Exotic invasive plant species in riparian habitats in the Fynbos in the Western Cape of South Africa have reduced streamflow, compromised habitat quality for other species, and outcompeted native species.  What is not clear is why the most problematic invasive species are able to outcompete native species and spread.  Previous studies in the riparian Fynbos of the Western Cape suggest that one of the most invasive exotic species, Acacia mearnsii may be more drought tolerant than native species, and that may contribute to its invasive potential.  However, this study examined attributes of adults of native species and A. mearnsii, yet competition during recruitment ultimately determines survival.  We were interested in determining whether observed differences in drought tolerance in adults would also be observed in seedlings.  We compared drought tolerance of co-occurring juvenile individuals of A. mearnsii and a native species, Brabejum. stellatifolium, on the Holsloot River near Rawsonville in the Western Cape of South Africa   We expected to find that A. mearnsii seedlings would have lower P₅₀ values; these values indicate the xylem water potential at 50% loss of hydraulic conductivity, and similar water potentials.  Vulnerability curves were determined for 6 individuals of each species, and P₅₀ values were calculated.  In addition, P₁₀₀ values were calculated, and mid-day and pre-dawn water potentials were measured. 

Results/Conclusions