Demographic Status and Conservation Concerns of the Rare Cactus Harrisia aboriginum

Abstract: Demographic trends can be used to understand population status and the potential for future success. For rare species, studying demographic patterns of extant populations is critical for conservation management and species assessment. Harrisia aboriginum Small ex Britton & Rose, commonly known as the aboriginal prickly-apple cactus, is a columnar cactus restricted to a narrow fringe of coastal habitat in southwestern Florida. Although H. aboriginum has been listed as endangered for nearly a decade, recent surveys of extant populations are lacking, and a number of tropical storms have passed through the geographic range since the last assessment was made. Over two field seasons, we visited ten known extant populations of H. aboriginum to collect demographic and phenological data. Our results indicate that the number of individuals in wild populations, which we estimated at fewer than 200, decreased by more than 50% over the past 15 years. Furthermore, of the 100 plants studied, only 21% were reproductive, with eight observed to have produced fruit while 13 were observed to be in bud. Only 31 seedlings were observed in 4 locations. We suggest that active management and restoration activities, using individuals reared in ex situ conservation management programs, are imperative for the conservation of the species. Future research efforts should focus on understanding patterns of geneflow and outcrossing to help prioritize conservation efforts, as well as the conditions needed for the recovery of the species.