Introduction

In Australia, 43.7% of the adult population report having experienced a mental health disorder in their lifetime, and one-in five (21.4%) experienced symptoms in the 12-months prior to the National Survey of Mental Health and Wellbeing (ABS, 2022). Internationally, over 60% of all lifetime cases of mental health disorders are identified as emerging by 25 years of age (Solmi et al., 2022), and consistent with this finding, young Australians aged 16–24 years report the highest prevalence of 12-month mental health disorder (39.6%) (ABS, 2022). Regrettably, less than half (47.7%) of these young people saw a health professional for their mental health during that time (ABS, 2022).

Providers of mental healthcare for young people in Australia include general practitioners; counsellors or psychologists in schools or the community including phone and online services such as the Kids Helpline, ReachOut Australia and Head-to-Health; the national youth mental health service, headspace; children and adult Head to Health hubs, private and public specialists e.g., psychiatrists, psychologists and paediatricians; and for those with complex and specialised needs specialised public mental health services. For people in crisis, emergency departments and public and private hospitals may also be accessed, as may Safe Haven Cafes where available. Services are thus available across the spectrum of community to tertiary care, through a system that is not always easily navigable or accessible.

For Australians with recent symptoms, existing data suggests that general practitioners (GPs) were the most commonly accessed provider (38%), followed by psychologists (22%) and psychiatrists (8%) (ABS, 2022). Telehealth options also provide many people with anonymous support; a key crisis support line in Australia, Lifeline, for example, receives over 1 million calls per year (Lifeline, 2023). The provision of mental health care by general practitioners (including those employed at the national youth mental health service, headspace), psychiatrists, paediatricians, psychologists, social workers, may potentially be subsidised through Australia’s national health insurance scheme Medicare.

One in nine Australians accessed mental health-specific services through Medicare in 2020–21, and the fraction of Australians seeking Medicare-subsidised mental health services has been steadily climbing for the last decade (AIHW, 2022). Trends in provider access demonstrate a demand for alternatives to the standard mental health care options with the greatest increase in service demand is for ‘other allied health professionals’ such as occupational therapists, social workers, Aboriginal health workers and mental health nurses (AIHW, 2022). This trend demonstrates demand for alternatives to the standard mental health care options.

Access to and acceptability of mental health services can be an issue. People with lower income, education, mobility limitations, and poor self-reported health often have trouble accessing care (Corscadden et al., 2019). And for many people, cost is a major barrier to accessing care (Corscadden et al., 2019; Fennell et al., 2018). Costs of care were a reason for 12.0% of all persons needing mental health care postponing or not pursuing care on at least one occasion in Australia in 2020–21, with younger people less likely to access care (Neil, 2023). Additional barriers include a desire for privacy, and a lack of trust in mental health practitioners (Corscadden et al., 2019; Fennell et al., 2018). Some clients report that the traditional (indoor) therapy makes them feel ill, constrained, bored, sad or disengaged and that the (indoor) setting feels too formal (Cooley et al., 2020; Fernee et al., 2019). Data from headspace suggests that low acceptability of services is a particular issue for clients who are male, heterosexual, Aboriginal or Torres Strait Islander, living in a rural location or socioeconomically disadvantaged (Seidler et al., 2020). The need for new models of mental health care is widely acknowledged, particularly for young people, with unaddressed psychological distress in this age-group a precursor to poor, potentially lifetime trajectories of mental and physical ill-health (Colizzi et al., 2020).

Meanwhile, mental health professionals face increased risk of psychological distress, mental ill-health and suicide (Dattilio, 2015). High-demands, low-control and limited support are factors that contribute to job strain and burnout in this workforce (Nahrgang et al., 2011). Workforce capacity in mental health services is understood to be particularly susceptible to strain and burnout, with lower productivity, high levels of absenteeism and increasing workers’ compensation claims exacerbating service delivery challenges (Morse et al., 2012). Further, since the COVID-19 pandemic, increasing demand for services (Bower et al., 2021; McGorry, 2022) has compounded existing workforce and capacity pressures (headspace, 2021) resulting in long waitlists for distressed young people (Seidler et al., 2020). Waitlists of 3-months and longer are common and demand management strategies, including single visits, have been implemented in some locations. Thus, not only are young people in distress, our workforce and mental health system is too. This situation points to an urgent need to develop new models of care that address these significant risks to a sustainable workforce.

