This chapter discusses the concept of sustainability using as a specific example concerns about the sustainability of oak-dominated forests in the northeastern United States. The discussion from the first edition is updated with current research, leading to the conclusion that climate is the most critical factor in determining species ranges even in human-dominated landscapes, and that fluctuations during the Holocene have been reflected not only in altered species composition of forests, but also in human populations and thus land use. At the same time, changes wrought by people have influenced decadal dynamics, such as secondary successional patterns, and often all but eliminated species within some plant communities, by land use change. Merely comparing present to inferred processes in the past misses vital factors in change; inference must be supported by historical data. Worldwide, droughts inferred from multi-proxy data can be correlated with declines in human populations as well as with changed vegetation, regardless of the complexity of the civilizations and agricultural systems. Managing systems for sustainability, requires consideration of legacies left by past land use.
Agricultural Adaptation to Urbanization in Southeastern Pennsylvania