Sex ratio and spatial pattern of males and females in the dioecious sandhill shrub, Ceratiola ericoides ericoides (Empetraceae) Michx

Sex ratio, size, age, and spatial pattern were investigated for males and females of the dioecious shrub Ceratiola ericoides ericoides (Empetraceae) Michx. within seven mapped populations in Georgia and South Carolina, USA. Among the sites studied, two are regularly burned and one site long-unburned. Age was estimated from node counts of individual shrubs. Only one (fire-suppressed) population showed a female-biased sex ratio, while all others did not differ significantly from 1:1. Mean age estimates did not differ between sexes at any site nor did mean shrub canopy diameter. Bivariate Ripley’s K analysis with a null hypothesis of random labeling was used to investigate whether any of the mapped populations exhibited spatial segregation of the sexes (SSS). No population showed strong evidence of SSS. Rather all sites but one showed males and females to be associated (though not significantly) at a scale of 1–10 m. At a scale of 10–35 m male and female shrubs were located randomly with respect to one another at all sites.     

Twenty years of vegetation change in five long-unburned Florida plant communities

Abstract. Rates and directions of change over a 20-yr interval in five long-unburned (> 60 yr) plant communities were studied using multivariate analyses and compositional vectors. The study sites were located in fire and summer-drought adapted, xerophytic vegetation with many endemics on acidic, nutrient-poor, sandy soils in south-central peninsular Florida. Sizes of individual stems from 72 sets of nested permanent quadrats were measured in 1969, 1979, and 1989. Patterns of vegetation change differed by community. Flatwood and bayhead quadrats showed rapid increases in densities and basal areas of Persea borbonia (red bay). In the southern ridge sandhill community, evergreen clonal Quercus species (oaks) and Pinus clausa (sand pine) increased in dominance and grasses declined. Oaks (especially Q. geminata) also increased in importance in scrubby flatwoods. Sand pine scrub was relatively stable in composition, but experienced marked structural changes due to substantial sand pine mortality (18% during 1969–1979, 39% during 1979–1989). Compositional changes in the absence of fire were greatest whereas structural changes were least in southern ridge sandhill and scrubby flatwoods, both communities which normally receive frequent, recurrent fire. Compositional changes were lowest in sand pine scrub, which is normally infrequently burned. Classic successional patterns such as species replacement, decreases in density, and increases in basal area were generally lacking. Tree densities increased in two of four community types (southern ridge sandhill, scrubby flatwoods); while basal area declined in the flatwoods/bayhead and sand pine scrub sites. Directions of compositional vectors included divergent, opposing, and complex patterns, suggesting vegetation change in the absence of fire has a strong stochastic component.