Different types of damage in mountain forest stands of the Czech Republic

Forests in the Czech Republic are highly influenced by the antropogenous factors - those are particularly air pollution, pollutant deposition, soil degradation, change of the natural forest ecosystems, and also global climate changes. Significant damages due to air pollution are visible already 50 years (the Ore Mts. region). Since 1989 the sulphur emission has decreased significantly. By the end of 90ies SO2 emission was reduced in nearly 90%. In the 1990-1995 period, the change of air pollution situation in mountain regions resulted into the spruce stands condition improvement, and good progress of transitory stands (birch, blue spruce, mountain pine, alder etc.). Following development was not that ideal, however. Since 1995, various symptoms of damage have been observed, caused by the complex of factors. During the winter 1995/1996, within the whole region of the Czech Republic, reddening of the last needle year class of spruce was observed in the altitude over 700 m. These symptoms were the most visible in the eastern part of the Ore Mts., where 3-4 needle year classes were affected, or even tree decay observed. An acute damage was caused by direct impact of the high SO2 concentrations. The average defoliation was over 60% in stands assessed. About 12,578 ha of spruce stands were damaged, 1,300 ha of them has completely died. The rest have regenerated successfully in following period. After following winter, in spring 1997, the damage of transitory birch stands was observed in all the northern mountain regions. In the Ore Mts. ridge birch did not flush at all, the leaf lost was observed in a vast area with variable intensity in altitudes over 800 m above sea level during the springtime. In total 3,400 ha of birch stands was damaged, in 1998 it was nearly 5,428 ha. Birch completely died at about 2,550 ha, in following period the damage development stagnated. Similar damage of smaller extent has been observed also in other parts of the country, in higher elevations, situated above the inversion layer during the spring months. After winter 1999, vast damage of the spruce stands, manifested in yellowing of older needle year classes, and gradual needle drying and fall, affecting the stand of all age categories, was observed in the western part of the Ore Mts. but also in other regions. Yellowing was observed on 2,000 ha in 1999, next year it was 6,500 ha, and in 2001 about 9,000 ha was damaged within the Ore Mts. A new type of damage has been observed in the Orlické hory Mts. ridge caused again by the stressing factors complex after the winter 2001/2002. Nitrogen deposition seems to be one of major problem. The damage presented shows that in spite of significant lowering of air pollution load the forest stands health state in air polluted regions is not stabilized.