Big Tree Measuring Methods
- Tape measure (> 3 m)
- A measuring stick for height
note: the steel tape-measure will work fine when held vertially since less than 50 cm is usually needed
- Measuring line (30-60 m in length) for determining distance from the tree
- notebook and pencil
- Geographical map of location
(eg. local Geological Survey of Canada topographical map or “Atlas of Nova Scotia”)
Circumference and Diameter
(Do not measure the diameter, measure the circumference)Wrap the measuring tape around the smallest part of the truck between the height of 1.4 metres (breast height or 4-1/2 ft) and the ground. Usually this will be at the 1.4 metre height. Read the distance around the trunk off the tape and record it. You may want to do this several times to be sure you have the tape properly positioned. Use the smallest of your measurements. If the tree is on a slope, use the upslope side of the tree to determine the 1.4 m above the ground.
The mean diameter equals the measured circumference divided by pi ( = 3.14).
The diagram illustrates how you can measure the tree height by not having to climb to the top with a measuring tape (We don’t recommend that method ;>)
Walk away from the tree until you can easily see the base and top branches without moving your head. Hold the measuring stick vertically at arms length (straight elbow) over your view of the tree and determine markings on the stick that correspond to the branch tip and the base of the tree. (I like to use my tape measure and position the tip at the top of the tree and read mark at the base of the tree) The distance between these marks is proportional to the height of the tree. Note: it is important that you NOT MOVE your head or body when you read the heights on the stick!
You will need to determine the distance your feet are from the base of the tree and distance the stick was from your eye when you took the measurements. You can use the measuring stick (tape-measure) to get the distance from your eye to hand that held the stick OR let a companion measure that distance while you are holding the stick. The distance to the tree can be measured with your tape measure (I have used pacing for distance but this is inaccurate in the woods or uneven ground. It is tedious to use the tape measure to measure the distance so I like to carry a long length of string marked off in 10 metre distance up to 60 metres)
Record the three measurements in your notebook (1. tree height on the measuring stick, 2. distance of your eye from the stick, 3. your distance from the tree base). Be sure to record the units you use with your measurement. Use the relationship below to calculate the height of the tree.
A tree’s canopy does not usually extend the same distance in all directions. You should measure its extent horizontally for the widest and the narrowest directions. Usually these are nearly at 90 degrees to each other. The Canopy width then is the average of your measurements.
Use the same method as you did for measuring the height of the tree but turn your measuring staff horizontal. If you use the tape-measure, you will have to hold both ends up.
An important part of the record is the tree’s location. Verbal direction are good when they indicate how to get to the tree. For mapping purposes, it is nice to have the geographical coordinates of the tree. These days, if you have a GPS, it is easy to mark the position and record the latitude and longitude (or equally well the Easting and Northing]. The coordinates by also be read off maps. The best would be one of the topographical maps (1:50,000) published by the Geological Survey of Canada. If you do use this technique, please record the datum of the map… some of the older maps are NAD27 rather than NAD83 (NAD = North American Datum). You could also use “The Atlas of Nova Scotia”
Locating a tree on a topographical map is approximate but so is a GPS reading. GPS are usually accurate to about 10 m or less. A determination of position to 0.5 mm on a 1:50,000 topographical map yields a location accurate to 25 m. The “Atlas of Nova Scotia” has a scale of 1:150,000 so the same precision gives a location accuraty of 75 m. Locations can be recorded as north latitude and west longitude OR as Easting and Northing in the UTM system. If you use the later form, state whether you are in zone 19, 20 or 21. Most of Nova Scotia is in zone 20.
Example of getting Coordinates from a Map
Note: If you use “The Nova Scotia Atlas” you will find that there is no UTM grid and that the black grid is a latitude-longitude grid. Determine the latitude and longitude in this case. Older versions of this book did use the UTM grid.
In the following calculations, I calculate first in English units then convert to metric.
Conversion of Units:
If you are like me, I still have measuring equipment deliniated in inches and feet (and still tend to think in those units). We do ask that all measurement be reported in metres but it is an easy conversion.