GERMINATION AND POPULATION-DYNAMICS OF CISTUS SPECIES IN RELATION TO FIRE

1. The shrubs Cistus monspeliensis and C. albidus are obligate seeders which are often dominant in Mediterranean habitats degraded by recurrent fires. 2. To determine the role of fire in the regulation of the population dynamics of these species, the germination requirements and population age-structure have been examined for populations in the South of France. 3. Germination of both species was enhanced by a change in light quality (red/farred ratio) similar to that which occurs when fire removes the light-filtering green leaves, but to a lesser extent than by a heat pretreatment designed to simulate fire temperatures. 4. In two mixed stands, one (12 years old) composed of the two Cistus species and a second (9 years old) composed of C. monspeliensis and Quercus coccifera, Cistus recruitment occurred steadily during the 5 post-fire years and then stopped. 5. For both Cistus species in the study area, age at first reproduction was 2 years, with seed production levelling off at 5 years; maximum plant longevity was around 14 years. 6. Pronounced stand decline was observed in 15-year-old stands. This was the result of a short individual plant life duration combined with restriction on new plant recruitment caused by unfavourable germination conditions. 7. The time for a stand to decline is correlated with the frequency of fire events which affect Cistus habitats. We therefore suggest that the demographic characteristics of C. monspeliensis and C. albidus stands favour their 'autosuccession' through periods of increased fire hazard.