First defined by Arthur Tansley approximately 90 years ago, ecosystems arguably remain less monitored and understood than other dimensions of biodiversity. While our characterisation and understanding of ecosystems has improved, many of the issues pointed out by Tansley remain unresolved. We highlight how combining geodiversity research and complex system science, while better integrating cultural diversity and research outcomes across biodiversity dimensions, could help to address these issues and rapidly improve our ability to predict long-term ecosystem behaviour and dynamics. As ecosystems continue to gain traction in policy spheres, such knowledge will be key to strengthening the legal framing for biodiversity conservation, use, and management.