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

Phenology and pattern (direction and distance from mother plant) of seed dispersal were monitored in a population of the facultative woodland biennial Arabis laevigata var. laevigata. Dispersal began soon after seeds matured in June and lasted >2.5 years in some plants. Fifty percent of the seeds on 1986 seed-producing plants in the population had been dispersed by 22 September 1986 and about 92% by 2 March 1987. Length of time an individual plant dispersed seeds ranged from 14 to 586 days (mean +/- SE = 202 +/- 12.8 days). The majority of seeds fell <0.5 m from the parent plants, direction of dispersal was preferentially to the south, and the shape of the dispersal distance-seed density curve was concave. Number of seeds retained on dispersing plants declined exponentially with increase in time after beginning of dispersal. The possible ecological advantages of an extended period of seed dispersal are discussed.