The SADC countries, like other countries elsewhere have had to introduce exotic tree species for the provision of a wide range of products and services, where native tree species were not suitable. In some instances however, some of these introduced alien tree species have, unfortunately become invasive. Australian acacias species (A. baileyana, A. cyclops, A. dealbata, A. decurrens, A. elata, A. implexa, A. longifolia, A. mearnsii, A. melanoxylon, A. paradoxa, A. podalyriifolia, A. pycnantha and A. saligna), which were introduced have been reported to be invasive at varying degrees in Lesotho, Malawi, South Africa, Swaziland and Zimbabwe. Among the pines, P. canariensis, P. elliottii, P. halapensis, P. patula, P. pinaster, P. pinea, P. radiata, P. roxburghii and P. taeda, P. kesiya, P. oocarpa and P. roxburghii are also regarded as invasive in some of the SADC with the exception of Botswana and Namibia that are generally dry for pines. The other notable aggressive alien invader tree species include Albizia procera, Bauhinia spp., Caesalpinea decapetala, Cupressus spp., Grevillea robusta, Hakea spp., J. mimosifolia, M. azedarach, P. grandiflora, P. canescens, Psidium spp., Rubus spp., Senna spp., Syzygium jambos, Salix babylonica, Toona ciliata and Ziziphus mauritiana. Among eucalypts, E. camaldulensis, E. cladocalyx, E. diversicolor, E. grandis, E. lehmannii, E. paniculata and E. sideroxylon have been reported as invaders. A separate study on invasive tree species in South Africa, Zambia and Zimbabwe was recently commissioned by FAO (Nyoka, 2003).
