The search was restricted to only systematic reviews of the literature. As this review of reviews is focused on what types of NBIs exist, there were also no restrictions in terms of the types of outcomes.

NBIs can be understood as an overall umbrella term for any of the types of NBIs in this review. Similarly, eco-therapy can also be used as an overarching term for both active (exercise, gardening) and passive (nature exposure) nature-based techniques and practices. Nature-Assisted Therapy can also be understood as a broad term covering such practices, with the aim of recovering a patient’s health using interventions involving plants, natural materials, or outdoor environments (Annerstedt and Währborg, 2011).

Horticulture-based interventions are the most common type of interventions appearing in the reviews of this review. The activities in these interventions mainly involve gardening and other forms of taking care of plants (Tu, 2022).

Nature exposure interventions typically involve exposure to outdoor nature, but can also include interventions using simulated nature indoors (Yeo et al., 2020). It is important to differentiate between outdoor nature exposure interventions and green exercise and wilderness therapy as nature exposure and nature viewing interventions should be more passive and at most include a light level of activity, as physical activity can have effects beyond nature exposure itself (Corazon et al., 2019; Kondo et al., 2018). For example, one review claimed forest therapy to involve nature viewing (Kondo et al., 2018).

Green exercise interventions consist of engaging in physical activity, such as walking or running, in nature (Bikomeye et al., 2022). These interventions are different from wilderness/adventure therapy in that although they do involve physical activity, their focus is not on overcoming challenges.

The key features of Wilderness/Adventure Therapy Programmes usually involve some form of more complex, longer-term outdoor exercise activities hiking, trekking, and camping from 2 weeks to as long as 3 months (Bettmann et al., 2016). Likewise, the core of adventure interventions involves a certain form of risk in nature, such as camping, backpacking, or skiing. As such, these interventions can encompass both wilderness and adventure intervention programmes (Rosa et al., 2023).

Forest bathing, also called shinrin-yoku, is a practice involving conscious and mindful immersion in the forest through all five senses. Forest therapy is related to forest bathing in the sense that it is a clinical application of forest bathing with a focus on specific physical and mental health difficulties (Caponnetto et al., 2022).

Most of the other NBIs mentioned cover green spaces, but blue spaces are just as viable for NBIs. Blue spaces can be defined as all visible, outdoor, natural surface waters with the potential to promote human health and wellbeing (Britton et al., 2020). As such, as of right now, all interventions involving blue spaces would be under the umbrella term Blue Space Interventions, and such interventions may include surfing (Carneiro et al., 2024), scuba diving (Guntur et al., 2023), or outdoor swimming (Overbury et al., 2023). Although there is some overlap between blue and green spaces, some reviews argue that blue spaces can offer original benefits which might be inaccessible in green spaces alone (Britton et al., 2020).

Care farming involves the use of farms and agricultural landscapes for promoting mental and physical health through regular farming activities (Gorman and Cacciatore, 2017).

Nature play interventions are nature-based, unstructured interventions aimed at children which allow them to play in environments containing natural elements such as gardens, forests, ponds, water, mud, plants, or rocks (Dankiw et al., 2020).

Nature-Based Education or Nature-Based Learning is an approach in education which utilises the natural environment to facilitate learning (Miller et al., 2021). Such activities can include simply using a natural area as an outdoor classroom to actively using the natural environment in classes.

Environmental volunteerism involves activities such as tidying trails, soil preparation, tree planting, or recycling (Chen et al., 2022) and whereas most of the aforementioned interventions used nature in some way to improve mental and physical health, environmental volunteerism gives back to nature and Earth to improve our health.

Also called “friluftsliv,” this Scandinavian tradition covers a wider range of interventions: outdoor life, outdoor recreation and education, or adventure recreation and education, with an emphasis on achieving closeness to nature (Mygind et al., 2019).

Caring for Country is less of an intervention and more of a tradition for Indigenous Australians. It involves spending time in the country, revegetation, harvesting, protecting sacred areas and threatened species, or controlling fires, weeds, or feral animals (Fatima et al., 2022). These activities express the deeply interconnected relationship between the people and the country, from which both the people and the country benefit. These activities may resemble environmental volunteerism, as perhaps environmental volunteerism is a way for our modern population to try to reconnect and care for their country again.

