| Popis: |
After a major disturbance (such as fire or soil upsetting), large numbers ofCistusspp. seedlings may appear and ensure population recruitment, but in the absence of such disturbances seedlings are rare or nonexistent in matureCistusstands. What are the causes? Two factors, little studied until now, have been examined: the influence of litter and of light reaching the soil surface. In two types of stands, one dominated by C.monspeliensisand the other byC. albidus, an experiment was undertaken by removing the vegetation cover and by the presence or absence of litter to examine the establishment of seedlings. The seed bank in the soil was also studied to determine its size. Seeds were also subjected to a temperature of 52 °C to simulate exposure to full sunlight in summer and determine whether this had any affect on their germination rate.Light and litter had no effect on the germination, irrespective of the quality or intensity of light reaching the soil or the presence or absence of litter; there were always few seedlings and there was no significant difference in numbers between treatments. There was a large seed bank in the soil and these seeds were capable of germinating following experimental conditions: the heat stress applied proved to be too slight to break seed dormancy, although they were viable because they germinated after scarification. In existingCistusspp. stands,Cistusspp. seeds germinate with difficulty, and lack of recruitment could lead to disappearance of local communities unless they are subjected to disturbances. |
