PS 22-43 - Seasonal variation of the growth and phenology of the endangered cacti Leptocereus grantianus in Culebra, Puerto Rico

Abstract: The natural history of the archipelago of Puerto Rico has been in a race against uncontrolled urban development. Because of this, there is a considerable lack of scientific data value on its ecology. The genus Leptocereus is part of that but, more specifically, the Leptocereus grantianus species, which is endemic to the island municipality of Culebra. The U.S. Fish and Wildlife Service designed a recovery plan, but data on the biology and ecology of the species is scarce, limiting the application of conservation plans. This project aims to fill in the ecological information gap of this critically endangered species. We monitored the demography and phenology of L. grantianus to understand its population dynamics better. We tagged 62 individuals in 3 sites (Psol, Pmel, and Pcasc), measured their growth, and used cameras to monitor their phenology and data loggers to register temperature and light index.

Results indicate growth rates do not differ significantly among the studied locations (p=0.601). However, we observed a significant difference (p= 6.751e-08) between the dry and wet seasons in all sites. For instance, we found that 46% of the individuals showed shrinkage during the dry season compared to only 11% during the wet season. Regarding phenology, there was no significant difference in bud production (p=0.52) and flowering (p=0.67). Although the studied populations produced buds and flowers, we recorded three (3) immature fruits that fell. Interestingly, even though there was recorded budding and flowering throughout the year, the Pmel site was more active in bud/flower production during the wet season and Psol and Pcasc during the dry season.