Extreme precipitation events in the Forest Promotion Complex of Silesian Beskid

Przemysław Szmit

An increase in frequency of weather phenomena in the Western Beskids that are disadvantageous for natural environment caused an upset of ecologic balance, especially within the scope of water management and retention. Concerns referring to forest groups maintaining their stability are fully justified, regarding that in many areas of the Beskids, there is an intensive reconstruction of stands of trees in the lower subalpine region. In turn, young generations of trees are continuously stresses, which arise from periodic shortages of precipitation within the course of the whole vegetation process. The presented work encompasses characteristics of extreme rainfall events that might have a negative impact on growth and development of Norway spruce stands in the Silesian Beskid in recent decades. The article makes use of meteorological data from a multiannual period (1951–2010), gathered in 26 meteorological stations of the Polish Institute of Meteorology and Water Management (IMGW) in Silesian Beskid one station located in the Carpathian regional gene bank and two under canopy posts located in Wisła forestry inspectorate area. Special attention was devoted to the presence of extreme phenomena and their repeatability. The analysis of parameters of rainfall sequences was complemented with indexes determining ecological requirements of spruce, such as: Schmuck moisture indicator, Vogel-Daniels habitat dryness index and abundance of rainfall indicator developed in this study. Results of climatological analysis confirmed that weather phenomena with, especially dynamic course may lead to destabilisation of even a properly formed and adequately developed forest ecosystem, and as a consequence, disturb stability in the natural environment. Diminishment of the index of precipitation size, which has been observed in recent years, may be one of the most crucial causes that limit the number of spruces in the stands of trees of the lower subalpine region in Silesian Beskid. The climatological analysis confirmed that during 60 years in Silesian Beskid, there were over 20 extreme weather (precipitation) episodes of different courses, intensity and surface reach, out of which at least 9 played a key role in lowering the health condition of the trees, as a consequence, it influenced destabilisation of the spruce stands in the lower subalpine region, regardless of their age or location within the area.