Post-dispersal seed fates of four prairie species.

After dispersal, seeds can germinate and establish as seedlings, persist as seeds, or die. Knowledge of these three seed fates is crucial for understanding the abundance and distribution of plant populations and ultimately, community composition and diversity. Few studies, however, have simultaneously measured these fates, while also examining the factors causing mortality. The goal of this research was to simultaneously quantify the three seed fates and factors causing death (predation and fungal disease) for four species found in prairies in western Oregon, USA. The most common seed fate for the four study species was death (44-80%). Fungal disease, which has seldom been quantified in natural ecosystems, generally caused less than 10% mortality for each of the four species. Vertebrate predation substantially reduced seed numbers only for Bromus carinatus (21%). Of the unmeasured mortality factors, indirect evidence showed invertebrate predation was a cause of death for seeds of only one species, Prunella vulgaris. In addition, competitive pressures caused seedling death for only the two grass species, Bromus carinatus and Cynosurus echinatus. Survival as established seedlings was generally much more common than survival as persistent seed, with the exception of Daucus carota, in which 14% of the sown seeds persisted the first year.