Forest therapy

The healing process

Forest therapy with repeated visits to the forest for an extended period of time improves mental health, reduces stress, improves sleep quality, reduces exhaustion, stress and fatigue (Vujcic & Tomicovic-Dubljevic, 2018; Dolling et al 2017; Sonntag-Öström et al 2015a). Long-term forest therapy promotes self-healing, and participants who, from the start, are not always comfortable with the intervention, increasingly identify themselves with nature, find calm, become less stressed and start to embrace their lives in order to create change (Lee et al 2019; Sonntag-Island et al 2015b). What happens in forest therapy is that participants experience a positive mood followed by cognitive and behavioural changes. The process can be described as a path of stimulation, acceptance, purification, insight and recovery leading to change (Oh et al 2020).

What is measured?

In experimental studies, different indicators are measured to determine the efficacy of forest therapy. They are usually divided into psychological and physiological indicators.

Psychological indicators – self-assessment

Mood, stress, anxiety, depression, sleep, pain, health and recovery are examples of measurements where test participants use validated surveys to assess their status themselves. In this case, there is the perception that, because participants can control their own outcomes, the results may therefore be exaggerated.

Physiological indicators - not influenceable

Physiological indicators measure the condition of the body regardless of what test participants believe they are experiencing and are therefore regarded as stronger evidence than self-assessment. Pulse rate, blood pressure, heart variability (HRV), serotonin and cortisol are physiological parameters that are measured to indicate decreased stress. Amongst other things, so-called natural-killer cells (NK cells) and antioxidants are measured to determine whether the immune system improves.

In order to develop a measurement system for the effects of forest therapy, 87 different indicators were measured during a three-day forest therapy (Park et al 2021). 46 of these showed significant changes, amongst other things, blood pressure dropped immediately after the forest stay but after a week the effect had worn off. HRV improved and the forest stay had a positive influence on the anti-cancer system and the immune system. Antioxidant levels increased immediately after the forest stay but then diminished quite rapidly. The serotonin levels rose after the forest stay and remained at high levels. The cortisol (which in many other studies went down) was not affected at all. Mental recovery and self-confidence increased, but mental strength decreased and stress levels (which usually go down in most studies) were not affected at all. The fact that the results vary so much shows that it is not easy to measure the effects of forest therapy. It is therefore not so strange that psychological and physiological parameters do not always accord. It is also particularly difficult to measure many of the physiological parameters because they can vary greatly between people over a 24-hour period and because they are affected by more than just stress levels.

Effects on different target groups

The mood increases in people with exhaustion disorders immediately after a visit to the forest, but the positive effect also lasts for an extended period, which can be up to three months (Sonntag et al 2015a). Two-month forest therapy improves mood and reduces anxiety in people with affective (e.g., depression) or psychotic disorders (Bielinis et al 2019). Forest therapy on your own facilitates more self-reflection and focus on your own internal condition, whereas guided forest therapy evokes positive feelings and promotes social ties (Kim et al 2021).

Fostered children improve their relationships with other people (Hong et al 2021). Young people under a supervision order boost their mental health and have better heart variability values when they are allowed to participate in forest therapy compared to young people who are left at a Young Offenders Institution (Jeon et al 2021). Adults have more positive feelings, become less stressed and have lower blood pressure (Yua CP & Hsieha H 2020).

NK cells, which are expected to ‘kill’ cancer cells, among others, increase in women with breast cancer after having participated in an adjuvant treatment consisting of daily forest therapy for 14 days (Kim et al 2015). Women who work in healthcare experience stress relief and good recovery using forest therapy, but the physiologically measured parameters (cortisol, heart variability and NK cells) showed the opposite effect (Jung et al 2015).

/Text: Ann Dolling