O Christmas tree, thy leaves are so unchanging

Trees in snow, Borovets, Bulgaria

Trees in snow, Borovets, Bulgaria . Copyright: Agnes Becker

Being half German, the carol “O Christmas Tree” or “O Tannenbaum” has accompanied me and my family every year as we decorate the house ready for Christmas.

This year, I wanted to make a card that looks at why Christmas trees are evergreen and celebrates the life they bring to a bleak winter.

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Why are evergreens ever green?

I decided to focus on the traditional tree, the Norway Spruce or Picea Abies. Thanks to The Woodland Trust, who suggested a paper on the advantages of being evergreen by Rien Aerts, I found that the main reasons evergreen trees stay green all year round is due to the long lifespan of their leaves, or needles, and the ability of the needles to survive in cold climates. Their leaves are shaped in a way that ensures they don’t freeze, they are able to photosynthesise in very low levels of light (in northern Europe, the winter days are short), and live for 4-5 years, rather than a few months as with deciduous trees, to make use of the light all year round.

Evolving to the cold climates of northern Europe

However, after getting in touch with a Norway Spruce expert, Daniele Castagneri, it was clear no one knows exactly why the leaves of evergreens have these properties. It is most likely to do with evolution; different adaptations being selected due to the environment. For example, at some point the ancestor of the Norway Spruce may have developed leaves with a slightly longer lifespan, and those trees survived better in the cold, northern European climes than other trees. Being evergreen seems to have been the way the Norway Spruce has adapted to the harsh, cold winters and climate of northern Europe.

Although we can never know the exact reason why certain trees are evergreen, in the words of Daniele, evergreens “are more common in ‘extreme’ environments, such as cold or dry-warm places, while deciduous are more common in mild environments”. However this is not a rule, as the Larix decidua, one of the very few conifer that lose needle during wintertime, survives high up in the cold mountains of the Alps.

Science of evergreen Christmas trees greetings card

This card celebrates the beautiful evergreen Christmas tree that gives us hope and a sense of rebirth during the long winter months.

The inside of the card contains a poem, written by Chris Raymond, which hints at the way the leaves stay green all year round to make the most of the weak winter light in northern Europe:

Norway Spruce

Above the sea lochs, when the snow falls wet
Night after night and the last of the geese
Have flown high into the south, sunset
Comes just hours after the slight increase
Of light that passed for sunrise. When the wind eases
Every branch of every tree holds snow,
Stacked high like icing, each needle freezes,
Black-green, but still survives, can even grow,
In the faint light that struggles through
The snow and clouds above. In December,
Working the short days, logmen take a few
As Christmas trees, so we might remember
The shortness of the seasons, how the earth
Renews, the cut tree a symbol of rebirth.

The text on the back explains how plants use sunlight to live (does it bring you back to your school biology classes?):

“Green plants use light energy to make the carbohydrates they need to live through a process called photosynthesis.
Plant cells contain chlorophyll, a pigment that reflects green light, so plants appear green, but absorbs energy from other coloured light. Photosynthesis uses the light energy to turn carbon dioxide plants get from the air and water they get from the earth into oxygen and carbohydrates.”

Environmentally friendly

As with all my cards, each one is printed on Forest Stewardship Council approved card (so you can be assured you are not contributing to the destruction of the world’s forests) and includes a brown envelope made from recycled paper.

Sold out

These cards were a huge hit this year and as a result I have sold out! However, I’ll get a few more printed for 2015.

I hope you’ve had a wonderful Christmas. Here’s to a fantastic 2015.

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