How old is that tree?

Here are two handy little tricks for gauging the approximate age and height of a tree (without cutting it down). 

You can get a rough estimate of age by measuring the girth of a tree. Simply measure around the trunk at human chest height. As a tree increases in girth by around an inch (2.5cm) per year, the number of inches equals years. So a 50" girth means the tree is somewhere around 50 years old.

Of course, the rate of growth will differ according to what type of tree it is. Oak and Beech, for example, grow quite slowly so you should divide the girth measurement by 1.88. Pine trees, however, are very fast growing so you should divide the girth measurement by 3.13. Other factors will affect the growth too, such as drought and how crowded the area is. If the tree is on its own, it has the space to grow faster than trees in a wood will. But, as a rough estimate, the one inch per year thing is pretty good. It's even used as a rule of thumb by staff at Kew Gardens (which is where it learned it from).

I measured a few trees in my local woods yesterday afternoon to get a sense of how old they are. The first was this Ash tree which the tape measure tells me is probably about 23-24 years old.

I then measured this modest Oak and found it be about 29-30 years old. That ties in with the reminiscences of some local dog walkers who have told me that many of these young oaks were planted in the late 1980s.

I then found a larger Oak and had a go at measuring its 'waist'. It was pretty big so a lady dog walker volunteered to help me. It took several lengths of the tape measure but we eventually agreed that the tree is about 130 years old. That means it was an acorn when Charles Dickens was writing Great Expectations and when the American Civil War was just kicking off. This tree is the same age as Canada. That's pretty amazing isn't it? And it's nowhere near the biggest or oldest tree in these woods.

When it comes to guessing the height of a tree, and you don't happen to be carrying a clinometer with you, there's a nifty trick you can use - if you're flexible enough. Choose a tree to measure, and walk away from it. Every so often bend forward and look through your legs at the tree. When you can just see the top of the tree through your legs, stop. Then measure the distance along the ground from the tree to this point. This is roughly equal to the tree’s height. 

Despite reaching the age of 61 and having a double prolapse of my vertebral discs (and a middle aged paunch), I can just about do this. But an easier option was to find a point on my countryman's stick which corresponds to where my eye line would be (a little above knee height as denoted by my thumb here). Thankfully, Dad's carving of the stick pretty much marked the spot for me.

I then had to sit on the ground and get my eye to the level of that mark (very top of photo) and then keep shuffling backwards until it lined up with the top of a nearby Lime tree. And it was pretty accurate - around 25 feet.

What you're aiming for is a 45 degree line between floor and tree top - this creates a triangle where the horizontal and the vertical sides are equal.

These are fun activities to get kids involved in too.

Although there's probably an app to do it for them these days.

(Oh right, I just checked. There are loads of them. Sigh.)