Competition strength of two significant invasive species in coastal dunes.
To investigate the effect of increased nutrient availability on competition amongst invasive and native plants, I measured changes in above and below ground biomass of Chrysanthemoides monilifera spp. rotundata (bitou bush) and Asparagus aethiopicus (asparagus fern) competing with two native species, Banksia integrifolia and Ficinia nodosa, under high- and low-nutrient regimes. Bitou bush, as a primary invader, was competitive under all conditions lowering the growth of native species in both high and low nutrients. Asparagus fern as a secondary invader, did not influence growth of native species but responded, like bitou bush, to high nutrients. Native species were generally negatively affected by increases in nutrients. With bitou bush soils often providing higher nutrients, the chance of secondary invasion by asparagus fern is more likely, although asparagus fern is unlikely to invade low nutrient soils quickly. The invasive species, therefore, differed in their competitive ability in these coastal dune communities.