Two types of interventions have emerged from the analysis. The first type explored the level of activity required for participants to engage with NBIs. Active interventions were characterised by the participants’ direct physical, behavioural, or cognitive engagement. These interventions included such activities as movement, decision-making, skill-building, or overcoming challenges that require sustained and intentional participation. In contrast, passive interventions referred to experiences in which individuals receive the benefits of nature with minimal physical or mental effort. These were less demanding and included such activities as simply being present in a natural environment, viewing nature, or engaging in undirected relaxation outdoors. The terms Nature-Based Interventions and Blue Space Interventions were excluded as they cover a wide range of interventions including both passive and active ones, making them unfit for this distinction. For more details on this active and passive distinction for each NBI please see Table 2.

The second type of NBI that has emerged refers to whether nature was a primary or secondary focus. In NBIs that viewed nature as a primary focus, nature was the central therapeutic or educational agent, and the benefits of NBIs could be easily linked to nature. These NBIs included activities such as forest bathing, where the primary focus is on connecting with nature, or horticultural therapy, which focuses on attending to nature. On the other hand, in NBIs that viewed nature as a secondary focus, nature played a supportive or contextual role. These NBIs included outdoor classrooms, where the learning experience was the primary focus or green exercise, where physical activity is the primary focus of an activity, and nature is the context within which it is conducted. Similarly to the previous table, the terms Nature-Based Interventions and Blue Space Interventions were excluded as they cover a wide range of interventions. For more details on this primary and secondary distinction for each NBI please see Table 3.

The social factor appeared in four out of five reviews discussing the moderating/mediating factors. In one study, a two-year exposure to a schoolyard improved children’s social well-being (Vella-Brodrick and Gilowska, 2022). However, social interaction was also an important aspect of NBIs for older adults (Yeo et al., 2020). Moreover, positive social interactions may improve hopelessness and feeling bad about oneself in depression (Rosa et al., 2023).

Many of the NBIs in this review involve some form of physical activity, which may be another factor in terms of many of the benefits of NBIs (Rosa et al., 2023; Vella-Brodrick and Gilowska, 2022), as physical activity and the outdoors are inherently linked.

In one review, nature exposure did not seem to have the same effects on school children aged 7–12 when compared to middle or high school students (Vella-Brodrick and Gilowska, 2022). Another review found mixed effects of age in relation to mental, physical, and social wellbeing (Ly and Vella-Brodrick, 2024).

As some NBIs can strengthen a participant’s nature connectedness (Rosa et al., 2023), or in the case of blue space interventions, water connectedness (Overbury et al., 2023), a person’s nature connectedness might impact how responsive they are to a given NBI.

In studies with older adults, a larger proportion of the studies which lasted more than 5 weeks (7 out of 9) reported significant findings compared to the proportion of studies lasting 5 weeks or less (3 out of 9) (Yeo et al., 2020). Another review also reported the benefits of NBIs on attentional functioning in children in the short term, while the benefits of long-term NBIs were difficult to assess (Vella-Brodrick and Gilowska, 2022). As the former review focused on older adults and the latter on children and cognitive benefits, the efficiency of short-term vs. long-term NBIs is difficult to disentangle. As for frequency, horticultural interventions of 2 or more in frequency were more beneficial (Wang et al., 2024).

One review found differences between the effects of gender on physical activity between boys and girls at school (Ly and Vella-Brodrick, 2024), where although boys were found to have more physical activity overall, it was girls’ physical activity which benefited most from NBIs.

One review on horticultural therapy and individuals with schizophrenia (Lee et al., 2024) found that symptom severity was important, as the effect sizes were larger for those with moderate severity compared to those with mild severity.

A review on horticultural therapy in older patients with dementia (Wang M. et al., 2024) found outdoor interventions to have a larger effect size than indoor interventions.

One review highlights the importance of participant motivation and preference on the effectiveness of NBIs (Rosa et al., 2023). The more the participants are motivated to participate in the intervention, and the more the intervention aligns with the participants’ preferences, the less likely they may be to drop out of the intervention.

Overcoming a challenge, which is an aspect present in some adventure therapies, has been found to be an effective way of improving the symptoms of depression by potentially improving the participants’ self-confidence and resilience (Rosa et al., 2023).

