Can you see any plants right now? If not, you might want to fix that.
The overall importance of plants is obvious, since they give us food, oxygen and a wealth of natural resources. But on top of all those tangible blessings, is it possible that plants also subtly reward us just for spending time with them?
The mere sight of a tree or a houseplant may seem unlikely to offer any significant benefits, but thanks to a growing body of scientific research, it has become clear the human brain really does care about scenery — and craves greenery.
This stems from the power of biophilia, a term coined last century by psychologist and philosopher Erich Fromm, and later popularized by renowned biologist E.O. Wilson in his 1984 book, "Biophilia." It means "love of life," referring to humans' instinctive fondness for our fellow Earthlings, especially plants and animals.
"[T]o explore and affiliate with life is a deep and complicated process in mental development," Wilson wrote in the book's introduction. "To an extent still undervalued in philosophy and religion, our existence depends on this propensity, our spirit is woven from it, hope rises on its currents."
The beauty of biophilia is that, beyond making us feel drawn to natural settings, it also offers big benefits for people who heed this instinct. Studies have linked biophilic experiences with lower cortisol levels, blood pressure and pulse rate, as well as increased creativity and focus, better sleep, reduced depression and anxiety, higher pain tolerance, and even faster recovery from surgery.
Here's a look at the science of biophilia, as well as tips for reaping its rewards, whether you're wandering through an ancient forest or just unwinding on your porch.
A force of habitat
Biophilia is a familiar feeling for most people, even if we rarely give it much thought. It often comes in small doses during daily life, occasionally punctuated by more deliberate excursions into wilderness, soothing us in ways we may not recognize or understand. But why? What makes certain kinds of scenery more serene?
The answer starts with our ancestors. Modern humans have existed for about 200,000 years, mostly in wild environments like forests or grasslands until the dawn of agriculture some 15,000 years ago. Farming allowed more of us to cluster into human-centric settlements, and as early villages paved the way for larger, livelier cities, our species grew increasingly insulated from the wilderness that created us.
Only about 3 percent of all humans lived in urban areas as recently as 1800, according to the United Nations Population Division, but that had swelled to about 30 percent in 1950, 47 percent in 2000 and 55 percent in 2015. By 2050, the U.N. expects approximately two-thirds of humanity to be city dwellers.
Civilization has been a game changer for our species, boosting health and longevity while cultivating technology that makes us more capable and efficient. Yet behind its many advantages, this shift has also cost us some key aspects of our wilder past.
The calm of the wild
Humans, like all species, evolve to fit our habitat — the environment of evolutionary adaptation, or EEA. That's a slow process, though, and it may lag behind if a species' behavior or habitat changes too quickly. Sitting indoors all day is a far cry from foraging and hunting in the wild, for example, but the human body is still built for the latter since that's what our EEA required for most of human history. Many people now suffer serious health problems related to chronic sedentary behavior.
Yet even if we exercise daily, our habitat itself can still betray us. Urban areas pose insidious threats like air pollution, which now affects 95 percent of humans and leads to millions of premature deaths every year. Cities tend to be loud, too, with noise pollution that's linked to ailments from stress and fatigue to heart disease, cognitive impairment, tinnitus and hearing loss. Light pollution, which disrupts circadian rhythms, may lead to poor sleep, mood disorders and even certain cancers.
Changes like these plague countless urban areas, especially where people have removed most of the living scenery, scents and sounds that permeated earlier human habitats. Given the soothing effects biophilia can provide, modern humans may be losing a valuable source of resilience when we need it most.
Fortunately, we don't have to choose between civilization and wilderness. Just as many people now exercise to simulate our ancestors' active lifestyles, there are lots of ways to enjoy the benefits of biophilia without giving up modern amenities.
Bathe in the woods
One of the most obvious routes to biophilia is through a forest, where people have long escaped civilization to do things like hike, camp or just relax. This comes naturally to us, but it can help to be reminded why it's worth leaving our bubble. That way, taking time to visit a forest feels less like a frivolous diversion than a basic part of self-maintenance — sort of like bathing.
In fact, that's the idea behind shinrin-yoku, a popular Japanese practice commonly translated to English as "forest bathing." Japan's forestry ministry coined the term in 1982, part of an effort to promote public health as well as forest conservation, formally branding a concept that already had deep roots in Japanese culture.
The Japanese government spent about $4 million on shinrin-yoku research between 2004 and 2012, and the country now has at least 62 official forest-therapy sites "where the relaxing effects have been observed based on scientific analysis conducted by a forest medical expert." Those sites draw millions of visitors every year, but similar benefits also lurk in forests all over the planet.
