Forest Mensuration. Brack and Wood

Standard terms and units ©

Australia is a signatory to the Metric Convention, which means that a commitment has been made to use the International System of Units (SI for short). These units are precisely defined so that, for example, 1 metre in Australia can be exactly compared with 1 metre in Europe.

The standard units are:

metre (m) - length
kilogram (kg) - mass
second (s) - time
ampere (A) - electric current
degree Kelvin (K) - thermodynamic temperature
candela (cd) - luminous intensity
mole (mol) - amount of substance

Other units can be derived through the inclusion of decimal prefixes (e.g. deci, kilo). Some units are not included in the SI, but are nevertheless commonly used and accepted:

hectare (ha) - area
day (d) - time interval
hour (h) - time interval
minute (min) - time interval
tonne (t) - mass

Historical standards

Throughout history standards have been developed and used in measurement, including:

yard - length from the nose to the tip of an out-stretched arm (in England).
yard - length of a yardstick kept by the King in medieval France.
rod - combined length of the left foot of 16 Englishmen.
cubit - length of a human forearm.
inch - length of 3 barley corns.
Hoppus measure - tree or log volume that approximates the true volume (without the need for the value calculating PI). The most famous is the Quater Girth or Hoppus measure. Many formulae giving approximations to true volume can be found in the literature, however the advent of modern calculating devices has meant that Hoppus measures are no longer used:
- V (s.ft. Hoppus) = (G/4)^2 x L / 12;
- V (c.ft. Hoppus) = (G/4)^2 x L / 144
  where G is girth in inches and L is length in feet
- To convert Hoppus volume to true, multiply by 1.27.
- To convert true volume to Hoppus, multiply by 0.79.
- Also 1 c.ft. true = 12 s.ft. true = 12 x 0.79 or 9.48 s.ft. Hoppus.
- Hence, a factor of 10 is often used to convert volume (c.ft. true) to volume (s.ft.Hoppus).
Log Rules
- In some countries, log volume is estimated in terms of the forecast product, e.g. Log Rules of North America. These are tables showing expected log output based on fixed assumptions about the product and the production method, e.g.:
- logs are cylindrical with diameter equal to that of the small end;
- logs are sawn into boards of a certain thickness with a saw of specified thickness or kerf;
- one fixed procedure for sawing and slabbing exists;
- all mills are equally efficient and produce equal lumber yields from similar logs. (In practice, each mill has an average under-run or over-run, i.e. log scale and lumber yield do not agree.)
- As many as one hundred log rules have been used in the U.S.A., the best known being the Doyle, Scribner and International Rules.
Stack measurement
- Log quantity is occasionally estimated on a stack basis but this practice is waning in favour of weight measurement.
- Stacked volume in the past was most common with material such as pulp billets comprising small regular logs of similar diameter in standard lengths. The common units of measurement are:
- Metric Stere - an imaginary rick (or stack) of bolts of dimensions 1 m x 1 m x 1 m. In Australia, cubic metre is used rather than stere.
- Imperial Cord - an imaginary rick of bolts of dimensions 4' x 4' x 8' = 128 c.ft.
- Cunit - 100 c.ft. of wood with stack space varying. The cunit was developed from experience by APM Pty Ltd with the cord which showed that, on average, 100 c.ft. of timber filled the tray of a truck.

There are some obvious deficiencies in these standards!

Unusual measurements

The Largest tree. Harlow & Harrar "Textbook of Dendrology" from 1950 says General Sherman tree was 6 000 tons (i.e. ca. 6 110 tonness).
Largest tree in Australia according to Ashton (1975) (Australian Jounral of Botany 23: 867-887) was a Eucalyptus regnans with a diameter of 10.8 m at 1.6 m above the ground. It had a defective butt which could "hold eleven horses inside".