In the struggle to understand the decline of a species, it is imperative to ascertain the basic biological constraints of the species related to its’ population dynamics. One of the most essential considerations in the conservation of threatened and endangered species is the determination of current population conditions and the vital rates of birth, growth and death. This requires an understanding of the biology of the species and the ecological factors affecting it. By identifying the critical life stage for a given set of habitat conditions, management practices can be formulated and applied with greater success in preservation of the species. Bowles et al. (1990) have already suggested that management is probably necessary for the continued existence of Schoenoplectus hallii, a state endangered wetland species that continues to decline in number of states and populations within its range. The purpose of our study was to gain an understanding of the habitat conditions (soil type, soil moisture, groundwater fluctuation, vegetation patterns), monitor and mark individuals of S. hallii to determine life stages and survival probabilities and develop a life cycle model of S. hallii with data collected at a population site in Scott County, MO. In October 1999, four, 50-m transects were established on a parallel elevation gradient to the ephemeral pond and four, 1-m2 vegetation sampling plots were randomly located on each transect for a total of 16 plots. Groundwater wells were placed on each transect and surface to depth of groundwater, soil moisture, and vegetation were monitored monthly. We determined that S. hallii does not survive below 14% soil moisture, establishes in significantly lower diversity communities and may have a more complex life cycle than previously considered. The advance and retraction of groundwater appears to dictate the distribution and survival of S. hallii.

Key words: diversity, endangered species, life cycle, Schoenoplectus hallii, vital rates, wetland