18. Summary and conclusions

Jerzy Wawrzoniak

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:

- 2003 saw a slight increase in the level of damage to forest stands when compared to previous years. The defoliation index for the older stands increased from 2.79 in 2002 to 2.84 in 2003. However, a statistically significant increase in the defoliation index was found only for the period between 2003 and 2001, 2000 and 1999.

- The highest level of damage in 2003 was noted in fir stands (defoliation index - 3,52), while the lowest one - in beech stands (defoliation index - 2.51).

- All the monitored species featured an increase in the level of damage. However, an increase in the defoliation index did not indicate statistically significant differences when compared to 2002. Statistically significant differences were found for pine stands in 2001 and 1999 and for birch stands in 2001, 2000 and 1999.

- Forest stands showed the highest level of damage in the Carpathian natural-forest region and the lowest in Baltic natural-forest region.

- In 2003, the level of damage to forest stands was lower than in 2002 in the Sudeten and Silesian natural-forest regions while in the Mazowsze-Podlasie and Mazury-Podlasie, Wielkopolska-Pomerania, Carpathian and Małopolska natural-forest regions it was higher.

- 352 vascular species of the herbaceous layer were found on 148 observation plots, including 114 species on only one plot while other 158 species - from 2 to 10 times. The most species-rich are hornbeam-oak forest, the lower number of species occur in the fresh coniferous forests

- There is a significant relationship between geographical location and species richness in vascular herbaceous plants in the fresh pine forest habitats (Leucobryo-Pinetum and Peucedano-Pinetum taken together). The correlation coefficient (0.439) and regression line parameters prove a steady growth in the species-richness of coniferous forests from west-to-east direction.

- Less than 40 plots featured lack of herbaceous species connected with the anthropogenic impact while about 30 plots have clearly disturbed species composition. More than 10% of the total number of species and about 10% of the total area coverage are species indicating strong anthropogenic impact.

- Among 148 second-level POPs, 40 plots represent 8 types of forests specified in the list of the Habitat Directive. Another 11 plots represent three types designated for legal protection by Poland.

- In 2003, no species threatened by extinction were found in the herbaceous vegetation which are listed in the "Red Data Book" nor species which should be embraced by protection in line with the Habitat Directive". Taxons subjected to species protection: 16 species under strict protection and 12 species under partial protection were more abundantly represented.

- Changes observed in the herbaceous layer over the last five years were connected with the abundance of species on POPs. This was reflected in the high variability of the species composition similarity index. Only on 28 plots, the similarity index value was below 60%, while on 86 it was higher than 70%.

- The averaging of the values of the forest floor diversity index was observed. For POPs which featured high index values in 1998, those values in 2003 were lower, while for POPs revealing low species diversity in 1998, the index values increased.

- A decrease in the coverage share of nitrophylous species was noted on many POPs in north-eastern and eastern Poland and a significant increase at the foreland of the Crpathians and Sudetes. Besides, an increase in the share of species representing ruderal and stress-tolerant strategy was found in southern and eastern Poland.

- Increased shading of the forest floor was recorded on many POPs throughout Poland, but it was most distinct in the Mazowsze-Podlasie natural-forest region which largely differed in this respect from the remaining regions.

- The number of stations of 14 species decreased (including 11 species under strict protection), while the number of stations of 10 species increased (5 species under strict protection). Substantial changes were found in the geographical distribution of species subjected to strict protection. In 1998, they occurred on 31 POPs, and in 2003 on 23 POPs. In both measurement years, species under strict protection occurred only on 19 POPs.

- The majority of changes in the ecological structure and character of the herbaceous layer vegetation illustrate fluctuation processes undergoing on the POPs resulting from both internal, specific for each plot separately, and external regional causes such as weather conditions.

- The number of types of sinusia during the last five years decreased by two on 41 POPs, while it increased at least by two types on 54 POPs.

- More distinct differences are found between the Baltic natural-forest region featuring on average an increase in the types and diversity of sinusia on POPs and the Mazury-Podlasie natural-forest region which featuring the largest decline in sinusium-richness on POPs.

- The changes and the trend of changes in the horizontal structure of the herbaceous vegetation that were noted over the last five years on the monitored POPs were less significant than those which occurred in the species composition, richness and ecological character of the herbaceous vegetation.

- Mosses are represented on POPs in great abundances with regard to both, the number of species and area coverage. In 2003, 64 species were found, half of which occurred sporadically on no more than 3 POPs, while the remaining 33% did not exceed the first degree of permanence.

- 14 moss species found on POPs are subjected to partial protection and one species is listed in the "Red Data Book of Endangered Moss Species in Poland".

- In 2003, 12 species of these plants were found on POPs.

- In 2003, 46 taxons of lichens were found on all second-level level POPs. Only two epiphytic species common throughout Europe Hypogymnia physodes and Lecanora conizaeoides occurred in higher abundance and were registered on about half of POPs. Other taxons were collected very rarely. Most of them were sporadic (3 and less occurrences). Apart from the above-mentioned species, only Scoliciosporum chlorococcum was found on over 10% of POPs. Six lichen species found on POPs are subjected to legal protection.

- In 2003, less species of mosses (64), liverworts (12) and lichens (46) were found on the second-level level POPs than five years before (78, 18 and 54, respectively). First of all, sporadic species that occurred in 1998 on one to several POPs were not found again. Most of the remaining moss species were found this time on a smaller number of POPs.

