Tuesday, 12 February 2008

A Nice Green Leaf: Too much too early


How do you feel about everything flowering much too early? Part of me wants to be really happy that spring flowers are arriving to cheer me up quite so promptly. But the explanation is likely to be depressing old climate change rather than some innate generosity on the part of the plants towards me.

Amateur Photographer magazine reported yesterday that while daffodils are only eleven days early, hawthorn bushes are expected to burst into flower some two months prematurely. Which is worrying for amateur photographers, who have resorted to using the internet to check out when to bunk off work for the best crocus shots.

Kew Gardens has kept records of the first flowering date of a hundred different species, since the 1950s. The science of when things come into flower is called phenology, and Kew's records are invaluable. Still, they only go back to 1952, so is there a chance that our traditional English flowers have flowered this early before? Well we also have many Victorian amateur
observations and even some from the eighteenth century (never knock the amateurs, whatever I said earlier).

And why are there such sharp differences between species - why aren't
all the flowers early by the same amount? Well that turns out to be
because different species use different environmental factors to decide
when to flower and come into leaf. Some use temperature, others use day
length. The day-length-determined plants aren't flowering very much
earlier at all - just a matter of a few days (like the daffodils). But
the ones which judge when to start growing again by temperature are
terribly confused - as the hawthorns, eight weeks out of whack,

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