1. Despite high levels of disturbance and habitat modification, urban ecosystems still host substantial levels of biodiversity. The processes that maintain existing levels of diversity, however, remain understudied. Identifying the links between urban ecological processes and patterns has, therefore, become a fundamental research goal to support urban biodiversity and ecosystem functioning. 2. We conducted a study to determine how the diversity and composition of urban plant communities is affected by spatially and temporally variable land use legacies. We constructed a chronosequence of vacant lot properties covering a range of 3-22 years since demolition, in an urban neighborhood in Baltimore, Maryland (USA). Surveys of herbaceous plant species abundance were conducted during the summers of 2012 and 2013 in sections of each vacant lot where the building previously stood (the ‘building footprint’) and sections of the lot that was previously a backyard or garden (the ‘remnant garden’). 3. We found divergent patterns in plant community composition between areas of vacant lots with varying land use histories. This includes significant shifts in the functional composition of biotically-vectored seed dispersal strategies, as well as an increase in seed mass and terminal velocity trait values of plant communities in building footprints over time. Additionally, we found that communities in different sections of the same vacant lot tended to become more functionally dissimilar in dispersal strategies over time. In contrast, we found no significant changes in taxonomic diversity over time for any of our measures. 4. Policy implications: Our study suggests that regional-scale patterns of seed dispersal interact with heterogeneous land use legacies to structure urban plant communities. Although it has been suggested that highly altered local environmental conditions and competition from introduced species limit native plant diversity in urban environments, we find dispersal to be a more significant driver of urban plant community assembly patterns. Implementing management strategies that focus on habitat connectivity and augmenting species pools via seeding may present an effective strategy for promoting more successful establishment of diverse flora in urban environments.08-May-2017