pine trees

12 Days of Christmas Science: Evergreens and Christmas Trees and the Traditions That Made Them.


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There are few things that signify Christmas than the Christmas tree. Whether it’s made of plastic, tiny light bulbs, tinsel, or natural, the inverted tapered shape is recognized by people of all ages.

Natural Christmas trees are usually evergreen conifers, such as a spruce, pine or fir. Of all the possible candidates, firs tend to be the most common.

Evergreens which appear to keep their leaves during late autumn and winter months stand in opposition to deciduous trees which lose their leaves depending on the season. Deciduous trees shed their leaves usually as an adaptation to extreme conditions such as cold or dry and wet seasons. While evergreen trees lose leaves as well, the process occurs gradually and not all at once. This gives the impression that the trees don’t lose their leaves. 

Most tropical rainforest plants are considered to be evergreens, in that they replace their leaves gradually throughout the year. Species growing in seasonally arid climates may be either evergreen or deciduous. Most warm temperate climate plants belong to the evergreen family as well. 

On the other hand, in cool temperate climates, fewer plants are evergreen. In this climate, there is a predominance of conifers because few evergreen broadleaf plants can tolerate severe cold below about −26 °C (−15 °F).

In areas where there is a reason for being deciduous, e.g. a cold season or dry season, evergreen plants are usually an adaptation of low nutrient levels. 

The evergreen’s hard leaves help it to save water when resources are scarce due to local conditions. Obviously, keeping their leaves helps them to continue accessing their nutrients. The excellent water economy within the evergreen species is due to high abundance when compared to deciduous species.

In warmer areas, species such as some pines and cypresses grow on poor soils and disturbed ground. Rhododendron, a genus with many broadleaf evergreens, can be found on highly acidic soil where the nutrients are less available to plants. In taiga or boreal forests, In conditions where it is so cold that organic matter decays slowly, nutrients are not readily available. Evergreens thrive in such environments.

Leaf loss helps deciduous trees survive below-freezing temperatures. It helps them to conserve water by getting rid of the stomata on leaves where water loss occurs. If deciduous trees kept their leaves in winter, the sun would evaporate water from the leaves that the tree couldn’t recover from the ground, slowly dehydrating the tree.

Evergreens have evolved a different set of protective adaptations that serve the same function: protecting the tree from dehydration during the winter. Evergreen leaves are covered with a thick waxy cuticle that prevents water loss from the leaf. Evergreen leaves also have fewer stomata than deciduous leaves, so less water evaporates from the leaves.

Fir trees can be distinguished from other members of the pine family by the unique attachment of their needle-like leaves to the twig by a base that resembles a small suction cup. Its leaves are significantly flattened, sometimes even looking like they are pressed. Firs differ from other conifers in having erect, cylindrical cones 5–25 cm (2–10 in) long that disintegrate at maturity to release the winged seeds. In contrast to spruces, fir cones do not hang. Even large fir cones grow upwards like “candles”, the new growth of the tree.

The modern Christmas trees originated in Renaissance Germany. According to tradition, its 16th-century origins are associated with Protestant Christian reformer Martin Luther, who is said to have first added lighted candles to an evergreen tree. Records indicate that German Lutherans in the 16th century placed a Christmas tree in the Cathedral of Strasbourg in 1539, under the leadership of the Protestant Reformer, Martin Bucer. The earliest confirmed representation of a Christmas tree is on the keystone sculpture of a private home in Turckheim, Alsace in 1576.

The Christmas trees may have been preceded by the “tree of paradise” of medieval mystery plays that were given on December 24. In many countries, it is the name day of Adam and Eve. In such plays, a tree decorated with apples (to represent the forbidden fruit) and wafers (to represent the Eucharist and redemption) was used as a setting for the play. The apples were replaced by round objects such as shiny red balls.

There are other possible origins for the Christmas tree. According to the Encyclopædia Britannica, “The use of evergreen trees, wreaths, and garlands to symbolize eternal life was a custom of the ancient Egyptians, Chinese, and Hebrews. Tree worship was common among the pagan Europeans and survived their conversion to Christianity in the Scandinavian customs of decorating the house and barn with evergreens at the New Year to scare away the devil and of setting up a tree for the birds during Christmas time.”

Finally, during the Roman mid-winter festival of Saturnalia, houses were decorated with wreaths of evergreen plants, along with other customs now associated with Christmas. The choice of December 25th is believed to have been chosen due to its proximity to Saturnalia to make the transition to Christianity easier.

IMAGE CREDIT: Dominika Gregušová.

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