Estimation of total species richness for a site can be challenging, particularly in extremely species rich ecosystems.  Protocols for sampling plant species richness have not yet been developed in the diverse seasonally inundated depressional wetlands of the longleaf pine-wiregrass ecosystem.  The primary objective of this study was to evaluate non-parametric estimators of plant species richness based on species incidence plot samples and to determine the minimum sampling regimen for accurate extrapolation.  We quantified species accumulation in varying sample plot areas and distribution within 9 depressional wetlands ranging in size from 1.3 to 7.8 acres.  Wetlands were classified into three groups, grass-sedge marshes, cypress savannas, and cypress-gum swamps.   We recorded species presence in 1m² and 4m² plots spaced 15 meters apart along each transect.  Transects were extended across the wetland from upland-wetland ecotones and spaced 30 meters apart.  We also sampled species richness in 100m² plots spaced 30 meters along each transect with transects spaced 90 meters extending across the wetland. 

Results/Conclusions

Average species richness for grass-sedge marshes, cypress savannas, and cypress-gum swamps was 172, 173, and 161 species, respectively.  We detected 5-27% fewer species in 100m² plots compared to the 4m² plots, despite sampling three to four times more area using the 100m² plot-transect method.  Increasing sample area from 1m² plots to 4m² plots resulted in an increase of species richness up to 68%.  We used EstimateS, a software program used to estimate species richness, in an effort to determine estimates of total species richness for each wetland and sampling method.  We specified sampling without replacement and 100 iterations and used non-parametric estimators such as Chao2, first and second order Jackknives, ICE, and Bootstrap.  The program also calculated the number of uniques (species detected only once in a wetland) and duplicates (species detected twice).  Species accumulation curves did not reach a plateau and none of the richness estimates showed a convergence of estimated and observed richness.  The percent of unique species ranged from 32% to 54% and number of duplicates ranged from 9% to 25% of the total number of species detected.  This measure of rarity suggests that the vegetation is heterogeneous and that there is a high likelihood that other species are present that were not represented in the dataset.  We conclude that accurate estimates of total species richness are not feasible for such hyperdiverse sites.