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Drivers of Plant Diversity in Temperate and Tropical Forest Canopies

Speaker: Dr. Michelle Elise Spicer, Yale School of the Environment

A fundamental challenge in ecology is understanding the assembly of diverse communities. Both abiotic habitat filtering (e.g, light) and biotic interactions (e.g., competition) likely contribute to compositional turnover, but these processes are rarely tested simultaneously. Dr. Spicer takes advantage of a unique system that allows her to test abiotic and biotic drivers of community assembly across a three-dimensional gradient: epiphytes, or plants that live non-parasitically on other plants. Within a single host tree, up to hundreds of different epiphyte species grow along a strong vertical abiotic gradient, from the shaded, humid understory, to the high-light, exposed canopy; epiphyte microhabitats also vary between vertical and horizontal surfaces and from the inner crown to the outer branches.

In addition, epiphytes frequently occur in such high densities that they grow over each other, providing ample opportunities for epiphyte-epiphyte biotic interactions. Dr. Spicer will discuss results from field and laboratory experiments testing the contributions of abiotic and biotic processes to epiphyte community assembly. Because plant community ecology theory comes almost exclusively from terrestrial plant research, the described research for the first time experimentally demonstrates whether assembly hypotheses such as niche differentiation and facilitation are generalizable to canopy plants. Furthermore, identifying drivers of epiphyte community change is particularly timely because canopy communities are extremely vulnerable to climatic warming and can take centuries to recover from ongoing deforestation.