13. Summary and conclusions

The results of the 2002observations and measurements made across the network of permanent forest monitoring plots have allowed for the formulation of the following statements and conclusions:

• 2002 saw a slight increase in the level of damage to forest stands when compared to previous years. The defoliation index for the older stands (above 40 years) increased from 2.73 in 2001 to 2.79 in 2002. However a statistically significant increase in the defoliation index was found only for the period between 1999 and 2002. An insignificant increase in the level of damage was also noted in younger stands. The defoliation index increased from2.30 in 2000 to 2.56 in 2002.
• The highest level of damage in 2002 was noted in fir stands, while the lowest one - in beech stands. Among younger stands the highest level of damage was noted in oak stands while the lowest level - in fir stands.
• Pine stands showed an increase in the level of damage. The defoliation index for older pine stands was significantly higher between the years 1999, 2001, and 2002. No statistically significant differences in defoliation index were found for other monitored species in the period 1998-2002.
• The trend of changes in mean defoliation between 1998 and 2002 showed a slight decline in defoliation in oak and beech stands. The trend of changes in mean defoliation for other monitored species was not significant.
• Forest stands located in the Carpathian natural-forest region showed the highest level of damage when compared to other natural-forest regions. The lowest level of damage was noted in the Baltic and Mazury-Podlasie natural-forest regions.
• In 2002, the level of damage to forest stands was higher than in 2002 in the Mazowsze-Podlasie and Mazury-Podlasie, as well as in the Wielkopolska-Pomerania and Małopolska natural-forest regions. The stands in the Silesian and Carpathian and, to the lesser extent, the Sudeten and Baltic natural-forest regions showed an improvement in the level of damage.
• Chemical analyses of pine needles confirmed the variability in chemical composition of needles expressed as an elevated content of macro- and microelements between the natural-forest regions of southern and northern Poland. The differences were not found for the magnesium (Mg) content.
• The chemical composition of spruce needles did not prove significant differences in the content of macro- and microelements between the natural-forest regions of southern and northern Poland. The exception was calcium (Ca) whose concentration of in 2-year-old needles of spruce was higher in southern Poland.
• The comparison of the content of elements in pine needles in 1997 and 2001 indicated a significant increase in the concentrations of nitrogen (N), phosphorus (P), magnesium (Mg) and a decrease in the concentration of potassium (K). The differences in the concentrations of sulphur (S) and calcium (Ca) were not significant. Among microelements a significant increase in concentration of manganese (Mn), boron (B) and zinc (Zn) were found in both needle-years of pine.
• The 2001 saw a significant increase in nitrogen (N) and phosphorus (P) and a decrease in sulphur concentrations in 1-year-old needles of spruce when compared with 1997. Two-year-old spruce needle samples collected in 2001 showed an increase in concentration of nitrogen (N), phosphorus (P) and magnesium (Mg), as well as microelements: zinc (Zn), manganese (Mn) and boron (B). A decrease in potassium (K) level was noted.
• The comparison between mean concentrations of macro- and microelements in current year pine and spruce needles in Poland and three ranges for elements concentration (low, medium and high) in Europe [4] indicates that the concentrations of all analysed elements except sulphur (S) in spruce needles stayed within the medium range. Only the concentration of S in spruce needles was found to be within the range of low values.
• Shortages of atmospheric precipitation during a period of intensive tree growth were the environmental factor, which most adversely affected the forest health status in 2002. The Regional Directorates in Białystok, Olsztyn, Warszawa and Lublin faced the greatest rainwater deficit amounting to 61-76% of the long-term mean.
• In addition, a marked increase in mean air temperature in May and June when compared to that of April 2002 negatively impacted the health of tree.
• In 2002, the seed output of pines, the seed mass of 1000 seeds and the dimensions and viability of embryos of seeds in 6 natural-forest regions were higher than the average. The exception was the Carpathian natural-forest region where the values of these indicators were lower than the long-term means.
• The 2002 saw an increase in the number of pine sawflies in the Mazowsze-Podlasie, Małopolska, Wielkopolska-Pomerania and Baltic natural-forest regions. The abundances of pine hawk moth and pine looper moth on POPs were higher than in the previous year in all natural-forest regions. The abundance of nun moth in 2002 remained on the high level, however, in most natural-forest regions it was higher than in 2001.
• The 2002 saw no increase in biotic threat to forests evaluated by means of intensity of Scots pine shoots dieback and occurrence of root pathogens and abundance of folivorous insect pests. The level of threat posed by pathogen fungi and folivorous insect pests remained stable and low during recent years and no circumstances predicting a sudden change were observed.
• The level of concentrations of SO2 in atmospheric air on a majority of the country showed a falling tendency and was distinctly below the norm. Concentrations of NO2 were higher than in 2001 over most forest areas in Poland, however, below the norm.
• In the last five years, a constant decrease in the pH of atmospheric precipitation was recorded in all the natural-forest regions. Higher pHs were noted in southern Poland than in northern Poland, and higher in winter than in summer.
• The 2002 saw a continuing tendency toward decrease in sulphate-sulphur deposition when compared to 2001 on a majority of the country. The deposition of ammonium and nitrate nitrogen in 2002 maintained at a level comparable to that in the previous year. The deposits of lead (Pb) and cadmium (Cd), measured for the first time in 2002, revealed low values, however in the south of Poland these values were lower.