Stability of spruce forests in the Beskids: an analysis of wind, snow and drought damages

During the past 150 years, only a few incidents have been recorded of more than 50,000 m3 being damaged by wind activity in the Moravian-Silesian Beskids. Such events occur with a frequency of approximately 25 years. Wind damage correlates with prevailing winds. Scattered forest damage is more prevalent than extensive areas of wind-fallen trees. The relative area of comprehensively damaged forests significantly correlates with increasing elevation above sea level. Historical references to snow-caused tree falls during which the volume of damaged wood exceeded 20,000 m3 are documented for several years. These occur with a frequency of approximately 10 years. No significant logistic regression has been determined between the maximum elevation of snow cover at the Lysá hora station and the probability for the incidence of damages to exceed 20,000 m3. No significant relationship has been determined between the duration of drought and unregulated fellings in the following year. For the period 2006--2008, the maximum snow cover was recorded at the end of the winter of 2005/2006. The greatest damage to spruce stands caused by snow was documented after the winter of 2005/2006. The share in damaged trees decreased with increasing age. Entirely undamaged stands were recorded in all age classes with the exception of forests 21--60 years old. The proportion of trees damaged by snow was not dependent on the elevation above sea level. The share of damaged trees was relatively even at all exposures. Damage on the steepest slopes (incline greater than 50%) is significantly different from the damage on inclines of 0--33%, as is true of the damage on slopes of 34--50% versus the damage occurring on inclines of 11--33%. Tree damage corresponds positively to the slenderness coefficient.