Report - ICP Forests

4. National Survey Reports in 2009 117
more apparent. However, in combination with other agents it can contribute to the degradation
processes of forests.
4.26 Sweden
The national results are based on the assessment of the main tree species Picea abies and Pinus
sylvestris in the National Forest Inventory (NFI), and concern as previously only forest in
thinning age or older. In total, 7 097 trees on 3 217 sample plots were assessed. The Swedish
NFI is carried out on permanent as well as on temporary sample plots. The permanent sample
plots, which are two thirds of the total sample, are remeasured every 5 th year.
The proportion of trees with more than 25% defoliation was in Norway spruce (Picea abies)
25.0% (26.2% in 2008) and in Scots pine (Pinus sylvestris) 7.1% (9.7% in 2008). The
improvement compared to previous years is mainly due to the development of forest condition
in northern Sweden. The share of discoloured Picea abies trees has decreased and was 5.7%. In
Pinus sylvestris discolouration was rare, 1.1%.
The outbreak of the European spruce bark beetle (Ips typographus) in southern Sweden has
declined. The volume of Picea abies killed by the European spruce bark beetle in 2009 is
estimated to 200 000 m 3 . This is clearly less than previous years and there are also indications
on decreasing populations of the bark beetles. However, the weather is crucial and new storms
and long hot summers could easily change the situation. A changing climate towards longer and
warmer summers increases the risk of damage by insects. In northern Sweden an outbreak of
chrysomyxa rust of spruce (Chrysomyxa ledi) was noticed. The fungi were not only found on
younger Picea abies trees but also on older trees and in some areas it changed the colour of the
forest. An increasing decline in Fraxinus excelsior has been observed during the last years in
southern Sweden. The decline is caused by a fungus (Chalara fraxinea). A special tailored
inventory on Fraxinus excelsior was in 2009 carried out in southern Sweden showing that about
25% of the trees were severely damaged or dead. Although tree species as Fraxinus excelsior
and Ulmus spp. cover less than 1% of the total standing volume in Sweden, they are significant
in the landscape of the agricultural areas. Both these species have been affected during the last
years by fungi and the number of trees decreases rapidly.
4.27 Switzerland
In 2009 the Swiss national forest health inventory was carried out on 48 plots of the 16 x 16 km
grid using the same sampling and assessment methods as in the previous years.
Crown condition in 2009 remained the same as in 2008. In 2009, 18.3 % of the trees had more
than 25% unexplained defoliation (i.e. subtracting the known causes such as insect damage, or
frost damage; 2008: 19.0 %) and 24.6 % of the trees had more than 25 % total defoliation (2008:
26.4%). Annual mortality rates were again average (4 out of 1000 trees died).
The relative low defoliation was somehow surprising as 2009 was an extremely high seed mast
year which followed a year without seeds. High seed production was found for almost all tree
species. For Fagus sylvatica on Level I plots in 2009 64% of all trees were recorded with seeds
as compared to only 2% in 2008, for Picea abies 63% had fresh cones in 2009 as compared to
only 14% in 2008. Usually, high seed production in Fagus sylvatica coincides with higher
crown transparency due to less and smaller leaves in the upper tree crown. On the other hand,