Putting Trees to Work for Our Health

forestI'm a treehugger, and proud of it. I love hiking and backpacking, and just generally being in the forest. My favorite fragrance ever is the smell of the woods - I wish someone would bottle it for me! Something about it always makes me feel lighter, freer and stronger. I had always believed that the effect was psychological, the mental equivalent of dropping a 40-pound suitcase of stress and worry at the trailhead. However, after reading the New York Times profile of scientist Diana Beresford-Kroeger, I'm starting to wonder if there's more to it than that. Like me, Beresford-Kroeger is a treehugger. Unlike me, she boasts bachelor's degrees in both medical biochemistry and botany. She is known for combining insights from the diverse fields of indigenous herbalism, modern medicine, and botany to reach some interesting conclusions.

When we think of ecosystems, we tend to think of the connections we can see, like predator/prey relationships and habitat requirements. What we can't see is the way that the organisms in the ecosystem are connected on a chemical level. Plants, animals, bacteria and fungi are constantly interacting with each other via the chemicals that they produce. Plants don't just take in oxygen and breathe out carbon dioxide, they also breathe out other substances and use them to modify their surroundings, and to attract or repel other organisms.

For example, in the article, Beresford-Kroeger describes the chemistry between wafer ash trees and butterflies:

The tree is a chemical factory, she explained, and its products are part of a sophisticated survival strategy. The flowers contain terpene oils, which repel mammals that might feed on them. But the ash needs to attract pollinators, and so it has a powerful lactone fragrance that appeals to large butterflies and honeybees. The chemicals in the wafer ash, in turn, she said, provide chemical protection for the butterflies from birds, making them taste bitter.- New York Times

There are countless other examples of plants using chemicals to create advantages for themselves and even to communicate with one another. For example, sagebrush shrubs use the chemicals they naturally produce to warn each other of attacks from insect pests, and the parasitic dodder vine is able to "sniff out" potential hosts by honing in on the chemicals they release into the air. Sunflowers and black walnut trees create their own herbicides to kill off unwanted plants growing nearby.

Diana Beresford-KroegerBeresford-Kroeger recommends planting more trees in the cities, and planting them with specific purposes, or eco-functions, in mind. She calls this bioplanning. For example, black walnut and honey locusts are especially good at filtering pollutants from the air, so they could be planted next to roads to capture some of the pollutants from the cars. Wafer ash could be used as "bait" in organic gardening to lure butterflies away from the crops. Basically, she advocates building an urban ecosystem where humans understand, appreciate and use their connections to trees and other life forms instead of pretending to be a separate, stand-alone species.

Then, she takes the concept of harnessing the natural chemicals produced by trees one step farther, assigning trees medicinal properties based on traditional medicinal uses and/or modern chemistry. This is where many fellow scientists believe she goes out on a limb, so to speak. Her hypothesis goes like this: Trees secrete chemicals into the air. Some of those chemicals have beneficial properties for humans, so if we plant trees that we know produce these chemicals, we might be able to protect ourselves from common ailments such as cancer.

Which brings me back to how great the smell of the forest makes me feel; after all, it's the smell of earth, decaying leaves, trees and the chemicals the trees give off. Can trees protect us from certain illnesses the way the wafer ash protects butterflies against birds? We don't know, and we won't know for sure unless someone decides to thoroughly research the issue. As the New York Times points out, black walnuts do give off limonene, which is a natural substance that has been tested before for cancer treatment. That doesn't necessarily mean that they give off enough to provide any protection against cancer for nearby humans. As Beresford-Kroeger herself says, "What trees do chemically in the environment is something we're only beginning to understand."

We hear so much about how long-term, low-level exposure to the chemicals and pollutants we produce can increase our risk of all sorts of nasty illnesses. It's comforting to think that Mother Nature might have an antidote somewhere in her medicine chest, and in a strange way, it  seems logical that long-term, low-level exposure to beneficial chemicals might play be able to decrease those risks. Even if Beresford-Kroeger's wilder ideas are totally bogus, however, trees can still help us be healthier by undoing some of the damage we do to the environment on a daily basis.

Aside from the unproven trees-can-prevent cancer hypothesis, there is a lot of scientific support for bioplanning. Besides their obvious benefit of removing carbon from the atmosphere, scientists have already proven that trees do a lot for the environment and for us. For one thing, they can help filter out toxic pollutants from the air and the soil, and that has beneficial health effects in and of itself. The Times article notes that kids who live on streets with lots of trees enjoy a 25% lower asthma rate than kids living on treeless streets. Also, this recent study showed that 3 rows of carefully chosen trees can filter out odors and emissions from poultry farms. Trees have also been used to remove toxic waste from soil, breaking it down into much less harmful compounds. This process, called phytoremediation, has even been used to clean up EPA Superfund sites.

There is no doubt that trees are good for us. The bone of contention between Beresford-Kroeger and more mainstream scientists is how good for us they are. Also, she appears to be speaking in the language of certainties even when she should be speaking in terms of possibilities. Personally, I find the idea intriguing, but I'm more interested in the proven benefits trees have on the environment. However, if you are interested in the potential medicinal properties of different trees, here is a list of a few species of trees she has recommended planting in the past:

  • Black Walnuts: These trees produce delicious and extremely nutritious nuts that were once a staple food for Native Americans. Beresford-Kroeger recommends planting them along roads and near gas stations to absorb and break down pollutants from the air. They also emit both limonene and ellagic acid, which are being investigated by scientists for possible uses in treating cancer.
  • Hawthorns: According to Beresford-Kroeger, the fragrance of hawthorn flowers helps prevent blood clots. Also, they attract songbirds and beneficial insects like bees and butterflies.
  • Cedar: Beresford-Kroeger says that cedar trees produce chemicals that strengthen the immune system. Also, the trees give off a chemical called fenchone, which herbalists classify as a cardiac stimulant. Camphor (the active ingredient in Vick's Vaporub) emitted by the trees may also make it easier to breathe.
  • Catalpa: Beresford-Kroeger says that catalpa flowers contain substances which promote respiratory and cardiac health. The tree's wax is antibacterial and anti-fungal, and the Cherokee used parts of the tree to repel insects.
  • Oak: Acorns provide a food source for many different types of animals. The mistletoe that often grows on oak trees produce a chemical currently being investigated as an anti-cancer agent, according to Beresford-Kroeger. 

Beresford-Kroeger recommended these trees during an interview with writer Deborah Donovan, published in the Daily Herald of Arlington Heights, Illinois on April 3, 2005.  

Further Reading:

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  • Posted on Sept. 9, 2008. Listed in:

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