Abstract
Ecosystem disturbances in the western United States are large-scale processes that are often
driven by small-scale mechanisms. Previous research on drought, bark beetles, and fire has
made significant progress connecting these mechanisms to their impact on landscapes.
Macro-ecological approaches can apply knowledge of mechanisms across large spatial
extents and over long periods of time in order to test the generality of mechanistic theory
across highly variable natural systems. The goal of this dissertation is to examine patterns of
drought, insect, and fire disturbance across the western United States and infer signals of
their underlying mechanistic process. Chapter 1 begins with a brief introduction to
disturbance ecology. Chapter 2 examines insect, disease, and drought mortality across
forested ecosystems and determines pattern of tree mortality across species and regions. I
find that mortality rates will likely increase in the future, although with high variability
between species and ecosystems. This chapter excludes fire in order to focus on individual-
tree mortality, and Chapter 3 therefore complements it by focusing on wildfire throughout
interior drylands. In agreement with the literature, Chapter 3 finds that predicting wildfire
occurrence across six interior drylands is dependent on climate, with smaller contributions
from land cover. To connect mechanisms back to predictions, Chapter 4 looks at plant cover,
soil cover, and biogeochemical differences between fires of varying age. It finds that changes
to ecosystem structure and function are evident in the Great Basin and Colorado Plateau,
with smaller effects in the Chihuahuan, Mojave, and Sonoran. Chapter 5 summarizes my
findings and discusses the implications of my research in advancing the state of knowledge in
disturbance ecology as well as directions for follow-up and future research. In addition, I
discuss the methods I utilized in my research and implications for landscape conservation.