Document Type
Honors Project - Open Access
Abstract
Puerto Rico has seen changes in the frequency and severity of disturbances in recent years as hurricanes become more frequent and more intense under climate change. In ecosystems experiencing increasing disturbances, we expect that species composition will shift as early successional trees become more common. These changes to species composition and community ecology are likely to affect terrestrial nutrient cycling both directly and indirectly, and it is still not well understood how shifting community composition may alter ecosystem functioning. To address this gap, I measured carbon (C) and nitrogen (N) variables in soils, microbial biomass, roots, leaves, and soil greenhouse gas fluxes within 1 m of individuals from three tree species (5 replicates per species) across a topographic gradient in El Yunque National Forest in Puerto Rico. The three species of interest are likely to be differently affected by changing hurricane regimes: an early successional tree species (Cecropia schreberiana), a secondary successional species (Prestoea montana), and a late successional species (Guarea guidonia). I hypothesized that the soil area surrounding early successional and late successional tree species would exhibit differences in carbon and nitrogen cycling and the resulting soil greenhouse gas emissions. I found that there were significant species-related differences in leaf composition, soil nutrients, and soil gas fluxes. G. guidonia had the highest %C and %N in senesced leaves compared to the other two species, having on average 6.39% and 8.38% higher %C compared to C. schreberiana and P. montana respectively. Senesced G. guidonia leaves had on average more than 50% higher %N compared to P. montana, and nearly double the %N of C. schreberiana at 90.55% more on average. All three species had statistically distinct C:N ratios, with G. guidonia having the lowest at 28.859 ± 2.435 (compared to 39.988 ± 2.274 for P. montana and 51.522 ± 3.751 for C. schreberiana), and thus likely decomposing the fastest. C. schreberiana and G. guidonia had statistically distinct amounts of extractable C and N associated with the soil at the base of each tree (p < 0.01). While the soil CO2 flux associated with each tree did not differ significantly between species, the CH4 flux was significantly higher in the soil near P. montana compared to the other two species, averaging around -0.052 ± 0.155 compared to -0.608 ± 0.123 and -0.685 ± 0.041 for C. schreberiana and G. guidonia respectively, suggesting that P. montana is associated with lower soil CH4 uptake. In combination, my results suggest that, as the successional state of the forest shifts to be dominated by early successional species for longer stretches of time due to increasing incidence of large-scale hurricane disturbance, the nutrient cycling of this forest may also be altered drastically.
Recommended Citation
Kleit, Miriam, "Ecosystem response to increasing hurricane disturbance: Comparing nutrient cycling dynamics associated with early- and late-successional tree species in a wet tropical forest" (2024). Biology Honors Projects. 29.
https://digitalcommons.macalester.edu/biology_honors/29
© Copyright is owned by author of this document
Comments
Advisor: Christine O'Connell, Environmental Studies Department