Wednesday, 16 December 2015

Christmas Science: The Needle Conundrum

Why do some Christmas trees drop needles, while others hang on to them until the bitter end?

Ho Ho Ho! Welcome to my Christmas Science series. Just a few thoughts about some of the everyday science of the festive season. There will be no flying reindeer here, but real science of real things. And if you enjoy this - it's not too late to buy my new book, The Science of Everyday Life.

When I was a kid, by Christmas day the floor around the tree was scattered with dried up needles. It added a frisson of excitement as you went to see what was under the tree - would your be-socked feet be skewered? Some - er - few years later and my own kids do not have to experience this pain if I so choose.

Inside your home it is very, very dry as far as a tree is concerned. Since you have also cut off the roots and source of water, the living tree does what it can to prevent dehydration that happens mostly through the leaves or needles. It actively walls up the way into the needles and allows them to drop. At least the old fashioned Norway Spruce (Picea abies) does this, as its needles are very fine and relatively loosely attached. The Norway Spruce is not adapted to drought conditions, and has no other way to deal with it. Other species like the Nordman Fir (Abies nordmanniana) and the more recently introduced Fraser Fir (Abies fraseri) are mountain species that have to cope with hot dry summers. Consequently they have adapted to have very long lived leaves and in drought conditions do not shed their needles.

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Science TV Presenter, live show performer, writer, strange prop builder and all round Science Bloke. All opinions expressed are mine alone. Not the BBC's, just mine.