 Ehrenfeld offers many examples of how natural communities are jeopardized through the actions of humans.For instance, the actions of the United States Army Corps of engineers, which threatened ecosystems within the Oklawaha River valley in Florida, and the numerous problems associated with preserving Pacific Coast Redwood communities, are utilized as case-studies to elucidate the impact of human activity on the environment.The case-studies are complemented with several discussions of how modern landscapes are changing due to human activities such as agriculture, public construction, and pollution.