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O Tannenbaum

Time to re-roast an old chestnut, a column I wrote several years that has become fresh in my mind due to the successful completion last night of Operation Dress-the-Tree (to be followed in a few weeks, of course, by Operation Curse-the-Tree as the needle-shedding skeleton is hauled out to the alley).

Is there scientific interest to be found in ol’ Tannenbaum? Indeed there is!

Consider, for instance a Christmas tree’s incredible capacity to “drink” water. A tree may slurp up six or seven litres when you first put it up, and as much as a litre or two a day thereafter. This seems like strange behavior for something that’s dead.

But of course, the tree doesn’t realize that it’s dead. As far as it’s concerned, it’s still alive, but increasingly thirsty. The roots that used to bring so much water into the tree (because of their vast surface area) don’t seem to be functioning any more. The tree has to make do with the tubes inside the trunk itself, and they can’t bring in enough water to keep the tree alive. It will eventually dry out and die, but in the meantime, however, it does its best to meet the water demands of its needles.

All of which is shameless anthropomorphizing: it’s really a very passive process. Trees draw water up into themselves because of evaporation. The needles constantly lose water to the relatively dry atmosphere. The cells in those needles contain large cavities called vacuoles, designed to hold water. As water evaporates out of the cell, the cell draws more water into the vacuole from other cells deeper inside the tree. Eventually this leads to the tubules, like tiny pipelines, in the trunk.

Even a completely dead tree with no needles left could draw some water up into itself by an even more passive process called capillarity, the tendency of water to “crawl” into tiny spaces. Water molecules attract each other and are attracted to other substances. If you stick a fine glass tube into a supply of water, the water will crawl up the tube; the leading edge of the water is attracted to the glass and it pulls the rest of the water up along with it. The water will climb to the height at which the molecular attraction exactly balances the force of gravity. The thinner the tube, the higher the water will travel. (This property of water is also why paper towels are able to soak up the water you spilled on the floor while trying to fill the Christmas tree stand.)

The Christmas tree probably originated in medieval Germany, and by the early 1800s had spread all over Northern Europe. Prince Albert of Saxony, Queen Victoria’s husband, brought the custom to England in 1841, and other German immigrants (albeit less distinguished) brought it to North America, where it caught on quickly.

Around 40 million trees are harvested every year in the U.S. and Canada, mostly from Christmas tree farms. A small to medium tree farm will harvest 10,000 trees. In total, some of the multinational giants harvest up to a million trees annually on plantations from North Carolina to Nova Scotia..

Nature rarely produces a perfect Christmas tree without some help. Trees can suddenly develop gaps or unsightly branches, so Christmas tree growers prune their trees every June from the age of three on, and cut off the bottom branches to give the trees “handles” long enough for tree stands.

Mature trees are usually cut in mid-November, then shipped, so the earlier you get your Christmas tree and get it into water, the fresher it’s likely to be.

The National Christmas Tree Association suggests three ways to test for freshness. First, bend a few needles and branches; they should both be springy. Then slip a few centimetres of a branch through your fingers. If the tree’s fresh, the needles should stay in place.

Finally, lift the tree and bang its trunk on the ground. If it’s fresh, it should only lose some brown inside needles and very few green outside ones.

Just be sure to conduct this final test before you decorate. The tinkling sound of expensive ornaments crashing to the floor is apparently not a reliable indicator of freshness.

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