Within this high-demand context, the provision of acceptable, accessible and sustainable multidisciplinary mental health services is a critical imperative. This need is confirmed by a collection of recent national inquiries and policy directives. For example, the 2020 Productivity Commission Inquiry into Mental Health, spoke to the need for the creation of a “person-centred” mental health system focussed on the wellbeing of young people, particularly early intervention and prevention (Productivity Commission, 2020). The National Suicide Prevention Adviser recommended the need for early access to programs, treatment and support for children and young people (National Suicide Prevention Adviser 2020). In the National Mental Health and Suicide Prevention Plan (Department of Health, 2021), funding was announced to support the expansion of headspace, to improve access to culturally safe and accessible services through child mental health and wellbeing hubs, and support for family members and/or carers of people dealing with mental ill health. To increase the range of mental health interventions available to young people, the need for collaborative integrated multidisciplinary services has also been highlighted in the academic literature (Colizzi et al., 2020); outdoor talking therapies are one such option.

The outdoor therapy option

Outdoor therapies, sometimes called ‘nature-based’ therapies or eco-therapies, are widely used and potentially scalable, but not yet -mainstreamed. These approaches offer health promoting and targeted mental health interventions for people with a therapeutic need (Colizzi et al., 2020) and usually comprise semi-structured activities in natural environments led by accredited practitioners (Cooley et al., 2020). Across their diversity, outdoor therapies tend to embody four key components: BIO (physical and experiential), PSYCHO (mental and emotional care, and intentional conversations), SOCIO (equalised social relationships) and ECO (nature contact/time in nature; Fig. 1)(Neil et al., 2023). Culture (culturally appropriate facilitation, including but not limited to First Nations approaches such as ‘on country’ programs for Aboriginal young people) is increasingly being embodied in these activities as a fifth element. These therapy components relate to some of the mechanisms connecting nature to wellbeing benefits (Hartig et al., 2014) including that; nature can benefit physical and social health by providing a place for physical activity and social interaction, and it can help us recover from stress (Hartig et al., 2014). In outdoor health practice, ‘nature’ can mean anything from urban parks and gardens, to coastlines, forests and wilderness areas (Cooley et al., 2020); ‘nature’ is often used to describe anywhere outdoors, with ample opportunity for humans to interact with non-human living beings though elements of nature (e.g. plants, animals) can be brought indoors for therapeutic benefits. Experiences in or with nature can also support greater connection with nature, and the eudaimonic wellbeing benefits (e.g. personal growth, autonomy, purpose in life, self-acceptance, positive relations to others and vitality), such nature connection can bring (Pritchard et al., 2019). Meanwhile, reported benefits of outdoor therapies include improved self-esteem and confidence, positive and negative affect, stress reduction and restoration, social benefits, and resilience (Roberts et al., 2020). Nature exposure and outdoor activities have also been associated with lower burnout (Hyvönen et al., 2018), a major risk factor in our mental health workforce.

Fig. 1
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Key common practice elements of outdoor therapies

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Outdoor therapies are employable across the continuum of care, from prevention to intervention (see Fig. 1 in Neil et al., 2023). For example, public health messaging suggests everyday contact with nature through outdoor recreation, gardening, conservation volunteering etc. can support wellbeing maintenance and disease prevention. At the other end of the continuum of care, nature-based health interventions, such as integrated outdoor therapy, can support people with specific physical, psychological or social needs. Outdoor therapies can be offered in primary care navigation delivery models (Carter et al., 2018) and are sometimes the preferred choice for social or nature/green prescriptions. Nature prescription, where a health professional ‘prescribes’ time outdoors/in nature to a client, is an area in which trials are currently being funded, such as the investigation of physical activity in nature for people with cardiometabolic disease (Nguyen et al., 2023). Outdoor therapies may be more accessible and acceptable than usual care for young people who find the traditional care options to be boring, formal, oppressive or constrained (Cooley et al., 2020; Fernee et al., 2019). Use of a non-mainstream workforce in this field has the potential to create additional system capacity and improve efficiency and sustainability in part by the possible flow-on effects to practitioner well-being (Cooley et al., 2020).

