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  • Writer's pictureSuzy Costello, workbooks

Scents of the forest and olfactory art

Gallery exhibitions offering olfactory experiences are becoming more popular and I would like to include the scents of the forest in my installation as the volatile oils produced by the beech forest profoundly affect our embodiment of the forest as we walk through it or settle in a quiet spot, whether we know it or not.

This video is by renowned perfumer Christophe Laudamiel as he discusses a new show (January 22, 2022) in the (only?) olfactory art gallery in the world, Olfactory Art Kellers in New York. He describes the complexity of smells and the subjective influence colours have on how we smell! Given humans can detect over a hundred shades of green but only a few dozen shades of other colour, it would be interesting to know how a background of green influences how we perceive smells in a forest?

Monoterpenes - Essential Oils

All plants emit monoterpenes - organic molecules of a simple, light 10 carbon structure - from their leaves, flowers and other parts, storing these substances in resin ducts or glands. When released, these monoterpenes exist in a volatile, gaseous state and each plant produces an essential oil that is a composition of multiple predominant molecules each with their own characteristic aroma and fragrance.

It is unclear what metabolic function monoterpenes play in a plant's life however it is known that stressed plants release more isoprene and monoterpenes with specific antioxidants to repel potential pests, and plants ready to pollinate release monoterpenes to attract insects, bats and birds. Recent research suggests trees talk to each other, sending chemical messages to warn of approaching pests or how they are feeling.

Trees Communicating

Wohlleben, a German forest warden and writer of the Hidden Life of Trees, describes in an interview with Smithsonian his insights into trees' communication -

"To communicate through the [fungal] network, trees send chemical, hormonal and slow-pulsing electrical signals, which scientists are just beginning to decipher. Edward Farmer at the University of Lausanne in Switzerland has been studying the electrical pulses, and he has identified a voltage-based signaling system that appears strikingly similar to animal nervous systems (although he does not suggest that plants have neurons or brains). Alarm and distress appear to be the main topics of tree conversation, although Wohlleben wonders if that’s all they talk about. “What do trees say when there is no danger and they feel content? This I would love to know.” Monica Gagliano at the University of Western Australia has gathered evidence that some plants may also emit and detect sounds, and in particular, a crackling noise in the roots at a frequency of 220 hertz, inaudible to humans.

Trees also communicate through the air, using pheromones and other scent signals. Wohlleben’s favorite example occurs on the hot, dusty savannas of sub-Saharan Africa, where the wide-crowned umbrella thorn acacia is the emblematic tree. When a giraffe starts chewing acacia leaves, the tree notices the injury and emits a distress signal in the form of ethylene gas. Upon detecting this gas, neighboring acacias start pumping tannins into their leaves. In large enough quantities these compounds can sicken or even kill large herbivores.

Giraffes are aware of this, however, having evolved with acacias, and this is why they browse into the wind, so the warning gas doesn’t reach the trees ahead of them. If there’s no wind, a giraffe will typically walk 100 yards— farther than ethylene gas can travel in still air—before feeding on the next acacia. Giraffes, you might say, know that the trees are talking to one another.

Trees can detect scents through their leaves, which, for Wohlleben, qualifies as a sense of smell. They also have a sense of taste. When elms and pines come under attack by leaf-eating caterpillars, for example, they detect the caterpillar saliva, and release pheromones that attract parasitic wasps. The wasps lay their eggs inside the caterpillars, and the wasp larvae eat the caterpillars from the inside out. “Very unpleasant for the caterpillars,” says Wohlleben. “Very clever of the trees.”

A recent study from Leipzig University and the German Centre for Integrative Biodiversity Research shows that trees know the taste of deer saliva. “When a deer is biting a branch, the tree brings defending chemicals to make the leaves taste bad,” he says. “When a human breaks the branch with his hands, the tree knows the difference, and brings in substances to heal the wound.”

Essential Oils Healing Humans

A small portion of trees' monoterpenes and essential oils are easily absorbed by humans through our skin and mucous membranes. However, it is the olfactory duct that offers monoterpenes the most direct pathway to our central nervous system and cerebral cortex, affecting instantaneous improvements to our cognitive processes, memory and mood. This instantaneous improvement is why we feel so good when walking in forests, and explains why the Japanese practice of 'Shinriu-Yoku', Forest Bathing, has become such a popular world-wide activity since its inception in 1982 by the Japanese Forest Service. More and more research is helping us to understand the medicinal properties of essential oils within forests and natural landscapes.

While the beneficial properties of essential oils to humans' health has been known for thousands of years it is only recently that we are beginning to understand their role as communication channels for the trees.

Essential oils of Aotearoa's Beech Forest

I have reached out to Francesco van Eerd at Fragrifert Victorian Perfumery in Wellington (027 607 1852 or 9348290) who has created distinctive New Zealand perfumes using distilled essential oils from our native flora. I hope to be able to use these essential oils in an installation.

I've also meet with Victoria University Earth Science librarian to see if there are any research papers and students interested in this area.

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