INVASION OF MARITIME CHAPARRAL BY THE INTRODUCED SUCCULENT CARPOBROTUS-EDULIS

Invasion by the alien succulent, Carpobrotus edulis, has become a comm on occurrence after fire in maritime chaparral in coastal California, USA. We studied post-burn Carpobrotus establishment in chaparral that lacked Carpobrotus plants before the fire and compared seedbank and fi eld populations in adjacent burned and unburned stands. Carpobrotus se eds were abundant in deer scat and in the soil before burning. Burning did not enhance germination: many seeds were apparently killed by fir e and seed bank cores taken after fire revealed no germinable seeds. L aboratory tests showed that temperatures over 105-degrees-C for five m inutes killed Carpobrotus seeds. In a field experiment involving use o f herbivore exclosures, we found that herbivory was an important sourc e of mortality for seedlings in both burned and unburned chaparral. Al l seedlings, however, died outside of the burn regardless of the prese nce of cages. Establishment there is apparently limited by factors aff ecting plant physiology. In the burned area, seedlings that escaped he rbivory grew very rapidly. Overall, it appears that herbivory limited seedling establishment in both burned and unburned sites but that the post-burn soil environment supported Carpobrotus growth in excess of h erbivore use, thus promoting establishment.