What kinds of benefits? Here are a few that scientists have documented so far:
Stress relief: This coveted effect of forest bathing is well-supported by science, which links the practice with lower levels of cortisol — the body's primary stress hormone — as well as lower sympathetic nerve activity and higher parasympathetic nerve activity. (Parasympathetic nerve activity is associated with our "rest and digest" system, while sympathetic nerve activity is associated with a "fight or flight" state.) In one study published in PubMed, experiments featuring 420 subjects in 35 forests across Japan found that sitting in the woods led to a 12.4 drop in cortisol, a 7 percent drop in sympathetic nerve activity and a 55 percent rise in parasympathetic nerve activity — "indicating a relaxed state," the researchers wrote. Other studies show similar physiological effects from either sitting or walking in a forest, with subjects commonly reporting less anxiety, less fatigue and more vigor.
Lower pulse rate and blood pressure: A 2010 study published in Environmental Health and Preventive Medicine is one of many that link forest bathing with significant drops in average pulse rate (6 percent lower after sitting; 3.9 percent lower after walking) and systolic blood pressure (1.7 percent lower after sitting; 1.9 percent lower after walking). This fits with other research, like a 2017 meta-analysis of 20 studies totaling more than 700 subjects, which found that both systolic and diastolic blood pressure were significantly lower in forests versus non-forest environments.
Stronger immune system: Forests have repeatedly been shown to enhance activity of natural killer (NK) cells and expression of anti-cancer proteins. NK cells are a key part of the body's innate immune system, prized for attacking infections and guarding against tumors. In a 2007 study, nearly all participants had roughly 50 percent higher NK activity after a three-day forest trip, a benefit that lasted anywhere from a week to more than a month in follow-up research. This is largely attributed to botanical compounds known as "phytoncides" (more on that below).
Better sleep: Maybe we should count trees instead of sheep? In a 2011 study, two hours of forest walking significantly boosted the length, depth and quality of sleep in people with insomnia. The effect, which was stronger from afternoon walks than morning walks, is likely due to both the "exercise and emotional improvement initiated by walking in forested areas," researchers wrote.
Pain relief: Forest bathing could make a big difference for people with chronic widespread pain, according to a 2016 study published in the International Journal of Environmental Research and Public Health. Participants who took a two-day forest-therapy retreat not only showed improvements in NK activity and heart-rate variability, but "also reported significant decreases in pain and depression, and a significant improvement in health-related quality of life."
Yes you canopy
The canopy towers above a coastal-plain forest in Italy's Nazionale del Circeo. (Photo: Nicola [CC BY 2.0]/Flickr)
So how exactly can a forest trigger all these health benefits? It depends on the effect, some of which may represent the comfort and tranquility of forests compared with cities. Woodlands are typically cooler and shadier, reducing physical stressors like heat and harsh sunlight that can feed psychological stress. They also create natural windbreaks and absorb air pollution.
Forests are known to muffle noise pollution, too, and even just a few well-placed trees can reportedly reduce background sound by 5 to 10 decibels, or about 50 percent as heard by human ears. In lieu of traffic or construction noise, forests tend to offer more soothing sounds like warbling songbirds and rustling leaves.
And then there are phytoncides, also known as "wood essential oils." A variety of plants release these airborne organic compounds, which have antibacterial and antifungal properties, as a defense against pests. When humans inhale phytoncides, our bodies respond by boosting the number and activity of NK cells.
As researchers showed in a 2010 study, even a single forest-bathing experience can continue paying dividends for weeks afterward. "The increased NK activity lasted for more than 30 days after the trip, suggesting that a forest bathing trip once a month would enable individuals to maintain a higher level of NK activity," they wrote.
There aren't many universal rules for forest bathing, which seems to work under a wide range of scenarios. Some studies find results after 15 minutes of walking or sitting in the woods, for instance, while others involve multi-day immersions. There are groups that train and certify forest-therapy guides — like the Global Institute of Forest Therapy (GIFT) or the Association of Nature and Forest Therapy Guides and Programs (ANFT) — and lots of books and websites offering advice. This advice varies by source, and the best method for you may hinge on factors like your personality, your goals or the particular forest you visit. The basic idea is to relax and embrace the ambience, but for more specific tips, here are a few examples from the ANFT:
• Be mindful. A forest-bathing excursion should ideally involve "a specific intention to connect with nature in a healing way," according to the ANFT, which recommends "mindfully moving through the landscape."
