The Ranger worked as a Tree Officer for some months not too long ago, and got quite an insight into the arcane world of TPOs and irate householders. A bit different from being a real Ranger, where pretty much everyone is glad to see you. A tree officer often has the thankless task of trying to preserve a tree against the wishes of the tree’s owner, who wants to fell the thing to get a sea view, or build a house. For some reason they rarely come out with the truth and say they want to fell it. They usually proffer some excuse, prefaced with “I like trees but…”. Perhaps the most common of these is the constant refrain heard by tree officers “But it’s a dangerous tree!“. Often the complainant then over-eggs the pudding with references to their little, blond grandchildren, innocently gamboling underneath the looming tree, which has regularly been heard to creak and groan ominously, and even, believe it or not, sway in the wind! It’s hard not to get cynical about some of these requests. It would be a lot better if they just came out and said “I want to sell off half my garden to build a block of eight flats on it.” Then at least we’d know where we all stood. But, can they always be wrong? Just how dangerous are trees, generically?
Indeed, some individual trees are dangerous and need work. But that does not mean they all are. Often the dangers of trees are considerably overestimated. Just what are the chances of a tree falling on you and killing you? Chris Hastie, arboriculturalist and webmaster of the The UK Tree Care Mailing List recently got fed up with the assumptions that are made about such things. He writes:
After the storms the other month I was phoned by a journalist who questioned me about various things, mostly to do with a very large horse chestnut by the side of a busy road which managed to blow over and do no harm to anything except a lamp post. Trying to explain the nuances of risk management to her and knowing everything I said was going to be massively dumbed down, I started to wish I had a few soundbites at my fingertips.
So Chris took the question at face value and worked out some statistics. He started by pointing out that the chances of being killed by a tree in a public space in the UK is about 1 in 20,000,000 (according to the UK Health & Safety Executive, “Management of the risk from falling trees – Internal guidance”). So, what about winning the lottery jackpot? Actually, Chris also demonstrated that rather than the 14 million to one which is usually quoted, the chances of winning it are actually better expressed as 1 in 268,920. This is because although the chances of winning with one ticket are indeed 1 in 13,983,816, accidental deaths are usually expressed as the chances of any incident happening to any person in one year. So, assuming a lottery player buys one ticket per week every week for a year, the odds are reduced to 1 in 268,920. Thus a regular lottery player is 75 times more likely to win the lottery jackpot than be killed by a tree in a public space. He goes on with some other sobering illustrations. The total number of accidental deaths in the UK number is over 12,000 per year. About 6 of these are due to trees. So you are 2000 times more likely to die from some other type of accident than by being hit by a falling tree. More specifically, 3,501 people were killed in road traffic accidents in the UK in 2005. So you are around 600 times more likely to be killed in a road accident than by a falling tree. The Ranger adds one of his own – the annual risk of being struck (and not necessarily killed) by lightning is 1 in 10,000,000. So you are more likely to be hit by a bolt of lightning than killed by a falling tree. That seems to put things into perspective. Anyone else want to have a try? Cite your sources if you do!