Experiences conducted in central and northern Europe have surprisingly demonstrated how forest immersion in winter, in an environment with a layer of snow and ice on the ground, can produce significant benefits for mental health, comparable with experiences conducted in the spring and summer periods.1 A view of snow and ice, with their relative repetitive structures – from great snow-covered expanses to the tiniest ice crystal, the true prototype of the “fractal” form – is the most relaxing thing and the least demanding of our attention. So, snow-covered winter environments provide direct ecosystemic services for human health, and these are but the tip of the iceberg of the services rendered by snowy and glacial environments.
In fact, snow cover and mountain and arctic glaciers render the fundamental ecosystemic service of gradually releasing rainwater, preventing disastrous floods and ensuring a relatively constant supply of water throughout the year to fulfil the demands of irrigation, drinking water and hydroelectric energy generation. In the high-mountain environment and at other high latitudes, the ice that remains all year round in the subsoil – permafrost – ensures the stability of the slopes and the ground itself, preventing instability and guaranteeing the stability of buildings.2
These natural elements are, however, subject to imminent danger: snow, ice and the glaciers are truly among the elements most sensitive to climate change. Snowfall is increasingly irregular, rises ever higher and the thawing cycle is ever more rapid, undermining the sustainability of ski resorts and accelerating the water cycle.3 As well as economic and territorial consequences, the presence and persistence of snow or ice has always represented the passing of the seasons and, more in the long term, changes to the high-mountain landscape. The swift retreat and increasingly marked loss of both the snow and entire glacier systems, with processes now measured in terms of the decade if not a few years, is a source of anxiety and stress for mountain residents and for all high-mountain lovers and visitors who have often been frequenting them for their entire lives.
The alpine glaciers have lost 70% of their volume in just over a century, making way for scree, landslides and risks for mountaineers.4 Following catastrophic collapse, the glaciers of Greenland and west Antarctica are threatening to flood coastlines worldwide.5, 6 The expanse of Arctic sea ice, perhaps the most obvious indicator of climate change, has more than halved in summer over the last 40 years, in a spiral that, in still uncertain times, might lead to a remodelling of all the Great Northern landscape with fatal consequences for fauna and local populations, and perhaps destined to generate a terrible new scenario of conquest and war.7

— Francesco Meneguzzo, Federica Zabini

Institute of BioEconomy, CNR - Sesto Fiorentino (FI) CAI Central Scientific Committee

The sense of well-being and relaxation experienced before natural landscapes compared with man-made ones is already established and documented. The first explanation stems from the fact that human beings respond in a far simpler and more immediate manner to stimuli present in the natural environment than in artificial ones – that is, with more “fluid perception” (the ease with which a stimulus is processed by the brain).1-2
For example, processing visual stimuli connected to natural environments requires less effort of us than to artificial ones, as demonstrated by several studies analysing the activation of different parts of the brain and eye movement according to the stimuli presented to us.2
Somehow, it is as if we were “programmed” to easily process the stimuli present in the natural environment, which has been our habitat for the greater part of human history. This is why certain features of natural environments, from geometric forms to the variability of sunlight and the soundscape, demand low levels of attention and cognitive load.
Several studies in the neuroscience field have, for instance, shown that people prefer so-called “fractal” shapes, that is repetitive and recursive ones. These structures are typical and frequent in natural environments as opposed to anthropomorphic ones.3-4 Forests, just like every single tree, are quintessential examples of fractal geometric structures. They are composed of similar structures which are repeated on different, ever smaller, spatial scales: the branches of a tree look like small versions of the tree itself and this applies down to the twigs and tiniest ramifications.
Visualising repetitive scenes encourages relaxation and therefore reduces the activity of the sympathetic system, particularly “hyperactive” in patients suffering from depression and anxiety, producing genuine therapeutic effects in these subjects but also in so-called “healthy” individuals in general.5
As well as the presence of repetitive structures (trees, forests), the mountain environment can also be a place of well-being merely because it is generally located far away from man-made infrastructures: well-being prompted by silence, punctuated by the relaxing sounds of the forest, as too by the quality of the night sky. In fact, darkness – in Italy found now only on a few remote islands and the most isolated mountain scenarios – translates into an opportunity to reconnect with an essential component of natural well-being. And yet, more than 70% of the world’s population has never seen the Milky Way: vegetation, fauna and humans themselves are subjected to constant and potentially harmful stress because of the poor quality of nocturnal darkness.6

