BIRDS AND THE BEES



Some years ago, I was told that eucalyptus trees could spontaneously combust. Initially, I dismissed this, but whenever I am in Italy I see a number of burnt-out eucalyptus tree trunks. Is there any truth in the story? I GREW UP in Sydney close by a large national park, and we learned bushfire safety at school. Eucalypts can indeed explode; in the heat of a fire, the sap of the tree expands and can seep through cracks in the bark. Eucalyptus oil gives off flammable fumes in a similar manner (although to a lesser extent!) as petrol, and these fumes can be ignited by flying sparks and cinders, causing the tree to explode - just as a spark outside a petrol tank can ignite and explode petrol inside the tank. I spent much of my childhood exploring bushland near my home and saw no evidence of spontaneous combustion. Instead, what can happen - and indeed, leads many Australian bushfires to spread so widely - is that sparks can be blown across several miles, igniting new 'spot' fires some distance away. It's an unfortunate fact of life that most of our native flora is happy to burst into flame if given half a chance, and this is a handy moment to ask Britons escaping the UK winter for summer Down Under not to throw cigarettes out their car windows. Lit cigarettes and arson are the two major causes of Australian bushfires. Corinne Podger, Finsbury Park, London (corinne.podger@bbc.co.uk) EUCALYPTUS trees cannot spontaneously combust as they do not have a flash point. As Ray Leggott states, during a large bush fire, the crown can be separated from the remainder of the tree by the excessive force of the fire. Once launched, it can reach heights of around 5,000 feet and travel up to 14 miles while still very much alight. Once it falls, it could possibly start a new fire. But the charred Italian "gum" trees are more the product of lightning or children - they just burn very well. Ewen Hill, Ealing, London W5.



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