- A rising tendency was found in the number of naturally regenerated species over the last five years on permanent observation plots. An increase in mean abundance for the majority of species in all natural regeneration categories was also recorded. Average vitality and average age of the natural regeneration of six main forest tree species showed a rising tendency.

- The year 2003 faced a slightly decreased output of pine which showed high variability throughout the country. Generally, pine seeds in Poland were shapely which was reflected in increased values (only exceptionally in a few regions - in average) of indicators: mass of 1000 seeds, length and width of embryo and length and width of endosperm. Germination capacity and germinative energy of seeds was minimally lower. Significant decrease in seed vitality was noted only on one POP located in the Bircza Forest District in the Carpathian natural-forest region. The resistance of seeds to the stress conditions of the accelerated aging test was very high which indicates that pine seeds collected in the winter 2003/2004 should preserve well.

- The abundances of folivorous insects did not pose threat to the stands. The highest increase in nun moth abundance was noted in Silesian and Małopolska natural-forest regions. Elevated abundances of pine sawflies were found in the Carpathian, pine webworm - in the Silesian region and pine hawk moth in the Mazury-Podlasie and Carpathian natural-forest regions. The abundance of the pine lappet moth drastically increased in the Małopolska natural-forest region. Increased population abundances of pine looper moth were noted in the Silesian and Carpathian natural-forest regions.

- The comparison of results obtained from the first and second observation series demonstrated an increase in the MIB values on 19 monitored POPs (73% of all POPs involved in the 2003 study).

- The threat to Scots pine caused by the dieback of shoots was low and its level was typical for a period between epiphytoses. The indices of the threat to stands posed by root pathogens in 2003 were significantly higher than in previous years. Spruce was found to be most threatened by the root rot fungi. The mountain regions (Sudeten and Carpathian natural-forest regions) were most threatened by root diseases which might have been associated with the high share of spruce in the species composition of mountain forests.

- The year 2003 saw an increased insufficiency of atmospheric precipitation during the growing season on a majority of the country. The largest shortages of atmospheric precipitation occurred in the Wielkopolska-Pomerania natural-forest region where the level of precipitation approached 65% of the long-term mean.

- High mean air temperatures in June accompanied by low atmospheric precipitation was an important factor adversely influencing the health condition of stands.

- The mean values of sulphur dioxide over the last twelve months were lower than those in 2002 in northern natural-forest regions but Mazowsze-Podlasie and higher in southern regions of Poland with the exception to the Silesian natural-forest region. In 2003, the concentrations of SO₂ did not exceed 50% of the country mean.

- The NO₂ concentrations were higher than the values found in 2002 in all natural-forest regions but the Mazowsze-Podlasie and Małopolska natural-forest regions. In 2003 the concentrations of NO₂ did not exceed 50% of the country mean.

- In 2003, the higher values for pH were noted in southern natural-forest regions in the winter season. For the first time the decrease in the mean pH value for the country was reported which accounts for a change in the trend during the recent years.

- The falling trend in the deposition of sulphur compounds in the precipitation during the recent years was reversed. In 2003, only the Sudeten natural-forest region exceeded the lower limit of the background deposition of sulphur compounds while it increased in other regions.

- When compared to 2002, a slight increase in nitrogen minimal and maximal value of deposition and a change in the order of individual natural-forest regions based on increase in sum of nitrogen deposition. An increase in the sum of nitrogen deposition occurred in six natural-forest regions while a decrease was noted in two natural-forest regions (Baltic and Wielkopolska-Pomerania).

- The concentrations of cadmium increased in 2003 in all natural-forest regions with the exception to the Mazury-Podlasie region. The highest in the Carpathian natural-forest region during the winter and summer seasons. The lowest mean concentration of cadmium was found in the Mazury-Podlasie natural-forest region in the summer. In all natural-forest regions, the concentrations of this element were higher in the winter the than in the summer with a single exception of the Mazury-Podlasie natural-forest region.

- The concentrations of cadmium increased in 2003 in all natural-forest regions with the exception to the Mazury-Podlasie region where the lowest values were reported. In the Carpathian region the highest concentrations were for lead. As compared with the previous year, the value of lead deposition was down in all natural-forest regions but Silesian. The minimal lead deposition was noted in the Baltic natural-forest region.

- The concentrations of a many ions in the throughfall waters on the POP in the Chojnów Forest District were higher in the winter than in the summer. However, the maximal concentrations of potassium, calcium, magnesium and phosphorus were recorded during the autumn season. This might be due to the leaching of ions from needles. The deposit of the troughfall in the analysed stand during half year was 50 kgˇha^-1. The chemistry of the stemflow waters was high, more acid than the canopy throughfall.

- The values of the molar ratio of calcium to aluminium and magnesium to aluminium in soil solutions account for the lack of threat to nutritional possibilities of trees with calcium and magnesium.

- Taking into consideration the dominant species in a stand the lowest amounts of organic carbon are accumulated in the soils under pine stands, slightly higher under oak and beech stands and distinctly highest under spruce stands. As regards forest habitat type the lowest amounts of organic carbon are accumulated in the soils of Bśw, medium - of BMśw and LMśw and the highest - of Lśw habitats.

- Organic carbon in the forest soils can be accumulated even at large depths. At a depth of 20 - 80 cm the monitored soils accumulate 46 to 58% of the total carbon pool measured in the mineral horizon.