G. Fogarty et Jm. Facelli, Growth and competition of Cytisus scoparius, an invasive shrub, and Australian native shrubs, PLANT ECOL, 144(1), 1999, pp. 27-35
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.