The average level of defoliation has remained relatively unchanged in Finland over the past few years. In 2002-2005 needle loss of Scots pines growing on mineral soils was approximately 9% and that of Norway spruces 18%. Needle loss of broad-leaved trees was about 12%. The results are presented in the report on the forest condition monitoring programme (Forest Focus/ICP Forests) carried out by the Finnish Forest Research Institute (Metla).
Needle loss was not found to be associated with air pollutant levels. Defoliation in Finland is mainly due to the aging of stands, unfavourable climate and weather conditions, and damage caused by fungi and pests. Damage caused by an external stress factor was detected in more than one third of the trees studied. The incidence of different stress factors varied considerably during the study period: for example, Chrosomyxa rust of spruce (C. ledi) was common in 2005.
Sulphur deposition during 2001-2004 decreased from the levels measured in previous years, especially on the plots in southern Finland . There was no corresponding reduction in nitrogen deposition. The change in sulphur deposition was also reflected as a slightly decreasing trend in sulphur concentrations in needles. No other significant changes were observed in the nutrient status of trees. The average deposition of sulphate and total nitrogen was clearly larger in southern than in northern Finland . During the period 2001-2004 there were no signs of soil acidification caused by acidifying deposition.
The highest atmospheric concentrations of sulphur dioxide and nitrogen dioxide were recorded in the south-east of Finland , near to the Russian border, and the lowest concentrations at measuring sites in Lapland . All measuring sites indicated the same trend: sulphur dioxide and nitrogen dioxide concentrations were at a peak during winter, and ozone concentrations during early spring.
The ICP Forests programme on forest condition monitoring is based on an international agreement on long-range transboundary air pollution. Forest health monitoring has been carried out in Finland since 1985. The Forest Research Institute (Metla) performs an annual inventory of tree condition using internationally agreed methods on approximately 600 permanent monitoring plots. Relationships between forest health, air pollutants and other stress factors are studied in 31 stands in various parts of Finland .
This report on forest condition monitoring published by Metla presents the 2002-2005 results of monitoring in Finland carried out under the EU-funded Forest Focus and the pan-European ICP Forests programmes. The report also contains results gained in other studies on environmental and forest damage monitoring, for example, “Forest damages in 2002-2005 based on data received by the Forest damage diagnostic service” and “Damages observed in the 10 th National Forest Inventory over 2004-2005”.
Publication: Merilä, P., Kilponen, T. and Derome, J. (eds.). 2007. Forest Condition Monitoring in Finland. National Report 2002-2005. Working Papers of the Finnish Forest Research Institute 45, 166 p.