73 Top height
Top height is little affected by thinning under most thinning regimes, therefore it is a more practical parameter than stand mean height for classifying growing condition (site quality, yield class).
There are two common ways to determine top height:
Defined by a number of largest trees (field height_top_abs)
Current practice is to determine the 100 trees per hectare (or less if growth plot is smaller) of largest dbh to calculate the mean basal area diameter of this sample (see EI 72) and to derive the corresponding height from a diameter-height function.
Defined by a percentage of largest trees (field height_top_rel)
Another procedure is to take the 10% or 20% of largest trees and do the calculations described above on basal area mean tree (see EI 72) to derive the relative top height.
In mixed stands the proportion of different species can be determined by their relative area or they are selected irrespectively of the tree species and the height is calculated then for each species.