64 Height to crown base
The vertical distance between the crown base and the ground level (measured from the dbh mark as described above).
The crown base is defined as the base of the lowest significant volume of foliage (or buds, if measurements are taken at winter time) and not the point where the branches supporting the foliage are attached to the trunk; epicormic branches are not included. When this is variable, average should be taken. If the crown is not continuous, the lowest part is considered to be the lowest branch with a minimum diameter of 3 cm within 2 m of the main part of the crown.
If the accepted national method differs from the described method the national method can be used. This must be documented in the data accompanying report.
In coppice forests, the crown of the stools is made up by the elementary crowns of the shoots and is considered as a whole. Height to crown base is therefore measured on each stool.
It is advised that recording of the crown base be carried out in the same position and at the same time as the tree height measurement.
Care should be taken to ensure subsequent assessments are carried out from the same spot.
If possible height to crown base should not be measured when tree crowns are covered with snow.
The periodic measurement of height to crown base is mandatory on each tree where tree height is measured.
Note: It is recognised that growth measurements do not necessarily express the same ”crown volume” as that determined by assessments of crown condition.