Effects of heat on dehiscence and germination in Eucalyptus globulus Labill.

Fire is a facilitating factor in the naturalisation of Eucalyptus globulus in countries where it has been introduced. In this study, we investigate the effect of heat on dehiscence and germination of free and encapsulated seeds. Twelve combinations of temperature (80, 150, 200 degrees C) and heating exposure time (30, 60, 120, 300s) were used and a corresponding heat index (H) was computed. Dehiscence was registered on a daily basis and germinability of encapsulated and free seeds was verified through germination tests. Results indicate that dehiscence was strongly dependent on individual trees, but no significant differences were found between the treatments applied, suggesting a direct effect of capsule desiccation rather than heat on seed shed. The percentage of germinated seeds was negatively influenced by the highest temperature and exposure times. The effect of capsule protection on seed germination was positive for 200 degrees C at 60 and 150s (H=139 and 220 respectively), but negative at 150 degrees C for 300s (H=269). No seeds germinated after treatment at 200 degrees C for 300s (H=358). Given the estimated range of temperatures and residence times during wildfires in eucalypt plantations, our results help to explain the high levels of seedling recruitment observed in burned stands.