Plant height determines phenological variation in Quercus suber L.

Phenological traits of vegetative apical buds were monitored in a Quercus suber L. (cork oak) montado near Lisbon during 2015. Natural regeneration plants, growing at a fenced plot, and mature trees (MT) from the surrounding montado were selected and divided in six groups ( n =8) according to height (H): Sd1 (small seedlings, H<0.1 m); Sd2 (seedlings, 0.16 m); MT (mature trees). Observations included budburst date, apical shoot elongation and leaf production. Vegetative phenology patterns of Q. suber changed according to height/age group. Average budburst dates occurred between early-April (day 99, Sd1) and mid-May (after day 120, mature and juvenile trees), at day lengths between 12.8 (Sd1) and 13.7 hours (Jv2). Height was positively related with average budburst dates, degree day sums and daylength at budburst. Shoot elongation followed different patterns according to size/age group. In seedlings, cumulative growth was smaller and restricted to the weeks immediately after budburst, whilst taller/older trees phenological patterns were more variable, with vegetative growth often maintained until mid-summer. The differences in budburst timing and vegetative growth patterns may be reflecting the different strategies to cope with resource limitation and maximize the length of the growing season among groups.