Tropical dry plant formations comprise diverse forests found in areas that experience pronounced seasonal changes in precipitation. Across broad regions, variation in the amount and distribution of precipitation determine the availability of water, and thus differences in species composition and phenology. Within any given region hydrology and topographic position, and geologic substrate may underlie additional differences in forest attributes. Of these three factors, geologic substrate is the least understood but it has been suggested that its influence on tropical dry forests, and more broadly speaking tropical forests, results from a combination of mechanisms regulating the use of water and nutrients. Phenological studies at population, community, and system levels acknowledge the significance of plan phenology for different ecological processes. Thus, characterizing phenological patterns at multiple levels of biological organization as a function of geologic substrate is important to assess the diversity of behaviors, and ultimately vulnerability of tropical dry forests to climate change. A study conducted in Curaçao between September of 1992 to February of 1995 at three sites underlaing by different geologies provided a unique opportunity to investigate the extent to which plant phenology diverges in regions underlain by different geologies.