Habitat distribution and competitive neighborhoods of two Florida palmettos

ABRAHAMSON, W. G. (Department of Biology, Bucknell University, Lewisburg, PA 17837). Habitat distribution and competitive neighborhoods of two Florida palmettos. Bull. Torrey Bot. Club 122: 1-14.-Two ecologically similar palmettos, Serenoa repens and Sabal etonia, co-occur on the Florida peninsula's central and Atlantic coast ridges. Inasmuch as they share many characteristics of growth form, reproductive strategies, responses to fire, and habitat occurrence, these palmettos may be able to coexist because they occur in different microhabitats or plant neighborhoods. Serenoa reached its highest dominance in poorly drained flatwoods and its lowest dominance in well-drained sandhills. Sabal, on the other hand, was uncommon in flatwoods but exhibited its highest dominance in well-drained sand pine scrub and sandhills. Nearest-neighbor and principal components analyses showed that Sabal neighborhoods potentially had more competitive interference and in flatwoods included more oak (Quercus geminata) and fetterbush (Lyonia lucida) than Serenoa neighborhoods. These differences in species microsite-distribution patterns suggest spatial displacement of palmettos based at least partially on competitive interference and adaptations to edaphic conditions. Local populations had different growth forms such that palmettos growing in flatwoods communities lived in more closely spaced but lower canopied neighborhoods and bore more leaves than palmettos growing in scrubby flatwoods. Palmetto leaf numbers of both species were higher in recently burned sites but Serenoa maintained more leaves than Sabal under all post-bum conditions. Measures of plant vigor and performance (e.g., crown size, biomass) did not exhibit the trends expected based on palmetto abundance patterns; rather, local effects (e.g., overstory canopy coverage) may more strongly affect performance. Seedling and adult palmettos had very low mortality rates and slow growth rates suggesting that extremely long-lived individuals (500 yr old palmettos may not be uncommon) compose populations that have remarkably low turnover of genotypes-a likely consequence of adaptation to long-lived, stable environments. These palmettos are vulnerable to human-caused disturbance because of their limited ability to quickly recolonize former habitats.