Shoot growth components and flowering phenology in grafted Pinus halepensis Mill.

Shoot elongation and flowering were assessed for a season (January-November) in 25 grafts from five clones of Pinus halepensis growing in a seed orchard. A co-dominant shoot from the upper crown and a dominated, low shoot were measured from each ramet. Upper shoots elongated continuously from a variable onset date between January and March and followed a logistic function against Julian day and a Gompertz function against heat sum above 0degreesC. Three to seven (averaging five) successive cycles were formed through the growing season; usually, two of them were preformed in the terminal bud (spring cycles) and one to four were neo-formed, summer cycles. The number of summer cycles and their contribution to the annual shoot growth were the only variables with a significant clonal influence. Ovulate strobili appeared from February to April and in October. Some ramets showing two female flowering cycles in the same shoot were observed. Lower shoots, bearing pollinate strobili always displayed a single spring cycle preformed in the winter bud.