The invasive potential of Australian banksias in South African fynbos: A comparison of the reproductive potential ofBanksia ericifoliaandLeucadendron laureolum

Abstract

AbstractSeveral taxa of the Australian Proteaceae have invaded South African fynbos and require costly management programmes to bring under control.Banksiaspp. have been introduced only recently to fynbos regions. The invasive potential ofBanksia ericifolia(Proteaceae) was investigated by comparing its recruitment potential with that of an indigenous proteaceous shrub,Leucadendron laureolum. Both species are overstorey shrubs that are killed by fire and rely on canopy‐stored seeds (serotiny) for recruitment. Eight year oldB. ericifoliashrubs produced an average of 16 500 seeds per plant, which is thirty times more than the average of 570 seeds produced by 10 year oldL. laureolumshrubs. The seed bank ofB. ericifoliawas not only larger than that ofL. laureolum(1098 vs 525 viable seeds m−2projected canopy cover), but also considerably larger than that described for the species in its native environment (200–330 seeds m−2in a 9 year old stand north of Sydney).Leucadendron laureoleumreleased most of its seed a few days after the cones were burnt, whereas seed release inB. ericifoliawas spread over 12 weeks. The seeds ofB. ericifoliahad lower wingloading and fall rates thanL. laureolumand were dispersed over greater distances. The relative seedling growth rates of the two species were very similar (0.03 g per day), but below‐ground biomass was greater and proteoid roots were more developed inB. ericifoliaseedlings than inL. laureolumafter 100 days. Four year oldB. ericifoliaplants growing in the field had attained over twice the height of indigenous pro‐teoids and accumulated up to 10 times the fresh biomass ofL. xanthoconus, a species which is ecologically similar toL. laureolum. The Bioclimatic Prediction System (BIOCLIM) was used to create a bioclimatic profile ofB. ericifoliaand identify climatically suitable areas in the Cape Province. Results show that its potential distribution covers most fynbos areas in the southwestern Cape. It is concluded thatB. ericifoliahas the potential to be highly invasive in fynbos.