Effects of thinning on epicormics have rarely been demonstrated especially due to inaccurate surveying methods. * Our objective was to assess the effect of contrasted thinnings on the ontogeny of epicormics on sessile oak. We used the epicormic composition defined as the arrangement of epicormics in different classes (isolated bud, clustered buds, short and long shoots and "picots") and quantified by the total frequency of epicormics and the proportion of each class. * Epicormic composition was recorded in a silvicultural experiment testing highly contrasted thinnings, at 3 different stand stages and on lower (0.5-3 m) and upper (3-6 m) boles. Ageing provoked an accumulation of bud clusters and of picots. After thinning, epicormic shoots emerged mainly from (1) still present short epicormic shoots, (2) buds either isolated or in clusters depending on the stand stage. Upper boles bore epicormic compositions close to those observed on lower boles in the few preceding years. Upper logs were more reactive than lower boles. * To conclude, the epicormic composition was a relevant tool to follow the dynamics of the epicormic ontogeny and to demonstrate the effects of thinning on it.