The Magic Behind The Christmas Tree Aroma

The aroma of pine trees is one of the most evocative scents of Christmas. But what is it about these trees that makes them smell so good? The answer lies in the presence of chemical compounds called terpenes, which are composed of carbon and hydrogen atoms. Terpenes are found in the resin of conifer trees and act as a defence mechanism against pests and pathogens. When conifers are brought indoors, the ambient temperature causes the terpenes to evaporate, releasing that characteristic Christmas tree aroma.

Terpenes

The compound that causes the distinctive Christmas tree aroma is pinene, which is most commonly found in pine needles. Pinene occurs naturally as two different isomers: alpha-pinene and beta-pinene. Alpha-pinene is the variation that causes the fragrant forest-like smell of Christmas trees. Beta-pinene, on the other hand, has a different scent and is present in rosemary, parsley, orange peel and dill.

In addition to pinene, other common terpenes found in conifers include limonene, which smells like citrus; myrcene, which smells like thyme; camphene, which smells like camphor; and phellandrene, which has a minty aroma. The specific aroma of a Christmas tree depends on its species, as the type and amount of terpenes vary.

Furthermore, terpenes could play a significant role in the future of chemistry as a replacement for crude oil. They are hydrocarbons, chemically similar to the molecules in crude oil, and can potentially be transformed into platform chemicals used in various industrial processes. Researchers are exploring the potential of using bacterial facilities to produce terpenes sustainably and in large quantities.

Pinene

Pine trees are known for their evocative aroma, and one of the molecules responsible for this is pinene. Pinene is a compound that occurs naturally as two isomers: alpha-pinene and beta-pinene. Alpha-pinene is the more prevalent of the two in most pine trees, but both are commonly found in the resin of the trees. The odour of alpha-pinene and beta-pinene is often described as turpentine-like, and they are the primary constituents of distilled pine oil.

In addition to its role in the Christmas tree aroma, pinene has therapeutic benefits. It exhibits anti-inflammatory, antimicrobial, and bronchodilation properties and is also a neuroprotectant. Furthermore, pinene is highly flammable due to its ratio of ten carbons to sixteen hydrogens, making it easy to burn and contributing to the rapid spread of forest fires.

While pinene is a significant contributor to the Christmas tree aroma, it is not the only terpene involved. Other terpenes found in pine trees include limonene, myrcene, camphene, and phellandrene. Each of these terpenes contributes to the overall scent profile of the tree. Additionally, non-terpene compounds like bornyl acetate, which varies in proportion across different pine species, enhance the fresh and clean pine odour.

Tree variety

The aroma of a Christmas tree depends on its species, as the type and amount of terpenes vary. Terpenes are chemical compounds that are abundant in the resin of conifer trees. They are composed of carbon and hydrogen atoms and are built from different numbers and kinds of molecules.

Pine trees, for example, contain two types of pinene isomers: alpha-pinene and beta-pinene. Alpha-pinene is the more abundant of the two, and it is one of the molecules responsible for the distinctive scent of pine trees. Turpentine, which is commonly described as having a turpentine-like odour, is obtained from the resin of pine trees and is composed mainly of alpha- and beta-pinene.

Other common terpenes found in conifers include limonene, which produces a citrusy aroma; myrcene, which smells like thyme; camphene, which has a camphor aroma; and phellandrene, which has a minty fragrance.

In addition to terpenes, some conifers also contain bornyl acetate, a non-terpene compound that contributes to the woodsy aroma commonly associated with pine, fir, and spruce trees.

Mold

Christmas trees can bring more than just festive cheer into your home. They can also bring mold, which allergists have dubbed "Christmas tree syndrome". Many live trees have mold spores on the pine needles, and the warm, humid environment of your home creates the perfect environment for those spores to grow.

To prevent mold from growing on your Christmas tree, there are several steps you can take:

• Rinse the tree with a vinegar and water solution before bringing it inside, or blow it off with a leaf blower.
• Wipe down the trunk with a vinegar solution or diluted bleach.
• Only keep the tree up for about a week.
• Store your tree in a temperature- and humidity-controlled area.
• Wash the tree and spray it with a mold spray before bringing it inside.
• Choose a self-cut tree that hasn't been exposed to high mold spore levels during storage and transportation.
• Unpack and wipe down all decorations with a mold spray before bringing them inside.
• Store decorations in a dry, temperature- and humidity-controlled area.
• Use an air purifier in the room with the tree to reduce mold exposure.
• Choose a different type of tree, such as an artificial tree.

Root rot

Phytophthora root rot is a common issue for Christmas tree growers, especially in North Carolina, Oregon, and Washington. It is caused by a fungus-like oomycete called Phytophthora, which inhabits the soil and infects the roots of many woody plants, including Christmas trees. Once established, Phytophthora can lie dormant in the soil for several years, waiting for favourable conditions to infect plant roots. Warm soil temperatures above 54°F and saturated soils are ideal for the pathogen to infect roots.

Phytophthora root rot can cause significant damage to Fraser firs, a popular Christmas tree species. The disease has been associated with Fraser firs since the 1960s, and it is one of the major limiting factors for Christmas tree growers. The symptoms of Phytophthora root rot include yellow-green needles, wilting, slow growth, delayed bud break, dead branches, and eventually, tree death. The needles on affected trees turn a reddish-brown or cinnamon brown colour, and the trunk may also begin to rot, contributing to a foul odour.

The disease is spread through contaminated equipment, infected nursery stock, or water runoff from nearby infested sites. Transplanting infected seedlings is a major contributor to the spread of the disease. Once introduced, Phytophthora can remain dormant in the soil for years and infect new plants.

To manage Phytophthora root rot, an integrated pest management approach is necessary. Healthy seedlings and transplants, as well as proper site selection, are crucial. If Phytophthora is present, management practices should focus on reducing the spread of the disease and minimising financial losses. This includes quarantining infected areas, removing diseased trees, improving soil drainage, and planting less susceptible tree species or grafting susceptible scions onto resistant rootstock.

To date, no fungicide has been proven effective in controlling Phytophthora on Christmas tree plantations. As a result, some growers are turning to species from Europe and Asia, such as Turkish fir and Nordmann fir, which have shown promising resistance to root rot.

Frequently asked questions