A comparison of demographic characteristics in a rare and a common species of Eupatorium

Demographic information on natural populations is essential to management of rare species. A comparative demographic study of a rare perennial plant, Eupatorium resinosum, and its closely related common congener, E. perfoliatum, was conducted to examine life history characteristics associated with rarity. Demography of three natural populations of each species revealed that E. resinosum has relatively lower sexual and asexual reproduction but more successful establishment of seedlings and asexually produced ramets than E. perfoliatum. Matrix projection analysis showed positive projected growth rates for two populations of E. resinosum, whereas E. perfoliatum showed a positive projected growth rate in only one of the populations studied. Survivorship of nonflowering ramets influenced projected population growth rates more in E. resinosum, while survivorship of flowering individuals influenced projected population growth rates more in E. perfoliatum. E. resinosum appears able to maintain populations in the short term, but over the long term lower seed production may make it difficult for E. resinosum to colonize new habitats as frequently as E. perfoliatum.