Forest ecosystems around the globe are undergoing rapid reorganization. The unabated continuation of climate change, the accelerating rate of alien species introductions, and the precipitous loss of biodiversity are altering the structure and composition of forest ecosystems. As a consequence, the emergence of novel ecosystems is virtually certain. However, the trajectories to novelty and the consequences thereof remain widely unknown. This limits the ability of forest policy and management to counteract undesired developments and safeguard the supply of ecosystem services to society. Here I will investigate the causes and consequences of reorganization in forest ecosystems, jointly studying the effects of global change on tree mortality and regeneration. I will use a concerted combination of complementary methodological approaches operating at different spatial scales to understand why reorganization takes place, when and where it is likely to happen, and what impacts reorganization will have on biodiversity and ecosystem services. Extensive experiments will be conducted both in the field and in walk-in climate chambers to answer whether compounding climatic extremes could result in bottlenecks of forest regeneration. A next-generation forest landscape model will be developed to investigate how climate change and alien species alter long-term forest dynamics. Based on these insights the FORWARD project will derive operational early warning indicators of reorganization, and conduct in-situ tests of their generality and applicability on three continents. Subsequently, a machine-learning aided synthesis will be used to compile the first map of global hotspots of forest reorganization, and robust strategies for addressing reorganization in management will be developed. The FORWARD project will bring about a new level of understanding of forest change, and will provide the data, tools and strategies to tackle one of the most pressing challenges of current forestry.