— Francesco Meneguzzo, Federica Zabini

Institute of BioEconomy, CNR - Sesto Fiorentino (FI) CAI Central Scientific Committee

Despite Aristotle’s ancient intuition, the fact that air has mass and so can exercise pressure was only fully understood 500 years ago by Galileo Galilei and Evangelista Torricelli. Continuously powered by the sun, wind and pressure play an endless two-handed game, with pressure gradients creating wind and wind equalising differences in pressure. At all scales, wind is determined by the atmospheric pressure gradient, as well as by the Coriolis force resulting from the Earth’s rotation. In their turn, pressure gradients form in response to differences in heating, usually inherent in different insolation, both at ground level and along the atmospheric column. Thanks to the research of the Russian physicists Anastassia Makarieva and Victor Gorshkov, since the end of the 2000s, it has been posited – and then widely confirmed – that the great natural forests, both tropical and boreal, generate far-reaching pressure gradients through the transpiration of water vapour and subsequent condensation and immense heat release. In this way, the great forests – but only natural, balanced ones – are capable of “recycling” the masses of moist ocean air, transporting it for thousands of kilometres and thus bringing rain to areas that would otherwise be semi-deserts.1, 2 This is the so-called “biotic pump” that generates rainfall and therefore networks of life.
Air is like Eros and Thanatos. Oxygen gives life, enabling cellular respiration, and, at the same time, oxidises and destructs our cells. Other compounds in the air are, instead, a direct consequence of our lifestyle: rich in either pollutants or in beneficial compounds, certain terpenes – components of essential oils – in particular among the latter, are emitted by the trees and ground of forests, as confirmed by consolidated scientific evidence. Over the long period in history when humans inhabited the forest, our organism adapted to best exploit the properties of the forest atmosphere. That is why whenever we immerse ourselves in the forest, certain terpenes become significant vehicles of mental (anxiolytic, sedative) and physiological (antioxidant, anti-inflammatory, anti-proliferative and activating immune defences) well-being.3-5 On a global level, more than 90% of people breathe air that does not meet World Health Organization (WHO) standards. As well as damage to the cardio-respiratory system, recent scientific evidence points to a connection between some neurological issues and air pollution, relative to both neurodevelopmental disorders in children and to neurodegenerative diseases in adults.6
For example, research conducted by a team of Mexican scientists found changes in the structure of the brain, cognitive deficits and pathologies similar to Alzheimer’s disease in a group of children in Mexico City – the most polluted city in the world according to the United Nations – compared to children who live in a less polluted city.7
Another study on almost three thousand schoolchildren in Barcelona found that cognitive development was slower in students who attended schools with greater traffic pollution.8
A growing number of studies supports the claim that greater exposure to atmospheric pollution is associated with a decline in cognitive functions in adults or is, in any case, a significant risk factor in cognitive decline and dementia in the elderly.9

— Francesco Meneguzzo, Federica Zabini

Institute of BioEconomy, CNR - Sesto Fiorentino (FI) CAI Central Scientific Committee

