In mature palm plantation, the number of harvested bunches is the main component of yield. In Ivory Coast it varies from 600 to 1600 ha-1 year' with large seasonal variations from 2 to up to 300 bunches ha' month-' for L2T x D10D material. Phenology of adult oil palm is complex. The apical meristem initiates new leaves (20 to 30 per year) with a constant plastochron. Leaf lifespan from initiation to senescence is more than 4 years. The first unopened leaf emerging from the crown is spear-leaf (rank 0). Approximately 60 developing leaves are hidden in the crown (ranks -1 to -60) and 40 autotrophic expanded leaves are visible (Corley and Tinker 2003). Each leaf bears a male or female inflorescence which is first visible at flowering (rank 18 to 20). Bunch is harvested 5 to 6 months after flowering. By dissection of the crown and electronic microscopy, the inflorescence primordia can be seen at rank -40 but the sex cannot be identified before rank 4 (Adam & al. 2005). The determinism of gender is highly dependent of environment and physiological stress but is not explained. The time and duration of sex differentiation are not known with certainty: it can be assumed at spikelet initiation (rank -5 to -10) or at bract initiation (rank -20 to -30) or at any time between rank -10 to -30 (Jones 1997). Abortions occur between ranks 8 to 12, but, because some leaves have no inflorescence, an ealier sensitive phase may occur. Because of weak evidence and of the difficulty of experiments, crop modeling is a way to test hypotheses. For example, in a model simulating seasonal trends at tree level, Jones (1997) introduced a feedback loop of bunch load to induce physiological stress in earlier stages responsible of abortion or sex differentiation.