Rachel Chelsea Nagy Defends Thesis on Amazon Land Use Change

September 11th, 2015 @   - 

Rachel Chelsea Nagy, a student in the Brown-MBL Graduate Program in Biological and Environmental Sciences, successfully defended her Ph.D. dissertation entitled “Ecological and Biogeochemical Consequences of Land Use Change in the Brazilian Amazon” on August 6 at Brown University. Nagy, a student in the Ecology and Evolutionary Biology Department at Brown, was co-advised by MBL Senior Scientist and Ecosystems Center Director Chris Neill and Steven Porder, Associate Professor of Ecology and Evolutionary Biology at Brown.

This month, Nagy began a post-doctoral position with Jennifer Balch in the Dept. of Geography at the University of Colorado-Boulder. She is studying the links between fire distribution and anthropogenic activities across the United States.

Chelsea Nagy installing a temperature/ humidity logger to monitor microclimate conditions in riparian forests in the summer of 2013 on the Tanguro ranch in Mato Grosso, Brazil.

Chelsea Nagy installing a temperature/ humidity logger to monitor microclimate conditions in riparian forests in the summer of 2013 on the Tanguro ranch in Mato Grosso, Brazil.

Nagy’s doctoral research compared the structure, composition, and diversity of plant species in intact riparian forests (adjacent to rivers or streams) to riparian forests that were isolated by clearing for agriculture. She found that the size distribution, number of dead trees, mortality, biomass and carbon storage of altered riparian forests surrounded by agriculture were similar to that of intact riparian forests. However, riparian fragments had fewer seedlings and saplings that indicated reduced potential for forest regeneration. Agricultural fragments also had lower tree species diversity and a different species composition than intact riparian forests.

Nagy's other projects looked at carbon storage in agricultural soils and regrowing secondary forests. Her work showed that the widespread conversion of forests to intensive soybean production did not lead to large reductions in soil carbon despite relatively large changes in microclimate that accompany the land conversion. She developed a mass balance biogeochemical model to understand how different disturbance and land use practices, such as land clearing, shape nutrient limitation and biomass recovery in tropical secondary forests. Her model indicated that nitrogen limits growth of young secondary forests but that this limitation progresses to phosphorus as the forest ages. These results show the importance of retaining nutrients, particularly phosphorus, in order to fully recover from the disturbance of forest clearing.

Nagy’s doctoral committee also included Ed Rastetter, Senior Scientist at the MBL Ecosystems Center and Susan Trumbore, Professor of Earth System Science at the University of California, Irvine, and Director of the Max Planck Institute for Biogeochemistry.

Chelsea Nagy conducting a forest inventory of woody plants, seedlings, and saplings in Mato Grosso, Brazil

Chelsea Nagy conducting a forest inventory of woody plants, seedlings, and saplings in Mato Grosso, Brazil

Funding for Nagy’s doctoral research was supported by an EPA’s STAR graduate fellowship, a NSF grant to Chris Neill and Michael Coe (Woods Hole Research Center), with additional grant support from Steven Porder. Nagy also earned a Dissertation Development Grant (DDG) from the Dept. of Ecology and Evolutionary Biology at Brown and a Center for Latin American and Caribbean Studies (CLACS) award for research in Brazil.
Citations:

Nagy, R.C., Porder, S.; Neill, C., Brando, P.; Quintino, R.M., Nascimento, S.A. (2015). Structure and composition of altered riparian forests in an agricultural Amazonian landscape. Ecological Applications 25(6): 1725-1738.

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