The wealth of historical botanical surveys in New England and New York allows ecologists to study changes in plant communities over time across well documented sites. Studies of floristic change in towns, counties, and preserves over the past 150 years reveal regional patterns of species loss and increasing proportions of nonnative species. These changes are often linked to land use change, deer herbivory, development pressures, and climate change. Here, we review patterns of change throughout the region and explore in-depth floristic change at a northern site: Mount Desert Island (MDI), Maine, which holds the largest section of Acadia National Park. We find floras across the region have lost, on average, one-quarter of their native species—ranging from a loss of 3.5% of species from the Finger Lakes Region in New York to a loss of 53.1% of species on Staten Island, New York. No variable that we examine (e.g., size of area, size of flora, conservation status, and data sources) explains differences in losses across all sites. Contemporary floras have higher percentages of nonnative species than historic floras: the percent of nonnatives in floras have increased by 1.5% to 19.7% across the region. We also explore a data set of 412 conspecifics found both on MDI and 324 km away in Concord, Massachusetts, and compare species-level changes in abundance over the past century to test whether changes in one location might be predictive of changes in the other. We find that at a community level, changes in abundance in Concord were predictive of changes on MDI—local floras throughout the region have lost roughly 25% of their original species over the last 50 to 150 years—but changes in abundance for particular species in Concord were not predictive of how the same species changed in abundance on MDI. In New England, analyses of changes in nearby floras may help land managers and scientists understand community-level changes likely taking place, but we find that documenting and understanding changes in particular species requires targeted local study. Finally, we highlight the importance of context: understanding the survey effort, expertise, and goals of earlier botanists allows contemporary ecologists to make the most of the available historical ecological data.