Understanding How Changes in Disturbance Regimes and Long-Term Climate Shape Ecosystem and Landscape Structure and Function

Long-term and anthropic climatic change intersecting with disturbances alters ecosystem structure and function across spatiotemporal scales. Quantifying ecosystem responses can be convoluted, therefore utilizing multiproxy approaches clarifies consequent responses beyond correlations. Throughout the Holocene, climate continuously changed, contributing to increasing drought duration in some regions, such as the Pacific Northwest (PNW) (early Holocene) of the United States (also late Holocene wetting), and more intense precipitation in others, like South America (mid to late Holocene). A dominant dictating force in terrestrial system compositions is climate (e.g., temperature and precipitation), which is observed through reoccurring biotic patterns existing across the globe (i.e., ‘biomes’). Some biome distribution schematics designate biomes based on a shifting relationship between temperature and precipitation in which biomes can transition into others consequently mirroring climatic change. However, shifts in biomes are instigated on a lower level, such as the ecosystem scale where ecosystems dynamically respond to internal and exogenous forces. Consequently, ecosystems are perpetually fluctuating where multiple regimes can coexist under the same environmental conditions in which feedbacks, perturbations, and regime resiliency can either reinforce ecosystem statuses or contribute to shifts. My dissertation aims to elucidate ecosystem responses to climatic and disturbance changes specifically looking through a lens of carbon sequestration and stability. Understanding the persistence of carbon within an ecosystem is more prudent than ever given our current climate crisis. My research spans different hemispheres and time periods, where I utilize different approaches in each chapter to quantify ecosystem responses from varying angles. In Chapter II, I quantify how forest and savanna ecosystems have changed over the late Holocene across a large ecoregion (i.e., Brazil’s Cerrado) using stable and radiocarbon isotopes within the soil. In Chapter III, I transition to a landscape scale in the PNW where I investigate how fire in tandem with post-fire management influence soil carbon stability and soil fungal community composition. Chapter IV encompasses the ecosystem level within the PNW, where I use a single sediment core and a multiproxy approach to reconstruct biogeochemical shifts throughout the Holocene in response to climatic and disturbance changes. My dissertation possesses previously published and unpublished coauthored research