Doctoral Dissertation Research: Regional Ecogeographical Impacts of Large Herbivores on Savanna Ecosystems

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This doctoral dissertation research improvement project focuses on geographical patterns and processes of savanna ecosystems by quantifying the broad-scale ecological and climatological impacts of the megaherbivores (large herbivores 100 kg), particularly elephants. Savannas and prairies cover a fifth of Earth's land surface, are home to over a half a billion people, and disproportionately affect interannual variability of the global carbon cycle. Yet, there is limited understanding of the factors that create and maintain the low woody cover (trees and bushes) of savannas. For decades, researchers have clearly documented how large herbivores suppress local savanna woody cover, while the large-scale effects continue to remain unclear. By quantifying a large herbivore's ecosystem-wide impacts, this dissertation will enhance understanding of the factors shaping savannas and their influence on global climate. Such understanding is critical for large herbivore conservation worldwide. The work will establish a field site that will benefit the early academic careers of the researchers and create a collaborative partnership with an established savanna researcher. The project will build capacity through a student internship and a week-long programming course for students and faculty. This Doctoral Dissertation Research Improvement award will provide support to enable a promising student to establish an independent research career.Despite decades of research, the scientific understanding of the determinants of woody cover in savannas and prairies lags behind that of other biomes. To this end, a growing number of site-specific studies have found that tree mortality rates in some protected areas are principally controlled by large herbivores. However, it is not known whether these impacts significantly affect the total woody cover of the larger landscapes and region. If they do, it will lend significant support to the growing argument that biome extent and persistence can be a direct product of herbivory. This project focuses on quantifying the relationship between African savanna elephant (Loxodonta africana) densities and savanna woody cover in twelve protected areas across elephants' eastern African range. It then asks whether elephants' impacts alter global climate. To answer these questions, the researchers used satellite imagery to map the woody cover in each of the study sites. NSF funding will be used to assess the accuracy of the maps through the collection of ground truth data at a select site. By incorporating the data into a global network, with plans to monitor the field site into the future, the researchers will establish important baseline data which will be made available to researchers for future studies. Globally, the world's megafauna populations continue to decline and the ecosystems, national revenues, and local livelihoods they support face detrimental consequences. Although this research project will focus on savanna ecosystems in eastern Africa, the research will provide new insights and approaches for megaherbivore conservation in many other countries, including the United States.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.