Ecological life history of the facultative woodland biennial Arabis laevigata variety laevigata (Brassicaceae): Survivorship

Survivorship was studied over an 8.5-year period in a population of the facultative biennial Arabis laevigata var. laevigata in a rocky deciduous woodland (Scott's Grove) in northcentral Kentucky, where most individuals of this species are associated with rock outcrops. Of the 2,269 seedlings marked in 1986 and 814 in 1987, only 101 (4.5%) and 35 (4.3%), respectively, survived 1 year, and only 24 (0.78%) of the 3,083 plants bolted before they died. In a separate study, only about 64% of the plants that bolted produced seeds. Thus, only about 15 (0.49%) of the 3,083 plants marked as seedlings in 1986 and 1987 actually reproduced. Cohorts exhibited a Deevey Type III survivorship curve. Small plants had a greater probability of dying than large ones. Survival was higher in microsites (on and near rock outcrops) with a thin, patchy leaf litter than in those with a moderate leaf cover; plants were not found in sites with a thick and persistent litter cover. Rosette herbivory also was a cause of mortality. Plants at Scott's Grove may flower in their second, third, fourth, fifth, or even a later year of life. Survivorship of A. laevigata in its woodland rock outcrop habitat is similar to that of facultative biennials of various other habitat types.