The effects of date of emergence and emergence order on seedling survival rates in Rumex crispus and R. obtusifolius

Abstract

Populations of the colonizing weeds Rumex crispus L. and R. obtusifolius L. were initiated from seed following disturbance on three occasions between May and September 1976. Three distinct cohorts were followed within each population. Cohorts which had the same order of emergence within a population but different dates of emergence had similar mortality rates. On the other hand, when cohorts of different emergence order and similar emergence dates were compared, those cohorts which emerged first had the lower mortality rates. For both species, the population arising latest in the season had the lowest percentage emergence but the greatest percentage survival of emerged plants to the time of flowering. These populations also had the best reproductive performance. The latest emerging population of R. crispus was the only one to produce as many seeds as had originally been sown, despite the fact that less than 10% of the emerged seedlings survived the winter and less than 1% of the seed pool gave rise to flowering plants. These results suggest that the timing of land management practices such as cultivation can have a profound effect on the success of weed populations.