Flowering synchrony, fecundity, and spatial distribution of Frasera caroliniensis in northern Alabama

Background/Question/Methods Flowering synchrony has not been well-documented in Frasera caroliniensis (Gentianaceae) even though it is a widely distributed, semelparous, perennial herb in eastern North America. Overall, it maintains a stable status as the only member of the genus Frasera in the region, but it is experiencing declines at the northern and southern edge of its range. F. caroliniensis is currently listed as a species of concern in Alabama and several other southeastern states.  In 2007, 3 relatively large populations flowered synchronously in northern Alabama. The objectives of this study were to 1) determine any significant differences in fecundity and average seed per capsule ratio among the 3 populations 2) examine the relationship between fecundity and stalk height, basal width, and density 3) determine the proportion of each population that flowered in 2007 by estimating the total number of fruiting stalks in the fall of 2007 versus juveniles or immature adults encountered the following spring.

Results/Conclusions In the fall of 2007, the total number of fruiting stalks was 754: 168 at population 1, 359 in population 2, and 227 in population 3. Across all populations, the mean number of seeds per capsule was 6.5 and the mean potential reproductive output was 772.1. Mean number of capsules per individual and corresponding mean fecundity was significantly different among the 3 populations (p<0.01), but mean number of seeds per capsule was not (p=0.09). Reproductive output is more strongly correlated to stalk width (r²=0.59, p<0.01) than it is to stalk height (r²=0.40, p<0.01). Point-pattern analysis showed that individuals are significantly aggregated between 1.2 m and 2.4 m (p<0.01), suggesting that reproduction in this species may be density-dependent. Spring sampling of juveniles and adults that did not flower during 2007 will determine the degree of flowering synchrony, which is often linked with semelparity but rarely studied in the field. This study provides insight to that link and documents an event that occurs every 4-30 years for F. caroliniensis, which could aid in future conservation efforts.