Browsing by Subject "Tropical ecology"
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Item Ecological Tradeoffs to an Agricultural Amazonia: Investigating the effects of increased agricultural production on Amazonia’s contribution to global climate and nitrogen cycling(2015-11) O'Connell, ChristineThe Amazon rainforest is experiencing widespread land-use/land-cover change, much of which is driven by agricultural expansion and shifts in agricultural management. These changes have contributed to high annual greenhouse gas emissions, changing regional climate due to shifts in energy balance, and disruptions to nutrient cycles, occurring on a scale large enough to have ramifications for the larger earth system. This dissertation investigates how human land use for agriculture affects Amazonia’s contribution to climate regulation and nitrogen cycling and the tradeoffs between agricultural production and ecosystem ecology. First (Ch1), I model the impact of agricultural expansion on four important ecosystem services (agricultural production, carbon storage, biodiversity, and regional climate regulation) using data from a combination of remote sensing, model output, and geostatistical datasets. I find that different regions within Amazonia are of primary importance for each non-agricultural ecosystem service, suggesting that using complementary conservation strategies that target a collection of environmental goals could minimize the ecological impacts of expanding agriculture. Second (Ch2), I show that at the site-level, patterns of trace gas concentrations throughout the soil column differ between eastern Amazonian forest and deforested soybean fields, indicating that agricultural expansion can affect the carbon (C) and nitrogen (N) cycles at depth in Amazonian soils. Amazonia’s current croplands are also undergoing management intensification. I conduct a multi-year field campaign to measure how emissions of nitrous oxide (N2O), a powerful greenhouse gas, carbon dioxide (CO2) and methane (CH4) change after fertilizer addition on an industrialized farm in Mato Grosso, Brazil. I find (Ch3) only modest increases in N2O emissions on intensified croplands in comparison to Amazon forest, suggesting that cropland intensification may not necessarily lead to increased greenhouse gas emissions in southeastern Amazonia. These projects use multiple spatial scales, multiple ecosystem response variables, and multiple approaches to quantify the ecological consequences of agricultural expansion and intensification in the Amazon rainforest. As global change continues, determining how to utilize dynamic tropical landscapes while minimizing ecological disruption will be key to tropical sustainability.Item Understanding the role of plant hydraulic traits in ecological processes(2021-11) Vargas Gutierrez, GermanAmong all ecosystems tropical forests play a disproportionate role in Earth’s carbon cycle as they account for one third of total primary productivity. Global environmental change is causing novel precipitation patterns, shifts in the timing of rainfall events and an increase of the atmospheric water demand in tropical regions. Such changes pose a threat to the ecosystem services provided by tropical forest ecosystems as there is great uncertainty of how tropical forests will respond to warmer and drier climatic conditions. Plant responses to drought occur at different biological and temporal scales, ranging from responses at the tissue level to responses that define species and populations. Plant hydraulic traits have proven to be key in the characterization of how plants respond to drought, as they allow to group species in those that avoid drought and those that resist drought. Therefore, quantifying the sources of variation in plant hydraulic traits presents a promising way to move forward our understanding of how tropical forests will respond to climate-change. The main objective of this research was to study the aspects that drive variation in plant hydraulic traits in tropical plant species, and how nutrient availability affects tropical forest responses to drought. In Chapter 1, I performed a study in which I investigated if it is possible to generalize tree species drought tolerance and growing strategies using their leaf habit (i.e., deciduous, evergreen and semi-deciduous). In this study I found that in the tropical dry forest deciduous species tend to share similarities in their physiological properties, contrary to evergreen species that tend to be physiologically different across sites. Generally deciduous species will show a hydraulically risky growing strategy, and evergreen species a hydraulically safe growing strategy. In Chapter 2, I carried out a large-scale ecosystem manipulation experiment to study how both water and nutrient availability control primary productivity in a tropical dry forest. I found that nutrient availability had a stronger but weak effect on forest productivity that a decrease in soil moisture. Forest productivity was more sensitive to inter-annual variation in climatic conditions, as we observed large decreases in productivity in warmer and drier years when compared to the effect of the experimental treatments. In Chapter 3, I performed a data synthesis to study how environment and evolutionary history shape plant hydraulic trait variation among evergreen and deciduous species across the world tropics. Through this pantropical data synthesis, I was able to point out biases in the assessment of tropical plants drought tolerance and that environment play a stronger role in shaping plant hydraulic traits than species’ evolutionary history. I also demonstrated that deciduous species tend to have similar vulnerability to drought across environmental conditions, while evergreen species hydraulic traits vary as a function of water availability. Collectively, these three studies help us to understand the drivers of drought tolerance in tropical plants and how environmental variation shapes responses to drought in the tropical forests.