Population structure and spatial pattern in the dioecious shrub Ceratiola ericoides

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Abstract
The dioecious shrub Ceratiola ericoides (Florida rosemary) dominates xeric, infrequently burned Florida scrub vegetation, often to the near‐exclusion of other woody species. We studied the spatial pattern, age, sex and size structure of four populations in Florida, USA: two coastal scrub populations subject to recurrent local disturbances due to sand movement, and two inland scrub populations in sites periodically burned by stand‐replacing fires. The age structure of individual genets was estimated from node counts and used to describe the age structure of the populations. The sex ratio of males to females was not significantly different from 1:1, except within a female‐biased coastal population subject to frequent sand movement. Node counts indicated that the mean age for reproductive individuals was 15 ‐ 16 yr for the inland populations and 13 ‐ 16 yr for the coastal populations. In all sites, there was no difference in mean age between males and females. Vegetative reproduction was uncommon except for the least‐disturbed coastal population where 72 % of the reproductive individuals originated through layering. Individuals were generally randomly dispersed at the coastal sites, whereas significant aggregation of males and females occurred in the inland sites where the populations were initiated following fire. Seedling recruitment was continuous in the disturbed coastal scrub site, where 35% of the individuals were juveniles. Most juveniles were dispersed from 0.5 to 0.75 m around females. At one of the inland sites, where juveniles comprised 11% of the population, juveniles were clustered at 0.25 to 5.75 m around females. Coastal populations were all‐aged, while inland populations were uneven‐aged. Recruitment appears to follow periods of disturbance; infrequent fire in the inland populations and continuous sand movement on the coast are factors initiating recruitment.