Defoliation (harsuuntuminen)

Defoliation, or needle loss, means the loss of needles or leaves from trees. It may be due to air pollution, but also to natural factors. Defoliation is estimated visually. The degree of defoliation is expressed as a percentage which denotes the proportion of needles or leaves lost in comparison to the normal volume. A tree is considered to be defoliated if it has lost at least one fifth of its needles or leaves.