 Here
is one of Tane's big rimu trees by the bike trail bridge,
helping to separate Rangi-nui from Papa-tua-nuku. The
fallen trees allow us to see this rimu from its base up to its
summit. Let's find its approximate height. You can find
the approx. height of any tree etc the same way.
1. Distance from the base
For many trees, we can walk to the base, counting our steps as we go, or using a long tape measure. But here I borrowed a laser range finder. 2. Find the ratio of height / distance a. I put cuts in my hiking 
staff every 10 cm. The palm of my hand is about 10cm, so I
used that.b. I measured the distance to my eye, about 7 cuts or 70 cm. c. I held my walking stick up so
that my hand was in line with the base of the tree and its end
was in line with the top of the tree.
d. I
counted 12 cuts up to the tip of my hiking staff.
e. I estimated the height of the tree to be about twelve sevenths of 24 metres. 12 ÷ 7 = 1.71 1.71 x 24m = 41m high 3. Check by finding the angle Here is another way if you have no walking stick, and if you do have your cellphone. When
you hold your fist out, it covers an angle of about 10°, about
2° for each finger.
When I
started at the base of the rimu, I used about six fists to get
to the top of it, about 60°.
 
 To find the height, I multiplied the tangent ratio of 60°, called
Tan (60), by the distance to the tree. I only bothered
with the first two decimal places.
Tan (60) = 1.73 1.73 x 24m = 41.5m high That's close enough. Now you can find the approximate height of any tree when you can see both its top and its base. TEENAGERS
- here's a STEM project for you
Your outstretched arms extend about the same distance as your height. So go across the bridge, make your way to the tree, and "hug it" a few times to estimate its diameter at hug height. Now make a hiking staff with centimetres on it, borrow the big tape measure your school uses to measure javelin and shot-put throws, and measure the height and diameter of as many as you can. Separate the open-country trees from the ones in heavy forest. Make a diameter-height chart with Open and Forest symbols. Now
you can estimate any rimu's height by hugging it!
Copy and print this QR sign for your own forest or class project.  |
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