Dissertation Research: Functional trait diversity and community assembly of trees and seedlings during tropical forest succession

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After cutting for timber or agriculture, forests often regrow naturally. As they regrow, there is typically a succession of different species that rise and fall in abundance over time, sometimes ending with a forest dominated by the same species of trees that were in the forest before cutting. However, some tropical forests seem not to recover this way: even after many years of natural regeneration, they fail to return to the same composition of species that would be found in a mature forest. This project will test what may prevent the recovery of tropical forests after clearing. Research will focus on two possible factors, the inability of some species to spread their seeds into the regrowing areas, and the inability of seedlings with certain traits to survive and mature under the conditions left after clearing. The project will measure the key traits of the dominant species in regrowing forests, termed secondary forests, and mature forests, and then observe how different traits may be favored in the different types of forest using annual censuses of trees made over 13 years in six secondary and two mature forests in Costa Rica. A field experiment will directly compare the survival and growth of seedlings with contrasting traits in pasture, secondary forest, and mature forest. Besides helping to answer basic scientific questions about how the functional capabilities of species determine the ability of forests to recover after disturbance, this project is designed to improve forest restoration in the tropics. The research will show what types of species are missing from regenerating forests and test if planting these species can speed regeneration. Results will be widely communicated, and data on species traits will be incorporated into global databases. In addition, the project will employ and train both local Costa Rican assistants and undergraduate students from the U.S., and work with mentoring programs.