Division II.1 Selection of sample trees on Level I points

At each sampling point, sample trees shall be selected according to a stringently defined, objective and unbiased statistical procedure (e.g. four point cross cluster orientated along the main compass directions with corner points at 25 m distance from the grid point using a six-tree sampling process on each subplot or sample trees chosen following a spiral from the plot centre). In younger dense stands where individual crowns are not assessable, the selection of sample trees should be based on a defined geometrical process. This process shall be repeated until a sufficient number of trees with assessable crowns have been found. The following selection criteria are to be taken into account:

• Member States may decide on the number of trees to be assessed at each point; however, the sample shall not consist of less than 20 trees or more than 30 and the number shall remain constant,

• all tree species shall be included in the assessment. Sample trees should have a minimum height of 60 cm. Only predominant, dominant and co-dominant trees corresponding to the Kraft tree classes 1, 2, and 3 respectively, qualify as sample trees for the purpose of crown condition assessment. Trees of these social classes with broken tops cannot qualify as sample trees,

• trees removed as part of management operations, fallen trees (e.g. blown over by the wind or broken) and dead trees must be replaced by new sample trees selected according to an unbiased procedure. A tree is defined as dead if all conductive tissues in the stem have died. A dead tree must be recorded but only once. Clear-cutting of the stands imply that the sample point ceases to exist until a new stand has been established,

• the centre of a sampling unit must be marked for reassessment of subsequent inventories. Sample trees should be identifiable for the following year's assessment, if possible without permanent labeling.