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Global change has been occurring at unprecedented rates throughout the last century. A source of recent heated debate has been how such global changes, including land transformation, affect species richness and ecosystem functioning. Growing scientific consensus suggests that more diverse communities support greater ecosystem functioning; however, species numbers might fluctuate over time, and ecosystem processes are shaped by both species richness and species identities. In recent decades, habitat loss and major biodiversity change has occurred on the edge of urban centres because of land transformation to suburban development. Biological surveys provide a valuable record of how biodiversity has responded to this habitat transformation, especially if they have been conducted in the same location over time. Here, we examine changes in species richness, composition and phylogenetic structure between two surveys of vascular plants conducted over 50years apart on Mont St. Hilaire, Quebec, Canadaa UNESCO Biosphere Reserve surrounded by residential development. We found 198 more species in the more recent survey, but failed to detect 70 species that had been recorded in the earlier survey. A significant number of species gains were closely-related introduced non-native species. Species found only during the first survey (species losses) were frequently native species of special conservation status, and these species tended to be more evolutionarily distinct than species gained. Our results demonstrate that, in a UNESCO Biosphere Reserve, there have been significant changes in species richness and composition over the last half-century that might have far-reaching effects on ecosystem properties.