Ecological Tradeoffs to an Agricultural Amazonia: Investigating the effects of increased agricultural production on Amazonia’s contribution to global climate and nitrogen cycling

Abstract

The 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.