Environmental and social impact assessment is now a widely accepted tool in the Mekong Region for assessing the impacts of hydropower dams and large-scale industrial tree plantations. However, the cross-sectoral and cumulative effects of such projects have not been sufficiently addressed. Where cumulative impacts have been considered, studies have focused on a single sector, such as multiple hydropower dams. A separation between land and water management frequently leads those assessing project impacts to overlook or underestimate project outcomes. Here we examine such interactions between industrial plantations and hydropower projects, demonstrating that it is the diverse livelihoods of local people-based on everyday use of multiple resources-that crucially connects aquatic and terrestrial environments. The combined social and environmental changes wrought by resource projects can thus produce particular challenges for these communities, as multiple systems are enclosed and degraded. We present case studies of social and environmental impacts occurring in the Mekong Region: in the Hinboun River Basin in Central Laos; the Xe Bang Fai River Basin, also in Central Laos; and the Sesan River Basin in northeastern Cambodia. We strive to demonstrate the practical usefulness of adopting political ecology frameworks for thinking about these crucial agrarian changes.