Defoliation (2.3)
Defoliation8 is an indicator of the general condition of trees. A
decrease in the biomass of photosynthesising needles or leaves
affects the vital functions of trees and reduces their growth.
Defoliation is assessed visually. In mineral soil in 2009, 6% of
pine, 20% of spruce and 5% of broadleaves were classified as
damaged.9 Forest defoliation is considerably less severe in Finland
than it is in most other European countries.
The proportion of undefoliated pines (defoliation less than 10%)
decreased and the proportion of slightly defoliated pines (10–
25%) grew slightly during the monitoring period 1986–2009.
However, the proportion of damaged trees in all tree species had
remained nearly unchanged over the past few years.
Figure 2.3 Defoliation frequency distribution for pine, spruce and broadleaves in mineral-soil sites, 1986–2008 (from 2004 the figures
also include reference trees on peatland)
Source: Finnish Forest Research Institute, annual monitoring of forest vitality.
In Finland, defoliation is primarily caused by ageing, unfavourable
weather and climate conditions and damage due to fungi
and insects. In the vicinity of local emission sources, in builtup
areas and along roads, defoliation is also caused by atmospheric
pollutants.
8 Defoliation, the loss of needles or leaves, is an indicator of vitality. The degree of defoliation is classified as slight when it is 10–25%, moderate >25–60%,
severe >60–99%, and dead 100%.
9 A tree is classified as damaged when defoliation is greater than 25%.
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