Story at-a-glance -

• Forest bathing has psychological and physiological effects
• Trees emit compounds that boost the immune system and provide relaxation
• 60% of medicines contain tree compounds
• Soil contains bacteria that work similarly to antidepressants
• Native forests are disappearing due to deforestation and tree farming
• Native forests are crucial to land, air, oceans and marine life

Most of us have experienced the positive results of immersing ourselves in nature and being enveloped by trees. We experience an immediate relaxation, an ability to forget our problems and often a profound awe at nature's secrets.

The documentary "Call Of The Forest –– The Forgotten Wisdom of Trees" adds to the scientifically supported psychological and physiological effects associated with spending time in the woods. It shows how trees and forests intricately affect the land, sea and air around them and are essential to flora and fauna.

Experts included in the documentary postulate that trees were the very beginning of life on earth, which was nothing but a "rock" until the appearance of trees and the organic matter called humus.

But "Call Of The Forest" also shows the devastating effects of deforestation, removal of native trees, "tree farming" (in which trees are made into monoculture crops) and the lumber industry. Luckily, some people like Diana Beresford-Kroeger, a classical botanist, medical biochemist and author who has studied rare tree species for more than 40 years, are committed to stopping these dangerous trends and instilling in the public a greater awareness and respect for forests.

Trees have formidable and healing powers

"We have missed the essentials of what a tree is all about," says Beresford-Kroeger at the beginning of the documentary, which brings viewers to Japan, Ireland and the Redwood forests in the United States, as well as the Boreal forest of Canada.1 Beresford-Kroeger says that in Japan, "forest bathing," also known as Shinrin-yoku, is a revered and long-standing tradition. It means taking in the forest through our senses.

Tree bathers avail themselves of medicinal properties, says Beresford-Kroeger, as 60% of all medicines use tree elements. Limonene, produced by trees, is an anticancer compound used in chemotherapy. Linolenic acids are "essential acids for development and functioning of the brain" and pinenes are an antibiotic compound. Trees also emit alpha-Pinene, beta-Pinene, bornyl acetate and camphor compounds, according to the documentary.

The bottom line, says Beresford-Kroeger as she forest bathes herself, is that the tree compounds "are giving me a slightly narcotic effect" boosting the immune system and relaxing the body. All those positive chemicals "are now in my lungs" she tells viewers as birds chirp and leaves rustle during her forest bath.

At home on the farm

Beresford-Kroeger, who is originally from Ireland, keeps a farm in Ontario, Canada, which displays the results of her steadfast and dedicated devotion to native and rare plants and reforestation. In the documentary she shows viewers a black walnut tree, known by the genus juglaus Nigra, which she says she planted 30 years ago as a seed. It is now towering.

Showcasing the globe-like fruit of the walnut tree (which she points out is actually a nut), Beresford-Kroeger says the nut possesses minerals and other valuable substances "that are scare in our food these days." The compounds protect the myelin sheaths in human cells and people should eat them three or four times a day, she advises. "These nuts are as good as any beef on the market," she remarks.

As the author of books like "To Speak for the Trees: My Life's Journey from Ancient Celtic Wisdom to a Healing Vision of the Forest," "The Global Forest: Forty Ways Trees Can Save Us," Beresford-Kroeger sees the development of native species as a crucial tool against environmental degradation challenges. Native forests are "our cheapest and best defense against climate change," she asserts.

Native forests are irreplaceable but disappearing

Professor Akira Miyawaki, who lives in Tokyo, has spent 50 years planting and restoring native species forest systems. Building small city forests is important to offset the effects of the built environment with its expanses of concrete and pavement, he says. But less than 1% of native forests now remain in Japan so the battle is far from won.

In the past, Japan cut down mass expanses of trees to make farmland, only to find devastation produced a barren desert where nothing could or would grow. According to the documentary, the decimation of trees, which has occurred in many developed countries, disregards the intricate mineral interplay that exists between natural forests and the rest of the environment since iron is the foundation of the food chain.

It is "fulvic acid which attracts and locks in the iron molecules," explains professor Katsuhiko Matsunaga, a marine chemist featured in "Call Of The Forest." And where does fulvic acid come from? Decaying leaves, he says. Moreover, marine life needs and depends on minerals emitted by natural forests as well as nitrogen. Without forests there are literally no fish, he warns.

Native forests affect the land, oceans and air

In addition to their land and marine benefits, trees also function as "condenser units," says Beresford-Kroeger –– collecting and preserving potable water. For example, redwood trees, the tallest conifers on the planet, participate in a crucial environmental cycle with the Pacific Ocean: They trap mist from the ocean, pull moisture up from the aquifer (rock which holds groundwater) and then replenish the aquifer with condensation from ocean mist.

"A redwood is the largest carbon-bearing living organism on earth," says Professor Emeritus Bill Libby, a geneticist at UC Berkeley who was featured in the documentary. "They are growing faster than they ever have in their life," yet the ones we see today are actually smaller and less robust than the redwoods our ancestors cut down.

