Population Dynamics of the American Ginseng Panax quinquefolium (Araliaceae)

Abstract

A 3-yr study of an aged population of American ginseng revealed four morphological classes among plants 1-18 yrs old. The youngest and smallest plants had a single prong of 3-5 leaflets and the oldest had four prongs with up to 20 leaflets. Age was positively correlated with prong and leaflet number. Prong development was linear, but not annual, i.e., a two-pronged plant formed from the single prong stage on an average only after 4.5 years, a third prong arose after 7.6 years, and the fourth prong after 13.5 years. All one-pronged plants were juveniles and, depending on the year, 22-44% of two-pronged plants were also juveniles. After the formation of an inflorescence during the two-pronged stage, flowering was annual thereafter. Flower number per inflorescence was correlated with morphological class and age. Most plants that developed flowers formed fruit (80-89%), except during the summer of 1980 when only 47% of flowering plants successfully matured fruit in a season typified by low precipitation and humidity, and high temperature. Younger adults in particular were more susceptible to failure in producing propagules and to earlier annual abscission under these stressful conditions than older members of the population. In fact, 53% of all flowering plants failed to develop fruit in 1980 compared to only 14% and 21% the previous 2 yrs. Seed survival was low and variable, the long afterripening period undoubtedly contributing to this vulnerable stage in the life cycle. Once germinated and established, however, seedling survival and development to adulthood, as well as adult survivorship, were high (97%). Even though a long-lived, woodland geophyte, year-by-year fluctuations in reproductive capacity, seed germination, and time of aerial stem abscission were marked. Annual growing-season dormancy, previously reported as a general phenomenon for American ginseng, was not found.