According to shinrin-yoku.org, forests help to improve the immune system, including the part that fights cancer:
But in the past several decades there have been many scientific studies that are demonstrating the mechanisms behind the healing effects of simply being in wild and natural areas. (some of this research is available here). For example, many trees give off organic compounds that support our “NK” (natural killer) cells that are part of our immune system's way of fighting cancer. The scientifically-proven benefits of Shinrin-yoku include:
- Boosted immune system functioning, with an increase in the count of the body's Natural Killer (NK) cells.
- Reduced blood pressure
- Reduced stress
- Improved mood
- Increased ability to focus, even in children with ADHD
- Accelerated recovery from surgery or illness
- Increased energy level
- Improved sleep
They link to a list of scientific literature, but I don't know the quality of those articles. Some refer to "essential oils", which rings a skeptical alarm bell in me, others look scientific (with DOI and 9 months from submission to acceptance). Anecdotally, I am ready to believe that being in a forest reduces stress in many people, compared to being in a city; I find this quite plausible. But does forest therapy (Shinrin-yoku) really boost the immune system, including the component that helps fight cancer?