NBIs which involved providing older adults with autonomy, responsibility, and some form of skill or knowledge acquisition, were more likely to be effective (Yeo et al., 2020). Another review shares a similar view, noting that the satisfaction of needs such as autonomy, competence, and relatedness might partly explain the mental health benefits of NBIs (Rosa et al., 2023). As such, an improved perception of autonomy through NBIs might improve their effectiveness. The acquisition of new knowledge and skills in older adults can thus not only improve the effectiveness of NBIs but also improve their lives.

This overall pattern of the importance of the social aspects of NBIs is difficult to ignore. NBIs can not only bring people together, but also improve people’s social skills (Bloomfield, 2017). As such, social NBIs might be effective at combating increasing loneliness (Buecker et al., 2021), and implementing group NBIs might bring about greater benefits than individual ones.

Nature can not only make it easier for people to achieve sufficient levels of physical activity, it can also enhance the amount and intensity of the physical activity itself (Gladwell et al., 2013). Researchers exploring NBIs involving physical activity should account for the benefits of physical activity and ensure the benefits are not purely based on the physical activity involved in the NBI. Similarly, practitioners may find it useful to account for patients’ physical ability when choosing appropriate NBIs and recommending NBIs involving physical activity when suitable.

The reviews included in our review cover all age ranges from children to older adults, and as such, NBIs appear to be appropriate for individuals of any age. However, age remains a factor (Shanahan et al., 2019), as not all NBIs are equally appropriate for all ages. For example, more physically intensive NBIs such as weeks or months-long hikes might be too difficult, if not detrimental, to older adults. Future research should thus take into consideration the differences in the effectiveness of NBIs between major age groups and throughout childhood and adolescence. In addition, practitioners may want to take age into account especially in combination with the physical requirements of an NBI.

Nature connectedness can change how individuals interact with nature (Martin et al., 2020). For example, blue space interventions such as swimming claim to involve more immersion in nature (Overbury et al., 2023) than green space interventions, as you are surrounded and within the water. The question is whether this complete connectedness of being within nature changes peoples’ nature connectedness differently than just looking at nature on a screen such as in nature viewing. Future studies may not only explore an individual’s nature connectedness before the study, they may also explore how a person’s nature connectedness changes throughout the different types of NBIs.

NBIs may last anywhere from a few minutes, hours, to weeks or months. As such, it is essential to narrow down the minimum efficient “dose” of NBIs (Wilkie and Davinson, 2021) in terms of both duration and frequency. Future research should thus explore experiment duration and frequency as an essential variable to determine NBI efficiency. Ascertaining the minimum effective dose of NBIs would be of special benefit to healthcare professionals and practitioners.

Symptom severity has been found to be an important factor, which aligns with other mental health literature, for example, with depression severity and antidepressant effects (Fournier et al., 2010), with patients with increased severity seeing more benefit from antidepressants. As such, NBIs might be especially beneficial for people with more severe mental health symptomology.

Outdoor interventions have been found to be more effective than indoor ones, aligning with previous literature on exercise and how people find outdoor exercise to be more enjoyable than indoor exercise (Noseworthy et al., 2023). Healthcare practitioners and clinicians should thus consider outdoor NBIs before indoor ones.

Treatment preference is associated with decreased rates of dropping out of treatments (Windle et al., 2020). Developing personalised NBIs and ensuring they are interventions people want to do themselves would thus increase the likelihood of them participating in the intervention and not dropping out.

Research shows confronting a challenge may lead to improvements in depression symptoms after NBIs (Rosa et al., 2023), however, this factor might have broader applicability. Improvements in peoples’ self-confidence and resilience might apply to non-depressed individuals as well (Liu et al., 2020). As such, when considering patients with impaired self-confidence, resilience, or depression, NBIs involving challenge confrontation might prove beneficial.

Autonomy refers to the extent to which a person can live an independent life and is often decreased in older adults (Sánchez-García et al., 2019). Learning new skills and knowledge is not just a way for older adults to spend time, it can also be a way for them to chase subjects and skills they did not have time to invest in during their life (Narushima, 2008), providing countless benefits. NBIs which improve a person’s autonomy and skills may thus be especially beneficial for older adults.