Recruitment, growth, survival, and fecundity of the threatened Florida endemic annual herb Paronychia chartacea ssp. minima

Background/Question/Methods

Detailed demographic data is critical in designing science-based management programs for species at risk. Paronychia chartacea Fernald (Caryophyllaceae) is a small mat-forming polygamodioecious herb endemic to Florida. Federally threatened and state endangered, the species is comprised of two geographically distinct subspecies differing in life history, habitat requirements, and sexual morphology. P.c. chartacea is a short-lived perennial, endemic to open sand scrub in the central peninsula. P.c. minima is an annual primarily found along karst pond margins in the western panhandle. While P.c. chartacea is relatively well studied and protected, our study is the first to investigate the demography of P.c. minima. We established 103 25-cm radius circular plots along an elevational or environmental gradient in the only three known protected populations to monitor recruitment, growth, survival, and fecundity. Two populations occur along the margins and upper slopes of ponds, while one population occupies a longleaf pine-wiregrass restoration area. Density, size, and fecundity were documented in four years (2008-2011), while survival was followed in two years. All populations have a history of anthropogenic disturbance and two populations experience periodic flooding; in the third year of our study, plots along the lower margin of the two pond sites were under water.

Results/Conclusions

Over all years, P. c. minima density per plot ranged from 0 to 1232 plants per m² and varied significantly, with highest densities occurring in 2009. Although densities declined among all populations in 2010 and 2011, recruitment persisted, even within flooded plots. Median plant size, measured as crown area, significantly varied among years and was smallest in 2011, but differences occurred only in one population. Plants were smallest in the densest population, but there was not a significant effect of density on crown area. Median survival of seedlings through flowering was 33.3% in both years and did not vary among populations. Among all populations and all years, the ratio of male to bisexual plants was 1.08 and did not differ significantly among populations or years. P.c. minima appears to have an ability to persist in habitats subject to periodic flooding which suggests its seedbank is capable of surviving inundation and rapidly colonizing subsequent available habitat. Demographic data collected on P.c. minima provides an important first step in understanding population dynamics and conservation needs of this highly imperiled herb.