Interactions after death: plant litter controls priority effects in a successional plant community

We performed a field experiment to test whether the presence of litter produced by the dominant species in the first successional year affects the plant community structure in the following year. We removed the litter of Setaria faberii (the first-year dominant) in midfall, early spring, mid-spring, or late spring. Both the fall and early spring removal increased the biomass of Erigeron annuus, which became dominant, and reduced the biomass of S. faberii. In the fall-removal treatment more plants of E. annuus flowered, while early spring removal increased the biomass of rosettes (non-flowering individuals) at the end of the growing season. In the other treatments and in the control S. faberii retained dominance, but its biomass was the highest in mid-spring removal plots. The removal of litter of S. faberii in the fall and in early spring allowed E. annuus to pre-empt the site and dominate the community. When litter was not removed, it strongly hindered the growth of E. annuus, favoring S. faberii. These results highlight the importance of litter as a historical factor linking interactions across successive generations, and controlling the community structure.