Juknys, R., Sujetovienė, G.*, Žeimavičius, K. and Šveikauskaitė, I. 2012. Comparison of Climate Warming Induced Changes in Silver Birch (Betula pendula Roth) and Lime (Tilia cordata Mill.) Phenology. Baltic Forestry 18(1): 25-32.

The aim of the study is to compare the shift in timing of main spring (bud burst, leaf unfolding) and autumn (leaf colouring, leaf fall) phenophases and changes in rate of seasonal development for tree species with different ecological requirements – birch (Betula pendula Roth) and lime (Tilia cordata Mill.). Long term dataset of phenological observations (1956-2010) from the Kaunas Botanical garden of Vytautas Magnus University (central Lithuania) was used for this study. Increased temperature was detected to be as a strong driver of spring phenology for both species. Higher sensitivity to the rise in temperature was characteristic of early season birch species. Length of the period between bud burst and leaf unfolding of birch has become shorter almost by 6 days during the study period, indicating acceleration of seasonal development during spring period for this early season species. Changes in the timing of autumn phenophases of lime and birch demonstrated opposite character. Leaf colouring and fall of lime were delayed, while advancement of these phases was detected for birch. Presumption is made that lower soil moisture caused by a rise in temperature and decrease in precipitation is one of the most important factors leading to the advancement of birch leaf senescence. Despite very different changes in autumn phenology of birch and lime, duration of the period between leaf colouring and leaf fall, has become longer almost by 2 days for both species, indicating deceleration of seasonal development during phenological autumn.

Key words: climate warming, bud burst, leaf unfolding, leaf colouring, leaf fall, growing season, birch, lime.