• Take your time. Although exercise also boosts mental and physical health, it isn't the primary goal of shinrin-yoku walks, according to the ANFT. Its forest-bathing walks are typically a mile or less, often lasting two to four hours.
• Make it a habit. Much like yoga, meditation, prayer or exercise, forest therapy is "best seen as a practice, not a one-time event," the ANFT argues. "Developing a meaningful relationship with nature occurs over time, and is deepened by returning again and again throughout the natural cycles of the seasons."
• Be a good guest. As forests heal us, the ANFT advocates returning the favor. Not only is forest therapy a non-extractive process (i.e., take nothing but pictures, leave nothing but footprints); it can raise awareness about why forests are worth preserving, and encourage people to help protect their local woodlands.
If you don't live near a forest, it's worth noting other ecosystems can be restorative, too. The ANFT defines forest therapy as "healing and wellness through immersion in forests and other natural environments," acknowledging that biophilia works in many settings. Scientists are still exploring which ecological elements spark which benefits and how, but humans generally respond well to the presence of plants and certain animals, like songbirds, as well as rivers, lakes and other bodies of water.
"The therapeutic benefits of forest bathing may be difficult to fully explain with only phytoncides, but most likely, the green scenery, soothing sounds of streams and waterfalls, and natural aromas of wood, plants and flowers in these complex ecosystems all play a part," according to the Forest Therapy Association of the Americas. "Forest therapy is a good example of how our own health is dependent on the health of our natural environment."
A walk in the park
There are inherent rewards when we manage to get away from civilization, as biologist Clemens Arvay recently wrote for MNN:
'Being away' means we are in an environment where we can be as we are. Plants, animals, mountains, rivers, the sea — they are not interested in our productivity and performance, our appearance, our paycheck, or our mental state. We can be among them and participate in the network of life, even if we are momentarily weak, lost, or bubbling over with ideas and hyperactivity. Nature does not send us utility bills. The river in the mountains does not charge us for the clear, clean water we get from it when we wander along its banks or camp there. Nature does not criticize us. 'Being away' means freedom from being evaluated or judged, and escaping from pressure to fulfill someone else's expectations of us.
Of course, fleeing civilization isn't always a practical option. Biophilia may be most effective when you're immersed in an old-growth forest or gazing across a rolling prairie, but many people can't escape their urban environments for those kinds of experiences on a regular basis. Fortunately, biophilia is not an all-or-nothing proposition.
A forest is more than the sum of its parts, yet those parts can still heal us even if they're not in a pristine, natural ecosystem. This includes everything from large urban forests to leafy neighborhood parks to a few trees on a city street. An array of research has explored the restorative powers of urban green space, which can offer many of the same effects as a wild woodland.
Briefly visiting a city park can boost concentration, for example, with just 20 minutes yielding results in children with attention deficit-hyperactivity disorder (ADHD). It can also calm us down and cheer us up, according to a 2015 study from Chiba, Japan, which found that a 15-minute walk in the city's Kashiwanoha Park "resulted in a significantly lower heart rate, higher parasympathetic nerve activity and lower sympathetic nerve activity" compared with an equivalent walk in a nearby urban area. Park-goers were more relaxed, comfortable and vigorous, with "significantly lower levels of negative emotions and anxiety," researchers reported.
That study was conducted in autumn, but similar effects have been found in all seasons — even at the same park in winter, despite the meager foliage on trees. And during January in Scotland, another study found that urban residents who live near public green space have lower levels of cortisol and less self-reported stress.
Proximity is key to city parks' healing powers, since we tend to visit more often when we can get there quickly, especially by walking or biking. "As a rule of thumb," the World Health Organization advised in a 2017 report, "urban residents should be able to access public green spaces of at least 0.5 to 1 hectare within 300 meters' linear distance (around 5 minutes' walk) of their homes."
If a park has enough greenery, it might provide other forest-like advantages for people living nearby, such as cleaner air, less noise pollution or even protection from dangerous heat waves — a risk often magnified in cities by the "heat island" effect. The latter benefit was reported in a 2015 study from Portugal, which found that urban vegetation and water bodies "appeared to have a mitigating effect on heat-related mortality in the elderly population in Lisbon."
Thanks to research like this, urban green space is increasingly valued not only for aesthetic and environmental reasons, but also for its effects on public health. As people around the world struggle with a plight informally known as "nature deficit disorder," this awareness can inform key decisions at many levels, from policymakers and city planners to urban residents shopping for a home.
