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Evidence of a Changing Climate?

This is a summary of an article entitled “Signs of Spring” which appeared in the autumn issue of Tree News: it seemed so relevant to what our recorders have been doing that I have inserted it here. The author, Tim Sparks, works at the Institute for Terrestrial Ecology at Monks Wood near Huntingdon, and would like to hear from any individual or society with long runs (20 or more years) of records.

He notes that from 1875 to 1947 a network of recorders was co-ordinated by the Royal Meteorological Society and that many other similar series of records exist, but he discusses an even earlier set begun by Robert Marsham in 1736 and continued until his death in 1798: his family continued his record down to 1958. (Marsham was a pioneer forester who conducted many experiments on his Norfolk estate.) It is very interesting to see that there is no evidence to support the old rhyme about oak and ash and that some trees such as hawthorn respond markedly to warmer temperatures during the January-March period, while others such as ash respond much less. The Meteorological Society records show how the very cold springs in the early 1940s affected the flowering dates of hazel and wood anemone, and also show that the flowering dates of ivy in the autumn are very much influenced by summer temperatures.

Does any evidence of global warming show up in more recent records? The answer would seem to be 'yes'. Ringlet butterflies are emerging and trees are coming into leaf almost two weeks earlier in the 1990s than in the mid-1970s, birds such as Chiff-chaff and Blackcap are also appearing ten days earlier than in the 1960s. But Sparks is careful to note that not all species respond in the same way - oak seems to be responsive to early Spring temperature, ash less so. Day-length, to which many plants and animals respond, increases or decreases as it always has, so the situation is complex. If spring temperatures rise, oak might spread at the expense of ash, and birds might get here before the insects they feed on have emerged. The one thing which is clear is that careful observations by naturalists such as ourselves are still of great value.

John D. Farquhar

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