Response of tree seasonal development to climate warming

The aim of our study was to investigate the response in timing of phenological events and the duration of the growing season to climate warming for three deciduous tree species: birch, lime, and maple. The most significant advancement in phenological spring (leaf unfolding) – 14.3 days through the investigated 1956- 2009 period – was detected in the case of the early-season pioneer species birch. A shift in leaf unfolding for other two late season species, maple and lime, was less expressed and consisted of 9 days through the investigated period. The changes in timing of phenological autumn were detected to be even more species specific and it was delayed by almost 16 days for maple, 12 days for lime and, in contrast, leaf fall advanced by 12 days was detected for birch. The occurrence of leaf unfolding best correlated with March and April temperatures. A statistically significant correlation of leaf unfolding with January temperatures was characteristic of early-season species – birch. The relationship between timing in leaf fall and temperature was much weaker and in most cases statistically insignificant. The growing season for maple and lime was extended by 25.4 and 21.5 days, respectively, through the study period. The length of the growing season of birch did not experience any statistically significant changes and the entire growing period shifted earlier by almost two weeks during the investigated period.