This paper examines the variability of climatological vegetative seasons and thermal resources on the Polish Baltic Sea coastline in the second half of the 20th century and the first decade of the 21st century. The annual variability of vegetative seasons and thermal resources determines the composition of forest communities and plays an important role in forest management. The paper identifies periods (seasons) of intensive plant vegetation and flowering; it also presents extreme air temperature values within these periods. The study area covers the Polish Baltic Sea coastline, where weather conditions are recorded at the waether stations: Gdynia, Hel, Leba, Ustka, Kolobrzeg, Dziwnow and Swinoujscie. Average daily air temperatures values taken from the measuring period of 1966–2009 were used in this study. The designation of vegetative seasons was made based on the methodology developed by Makowiec (1983) and thermal resources were identified as described by Niedzwiedz (2003). The results presented allowed to determine the trends in climatic conditions of the Polish coastal area of the Southern Baltic Sea and their potential impact on the composition of coastal forest communities. The variability of vegetative seasons and thermal resources were described for the regions of forest communities within the Polish Baltic Sea coastal area.

Key words: climatological vegetative season, thermal resources, forest communities, the Baltic Sea coastline, thermal extremes.