Although generally an unconscious act, breathing forms the basis of our exchange with the outside world: in fact, when we immerse ourselves in a wood, we inhale volatile substances emitted into the forest atmosphere by vegetation and the ground.
Forest ecosystems release large quantities of these substances, called BVOCs (biogenic volatile organic compounds).1 These are molecules, whether heavy or light, formed of carbon and hydrogen; some also of oxygen. They fall under several chemical classifications (more than 1700 compounds from a total of 90 families of molecules have been identified to date) and have the common characteristic of being volatile, to an extent also related to their molecular weight, so they can disperse in the air.
Resulting from the secondary metabolism of plants, these compounds are a “language of smells” that enables immobile plants to communicate with other plants, and above all to ward off parasites and, on the contrary, to attract pollinator insects. The emission of BVOCs increases when a plant is moderately stressed, in particular in response to an attack from parasites.2
When inhaled, some of these substances, the low-molecular-weight light monoterpenes in particular, easily overcome the blood-brain barrier and, thanks to their solubility in blood, enter into circulation and reach all the organs, performing important “bioactive” functions: antioxidant, anti-inflammatory, immunoregulatory and relaxing (anxiolytics, sedatives and antidepressants) actions that are beneficial for cognitive processes. The best known and most functional monoterpenes are a- and ß-pinene, ß-ocimene, d-limonene, sabinene, myrcene and camphene. Their beneficial effects are evinced both locally, on the respiratory tract,3 and systemically, via a calming and anxiolytic action,4 dependent on the dose inhaled. A significant boost to the immune system has also been postulated.5-8 The properties of these compounds – which make the forest a natural dispenser of aromatherapy – therefore contribute decisively to the mental and physical well-being we can gain from exposure to a natural forest environment.
The quantity and type of terpenes emitted by plants depends in the first place on the type of species. Conifers emit the most efficacious monoterpenes; other broad-leaved trees such as holm oak and beech are more productive but emit terpenes that are relatively less functional for our health.
Climate conditions (temperature, radiation) and the vegetative phase of the plants strongly influence emission in the atmosphere, making the season and also the time of day fundamental factors in the modulation of concentrations of precious terpenes in the air.9

— Francesco Meneguzzo, Federica Zabini

Institute of BioEconomy, CNR - Sesto Fiorentino (FI) CAI Central Scientific Committee

Researchers in Japan have tried to find a new method to reduce stress by visiting forests and have proposed a new concept called “Shinrin-Yoku or Forest Bathing” in 1982.
Shinrin in Japanese means ‘forest’, and yoku means ‘bath’. So shinrin-yoku means bathing in the forest atmosphere, or taking in the forest through our senses. This is not exercise, or hiking, or jogging. It is simply being in nature, connecting with it through our sense of sight, hearing, taste, smell and touch.
Shinrin-Yoku is like a bridge. By opening our senses, it bridges the gap between us and the natural world.
In Japan, since 2004, serial tudies have been conducted to investigate the effects of this practice on human health. We have established a new medical science called Forest Medicine.
The Forest Medicine is a new interdisciplinary science, belonging to the categories of alternative medicine, environmental medicine and preventive medicine, which studies the effects of forest environments (Forest Bathing/Shinrin-Yoku/Forest Therapy) on human health. In 2007 we established the Japanese Society of Forest Medicine.
It has been scientifically reported1 that Forest Bathing/Shinrin-Yoku (forest therapy) has the following beneficial effects on human health:

1. Boosts immune function by increasing human natural killer (NK) activity, the number of NK cells, and the intracellular levels of anti-cancer proteins, suggesting a preventive effect on cancers.
2. Reduces stress hormones, such as urinary adrenaline and noradrenaline and salivary/serum cortisol contributing to stress management.
3. Improves sleep.
4. Shows preventive effect on depression by improving positive feelings and serotonin in serum and reducing negative emotions.
5. Reduces blood pressure and heart rate showing preventive effect on hypertension. 6. May apply to rehabilitation medicine.
7. In city parks also has benefits on human health.
8. Has preventive effect on lifestyle related diseases by reducing stress.
9. Shows preventive effect on COVID-19 by reducing stress and boosting immune function.2
10. Phytoncides3 play an important role in Shinrin-Yoku.

— Qing Li, MD, PhD

Professor at Nippon Medical School, Tokyo
Vice-president and Secretary General of the International Society of Nature and Forest Medicine (INFOM)
President of the Japanese Society of Forest Medicine