Rest on your laurels
One of the best things about biophilia is its flexibility, which lets us draw strength from slivers of nature as small as indoor plants or trees visible through a window. This makes its benefits accessible to a broader range of people, although it may be relevant even if your home abuts a forest or a park. In the U.S., people now average about 90 percent of their time inside buildings or vehicles, often failing to appreciate how these environments affect us — or how far a little sprucing up could go.
Some houseplants, for example, can improve indoor air quality by filtering out known human carcinogens like benzene, formaldehyde and trichloroethylene, which can seep into indoor air from certain building materials, household chemicals and other sources. Yet studies show they can also be absorbed by houseplants including aloe vera, peace lily, snake plant and spider plant, along with other harmful air pollutants like ozone, a component of smog that sometimes wafts indoors.
Aside from purifying the air, indoor plants have also been shown to boost productivity of office workers, and to both reduce stress and increase reaction time in windowless environments like a university computer lab. They can even improve pain tolerance, according to a 2002 study, which induced pain by immersing subjects' hands in freezing water. Those who could see indoor plants endured this for longer and reported lower levels of pain, researchers found, especially if the plants had flowers.
Plant life can be a big deal at hospitals, even if it's only visible through a window. Surgical patients in rooms with a window view of natural scenery, for instance, "had shorter postoperative hospital stays, received fewer negative evaluative comments in nurses' notes, and took fewer potent analgesics" than patients whose windows faced a brick wall, a 1984 study found.
Despite a long history of gardens on hospital grounds, they were "dismissed as peripheral to medical treatment for much of the 20th century," as Scientific American reported in 2012. Hard evidence of their healing power was thus eye-opening in the 1980s, when biophilia was still a relatively obscure concept and the austere atmosphere of hospitals was generally taken for granted. The idea has become mainstream in recent decades, as seen in the prevalence of biophilic amenities like healing gardens.
While it's important to keep realistic expectations about biophilia, these gardens really can be powerful tools for health care, as University of California-Berkeley professor emerita of landscape architecture Clare Cooper-Marcus told Scientific American.
"Let's be clear," said Cooper-Marcus, an expert in healing landscapes. "Spending time interacting with nature in a well-designed garden won't cure your cancer or heal a badly burned leg. But there is good evidence it can reduce your levels of pain and stress — and, by doing that, boost your immune system in ways that allow your own body and other treatments to help you heal."
Biophilic by design
If looking at flowers can help us endure pain, and seeing trees through a window can help us recover more quickly after surgery, just imagine how we might fare if more of our built environment was designed with biophilia in mind.
That's the idea behind biophilic design, which takes a holistic approach to helping modern human habitats mimic the natural environments that shaped our species. This can mean a variety of things, from the basic form and layout of a building to the construction materials, furnishings and surrounding landscape.
"The first step is, 'Why don't we just go outside?' The second step is, 'We'll just bring some trees inside,'" biophilic design expert and International Living Future Institute CEO Amanda Sturgeon recently told NBC News. "We're trying to go to the place after that — which is, 'What could we learn from what makes us love being outside and incorporate it into the design of our buildings?'"
A lot, it turns out. Interest in biophilic design has flourished lately, fueling research that has revealed a wealth of details. These include visual elements like natural lighting or "biomorphic" forms and patterns, along with less obvious things like variability of temperature and airflow, presence of water, sounds, smells, and other sensory stimuli. For more specifics, check out the in-depth "14 Patterns of Biophilic Design" by consulting firm Terrapin Bright Green, or this MNN story about the Living Building Challenge.
Try a little wilderness
Since so much of our lives unfold inside buildings, biophilically redesigning those spaces may be an ideal solution for many people's nature deficiency. But there are also cheaper, easier ways to benefit from an attention to biophilia, including one that happens to need our attention now more than ever: wilderness itself.
Even as we remodel and redecorate our built environment to evoke natural ones, biophilia could be our best hope for pushing ourselves to save what's left of the source material. Intelligence and ambition may have helped us create civilization, yet no matter how sophisticated we become, this strange instinct won't let us completely forsake the wilderness that made it all possible.
And considering how much civilization still relies on Earth's biodiversity, biophilia might prove even more vital to humanity than we thought. As E.O. Wilson argued in his 2016 book "Half-Earth," independence from nature is a dangerous delusion.
"Like it or not, and prepared or not, we are the minds and the stewards of the living world," Wilson wrote. "Our own ultimate future depends upon that understanding."