The study was conducted at Vokė Branch of the Lithuanian Research Centre for Agriculture and Forestry employing the archival data of phenological observations in Lithuania during 1961-2010. The aim of the research was to estimate the influence of climate change on phenological phases of spring and autumn indicator plants (Corylus avellana L. and Acer platanoides L.) and the length of spring-summer period in Lithuania during 1961-2010. In Lithuania, over the 50 years flowering time of spring season indicator European hazel (Corylus avellana L.), which starts on March 27 on average, exhibited higher variation (SD = 16.1) and earlier onset (-0.43 days per year) compared with the beginning of Norway maple leaf colouring. Larger scale of advance in 1981-1990 (-3.92 days per year) and 1991-2000 (-1.28 days per year) periods are associated with the increased average air temperature related to climate warming. Reliable correlations (p-value <0.01) between the dates of European hazel phenological phases and the average air temperatures of January–April were established. Norway maple (Acer platanoides L.) leaf colouring started on September 16 on average and just slightly varied during the entire study period (SD = 4.9). The influence of meteorological conditions on the beginning of Norway maple leaf colouring was very weak (r <0.3 in 72.5 % of cases). Variations of the beginning of spring season affected the length of spring-summer period. It was determined that the length of spring-summer period strongly correlated with the dates of the beginning of flowering of spring season indicator European hazel (R² 0.8492, p-value <0.01).

Keywords: climate change, phenology, indicator plants, spring-summer period, growing season