Date of this Version
Keeler in American Midland Naturalist (July 1991) 126(1): 44-60.
Little is known of the lifespans of herbaceous plants, especially in grasslands, although this information is basic to understanding the dynamics of species and ecosystems. Permanently marked plants of the bush morning glory, Ipomoea leptophylla (Convolvulaceae), in Nebraska sandhills prairie were censused annually from 1979-1989. While the average annual death rate was 2.6 per 100, virtually all the mortality was among smaller and probably younger plants. Recruitment varied greatly among years. Of plants of known age, the median age at first flowering was 6 yr. After 9 yr 30% had never flowered. Larger size classes flowered more frequently than smaller mature plants and were more likely to mature seeds successfully. For this polycarpic nonrhizomatous herb, a generation is probably over 2 decades and some plants may live more than a century. As a result, environmental variation on the scale of even the Great Drought may be a passing interval of minor impact on lifetime fecundity for established adults, although until extreme years have been observed this cannot be proven.