Catkin frost damage in Mediterranean cork-oak (Quercus suber L.)

During a period of study of floral phenology and pollen production in the c ork-oak, Quercus suber L. (1997-99), an interruption of catkin development was detected in spring 1998. The cause might have been a sharp drop in mini mum temperatures during that period, which coincided with the initial stage s of microsporogenesis. Results show that environmental temperatures close to 0 degreesC halted microsporogenesis and catkin elongation, resulting in their complete death. No fruits were observed in the affected zone, as a po ssible consequence of the lack of pollen. Phenological, histological, and a erobiological data are analyzed as a whole in order to gain a better unders tanding of the phenomenon. Cold spells during flowering may be one of the f actors influencing the high interannual variability of acorn production in Quercus species.