COS 83-2
Seed dormancy and dispersal promote nonnative invasion of deciduous forests in southeastern Ohio, USA
Plant species lacking obvious means of spatial dispersal present a challenge to conceptual models of biological invasion. To test the potential of nonnative forest species for invasion and long-term site occupancy, we experimentally examined the dispersal and soil dormancy behavior of two aggressive invasive herb species and a native analog at forest sites in SE Ohio, USA. Dispersal was described as seed arrival in sticky traps arrayed around reproducing populations. Dormancy condition was tested by burying seeds in nylon mesh bags at the humus/mineral interface and retrieving them at two-month intervals over a span of two years.
Results/Conclusions
One herbaceous invader, Microstegium vimineum, showed a buried seed half-life of 3 months with few seeds surviving to the end of two years, similar to the native analog Eupatorium rugosum. Both species switched from induced to enforced dormancy at times corresponding to natural germination and reverted to induced as the season passed. The other herbaceous invader, Alliaria petiolata, showed ca. 95% survival[HCD-1] over the two-year study, with < 5% enforced. A. petiolata germinability was independent of date. Spatial dispersal was minimal (40-80 cm yr-1) in both nonnative species. Microstegium persists by a combination of low vegetative mortality and consistent reproduction similar to disturbance-oriented native species. In contrast, A. petiolata persists through a wide environmental tolerance and flexible germination requirements. Dormancy appears to allow passive dispersal of these invaders by processes which move soil. Thus, metapopulation models which postulate extinction of invaders in late successional stages need to be revised to accommodate above- and below-ground longevity.