The Age Of A Tree

The teddy bears were enjoying a walk through their local woodland. Although the trees didn't yet have many leaves, the bears still liked to walk amongst the huge tree trunks and look up to see just how tall some trees could grow - much, much taller than any of the bears!

"Oh, look!" shouted Henry. "That tree has been chopped down! That's very sad. Why would anyone do that?" he asked.

"Actually, it was probably the forest ranger," replied Bubbles. "Remember last time we were here after that awful storm and the tree looked like it had been struck by lightning? It seemed a little unsafe - some of the branches seemed ready to fall off and hit someone on the head."

"Yes, I remember now - it had looked a bit dangerous," said Henry. "I wonder how long it had been here?"

"Well, we can try and work that out," replied Charlie. "Let's look at the stump that's left. Look at the rings showing. Each of those rings is one year's growth for the tree, so if we count the number of rings, that will be how many years old the tree was."

Henry was fascinated by this bit of knowledge and Charlie lifted him up onto the tree stump so he could count the rings. It was a tricky job because some of the rings were only faint whilst others were really dark and they were all different widths.

"Why aren't all the rings the same size and colour?" Henry asked.

"Well it depends on all sorts of things like what the weather was like in any year, and what kind of tree it is," replied Charlie. "If the tree had sunshine and showers it would grow more than if the weather had been cold and miserable all year. So the rings would be thicker in the good years, and thinner in the bad years. And yew trees may not grow at the same rate as beech trees for example, so their rings would be different too."

"I think there are 37 rings," Henry finally decided. "So that means the tree was 37 years old!"

"Correct!" responded Charlie. And they continued on their way.

"Charlie," said Henry after they'd walked some distance in silence, "can we find out how old a tree is without having to chop it down?"

Charlie paused. Obviously, Henry had been thinking a lot about this - no wonder he had been so quiet!

"There are some ways we can estimate how old a living tree is," Charlie replied, "but it will only be a general idea - it's not as precise as counting growth rings."

"Can we try anyway?" asked Henry, full of enthusiasm for working out the age of a tree without damaging it.

"OK. Let's try a very easy way first. We need to measure right round the trunk of the tree," Charlie replied. "I wish we'd brought some string with us to circle the tree trunk, but we can manage without. And then we will have to do some workings-out when we get home."

Henry was very intrigued. "How are we going to measure the trunk without any string?" he asked. Although Charlie had a tool box full of measuring equipment and tools, he had obviously not brought it with him on their walk through the woods.

"Extend your arms out from your sides," Charlie began, "and then go hug that tree!"

Henry was a bit taken aback. "Hug the tree?" he exclaimed. "Whatever for?"

"We need to see how many hug lengths it takes to go right round the tree trunk," explained Charlie, "and then when we get home, we can measure the length of your hug, and multiply it by the number of hugs it takes to go round. That is called the tree's girth. Your hugs need to be about a metre up from the floor so we can avoid the fattest part of the tree at its roots."

Henry thought it seemed a bit strange, but did as he was told. Teddy gave him a lift on his shoulders so he would be at the correct height. Henry spread his arms out and Teddy moved over to the tree and gave it a big hug. It actually felt rather good - Henry was convinced he could feel the tree breathing! Charlie noted where Henry's paws started and finished then Teddy moved round and Henry gave the tree another hug. It took Henry's little arms just over 7 hugs to get right round the tree. Then they set off back home before they could forget.

At home, Charlie opened his tool box and took out a ruler. He measured the distance between Henry's paws when he had his arms stretched right out from his sides and noted it was about 20cms.

"Now we just need to do a few sums," began Charlie, taking a pencil and paper out of his toolbox, "we're going to multiply your hug length by 7 because it took you 7 hugs to get round the tree, and then we are going to divide the answer by 2.5 which is the average length that a tree's girth will expand in a single year. Of course, this is a very rough estimate because, as we noticed with the tree stump, a tree can grow different amounts in different years. But for our purposes, this will do."

The tree's girth turned out to be 140cms. Charlie divided that by 2.5 and estimated that the tree they had measured had been about 56 years old!

All the other bears had listened with interest about how to find out the age of a tree, even if it wasn't quite exact, and they all decided that they would like to try it out the next time they went to the woods.

"We could take a tape measure and do the workings out while we were there," suggested Charlie, "and if anyone didn't want to hug a tree - but who wouldn't? - then we could simply place the tape measure around the tree to measure the girth."

"We'd need to take a calculator, too" Bubbles proposed. "Not all of us can work sums out with just a piece of paper and a pencil like you Charlie." Everyone giggled - quite a few bears might need some help when it came to doing the sums!

The bears can't wait for their next trip into the woods. They were all eager to choose a tree and see who could find the oldest! Or the youngest! And to go back to the same tree the following year and see how much it had grown! Very exciting!