To convey their immensity, Beresford-Kroeger says it would take an entire town of 13,000 people to balance the weight of a redwood tree if it were put on a scale.

Nature produces a natural antidepressant

The soil of the forest also has healing powers, according to a report in The Atlantic: '"If you hold moist soil for 20 minutes,'" says Craig Chalquist, chair of the East-West Psychology Department at the California Institute of Integral Studies, 'the soil bacteria begin elevating your mood. You have all the antidepressant you need in the ground.'"2

Chalquist is not the only scientist noting this additional benefit of forests and trees. A 2007 article in the journal Neuroscience found soil bacteria called Mycobacterium vaccae can increase serotonin, so soil works in a similar fashion to an antidepressant:3

"We have found that peripheral immune activation with antigens derived from the nonpathogenic, saprophytic bacterium, Mycobacterium vaccae, activated a specific subset of serotonergic neurons in the interfascicular part of the dorsal raphe nucleus (DRI) of mice, as measured by quantification of c-Fos expression following intratracheal (12 h) or s.c. (6 h) administration of heat-killed, ultrasonically disrupted M. vaccae, or heat-killed, intact M. vaccae, respectively ...

The effects of immune activation were associated with increases in serotonin metabolism within the ventromedial prefrontal cortex, consistent with an effect of immune activation on mesolimbocortical serotonergic systems."

More soil benefits hypothesized

In 2017, it was reported in the journal that when mice ingested Mycobacterium vaccae it also reduced anxiety:4

"In this preliminary research, we show that mice fed live M. vaccae prior to and during a maze learning task demonstrated a reduction in anxiety- related behaviors and maze completion time, when tested at three maze difficulty levels over 12 trials for four weeks. Treated mice given M. vaccae in their reward completed the maze twice as fast as controls, and with reduced anxiety-related behaviors.

In a consecutive set of 12 maze trials without M. vaccae exposure, treated mice continued to run the maze faster for the first three trials, and with fewer errors overall, suggesting a treatment persistence of about one week."

Research in Annals of Oncology even suggests the soil component may be useful in treating cancer:5

"In this non-placebo controlled trial, SRL172 when added to standard cancer chemotherapy significantly improved patient quality of life without affecting overall survival times."

Exposure to trees may have other health benefits

The widely observed calming effects of trees may also have a biological component, according to research published in 2015 in the Proceedings of the National Academy of Sciences of the United States of America:6

"We show in healthy participants that a brief nature experience, a 90-min walk in a natural setting, decreases both self-reported rumination and neural activity in the subgenual prefrontal cortex (sgPFC), whereas a 90-min walk in an urban setting has no such effects on self-reported rumination or neural activity.

In other studies, the sgPFC has been associated with a self-focused behavioral withdrawal linked to rumination in both depressed and healthy individuals. This study reveals a pathway by which nature experience may improve mental well-being and suggests that accessible natural areas within urban contexts may be a critical resource for mental health in our rapidly urbanizing world."

Recovery from gallbladder surgery was even hastened when patients viewed trees, according to research in the journal Science:7

"Records on recovery after cholecystectomy of patients in a suburban Pennsylvania hospital between 1972 and 1981 were examined to determine whether assignment to a room with a window view of a natural setting might have restorative influences.

Twenty-three surgical patients assigned to rooms with windows looking out on a natural scene had shorter postoperative hospital stays, received fewer negative evaluative comments in nurses' notes, and took fewer potent analgesics than 23 matched patients in similar rooms with windows facing a brick building wall."

A prescription for parks?

With all the benefits of trees and natural forests will doctors soon be prescribing parks to their patients? It is already happening, according to a report in The Atlantic.8 Dr. Robert Zarr, a pediatrician in Washington, D.C., actually writes prescriptions for parks:

"He pulls out a prescription pad and scribbles instructions — which park his obese or diabetic or anxious or depressed patient should visit, on which days, and for how long — just as though he were prescribing medication ...

Zarr is part of a small but growing group of health-care professionals who are essentially medicalizing nature.

He relies on a compendium of 382 local parks — the product of meticulous mapping and rating of green spaces, based on accessibility, safety, and amenities — that he helped create for DC Park Rx, a community-health initiative. The Washington program was one of the first in the United States; there are now at least 150 others.

Park prescriptions are a low-risk, low-cost intervention that, in Zarr's experience, people are quick to accept. And sure, people are more likely to move around in a park than they are when watching TV, but there may be more to it than that.

Researchers in the United Kingdom found that when people did physical activities in natural settings instead of "synthetic environments," they experienced less anger, fatigue, and sadness. A 2015 study in Proceedings of the National Academy of Sciences reported that walking in a park reduced blood flow to a part of the brain that the researchers claimed was typically associated with brooding."