The soils from thousands of forests were characterized in the past century. These characterizations often aimed at answering focused questions, such as the relationships between forest growth and soil properties. Important insights will be gained in the next century by characterizing soils with explicit attention to changes across time, and across space. How rapidly should we expect soil properties to change, under normal processes of ecosystem development and in relation to forest management? How variable might these changes be across the wide variety of soils in forested landscapes? This presentation highlights some case studies about the rates of change in forest soils across landscapes of intensively managed plantations, emphasizing the power of well designed, long-term monitoring. In the 20th Century the high spatial variability in forest soil properties was cited as a reason for low expectations of tracking changes over time. Some forest soils are indeed highly variable, especially in areas of high rock content. Most forest soils in tropical areas have remarkably low variability, and moderate sampling efforts may detect differences over time or across space of just 5 to 10%. Long-term monitoring needs to be documented precisely within a landscape, and well designed to incorporate variations across landscapes.