Ecologists have long recognized that human activities modify climate and alter the supply of limiting resources. To understand the community and ecosystem-level consequences of these changes, ecologists have developed single and multifactor experiments that modify atmospheric CO₂ and O₃ concentrations, soil nitrogen availability, temperature and precipitation. Many experiments have been in existence for over a decade. These studies can now distinguish “initial,” often-transient responses that arise from step-increase experimental approaches, from long-term responses as these systems re-equilibrate. In some cases, long-term responses have lead to important breakthroughs in our conceptual models of community organization and ecosystem function. In this organized oral session, speakers will synthesize data from long-term global change experiments and discuss how their initial ideas about ecosystem responses were challenged by long-term responses. The speakers will represent a diversity of ecosystems and experimental approaches.