Demography of Conyza bonariensis (Asteraceae) in a ruderal Mediterranean habitat.
Conyza bonariensis is an invasive weed of increasing importance in subtropical and warm-temperate regions worldwide, both in non-agricultural habitats and in annual and perennial crops, especially under no-till management. To gain insights on basic life cycle processes determining the demographic success of C. bonariensis, we studied for this species during two seasons seedling emergence patterns, survival to the adult stage and fecundity in a ruderal Mediterranean habitat in which C. bonariensis was a component of the plant community. The influence of emergence date on survival and fecundity was studied using four successive sowing dates, i.e. cohorts, encompassing the favorable season for plant establishment. The mean rate of seedling emergence was 61%. Emergence patterns were characterized by high initial emergence rates, which were highly dependent on rainfall. The mean rate of survival to the adult stage was 33%. Fecundity reached a mean value of 86,066 achenes and presented density-dependent regulation. Plant survival and fecundity were positively related to cohort earliness and thus earlier cohorts should preferably be targeted for an effective management of C. bonariensis.