The effects of frost conditions on forest management based on the example of the July 1996 period at Hala Izerska in the Izera Mountains

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Abstract This paper presents the characteristics of a frost episode that occurred July, 20-23, 1996 in the centre of the Izera Mountains and its effects on forest management. Source data consisted of air temperature measurements originating from the author’s own and archival databases of the Institute of Meteorology and Water Management (IMGW), Voivodeship Inspectorate of Environmental Protection (WIOŚ), University of Wrocław (UWr) and the Bureau of Forest Management and Geodesy in Brzeg (BULiGL). The intensity, time of occurrence and effects of this particular episode were extreme. The estimated probability of frost in the centre of the mountain dale Hala Izerska in July at a temperature of -5.5°C two meters above ground level is 2.4%. Therefore, it can be stated that such a sharp decline of Tmin in the middle of the growing season can occur in this area once every 40-50 years. Strong, nocturnal decreases of Tmin below 0°C during the growing season occur in the Izera Mountains almost every year, causing significant damage to silviculture. The interior of the Izera Mountains, represented by mountain dale Hala Izerska, is one of the coldest or even the coldest site in Poland in terms of absolute minimums of air temperature during the growing season. In the mountain areas, knowledge of the impact of climate, such as thermal factors, on tree stands enables silviculture work to be optimised, ultimately allowing funding to be rationalised. The distinct climatic conditions of mountain basins and valleys, slopes and plateaus located at similar altitudes need to be considered.