were related to the six outcome
indoors, making categories, interventions for
crafts with live adolescents with emotional and
plants, arranging behavioral disorders were related
flowers, making to 5 outcomes, interventions for
crafts with artificial adolescents with mental illness
or pressed flowers, are related to psychological/
other activities emotional outcomes
related to
horticulture
Notes:
(a) Includes original intervention studies Harper et al. (2007) and Hoag et al. (2013)
(b) Includes original intervention studies Caulkins et al. (2006), Russell (2000), Russell (2005), and Russell and Phillips-Miller (2002)
(c) Includes original intervention studies Bettmann et al. (2013) and Harper et al. (2007)
(d) Includes original intervention studies Bettmann and Tucker (2011), Combs et al. (2016), Harper et al. (2007), Russell (2003), and Russell (2005)
(e) Includes original intervention studies Bachi et al. (2012), Balluerka et al. (2015), Conniff et al. (2005), and Gabriels et al. (2015), and Trotter et al. (2008)
(f) Includes original intervention studies Hanselman (2001), Hartwig (2017), Lange et al. (2007), Stefanini et al. (2015), and Stefanini et al. (2016)
(g) Includes original intervention studies Kemp (2014), Maujean et al. (2013), and Trotter et al. (2008)
(h) Includes original intervention studies Bachi et al. (2012), Balluerka et al. (2014), Ewing et al. (2007), Hanselman (2001), Kemp et al. (2014), and Lange (2007)
(i) Includes original intervention study Gabriels et al. (2015)
(j) Includes original intervention studies Bachi et al. (2012), Kemp et al. (2014), and Trotter et al. (2008)
(k) Includes original intervention study Leck et al. (2015), Kogstad et al. (2014), and Schreuder et al. (2014)
 INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH 47

groups, and post-treatment assessment. The majority of sample sizes is small with only 13 original
studies including more than 100 study participants. Interventions vary in their focus, ranging from
broadly designed, multi-faceted tasks in care farming and horticulture-based interventions to highly
specific activities in animal-assisted interventions. The key findings reflect the nature of the
interventions, in particular, the most robust findings can be associated with the more narrowly
defined animal-assisted interventions. Outcomes were largely positive across a wide range of
psychosocial and behavioral measures and often maintained post-treatment. The psychosocial
and behavioral measures that the nature-based intervention contributed to the most include mental
health measures, such as hyperactivity, anxiety, depression etc., social measures, such as relation­
ship building, interpersonal skills, etc., and measures of personal development, such as self-concept,
meaningfulness etc.
This scoping review identifies several avenues for future research. A first avenue for future
research that emerged from the analysis of the study designs is the need for a greater emphasis on the
use of methodologically robust empirical designs, to achieve a higher degree of external validity.
The majority of studies in this scoping review are based on pre-post evaluation-type repeated
measures. The approach is often justified with the special nature of the intervention which makes
a comparison group difficult to obtain, a challenge that is particularly evident in wilderness-therapy
interventions (Russell 2003; Clark et al. 2004; Roberts et al. 2017). To some extent, the animal-
assisted interventions literature can serve as a role model here, with its larger number of statistically
robust research designs that often include larger sample sizes and randomized approaches with
control groups. Alternatively, newer statistical approaches, such as intent-to-treat designs (Gupta
2011), or staggered research designs, such the step-wedge designs (Hemming et al. 2015), deserve
greater attention in this literature.
A second avenue for future research comes from the analysis of the interventions covered in this
review and points to a continued need for evaluating youth-based interventions. In particular,
knowing of the large number of interventions targeting adolescents and young adults with mental
health difficulties, future research should examine how well the literature reflects the breadth of the
field. This analysis could be beneficial for identifying additional research needs and initiate
a discussion of best practices in areas that are better understood. Ideally, this research should be
approached from an international perspective, to increase the understanding of effective interven­
tions from a cultural lens (e.g. Levinger et al. 2021). A second, intervention-related observation is
the often limited amount of information on the actual intervention in the research studies. On the
one end are the highly-focused studies that list the exact number of hours of each intervention
within a therapy plan, while on the other end of the spectrum are studies that provide a list of
interventions but lack detailed information that would facilitate a better understanding of which
components were particularly effective (e.g. Caulkins et al. 2006). A third, related observation is the
challenges with establishing causality and demonstrating which part of an intervention has bene­
ficial effects for which group of users. Although beyond the scope of this review study, our evidence
synthesis suggests a greater need for critical engagement with the reported benefits that takes into
account issues, such as self-selection bias or negative outcomes and challenges, that are typically not
reported in original studies. For this reason, it is difficult to assess the factors for successful
interventions and groups (e.g. with more severe clinical depression or disabilities) for whom nature-
based therapy is not a viable option.
A third avenue for future research emerged from the analysis of the study participant samples in
this scoping review. Future research should identify the subgroups more clearly for whom the
treatment is most effective, i.e. by age group, gender, or diagnosis (Berman and Anton 1988; Gillis
et al. 2016). In particular, more understanding is needed how well the treatment modalities work for
the variety and severity of psychosocial, behavioral, clinical, and non-clinical issues experienced by
youth in the short and long-term. For example, some of the wilderness therapy studies have
examined target groups, but typically with mixed results and not enough consistency across the
studies to make strong recommendations (Berman and Anton 1988; Harper et al. 2007; Bettmann
48 T. A. OVERBEY ET AL.

