Canopy effects of the invasive shrub Pyracantha angustifolia on seed bank composition, richness and density in a montane shrubland (Córdoba, Argentina)

Invasive woody species frequently change the composition of the established vegetation and the properties of the soil under their canopies. Accordingly, invasion may well affect regenerative phases of the community, especially at the seed bank level, likely influencing community restoration. Pyracantha angustifolia (Rosaceae) is an invasive shrub in central Argentina that affects woody recruitment, particularly enhancing the recruitment of other exotic woody species. There is though no information regarding its effect on the soil seed bank within the invaded community. The present study was set up to gain further insight into the canopy effects of P. angustifolia. We aimed to assess whether the invasive shrub affects seed bank composition, richness and seed density as compared with the dominant native shrub Condalia montana (Rhamnaceae), and to relate the observed seed bank patterns with those of the established vegetation. We evaluated the composition of the germinable seed bank and the established vegetation under the canopy of 16 shrubs of P. angustifolia, 16 shrubs of C. montana, and in 16 control plots (10 m²) without shrub cover. The floristic composition of the seed bank differed among canopy treatments. However, seed bank richness did not differ significantly. There was an overall high seed density of exotic species throughout the study site, though exotic forbs showed significantly lower seed densities under the invasive shrub. Pyracantha angustifolia would not promote the incorporation of new species into the seed bank of the invaded community but rather favour the establishment of woody species that do not depend on seed banks. The absence of dominant woody species in the seed bank, the dominance of exotic forbs, and the high similarity between established exotic species and those present in the seed bank may surely affect community restoration following the main disturbances events observed in the region.