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Trees, Seeds and Envelopes

After a couple of rather melancholic weeks looking at the writing of W.G. Sebald, I promised something a bit more upbeat this week, for which I turn to a book about trees, a few thoughts about seeds and some mathematical puzzles offered via the back of an envelope.  It may all be a bit eclectic, but at least it's less gloomy.

Having said that, I confess I was disappointed by Peter Wohlleben’s book ‘The Hidden Life of Trees’, which I had been hoping would be a bit more enlightening.  To be fair to the author, I am not really a tree person, though I fully appreciate how important they are in our world.  I did not enjoy climbing them as a child, I find their autumnal leaf-shedding irritating because there is always so much debris to clear up, and I can scarcely tell a horse chestnut from an oak, which leaves me frustrated on my rare attempts to commune with nature.

Wohlleben tries to persuade us that we have more in common with trees than we might think.  Apparently, trees are often connected via fungi that spread for miles and miles underground.  In what was probably the best line in the book, the author tells us that these fungal connections help to transmit signals from one tree to the next, helping the trees exchange news about insects, drought and other dangers, and have been called the ‘Wood Wide Web’.

There are apparently more life forms in a handful of forest soil than there are people on the planet.  A mere teaspoon contains many miles of fungal filaments, all of which work the soil, transform it and make it so valuable for the trees, which in turn play host to abundant life forms.  When tree researcher Dr Martin Gossner sprayed the oldest (600 years old) and mightiest (170 feet tall and 6 feet wide at chest height) tree in the Bavarian Forest National Park with pyrethrum, an insecticide, it brought dead spiders and insects tumbling to the ground.  The lethal results show how abundant life is way up high, as the scientist counted 2,041 creatures belonging to 257 different species.

Trees certainly do not have it easy.  For example, the author describes how every five years, a beech tree produces at least thirty thousand beechnuts.  It is sexually mature at about 80 to 150 years of age, depending how much light it gets where it is growing.  Assuming it grows to be 400 years old, it can fruit at least sixty times and produce a total of about 1.8 million beechnuts.  From these, exactly one will develop into a full-grown tree – and, in forest terms, that is a high rate of success, similar to winning the lottery.  All the other hopeful embryos are either eaten by animals or broken down into humus by fungi or bacteria.

I used some other people’s wisdom about seeds and trees recently when I was speaking to our Upper Sixth leavers, urging them to find a passion in life and pursue it if they could.  As the landscaper Gertrude Jekyll put it, ‘The love of gardening is a seed that once sown never dies.’  I do not know who said it, but I like the idea that, as educators, we must be seed planters who have the courage to plant a seed to grow a tree under the shade of whose branches we will never be able to sit.

There is a Chinese proverb that tells us that the best time to plant a tree was twenty years ago and the second-best time is now.  The publisher Felix Dennis said that whosoever plants a tree winks at immortality, and the financier Warren Buffet made the point that someone is sitting in the shade because someone else once planted a tree.

A proverb from the Caribbean wisely points out that trust grows at the speed of a coconut tree and falls at the speed of a coconut, while Albert Einstein in his inimitable wisdom said that if you judge a fish by its inability to climb a tree, it will spend its whole life thinking it’s a failure, and US president Abraham Lincoln offered the sound advice that if you have eight hours to cut down a tree, spend six of them sharpening your axe.

There does not seem to be an obvious link, so let us just jump to a nice little book by Rob Eastaway called ‘Maths on the Back of an Envelope’, which would probably be well received by anyone with an interest in numbers, puzzles and maths-related humour.  For example, a tourist in a natural history museum was very impressed by the skeleton of a Tyrannosaurus Rex.  ‘How old is that fossil?’ she asked one of the guides.  ‘It’s 69 million years and 22 days,’ said the guide.  ‘That’s incredible, how do you know the age so precisely?’ asked the tourist.  ‘Well, it was 69 million years old when I started working at the museum, and that was 22 days ago,’ replied the guide.

Eastaway asks us how many cats there are in the world and then leads us through a series of sensible steps to find the answer.  (You might want to make your own guess before you read on.)  Some people have more than one cat, but usually a household has only one cat, if any at all.  In the UK, and thinking of his own street as an example, the author says it seems reasonable to suppose that there might be one cat in every five households.  And, if a household contains on average two people, that means there is one cat for every ten people.  So, with 70 million people in the UK, let’s say there are, perhaps, seven million cats here.  What about the rest of the world?  It seems reasonable to assume that not everyone loves cats quite so much as they do here, so let’s suppose there is one cat for every 20 people.  If there are 8 billion people in the world, that would mean about 400 million cats.  If you Google it, you may find the number 600 million, but, Eastaway asks, who is to say that one is more accurate than the other?

We are told that in December 1998, NASA launched a space probe called the Mars Climate Orbiter to study the Martian atmosphere.  Several months later, as the orbiter approached the planet, it fired the thrusters that were designed to put it into a stable orbit.  But to the horror of the NASA team who were monitoring progress, the rocket thrusters were much too strong and the probe hurtled into the planet and was destroyed.  A NASA review board later discovered that the software designed by the Jet Propulsion Laboratory at NASA had used the metric system in its calculations, but the engineers at Lockheed Martin Astronautics who built the spacecraft had based their calculations on traditional feet and inches – in the report, this was referred to as the ‘English system’, as if this were somehow not the Americans’ fault.  Instead of applying pound-force, the rockets applied Newton-force, about four times bigger.  The cost of this simple error was $125 million of lost space probe.

Calculations that are done without access to much proper data have become known as Fermi problems, named after the physicist Enrico Fermi who was known for his ability to make very good approximate calculations with little or no helpful information.   These calculations are typically done as an intellectual exercise: working things out for the sake of it.  There is, however, a practical benefit to honing your skills at solving Fermi problems, because this type of problem is notoriously used in job interviews, for example:

  • What does an Egyptian pyramid weigh?
  • How many words are there in your favourite book?
  • How many hairs are there on an adult human’s head?
  • Do more people go to football matches at the weekend than go to church?
  • How many tennis balls are used at Wimbledon?

If you want to know the answers to these questions, you will have to work them out for yourself – or you could buy the book, of course!

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