In this blog about health from aromatic compounds given off by trees I focus on key essential oil constituents and examples of trees to distil. Here in Part 1 you can read about pinenes and their effects, with some suggestions of trees to harvest. In Part 2 there are more medicinal constituents such as caryophyllene and limonene with further species suggestions for distillation.
Fresh smell of trees
Trees smell fantastic don’t they! The aroma of leafy material, bark, flowers and more from trees, as well as other plants, is part of the joy of walking in woods. Many plants emit volatile organic compounds (also known as VOCs) and these include some key constituents of essential oils which have been extensively researched. For example, a monoterpene called α-pinene gives many conifer trees their familiar fresh and resinous smell. But α-pinene is not only found in pine trees, it is also present in plants like cannabis, myrtle and sage, and it provides a precursor for numerous other aromatic molecules. There is also β-pinene which has a more woody smell with a different structural arrangement – it is found along with α-pinene in citrus and eucalyptus trees. The terpene molecules are very reactive and quickly dissipate in the air. The reasons why such aromatic molecules are produced by plants are varied but it is thought that some may be produced to repel predatory insects, while others attract beneficial insects or may be involved in wound protection and repair. Studies show that monoterpenes can offer therapeutic benefits in human health ranging from antimicrobial to anti-inflammatory actions (Salehi et al., 2019). While terpenes are not readily soluble in water they can be taken up through the skin tissues and by inhalation into the lungs.
Forest bathing and volatile organic compounds
Over 1000 different volatile compounds are known to be released from plants, (mostly leaves) and many of these are terpenes and other low molecular-weight molecules (Antonelli et al., 2020). These molecules are lightweight and can be dispersed in the air, so small doses of volatile organic compounds can be taken up in the lungs when walking through the forest. One study looked at how monoterpenes might be available to breathe in while in a Mediterranean oak forest (Bach et al., 2020). Measurements of the air at nose height in the forest showed that the emission of monoterpenes (including α-pinene) from the trees was highest in the summer months, and the amounts varied during the day with peaks in the early morning and afternoon. The amounts of inhaled volatile compounds can be identified. through blood tests. Walkers in a Japanese conifer forest were found to have increased levels of α-pinene and other monoterpenes in their blood (Sumitomo et al., 2015). The increases were several fold after two hours of walking, and the authors of the study noted that monoterpenes can accumulate in the brain and tissues of the body, potentially having lasting effects.
Distill your own pinenes!
You can distill a quantity of leafy material and obtain an aromatic water or hydrosol containing key ingredients like the pinenes. Many trees produce copious material for distillation, especially if coppiced or pollarded. In our experience, pruning also provides plenty of leafy material, for producing quantities of hydrosols. To produce up to 1 litre of hydrosol you will need at least 2-3 kg of chopped leafy material. The amounts of essential oil that are produced are quite small, perhaps less than 1-2% in output, and will float on the top of the distilled liquid. Some essential oil constituents also remain dispersed in the aromatic water along with many water-soluble compounds. For more on distilling equipment and practice see The Medicinal Forest Garden Handbook. Note that distilled essential oils are not intended for internal use without professional advice, whereas hydrosols may be used with caution.
Some aromatic trees we have tried
Juniper (Juniperus communis or J. virginiana)
Most information sources focus on the use of juniper berries to distil, but you can also use the foliage. Branches are very prickly so take care to wear thick gloves. You can use the needle-like leaves fresh by snipping off from the twigs, or less time-consuming if you lay the branches out to dry and then gather the needles falling off the branches. The plant is high in fresh-smelling α-pinene and makes a great aromatic hydrosol. Use as a skin cleanser, clothes freshener or a room spray
Myrtle (Myrtus communis)
In sheltered sunny spots myrtle makes a fabulous fragrant shrub in the UK and is rich in α-pinene. It can be readily pruned to make a hedge or just to reduce in size. The pruned branches can be stripped to provide plenty of leaf for distillation. The essential oil is good in a diffuser for clearing blocked sinuses and helping restful sleep. The hydrosol is gentler than eucalyptus and so is recommended for use as a skin tonic or with children in colds and flu, and it can be used as spray to freshen face or skin.
Eucalyptus (Eucalyptus spp.)
There are many species of eucalyptus tree used for harvesting essental oils, such as the blue gum (Eucalyptus globulus), and these give rise to differing products. Although rich in pinenes, eucalyptus essential oil mainly consists of the mint-scented monoterpene eucalyptol (also known as 1,8-cineole) providing considerable antiseptic properties. It is ideal if you know someone willing to prune some younger branches from an established eucalyptus tree (we found older leaves less productive). Or if you have space in a greenhouse then consider the less hardy lemon eucalyptus (E. citriodora). Useful as a first aid spray or a deodorant.
Do note that essential oils are not advised in pregnancy or for use with children without professional advice.
Antonelli, M. , D. Donelli, G. Barbieri, et al. 2020. Forest volatile organic compounds and their effects on human health: A state-of-the-art review. International Journal of Environmental Research and Public Health17:6506. DOI: 10.3390/ijerph17186506.
Bach, A., A.M. Yáñez-Serrano, J. Llusià, et al. 2020. Human breathable air in a Mediterranean forest: Characterization of monoterpene concentrations under the canopy. International Journal of Environmental Research and Public Health 17: 4391. DOI: 10.3390/ijerph17124391.
Salehi, B., S. Upadhyay, I.E. Orhan, et al. 2019. Therapeutic potential of α- and β-pinene: A miracle gift of nature. Biomolecules 9(11): 738. DOI: 10.3390/biom9110738.
Stobart, A. 2020. The medicinal forest garden handbook: Growing, harvesting and using healing trees and shrubs in a temperate climate. East Meon, Hampshire, UK: Permanent Publications.
Sumitomo, K., H. Akutsu, S. Fukuyama, et al. 2015. Conifer-derived monoterpenes and forest walking. Mass Spectrometry 4(1): A0042. DOI: 10.5702/massspectrometry.A0042.