This study mapped and analyzed the alpine-treeline ecotone (ATE) boundary and alpine plant communities on the Presidential Range, New Hampshire and Mount Katahdin, Maine. These are sensitive biomonitoring parameters for plant community responses to climatic change. The ATE boundary spans a considerable elevational range, suggesting that shorter growing seasons with increasing elevation only partially explain the upper limits for this boundary. This ecotone boundary may be influenced by topographic exposure factors related to mechanical damage caused by winter ice events and wind. Climatic changes that alter cloud frequency, wind, precipitation and ice loading at the upper elevations could influence shifts in the ATE boundary.