Collaborative Research: LTREB Renewal: RUI: Cyclic vs. anthropogenic causes of long-term variation in the regeneration of tropical forests with contrasting latitude and diversity

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Successful plant reproduction – flowering and fruiting – is sensitive to environmental conditions, as are the early life stages that follow – seed germination and seedling survival and growth. Plants often use variation in their environment as a cue to reproduce, ensuring, for example, there is adequate energy and moisture for fruit development or that their seeds are dispersed when conditions are favorable for the growth and survival of young seedlings. The reproduction and regeneration of tropical forests are therefore vulnerable to a changing climate. This project, renewed for five more years, uses long-term data to understand how the timing and success of reproduction in tropical plants varies year-to-year as the cues and conditions for flowering, fruiting, and seedling survival vary due to within-year seasonality, multi-year climate cycles such as El Niño, and/or the effects of climate change. The research takes place at three tropical forest study sites (Ecuador, Puerto Rico, and Panama) to separate the effects of local site conditions from long-term regional climate patterns. Undergraduates and early career interns participating in this research receive training each year and support for projects that expand on the long-term scope of this work. Tropical forests are globally important because of their high biodiversity and large contributions to carbon storage, and thus a better understanding of the environmental conditions that affect tropical plant reproduction will strengthen our ability to predict the survival of tropical forests and the benefits these forests confer.This research spans forests differing in diversity, seasonality, disturbance, and climate to test hypotheses concerning: (1) environmental cues that induce flowering; (2) effects of multiyear or multidecadal natural climate cycles on reproduction in tropical forests; (3) survival and growth of seedlings from species with different functional traits in response to climatic variation; and (4) how episodic reproduction structures adult populations, effectively closing the demographic gap between studies of early reproduction and the dynamics of sapling and adult tree populations. Standardized methodology used at our three sites includes weekly or biweekly recording of species-specific flower, fruit, and seed rain in permanent traps and annual censuses of all woody seedlings in plots adjacent to the traps. The research take place within large (16-50 ha) mapped forest dynamics plots where all trees 1 cm in diameter are identified and regularly measured. Similar methodology is also employed in multiple temperate and tropical forests, which facilitates cross-site comparisons that broaden the generalizability of our results.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.