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KELSALL, N., C. HAZARD, AND D. J. LEOPOLD (Department of Environmental and Forest Biology, SUNY College of Environmental Science and Forestry, 1 Forestry Drive Syracuse, New York 13210). Influence of climate factors on demographic changes in the New York populations of the federally-listed Phyllitis scolopendrium (L.) Newm. var. americana J. Torrey Bot. Soc. 131:161-168. 2004.-Approximately 92% of the U.S. population of American hart's-tongue fern (Phyllitis scolopendrium var. americana) is found in Onondaga and Madison counties, New York, in 17 distinct colonies. All New York colonies have been periodically censused since 1916, though rarely in the same year. This study examines census data of the total New York population during and following the severe drought of 1999 and during the summers of 2000 and 2002. Additionally, the long-term (1922-2002) census data of seven colonies are examined relative to climate data for the same period. The total New York population has declined overall since the last previous census in 1995. No climate variables explained more than 23% of variation in population size of any growth phase. The lack of controlling, largescale climate factors suggests that the distribution of hart's-tongue fern in New York is determined mostly by the occurence of habitat capable of buffering climatic fluctuations. Future work should combine small-scale habitat and large-scale climate factors in any analysis.