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The aim of the study was to determine the spatial variation of vapour pressure (e), relative humidity (f) and vapour pressure deficit () on the clear−cut and gap as well as to compare the spatial distribution of air humidity conditions on both areas. The research was carried out in Rogów Forest Experimental Station (51.827023°N, 19.922315°E) on a clear−cut with a width of 60 m and on a gap of an ellipsoid shape (40×70 m). The measurements were carried out in two series: spring−summer, i.e. in the period when the height of the sun during the day conditioned inflow of direct solar radiation to any surface (May−August 2006), and autumn, i.e. when direct radiation was limited by neighbouring stands (October−November 2006). We found the modest spatial diversification of vapour pressure that, on average, amounted to 0.4 and 0.2 hPa in the clear−cut and gap, respectively, in spring−summer period as well as 0.3 and 0.7 hPa, respectively, in the autumn. The major impact of the clear−cut and gap location was marked in relative humidity and humidity deficit. Differences in relative humidity on the clear−cut amounted averagely to 3.7 and on the gap 12.7%, whereas the humidity deficit equalled 0.3 and 5.4 hPa, respectively. Particularly large diversification of relativity humidity and vapour pressure deficit was in spring−summer period in the situation of heat waves. In that weather conditions in sun−filled clear−cut and gap parts, the relativity humidity fall to about 17%, whereas vapour pressure deficit increased to about 60 hPa. In the same clear−cut and gap parts the occurrence of dry days was more frequent that in other places. It was noticed that in the positions located in sun−filled clear−cut and gap parts (z4, g3), the diurnal vapour pressure course was very similar to the one observed in the forest, whereas the course of the relativity humidity and vapour pressure deficit was significantly different. That is mainly involved with the extreme thermal conditions in this parts of the studied areas. The least beneficial humidity conditions for plants growth occurred in the north−east parts of clear−cut and gap, that’s why it necessary to take particular note of these locations when undertaking the silvicultural treatments., Sylwan 164 (7): 594-603

In the context of climate change and global warming, a growing number of studies reported lengthening of the growing season for most of the Northern Hemisphere, which is associated with increase of air temperature. Evidences of the increase of the growing season length were noted through satellite data and phonological and meteorological observations. This article presents the studies on the temporal and spatial tendencies in the thermal growing season (TGS) length in north−eastern Poland in 1951−2015. The analyses were conducted using long−term and homogeneity daily data sets from 13 meteorological stations (fig. 1). The dates of beginning and end of the TGS were determined by Huculak−Makowiec method. Trends in the TGS length as well as start and end dates were analysed for the whole study period as well as for successive 30−years periods: 1951−1980, 1961−1990, 1971−2000 and 1981−2010. The results show a general increase of the length of the TGS in the north−eastern Poland in 1951−2015 period, however, there are spatial and temporal differences in TGS evolution. In the western and central part of the region, the growing season in the past 65 years became ca. 20 days longer, while in the eastern part the lengthening of TGS was weaker and amounted to 7−10 days. Most of this change is due to earlier onset of the TGS in spring (average for the western part =2.1 days/10 years, while for the eastern one – 1.2 days/10 years). The observed trends and tendencies show spatial and temporal variability in TGS evolution. Trends in parameters of TGS, calculated for 30−years period, varied directionally and spatially with no significant trends before 1980. In the period 1981−2010 the growing season was longer than in the previous years, the largest increases were found in the central part of the region (1.2 days/year), while the smallest in the south−eastern part (0.5 day/year). Since the 1980s the frequency of long growing seasons increased. A particularly large and steady increase of TGS occurred over the first 15 years of the 21st century. Length as well as start and end dates of the TGS displayed large inter−annual and decadal variability with tendencies for increased range of variability., Sylwan 162 (6): 479-489

Climate change, which was particularly marked at the turn of the 20th and 21st centuries, was accompanied by unfavourable weather phenomena. One of whose effects cannot be prevented is hurricane. Much of the most devastating storms (e.g. Kyrill in January 2007, Carmen in November 2010), which crossed over Poland, was associated with low pressure systems. The occurrence of high wind speeds in the cold season is a natural feature of Polish climate. Hurricanes in the summer are generally characterized by more complicated origin. The cause of the damage at this time of year may be squall fronts and tornados (e.g. July 4th, 2002 – Puszcza Piska; July 20th, 2007 – Częstochowa region). An important issue is to develop a category of winds for the forest district, which can have destructive effect on the stands. Current research shows that gusty winds exceeding 11 m/s may cause first damage to the trees, while blows with velocity exceeding 30 m/s result in severe damage. Knowing and monitoring the mechanisms that leads to strong winds, assessing their impact, and managing risk in the context of their effects is one of the important elements of a forest management strategy. On August 11th, 2017, after the influx of hot tropic air, much cooler polar air began to flow from the west. In the afternoon and evening storm cell and supercell began to form in the south−west of the country. Later on, they moved in the north direction forming a squall line. With a Mesoscale Convective System (MCS) moving to the north, there was a gusty wind exceeding 40 m/s in some places. A gust of wind occurred around 18.30 (EET) in Dolny Śląsk (SW Poland) and after about 2 hours in Pomerania (N Poland). The pressure tendency during the transition reached 4−5 hPa. In the northern part of the country, gusts of wind were the largest and occurred several times in 2−3 hours. The system was accompanied by heavy precipitations, which in north Poland determine more than 60% of the average monthly rainfall. The effect of moving MCS was the damage of almost 80 thousand hectares of forests in Poland, which of more than 39 thousand hectares were classified to complete restoration., Sylwan 162 (3): 200-208