Management of change is essential to ensure the long-term reusabilityof digital assets. Change can be brought about in many ways, includingthrough technological, user community and policy factors. Motivated by casestudies in space science and time-based media, we consider the impact ofchange on complex digital objects comprising multiple interdependent entities,such as files, software and documentation. Our approach is based on modellingof digital ecosystems, in which abstract representations are used to assess risksto sustainability and support tasks such as appraisal. The paper is based onwork of the EU FP7 PERICLES project on digital preservation, and presentssome general concepts as well as a description of selected research areas underinvestigation by the project.