Urbanisation is a major driver of unidirectional ecological change, yet its long-term impacts on biodiversity remain difficult to quantify. This study proposes and applies a model-based framework to assess temporal beta diversity over a 35-year period in a suburban bird assemblage in Tokyo, Japan. By estimating species abundances, the framework derives species-specific contribution ratios, enabling the identification of those species and groups most responsible for changes in assemblage over time. This contribution ratio approach facilitates the decomposition of temporal beta diversity, more specifically changes in assemblage composition, into interpretable components, thereby offering insight into ecological dynamics under anthropogenic pressure. This framework provides a practical tool for biodiversity monitoring and highlights the importance of long-term, high-resolution data for understanding assemblage responses to environmental change.