Dynamics of phenological stages due to climate change in plum trees in southern Romania

The paper analyzes the climate change impact in plum trees for the first four phenology stages: bud swelling (1), budburst (2), beginning (3) and end (4) of flowering in a continental climate, southern Romania. The objective of the paper is to test the hypothesis that the duration of phenological stages (SD) shortened significantly versus the time due to climate change. Weather data are from 1969 till 2018, and phenological data during the same period, with some missing years. There was a rise in air temperature (T) during the first five months, specifically in March and April; significant linear relationships show a decrease in SD for the four stages, i.e., an advance in the starting date with the years. Linear relationships were obtained between SD, maximum T (T_max), mean T (T_mean), minimum T (T_min) and sunshine hours (Sh). The relationships between SD and T_max are the strongest. In the last half century there was an advance of 15 days for phenology stage 1, 9 days for stage 2, 11 days for stage 3, and 8 days for stage 4 for plum trees. The advance of the phenological stages is similar in other continental climate countries and the risk of late frosts damages increased.