The natural and human environments form an inter-related system. The natural environment can be seen as a total ecosystem, comprising subsystems, influenced by such ecological factors as climate, plant succession, trophic levels, energy exchanges, and biogeochemical cycles. Human factors include: (1) population pressures on the land, (2) the market economy and its flucuations, (3) technology (including agricultural improvement), (4) the social structures and social relations involved in the use, exploitation, and conservation of a particular natural resource, and (5) human attitudes contributing to changes in the natural-human system. The actual environmental history of the period and place is a matter of interpretation. For each chapter in Major Problems in American Environmental History, teachers and students are encouraged to construct their own environmental histories by using the documents, essays, and further reading suggestions in the book, as well as the discussion questions, films, and other materials included here.