Nature prescriptions have the potential to greatly benefit individuals with a diverse spectrum of health and social care needs. However, it is important that all interest, investment and innovation in these areas is supported and informed by high-quality research (Husk et al., 2019).

The current evidence base

Since 2020, rigorous scientific evidence of the benefits of outdoor therapies in young people has increasingly appeared, and been the subject of evidence reviews including: a mixed-methods meta-synthesis (n = 38) of the experiences of practitioners and clients who have practiced outdoor therapies in natural, outdoor spaces to establish a framework for best practice (Cooley et al., 2020); a systematic review (n = 14) of nature activities and wellbeing in children and young people (Roberts et al., 2020); and a systematic review (n = 84) of the wellbeing benefits of immersive nature-experiences for young people (Mygind et al., 2019). Here we summarise the findings of these key reviews of relevance to outdoor therapy for young people, and the single randomised clinical trial in this field.

Cooley et al. (2020) meta-synthesis on outdoor-based therapies examined 38 articles, representing data from 322 practitioners and 163 clients. The articles came largely from the US, UK and Israel (n = 1 from AU), and 11 focussed on child/adolescent clients (Cooley et al., 2020). The resulting outdoor talking therapy framework included potential challenges and solutions and client suitability characteristics, including discomfort with conventional therapy. Several therapeutic enrichments were noted by clients and/or practitioners, including interconnectedness and improved practitioner wellbeing through more holistic practices, which may lead to reduced staff burnout. Future research was considered essential to “shape the implementation of therapy outdoors in practitioner training programmes and mainstream services.” (Cooley et al., 2020, p12).

Roberts et al. (2020) reviewed the wellbeing benefits of nature-based activities for young people up to 21 years of age, including talking therapies ranging from outdoor education to wilderness therapy programs. Their systematic review examined 14 studies; most were conducted in the UK, and only one (Rose et al., 2018) from Australia. They found positive outcomes for wellbeing across all ages, including self-esteem (although self-esteem was inconsistent for adolescents) and confidence, positive affect, stress reduction and restoration, social benefits, and resilience. However, all quantitative studies undertaken with adolescents were considered of weak quality, with sample size and/or lack of power calculations ubiquitous concerns and the relative importance of including a therapeutic aspect could not be determined. Reviewers considered the use of objective physiological assessments, in addition to subjective measures, to be a positive feature of some included studies. Only two studies considered negative outcomes from nature-based activities including feelings of anxiety and claustrophobia (Milligan & Bingley, 2007) and fear of attack or harassment by other humans in the natural environment (Burgess, 1996). Adequate follow-up, assessment of connectedness to nature as a potential mediating effect, and the use of objective measures, such as physiological stress as well as subjective measures were considered important in future research.

A systematic review from 2019 by Mygind and others, summarised and evaluated the evidence from 84 articles for benefits of immersive nature-experience on children and adolescents’ mental, physical and social health (Mygind et al., 2019). The review found conditional support for benefits for self-esteem, self-efficacy, resilience and academic and cognitive performance, consistent with Roberts et al (2020). However, similar to other reviews, Mygind et al. (2019) found the quality of evidence to be low due to risk of bias, insufficient sampling methods and unsuited comparison groups, although the difficulties of blinding in behavioural, psychosocial intervention research was noted. To maximise trial quality the blinding of participants and personnel to specific research aims was raised. No reporting of harms was noted in the included trials.

There was one RCT identified in the Mygind and Roberts reviews (Greenwood & Gatersleben, 2016) which tested restoration of stress and mental fatigue in an outdoor or indoor environments in the UK – alone, with a friend or while playing a game on a mobile phone – amongst 120, 16–18-year-olds over 20 min. Teenagers were found to recover more quickly from stress and mental fatigue in an outdoor natural setting than an indoor one, and that being with a friend increased positive affect. Selection bias, the treatment of confounding and withdrawals as well as uncertainty about whether power was achieved were identified in the review as key concerns.

