# Leafing through some confusing tree statistics

So how many leaves are there on an oak tree? One, two, three... hang on, just start again... Picture: Ian Burt - Credit: Ian Burt

Nature: How many leaves are there on a tree, wonders Rex Hancy.

There are 700,000 leaves on a mature oak tree. When this was suggested to me I was perfectly willing to accept the figure. But are there actually more or considerably less? At the time the source of the quotation was unknown so that evening I took the most obvious reference book on trees from my shelf and sure enough the magic number was there in black and white. Greater authenticity was given by the further information in the same book that an American elm bears five million leaves while the poor old apple tree, though it may be large for its kind, has to manage on a meagre fifty thousand. Further delving revealed the obvious truth that no-one really knows. Figures I found vary between a quarter of a million to a massive million and a half.

Years ago when teaching maths, I had the freedom to invent ways to help children understand very large numbers. Sampling, averaging, using small areas to a create a base on which to build a huge total all contributed. And it was fun. In the end we had no more than a reasonable estimate of whatever we were researching. Appreciating the fact that arriving at exact figures is often impossible does help us think realistically when so-called facts and figures are constantly thrown at us. Of course, I am nagged by the thought that I should try to dream up a way to estimate those leaves.

The 'wild west wind', which is the subject of an ode by Shelley, did me a huge disfavour this spring when it blew down a rather special ivy-covered dead tree trunk. As if it was trying to compensate for all the extra work and worry it had given me, during the autumn the west wind became a more kindly entity. I expected to cope with the normal masses of leaves covering part of the garden. The west wind puffed its cheeks then blew huge numbers I know not where.

Another modest bonus was to see the wind from a different direction creating swirls and elegant curved outlines on the drive as it was channelled by gates and trees aided by even tiny obstructions in its path.