Contrasting soil seed-bank dynamics in relation to local recruitment modes in two clonal shrubs, Rhus aromatica Ait. and R. glabra L. (Anacardiaceae)

Soil seed bank dynamics, greenhouse seed germination and field seedling survival were compared in the weakly-clonal shrub Rhus aromatica Ait. and the strongly clonal shrub R. glabra L. (Anacardiaceae). Although both species had persistent soil seed banks, their sizes and dynamics differed greatly. The high seed density (5668 ± 1267 m^-2 to 8739 ± 3303 m^-2) in R. glabra was depleted by ca. 5% annually and replenished with 1102 ± 316 to 1828 ± 486 seeds m^-2, whereas the low seed density (9 ± 5 to 138 ± 68 m^-2) in R. aromatica was depleted by ca. 50% annually and replenished with 37 ± 7 to 69 ± 18 seeds m^-2. Seeds of both species germinated within established populations. However, recruitment from seedlings was successful in R. aromatica but not in R. glabra, which depended exclusively on root suckering for aboveground population increase. This difference in local recruitment modes between the two species was correlated with differences in soil seed bank dynamics and other life history traits, such as fecundity, seed weight, seed dormancy, seed dispersal, seedling establishment and growth form. The results of this study have important implications about life history evolution in that they suggest that various traits related to increasing sexual reproduction in time and space evolved in concert with clonal reproduction in clonal woody species.