There are major challenges in undertaking a randomised-controlled study with vulnerable populations such as youth seeking mental health treatment. At least one RCT in this field was terminated due to the ethical, practical, and methodological challenges presented by this study design (Gabrielsen et al., 2015). In this study, the randomisation process left already distressed adolescents being treated through specialist services feeling disappointment and rejection if they were allocated into the control group despite the offer of being in the outdoor option at a later date. notwithstanding the specifics of the therapy and the population, the potential for negative impacts is a major challenge of any RCT in this field.

Other studies have instead opted for quasi-experimental designs; one study in America used an exploratory, non-equivalent groups pre-post design and found that community-based adventure therapy significantly reduced problem severity for youth with emotional and behavioural disorders, with the largest improvements for females and African American participants (Tucker et al., 2012). Other studies have opted for mixed methods approaches using surveys and focus groups to demonstrate the benefits of outdoor (adventure) therapy for youth with Adjustment Disorder on trauma symptomology and family functioning (Norton et al., 2019).

Further notable studies have examined the longitudinal impacts of different outdoor therapies for functioning (DeMille et al., 2018), behavioural and emotional outcomes (Behrens et al., 2010) and substance abuse (Lewis, 2013), finding improvements can last for at least a year after treatment. Parent-perceived functioning of adolescents post-outdoor behavioural therapy treatment has been shown to persist for at least 18 months (Combs et al., 2016). Further research on the persistence of these (and other) therapies is warranted.

Despite the challenges, an effective and ethical RCT could help to remove existing barriers to greater integration of outdoor therapies across the continuum of mental healthcare in Australia.

The evidence gap

While the evidence of effectiveness of outdoor therapies is building, there are clearly some remaining questions about outcomes, active mechanisms, cost-effectiveness, and risks. In therapy outcomes, there are important influences from client and practitioner characteristics, the type of natural setting and how it is incorporated into practice (e.g. from active to passive incorporation, with low to high nature-interaction) which can make it hard to unpick the mechanistic drivers of clinical outcomes (Cooley et al., 2020).

Regarding mechanisms connecting nature-based interventions and depression, Owens and Bunce developed the nature-depression nexus model where stress, rumination, mindfulness, sleep and exercise were identified as five putative, candidate mechanisms underlying observed beneficial effects (Owens & Bunce, 2022). These mechanisms are consistent with Green Mind Theory which links the mind with the body and the brain through reciprocal relationships, and draws on evidence from neuroscience and brain plasticity, spiritual and wisdom traditions, mindfulness-related and talking therapies, green exercise in nature, the lifeways of original cultures, and material consumption behaviours (Pretty et al., 2017).

However, the mechanisms identified by Owen and Bunce for nature-based interventions were specific for depression and mechanisms may differ depending on the disorder experienced by participants (Owens & Bunce, 2022). An umbrella review by Harper and colleagues examined 14 systematic reviews or meta-analyses to identify the theories and mechanisms of change in outdoor therapies. The therapy types represented in the reviews included nature-based, forest, horticultural, wilderness and adventure therapies. They found that while studies on outdoor therapies often demonstrate positive outcomes for participants, they rarely identify underlying theories and causal mechanisms and observed outcomes were weakened by study design and biases (Harper et al., 2021).

There are likely complex and multiple pathways connecting nature-based therapies to good mental health and wellbeing, with important and interacting contributions from client and practitioner characteristics, the natural setting, and therapeutic program. To unravel these pathways, Harper et al. (2021) have advocated that future research include larger randomised controlled trials (RCTs), longitudinal studies and cohorts, qualitative analyses and advanced multivariate modelling. These features were also recommended by Owens and Bunce (2022) for nature and depression. For such studies to effectively close the gaps in the current evidence base, Harper et al. (2021) further recommend that future outdoor therapy studies:

  1. (1)

    Use validated psychometric assessment tools and physiological measures, in addition to self-reported questionnaires and observational measures, to capture a fuller picture of the therapeutic effects of outdoor therapies;

  2. (2)

    Identify and measure process factors;

  3. (3)

    Provide matched sample results, as well as means, standard deviations and sample sizes for each outcome at each measured time point;

  4. (4)

    Include follow-up and longitudinal assessments to test longer term effects;

  5. (5)

    Involve more studies with clinical samples;

  6. (6)

    Increase involvement of participants’ perspectives in the design and delivery of interventions;

  7. (7)

    Increase attention to participants’ perceived experience of and attitudes toward particular outdoor environments and activities, as well as their previous engagement, or lack of engagement, with nature;

  8. (8)

    Describe any side-effects, adverse events or harmful phenomena, including reasons for withdrawal and non-participation, in outdoor therapy studies;

  9. (9)

    Include cost-effectiveness information; and,

  10. (10)

    Utilise randomised control designs when possible and appropriate.

