Plant litter feedback and population dynamics in an annual plant, Cardamine pensylvanica

The presence of litter has the potential to alter the population dynamics o f plants. In this paper, we explore the effects of litter on population dyn amics using a simple experimental laboratory system with populations of the annual crucifer, Cardamine pensylvanica. Using a factorial experiment with four densities and three litter levels, we determined the effect of litter on biomass and plant fecundity, and the life stages responsible for these changes in yield. Although litter had significant effects on seed germinati on and on seedling survivorship, we show, using a population dynamics model , that these effects were not demographically significant. Rather, the pote ntial effect of litter on population dynamics resulted almost entirely from its effect on biomass. Persistent litter suppressed plant biomass and appa rently removed the direct density effect present in the absence of litter. Thus, litter changed the shape of the recruitment curve from slightly humpe d to asymptotic. In addition to changing the shape of the recruitment curve , litter reduced the carrying capacity of the populations. Thus, the popula tion dynamics model indicated that not all statistically significant respon ses were dynamically significant. Given the potential complexity of litter effects, simple population models provide a powerful tool for understanding the potential consequences of short-term responses.