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Table 2 Description of the stages of spring (S) and autumn (A) phenology that were recorded in the hybrid aspen progeny trial during the third and sixth growing seasons

From: Spring and autumn phenology of hybrid aspen (Populus tremula L. × P. tremuloides Michx.) genotypes of different geographic origin in hemiboreal Estonia§

Stage Description
Spring
 S1 Bud-burst, leaves emerge from the bud about 5 mm
 S2 All the leaves are unfolded
 S3 All the leaves have attained full size
Autumn
 A1 Half of the leaves are yellowed, defoliation has not started
 A2 Defoliation of half of the leaves
 A3 Defoliation of all the leaves, bud-set