and Tucker 2011; Combs et al. 2016). A related topic for future research is disparities in nature-
based interventions due to a program’s funding structure. Whether self-paid, government funded,
or a combination of both, the financial foundation of an intervention can determine participant
composition and quality of an intervention (Frankford 2007). Information on the funding structure
and its implications would provide additional transparency in this literature and also will help
eliminate biases in who participates in the different programs (Bettmann et al. 2016).
A fourth avenue for future research emerged from the analysis of key findings for this scoping
review. Few studies acknowledge the fact that nature-based interventions are generally used after
other treatment modalities have been tried or can be part of an integrative treatment model (e.g.
Compitus 2019). Yet the literature does not control for the impacts of this prior treatment.
Furthermore, few studies have included discussion of aftercare plans. Future research should
examine the best placement of nature-based intervention within a holistic assessment of treatment
models. In a related perspective, many nature-based interventions, especially care farming, have an
integrative function which aims to reconnecting youth with the community. This aspect could be
more widely investigated in the literature.
Several limitations should also be noted for this study. First, we excluded reports and other gray
literature, to keep the focus on the peer-reviewed studies. Second, the context of most of the studies
is often highly location specific, which limits their generalizability. For this reason, we describe
rather than measure differences and similarities in the literature. Third, we excluded the miscella­
neous categories of nature-based interventions from this review, such adventure therapy, green
exercise activities, challenge programs, therapeutic camping and other outdoor experiential pro­
grams that may include youth participating for recreational rather than therapeutic reasons (Wilson
and Lipsey 2000; Gillis et al. 2008). Difficult to categorize, these interventions should be examined in
a separate study that focuses on this diverse array of approaches to working with youth. Fourth, our
understanding is also limited by the publication of findings from only a small percentage of all
possible programs that exist. Increased attention to nature-based interventions by scholars across
disciplines can increase the potential for collaborative research efforts and help build capacity of
residential and community-based programs to implement research studies, disseminate findings,
and add to the evidence base (Cunningham et al. 2015; Thompson et al. 2017; Wainberg et al. 2017).

Acknowledgments
The authors thank Dr. Cäzilia Loibl for her review of an earlier version of this manuscript.

Disclosure statement
No potential conflict of interest was reported by the authors.

Funding
The authors reported there is no funding associated with the work featured in this article.

ORCID
Florian Diekmann http://orcid.org/0000-0002-7961-6769

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