The Adirondack Mountains of New York State hold some of the southernmost communities of alpine vegetation in the eastern United States. Containing the greatest concentration of rare and endangered species in New York State, this ≈12,000-year-old ecosystem is important to understanding the ecological history of northeastern North America. In order to monitor floristic and vegetational shifts over time, 11 permanent transects were established in 1984 on four summits (Wright, Algonquin, Boundary, and Iroquois) of the MacIntyre Range in the Adirondack High Peaks region. Using the point-intercept method, all 11 transects were sampled in 1984, 1994, 2002, and 2007. Vegetation composition changed significantly over the 23-year period, with an overall decrease in bryophytes/lichens and an increase in vascular plants, indicating that vascular plants were replacing bryophytes, particularly in areas not disturbed by hikers. Community similarity was high among all transects, and increased with time for vascular plants as they became more abundant, indicating a successional convergence. Compositional shifts may also reflect effects of global warming and atmospheric deposition on alpine plant communities.