Climatic hazards for native tree species in Poland with special regards to silver fir (Abies alba Mill.) and European beech (Fagus sylvatica L.)

The study defines the hazards for European native trees, such as silver fir and European beech generated by extreme weather events in Poland in 1954–2015. For this purpose, these extremes have been ranked in terms of their frequency. Trends of their frequency over studied period have also been tested. The study was based on meteorological data collected from 6 weather stations situated in central and eastern Poland, in the vicinity of the northeastern edge of the silver fir and European beech ranges. It was found that weather extremes which pose the largest threat to trees in Polish forests were late spring frost and strong winds. On average, these extremes occurred several times a year. Droughts and heavy snowfalls were less frequent and occurred every 1.3–4.7 years, on average. Winter severe frost was the rarest and occurred every 5.1–10.1 years. It should be emphasised that, despite the observed global warming, the weather extremes typical for winter and spring, namely severe frost, late spring frost and heavy snowfalls, were also present in Poland in the twenty-first century and no negative trend in their frequency was identified. However, a negative trend in the De Martonne aridity index was identified at some weather stations, which indicates an increased risk of drought.