The introduction of alien species represents one of the greatest threats to biodiversity worldwide. Highway construction increases the dispersal and invasion of exotic plant species. This study examined the assembly process of the plant communities to determine whether the roadsides of the Patagonian steppe represent a reservoir and dispersal source of invasive exotic species. We analyzed the composition of exotic and native species and functional groups present in the established vegetation and seed banks of roadsides and reference areas nearby. The type of dispersal of exotic and native species at the roadsides was also evaluated. Total cover and that of exotic and native species was lower at the roadsides than in the reference areas; however, at the roadsides the cover and seed abundance of exotic species was higher than that of native species. In the roadsides vegetation, native shrubs such as Acaena splendens predominated, along with exotic perennial herbs and grasses which were mainly represented by Rumex acetosella. In the seed bank the predominant species were exotic perennial herbs, also represented by R. acetosella, annual exotic species such as Epilobium brachycarpum and Verbascum thapsus, and annual native species such as Heliotropium paronychioides. No exotic shrubs were found either at the roadsides or in the reference areas. The species at the roadsides did not present a dominant type of dispersal. The abundance of exotic species at the roadsides, both in the aboveground vegetation and the seed bank, may be due to the stressful environment and the characteristics of the species themselves, such as the ability to form seed banks. This work revealed that the roadsides of the Patagonian steppe constitute reservoirs of invasive exotic species, highlighting the importance of identifying them and controlling their spread, with a view to generating ecosystem management programs.

El objetivo fue evaluar los requerimientos de germinación de Phacelia secunda J.F. Gmel. y Eryngium paniculatum Cav. y Dombey ex F. Delaroche, herbáceas perennes colonizadoras de ambientes degradados del noroeste patagónico argentino y de interés para la restauración ecológica. Se evaluó el porcentaje, tiempo medio e inicio de germinación en un control (C) y dos tratamientos pre-germinativos: escarificación mecánica con bisturí (EM) y estratificación húmeda fría durante 45 días (EHF). En P. secunda, el porcentaje de germinación en el tratamiento EHF (2%) fue menor que en el C (24%) y el tratamiento EM (16%). En E. paniculatum se encontraron diferencias entre el C (94%) y el tratamiento EHF (82%), pero no entre el C y EM (91%). El tratamiento EHF aceleró el inicio de la geminación en ambas especies. Las semillas de P. secunda mostraron baja capacidad de germinación siendo necesario evaluar nuevos tratamientos. Eryngium paniculatum mostró alta capacidad germinativa aún en el control, lo que evidencia que no requiere tratamientos pre-germinativos específicos.

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