Читать книгу Forests and Woodlands - Nick Baker - Страница 11

The most accurate way to tell the age of a tree is to look at a slice through its trunk and count the growth rings. The cells under the tree’s skin (the bark) produce new wood as the tree grows and each summer, more new cells are made when conditions are best for growth. Growth rings show each year’s new growth – one for each year of the tree’s life. In years of good growth, the rings will be wider.

Obviously getting to see these growth rings in a healthy tree is impossible without cutting it down and destroying the thing you are studying! But if you come across stumps that have been sawn through and the cut is a smooth one, you should be able to see how old it was when the tree was felled. This will give you an estimated age of any tree of the same species in the same area.

Some trees grow very slowly indeed, but others have many a growth spurt, such as the commercially grown pines, various cedars, spruce and fir, poplars, cricket-bat willow and other non-natives such as eucalyptus. Slower-growing trees include pine, yew, chestnut, lime and most smaller-growing trees.

Fab facts

* Trees grow from the outside in! The growth cells are all in the surface of the wood, under the bark. They lay down new wood as the tree trunk expands. The wood in the middle of an old tree is usually dead and when a branch falls off, it is this that sometimes gets hollowed out by fungus and birds.

YOU WILL NEED

> a tape measure

> pencil

> paper

> calculator

1 Another way to estimate a tree’s age is by measuring the girth of the trunk about 1m up. Because large trees tend to grow at a predictable rate, their trunk gets thicker as they grow and on average, trees put on about 2.5cm a year.

2 So measure your tree’s girth in centimetres and divide it by 2.5. You will then have an approximate age for your tree. This is a very rough guess and growth rate does vary from species to species and from place to place.

Take it further

* Try to find a tree stump that shows the tree is, say, at least 100 years old and take a photograph of it.

* Either have the photograph enlarged or I enlarge a photocopy. If you have a digital camera, print out the image to whatever size you want. You can then mark important years on the trunk by counting back rings.

* Show the year 2000; the year you were born; when the Second World War started, and add anything else that is of interest to you and your family.