In terms of risks, unlike in drug trials, the monitoring of harm is not compulsory in psychological trials although it remains of integral importance (Berk & Parker, 2009). A review of the assessment of harms in talking therapy trials in children and young people (Hayes & Za’ba, 2022) has identified just over half (51%) of relevant trials registered in the International Standard Randomised Controlled Trial Number (ISRCTN) database mentioned harm or adverse events during the trial or its follow-up in at least one piece of documentation. Inclusion of an explicit, clear and transparent process for monitoring and recording adverse events as per CONSORT-SPI (Grant et al., 2018) was recommended, as was a need to develop a comprehensive understanding of the types of harm and side effects of therapy.

As highlighted earlier, mental health professionals are at risk of psychological distress, mental ill-health and suicide (Dattilio, 2015) with high work pressures and poor working conditions common (Cetrano et al., 2017; Teles et al., 2014). Advice to psychologists for protecting their own mental health includes early engagement with clinically therapeutic programs, positive psychology approaches and self-care strategies (Dattilio, 2015). Work engagement, however, is protective for mental health, as represented by three psychosocial markers: Vigour (high levels of energy and mental resilience while working), dedication (feelings of a sense of significance, enthusiasm, inspiration, pride, and challenge) and absorption (being fully concentrated and deeply engrossed in one’s work) (Salanova & Llorens, 2008). It is not yet known whether engagement in the provision of regular outdoor therapy may help boost work engagement among therapists, by providing a buffering effect in relation to negative mental health impacts.

A randomised controlled trial proposal

To establish the most rigorous, quantitative evidence-base to understand the benefits of outdoor talking therapy in clinical practice, we propose a design for an unblinded RCT that compares outdoor talking therapies with conventional indoor talking therapies (usual care) in young people with moderate psychological/emotional distress. A RCT study design allows for holistic data to be collected about clients and practitioners, and pairing with advanced multivariate modelling to progress understanding of causal pathways between nature interventions and good mental health and wellbeing (Owens & Bunce, 2022). Our proposed design is informed by the aforementioned framework for outdoor talking therapy (Cooley et al., 2020), putative mechanisms of outdoor therapy in depression (Owens & Bunce, 2022), and prior research and publications by the leading national organisation for outdoor therapies in Australia, Outdoor Health Australia (previously the Australian Association for Bush Adventure Therapy) (Rakar-Szabo et al., 2019). The trial’s design will address known limitations and provide information for implementation to guide scalability.

There are many different models and methods for outdoor therapy, as exemplified by the umbrella review by Harper et al. (2021), and the RCT would need to standardise one therapy model. With this in mind, a basic five-session therapy approach (Box 1), was developed by experienced accredited practitioners and clinical supervisors from Outdoor Health Australia. In Australia, outdoor therapy practitioners are from wide-ranging cross-disciplinary backgrounds and professions. The advisory OHA professionals are from training and experience pathways that include psychotherapy, counselling, psychology, social work, family therapy, outdoor education, adventure education, outdoor activity specialists and Aboriginal mentors. This model, endorsed by Outdoor Health Australia, integrates best practice principles and is a cost-effective starting point, comparable with ‘treatment as usual’ for generating beneficial effects, is considered a minimum ‘dose’ of individually-tailored group-based outdoor therapy. Because indoor and outdoor therapies can be conducted in individual or group settings, and both location and setting may influence client outcome, the proposed study has four arms:

  • Treatment Arm 1: Individual indoor therapy, in accordance with usual care, would comprise provision of up to 10 × 1-h sessions provided by 1 headspace counsellor to 1 young person on a negotiated frequency within a 6-month timeframe, or up to 20 sessions in 1-year.

