Growth and competition of Cytisus scoparius, an invasive shrub, and Australian native shrubs

English broom (Cytisus scoparius) is an aggressive invasive shrub in native sclerophyll forests of South Australia. We studied its relative growth rat e (RGR) and competitive ability in soils from invaded and uninvaded woodlan ds, in comparison to three native species it commonly displaces:Hakea rostr ata, Acacia verniciflua, and A. myrtifolia. Hakea was the slowest growing s pecies throughout the year. Both native species had their highest RGR durin g spring. The RGR of broom was higher than that of both hakea and acacia in the winter and spring. Despite losing its leaves in the summer, the RGR of broom through the year was higher than that of either of the native specie s. Soil from the invaded stands had higher organic C, N and soluble P than that from uninvaded sites. Broom and acacia grew better in the higher nutri ent soil than in the lower nutrient soil. Competition did not decrease the final biomass of any of the species in low nutrient soil. In the higher nut rient soil the biomass of broom was reduced by competition with acacia, but not by competition with hakea. Competition by broom reduced the biomass of hakea but not that of acacia. Broom's earlier and higher RGR, high competi tiveness in nutrient rich soils, and probably its ability to change nutrien t availability could be important contributors to the mechanisms by which i t invades native woodlands.