The Life History Characteristics of Three Ecologically Distinct Groups of Forbs Associated with the Tallgrass Prairie

Abstract

Forbs characteristic of the easternmost extension of the tallgrass prairie of North America were allocated to one of three categories (indicator species, modal species and weedy species) on the basis of their association with sites originally mapped as tallgrass prairie. A comparison of selected life history characteristics of the three groups by means of discriminant analysis suggests that seed production is the major variable differentiating these groups. Indicator species typically have relied very heavily upon the actively growing, largely aboveground fraction of the population. Their weedier counterparts have emphasized the more resistant belowground, seed-bank phase of the population's life cycle. INTRODUCTION Prior to European colonization, the midwestern portion of the United States was largely dominated by closed deciduous forests and open oak savanna. Along the western edge of the deciduous forest formation, however, open treeless areas dominated by graminoids and forbs were also common. In Ohio and Indiana, outliers of the tallgrass prairie represented the easternmost extension of the prairie peninsula (Transeau, 1935). The conversion of over 80-957O of the midlatitude grasslands to crop production and pasturage in the 19th and 20th centuries (Klopatek et al., 1979) resulted in the elimination of the more intolerant or sensitive elements of the grassland vegetation (Curtis, 1956). Many of these species today are confined to sites which were initially mapped as prairie by agents of the General Land Office Survey (Gould, 1941; Thomson, 1940; Troutman, 1981). Due to their low rate of invasion and reestablishment and their relatively sedentary nature, they have been used as indicators, sensu Peterken (1974), of the original tallgrass prairie. Shanks (1938), for instance, listed Silphium terebinthinaceum, Asclepias sullivantii and Solidago rigida as representative of the presettlement prairie sites of northwestern Ohio. Noted for their high fidelity, these species were the first to disappear when the original prairie sod was broken (Hanson and Churchill, 1961). The destruction of the intervening woodlands and the creation of old-field conditions encouraged the spread of another group of species, a group typical of the more open habitats of the grasslands. Many aggressive species like Ambrosia artemisiifolia, Rudbeckia hirta, Oenothera biennis and Erigeron canadensis invaded the newly created habitats, advancing far beyond their original areas of prominence (Curtis, 1956; Gray, 1879). Formerly limited to disturbed sites on prairies, i.e., gopher mounds (Ross et al., 1968), badger mounds (Platt, 1975), prairie dog towns (Osborn and Allan, 1949), ant hills (Baxter and Hole, 1967) or newly eroded surfaces (Betz, 1968), these migrant grassland species today represent an important native element of a largely weedy alien flora (Fogg, 1975; Shimek, 1932). 1 Present address: Department of Biology, The College of Wooster, Wooster, Ohio 44691.