Fitted height is to be determined in all stems with a non-zero diameter at breast height according to Näslund’s regression function

`h = d^2 * (a + b*d)^(-2) + 1,3`

,

where

h is fitted height,

d diameter at breast height, and

a, b are regression parameters.

Regression parameters are determined for each tree species by linear regression using the least square method of the function

`H = a + b*d`

,

where

`H = d * (h - 1,3)^(-1/2)`

,

h being the measured height of healthy stem [S;X;*;0] and d being the corresponding breast height diameter.

Diameter of the breakage or stub top determines the stem diameter

- at adjusted height of breakage or stub from the pair [stub or breakage, lying stem], or
- at a height of isolated breakage or stub.

The calculated breast height diameter of lying stem from the pair [stub or breakage, lying stem] determines the stem diameter at 1.3 m of stem length.

These parameters are calculated by using the formula for the calculation of tree stem diameter at a desired height. The formula is further introduced the breast height diameter and the fitted height of breakage or stub.

The calculated breast height diameter is used to calculate the basal area.

Basal area is to be calculated from the breast height diameter or from the calculated stem diameter at breast height according to the formula for the calculation of basal area.

Volume *healthy stem* [(S);(X,O);*;*] is determined from the volume
tables of tree species according to breast height diameter and fitted height.

Should a stem have a diameter larger than the largest diameter stem of given height in the volume table, the volume is to be calculated as a product of the stem basal area and the form height of the stem of corresponding height.

Should a stem have a greater fitted height than the tallest stem of given diameter in the volume table, its volume is to be calculated as a product of its fitted height and the ratio of the tallest stem volume of corresponding diameter from the volume table to its height.

Should a stem have a greater fitted height and at the same time a larger diameter than the tallest stem of the largest-diameter in the volume table, the volume is to be calculated as a product of stem basal area, stem fitted height and stem form factor. Stem form factor is to be calculated as a form height to height ratio of the tallest stem.

Volume of *isolated lying stem* [(L);(X,V);*;*] is determined similarly
as in the healthy stem with measured length to be used instead of fitted height.

Should the volume table not include the value for height at a value of the measured length of isolated lying stem and the corresponding diameter, and should this not be the case of a taller or larger-diameter stem than presented in the volume table, the volume is to be determined as a sum of the volumes of blunted cones of identical height of max. 0.5 m, approximating the stem body. For the calculation of approximation cone base diameters the relevant form function is to be introduced breast height diameter, fitted height and lying stem length.

Volume of *isolated breakage or stub* is to be calculated as a sum
of the volumes of approximation cones with using breast height diameter and
the height of stub or breakage.

Should the height of isolated breakage or stub be zero, the volume is to be calculated as for the healthy stem with the corresponding fitted height.

Volume of *breakage or stub from the pair* [stub or breakage, lying
stem] is calculated similarly as the volume of isolated breakage or stub except
for cases in which the volume is established to be zero.

Volume of *lying stem from the pair* [stub or breakage, lying stem] is
calculated as a difference between the stem volume with a breast height diameter
of the concerned breakage or stub and the height equal to a sum of the breakage
or stub height and the length of the lying part, and the volume of the concerned
breakage or stub from the pair [stub or breakage, lying stem].

Should this difference come out as a zero or negative, the volume is determined
at 0.05 m^{3}.

Should the volume table not include the value for height corresponding to the sum of breakage or stub height and length of the lying part and the corresponding diameter, and at the same time the case in question is not that of a stem taller or with a larger diameter than presented in the volume table, the volume is to be determined by means of approximation cones with the use of breakage or stub breast height diameter and a sum of the breakage or stub height and the length of the lying part.

*Authors:* Martin Ambroz & Virgin Forest Team

*Contact:* Bat.Mika@seznam.cz