Drop of leaves or needles, expressed in percent, estimated by relative to standard full-foliage crown, caused by feeding grounds of insects, air pollution or soil.

The results of estimating defoliation are grouped together, according to species, to form the following classes:

Class 0 – from 0% to 10% – no defoliation

Class 1 – from 11% to 25% – slight defoliation (early-warning level)

Class 2 – from 26% to 60% – mild defoliation,

Class 3 – above 60% – severe defoliation,

Class 4 – dead trees

and class groups: classes 1 –3, classes 2 and 3, classes 2 –4 and classes 3 and 4.