  • Treatment Arm 2: Group indoor therapy, in accordance with usual care, would comprise the provision of up to 6 × 1.25 -hour weekly cognitive behavioural therapy (CBT) based sessions provided by one headspace counsellor to 6–8 young people.

  • Treatment Arm 3: Individual outdoor talking therapy would comprise therapy sessions in a park or other easily accessible greenspace and provided in alignment with best practice outdoor therapy. Consistent with person-centred care, location, intensity (low to medium) and timing of sessions will be negotiated between the client and their accredited outdoor therapy practitioner.

  • Treatment Arm 4: Group-based outdoor talking therapy: We propose to use the 5-session Model (Box 1; see also Neil et al., 2023) endorsed by Outdoor Health Australia. The group-based outdoor therapy would be provided by accredited counsellors who have been specifically trained in outdoor therapy modalities within a 3- to 6-month period, and co-designed with participants.

Box 1 Proposed five session outdoor group therapy model

Meeting each other: a 60-90min session provided by one outdoor therapy practitioner to one young person*. Location options: A. outreach in the home or a setting familiar to the participant, B. online, C. onsite at headspace, or D. outdoors at a mutually agreed public park or natural environment.

Joining up: 3h (180min) group-based session provided by two outdoor therapy practitioners to a closed group of 4–8 young people. Location: outdoors at a negotiated park or natural environment. This session will involve introductory processes that include safety, social agreement, purpose and intent, and gentle physical activity in nature.

Challenging ourselves: 3h (180min) group-based session provided by 2 outdoor therapy practitioners to the same group of 4–8 young people. Location: outdoors at a negotiated park or natural environment. This session will involve processes that include tailored and gradated physical, social and mindful activities in nature.

Reflecting together: 3h (180min) group-based session provided by two outdoor therapy practitioners to the same group of 4–8 young people. Location: outdoors at a negotiated park or natural environment. This session will involve review, future-oriented and closure processes that include reflective physical, social and mindful activities in nature.

What now: a 60-90min session provided by one outdoor therapy practitioner to one young person*. Location options: outreach in the home or a setting familiar to the participant, online, onsite at headspace or outdoors at a mutually agreed park or natural environment.

*Participants are invited to bring a trusted adult friend, family member or mentor of their choice to the first and fifth sessions.

The proposed study would require genuine collaboration between industry and research with practitioners, researchers and clients at the heart of the planning process. The study would also include an investigation of the types of harm and side effects of outdoor therapy and the relationship between therapy and practitioner well-being. The study would result in a holistic understanding of the impact of this therapy type for all participants. To promote the systematic uptake of research findings, qualitative research would be included to identify enablers and barriers to implementation from the perspective of therapists, providers and clients. Co-production of training outputs for practitioners would increase sector capacity for outdoor therapies for young people experiencing psychological distress. To date, outdoor therapy is not formally recognised nor accredited by Australian tertiary institutions. While training programs are offered in various settings under various terms, consolidation of training pathways and standardised criteria are a ‘work in progress’ for the field. Findings from this study could be used to inform decisions regarding implementation of outdoor talking therapy, transforming health system practice, and widening community-based prevention and early intervention efforts.

Participants

Using an RCT design in mental health settings presents difficulties in balancing scientific rigour alongside client preferences (Gabrielsen et al., 2015). We propose including young adults who are 18–25 years old, assessed as having moderate psychological distress (Kessler 10 scores in the 25–29 range) at intake and considered as suitable for the study by their clinician during initial screening and triaging stages. In addition to the high demand for mental health care, this age group is more independently mobile to access outdoor health options, are able to provide consent to participate, and may be more resilient to potential disappointment of randomisation than younger youth. Potential participants would be advised about the study by their clinician and referred to study staff.

Any client with severe or low levels of distress, or with language or cognitive barriers that make them unable to provide consent or to complete surveys with or without the assistance of study staff would be ineligible to participate.

