Ness Island

WE WALK along the towpath beside the Caledonian Canal for a lunch break at the café at the Floral Hall then return to the centre of town via the footbridges to Ness Islands. I draw the standing waves at the upstream tip of the first island. It’s like sitting at the prow of a ship. Anglers stand waist deep in the river.

Giant Sequoia

At the downstream end of the second, longer island, there’s a large Wellingtonia or Giant Sequoia, Sequoiadendron giganticum, with drooping lower branches which make an effective umbrella when there’s a passing shower.

The reddish bark feels slightly spongy which must provide effective insulation from winter frosts and from the forest fires that occasionally sweep through the tree’s native habitat on the western slopes of the Sierra Nevada in California.

Each leaf scale is 2 or 3 millimetres long

Looking up into the branches (top photograph) it appears as if the tree has long slender needles like a pine or fir but if you look closely the leaves are scale-like, as seen in this photograph of a dry twig (they’re green when fresh) that I’ve taken with a low-power microscope.

The Top of the Tree

Sequoias can grow to 50 metres but how tall is this specimen?

I made a rudimentary clinometer using my hand lens (which hangs on a loop of string) as my plumb-line to establish the vertical and the long edge of my sketchbook, held to my eye, to point at the top of the tree, marking the vertical across the inside back cover of the sketchbook.

I measured the distance to the tree as 76 lengths of my hiking boots and added another four lengths to get me near the centre of the tree, which was probably an underestimate. Because the ground fell away sharply at one side I was unable to measure the girth of the trunk.

By drawing out the angle to the horizontal and the baseline distance to scale (right), I can measure the height as 96 hiking boot lengths so that’s 96 x 34 centimetres (they’re big boots, but very lightweight!); that’s 3264 cm, making the Sequoia approximately 32.64 metres tall, about 107 feet.

Errors include the gentle slope of the ground down to the river and my eye being about 1.8 metres above ground level but those two probably cancel each other out. Also from such an oblique angle I couldn’t actually see the top of the tree.

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  1. Richard, your blog is one of the very few I follow but I enjoy the most!
    Thank you for showing how to figure the height of that tree. We have a huge Norway Spruce in our side yard, just over 100 years old, and my husband and I were trying to remember how to do just what you did. Now we can get an estimate of our tree’s size. Without spending hours trying to find out how we did this in school. (do kids even get this anymore?)
    Lovely stuff.

    1. Thank you Susie, hope it works for you. We never got to work out the height of the large ash tree at school, which was crying out to be measured – perhaps the slope on the playground made it too complicated – but my introduction to geometry was Mr Douglas the headmaster using cones of clay on a blackboard laid on a desk-top to represent the triangle formed by the summits of the Three Peaks on the limestone plateau of the Yorkshire. Even better they took us off on school trips to trudge around the Dales and the Lake District.

      I’ve just been reading ‘The Musgrave Ritual’, Sherlock Holmes first case, which he can solve only because Reginald Musgrave’s old tutor made him measure the height of ‘every tree and building on the estate’ and he remembered the height of an old elm, later struck by lightning. Just shows what an essential skill tree-measuring can be!

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