17. Evaluation of the impact of environmental factors on the health condition of forests in 2003 and the anticipated direction of changes in the upcoming years
Jerzy Wawrzoniak
Deterioration of the health condition of forest stands is usually accompanied by many negative effects impacting their functioning. They are reflected in the lower resistance of stands to stresses of biotic and abiotic origin. Moreover, they cause disturbances in the nutritional balance and have impact on stand growth. The significance of these disturbances is considerable if the deteriorated health condition of stands continues into another year. The adverse changes taking place in stands accumulate through the deformation of physiological processes in trees thus creating a specific stand's "memory" which slows the process of their recovery under more favourable conditions. Such a situation may occur in some regions of the country where, for some years, the health condition of stands have been deteriorating. In the Regional Directorate of the State Forests (RDSF) in Krosno and Gdańsk, the percentage of damaged trees has been growing for 5 years (2nd-3rd damage class). In Regional Directorates in Poznań, Szczecin, Szczecinek, Radom, Toruń and Warszawa, the percentage of damaged trees has been growing for 3 years. In the stands where the initial level of damage was higher, after five years of continuing damage growth, this "memory" will be deeper and stronger, and the improvement of the health condition of stands may be slow and take place several years after the disappearance of the adverse environmental factors. Stands in RDSF in Krosno, which for five years have been showing an increase in damage at a relatively low initial level of damage, can be included in this group. Stands in RDSF in Szczecinek are in a different situation. The percentage of damaged trees there has been growing for three years. It means that this negative trend has been shorter. Moreover, the level of damage to stands in the initial period was low. In this situation, reversal of the negative trend will be relatively fast after the adverse effects cease.
While analysing the level of damage to forests in Poland between 1989 and 2003, on the basis of the percentage of damaged trees in a stand, several periods featuring a changing trend direction can be distinguished. Between 1989 and 1994, an increase in the level of damage to stands was observed. Then, the trend was reversed, which was reflected in the continuing improvement of the health condition of stands in the following five years (1995-1999). In 2000-2003, deterioration of stands' health condition was observed, with a slight fluctuation of the trend in 2001. It seems that the health condition of stands is a parameter featuring a significant level of inertia and that its change occur at a slower pace than the changes of individual environmental factors. In 2003, health level of forests in Poland was lowest in the last five years. Precipitation deficit is the main factor responsible for such a low health level of stands in recent years. Both in 2002 and in 2003, the country's mean precipitation sum in the growing season did not exceed the long-term mean, and in 2003 it was the lowest in the entire 5-year period. Water deficit was reported across the country, peaking in the Wielkopolska-Pomerania and Mazowsze-Podlasie regions.
The level of atmospheric air contamination and its deposition in forest areas is an essential abiotic factor affecting the health condition of stands. In the past 5-year period ending in 2002, a slow but steady decline of annual concentrations of SO2 was observed in the country. This decline occurred both in northern Poland and, to a greater extent, in southern Poland. The year 2003 saw however an increase in mean concentrations of SO2 and further growth of NO2 concentrations started in 2002. This increase occurred mainly in southern Poland. The stated values are low and do not exceed the obligatory norms, however the recent dominant trend has been reversed. As a result of growth of SO2 and NO2 concentrations, a slight growth of precipitation acidity has been noted for the first time, particularly in southern Poland. If these trends continue and consolidate, they will have a negative effect on the health condition of forests in Poland. Moreover, the deposition of acidifying and eutrophicating ions has increased in southern Poland too. This phenomenon leads to an increase of stand fertility, improvement of stand quality (bonitet) and acceleration of tree increment. It is not always advantageous from the point of view of the health condition of stands. It is most often associated with reduced resistance of stands to abiotic and biotic stresses.
The level of impact of biotic factors in 2003 was low. The number of the population of folivorous insects did not pose a threat to stands in spite of the population growth of some species in comparison with 2002. The threat of pine shoot dieback continued on a low level typical for the period between epiphytoses. The indicators of threat to stands from root pathogens significantly grew in 2003 in comparison with previous years. The analysis of stump colonization by fungi showed that spruce represented the highest percentage of stumps colonized by pathogens. However, the level of this threat has no significant effect on the health condition of stands in Poland. .
While anticipating changes in the health condition of stands in Poland, the dominant trend of health condition deterioration in stands over the past two years as a result of water deficit should be taken into consideration. Even a significant precipitation growth in the growing seasons in the upcoming years will not cause an immediate reversal of this negative trend. As aforementioned, stands feature a specific "memory" which disappears slowly regardless of favourable conditions. Moreover, a reversal of the trend of decline of SO2 concentrations and of precipitation acidity, and continuation of the slow growth of NO2 concentrations were observed in 2003. If the growth of concentrations of air pollutants continues and the growth dynamics strengthens, this can within a few years have a negative effect on the health condition of stands. Growth of the deposition of nitrogen compounds and growth of CO2 concentrations in the air favouring forest stand eutrofication and augmenting the tree volume increment are a significant factor impacting the health condition of stands. This phenomenon makes stands less resistant to adverse environmental effects.
Recapitulating, the direction of changes in the health condition of stands in Poland is much uncertain. In the upcoming years, even if the weather conditions prove favourable, improvement of the health condition of stands should not be expected. In the following years, changes in the health condition of stands will depend on both the satisfaction of their water requirements and the pace of growth of concentrations of air contaminants.