Mixed methods data collection

As has been called for by others, we propose a study design that focusses on multifaceted wellbeing as measured by subjective and objective data (Table 1). Baseline measures would include validated tools of health and social behaviours that represent different aspects of holistic wellbeing and cover the mechanism through which outdoor therapy may be supporting wellbeing. To minimise burden and enable long-term follow-up, we would seek consent for linkage to routine data assessments for example Medicare Benefits Schedule (MBS) and Pharmaceutical Benefits Schedule (PBS) data. A questionnaire could be developed to collect resources not captured through MBS/PBS linkage including presentations to the emergency department, admissions to hospital, costs associated with attending therapy, and other wellbeing-maintenance measures used outside of the study. Clinicians involved in the study could also keep a time log of their study-related activities to facilitate an economic analysis.

Table 1 Data collection types to monitoring changes to holistic wellbeing of participants
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A potential sampling timeline is proposed in Fig. 2; the final sampling protocol should be codesigned with a youth reference group to ensure minimal burden for participants and an acceptable sampling procedure.

Fig. 2
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A timeline for the proposed RCT study

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Randomisation

Eligible people who agree to participate in the study would be randomly allocated into one of the four treatment arms. Consenting individuals could be randomised using the using a computerised protocol with a 1:1:1:1 ratio across four treatment arms: group outdoor therapy, individual outdoor therapy, group indoor therapy and individual indoor therapy. Randomisation should be stratified according to clinic site and sex, given males are more likely to withdraw from mental health care treatment (according to headspace data (Rickwood et al., 2015).

The comparative cost-effectiveness of outdoor group-based counselling could be assessed with reference to accepted Australian thresholds for incremental cost-effectiveness ratios. Several supplementary analyses could be included, such as individual versus group outdoor treatment, and the longevity of treatment impacts. Thematic analyses of lunchtime focus groups, walk-along interview data and observation field notes would be used to deepen understandings of the nuances of the intervention, from participant and practitioner perspectives, and identify any social or structural barriers and/or enablers to the outdoor healthcare treatments.

Safety/Harms

The focus of this study component would be: 1) understanding the adverse events (AEs) and serious adverse events (SAEs) that are likely to arise in the study population (Dunleavy et al., 2021); and 2) developing procedures for effectively monitoring these events throughout the trial (Dunleavy et al., 2021). First informed by recommendations from the literature (Dunleavy et al., 2021; Hayes & Za’ba, 2022), we would develop an indicative list of AEs and SAEs, with all AEs plausibly related to the interventions proposed (Horigian et al., 2010). Second, we propose the development of a safety assessment protocol, including active (regular, systematic and standardised assessments) and passive surveillance for harms (open-ended questions) and a process for AE attribution, and a training protocol to optimise standardisation across trial sites.

Practitioner wellbeing

Whilst there is some evidence (Hyvönen et al., 2018) that nature exposure and outdoor activities during leisure time is associated with lower burnout in a general sample of Finnish employees, nature exposure during the working day is seen as an important future research direction in the field of occupational wellbeing. Hence, in addition to demographic characteristics, occupation/employment conditions (Cetrano et al., 2017), and tenure as a therapist, we propose the use of validated instruments to monitor practitioner wellbeing.

Conclusions

There is strong evidence that outdoor therapies can contribute to the wellbeing of participants, including young people with moderate psychological distress (Cooley et al., 2020; Harper et al., 2021; Roberts et al., 2020). However, existing evidence suffers from a lack of multifaceted measures of wellbeing, small sample sizes, no or limited follow-up to determine the longevity of treatment effects, no assessment of treatment side-effects or adverse events, no participant involvement in study delivery and design, and cost-effectiveness of treatment models. The RCT proposed here would build on other outdoor health RCT efforts, longitudinal and quasi-experimental work to be the first clinical trial of outdoor therapy for young people with moderate psychological distress in Australia. Our proposed method aims to balance scientific rigor with realistic delivery by adopting the treatment as usual (indoor) care models, and pair them with standardized individual and ‘minimum dose’ group outdoor therapy models. If this program leads to greater uptake of outdoor therapy, the group models could adopt different lengths, intensities and levels of flexibility to meet the needs of local clients and services. The RCT would generate the robust evidence required to determine the comparative benefits, harms, cost-effectiveness, mechanisms and overall potential of outdoor talking therapy as an effective mainstream mental health treatment option. This holistic study could actively and efficiently translate findings to improve care pathways, population health outcomes and system sustainability in resource-constrained environments and help ensure young people in Australia and elsewhere are provided with the care they need.