Invasion and control of alien woody plants on the Cape Peninsula Mountains, South Africa - 30 years on

  • Published source details Moll E.J. & Trinder-Smith T. (1992) Invasion and control of alien woody plants on the Cape Peninsula Mountains, South Africa - 30 years on. Biological Conservation, 60, 135-143.


In South Africa, many alien tree and shrub species have become invasive, with resultant detrimental impacts on native fynbos plant communities. Various (usually uncoordinated) eradication programmes by various organizations and landowners have been implemented on the Cape Peninsula Mountains in an attempt to control invasives but records of outcomes are rarely kept. The aim of this study was to make an assessment of current distribution and densities of alien populations on permanently marked sites surveyed in 1959/60, and to assess the success of control measures.

The survey area comprised around 102 km² of the Muizenberg, Constantiaberg and Table Mountains. In 1989/1990, vegetation surveys were repeated at 87 sample sites/points established in 1959/60 and also surveyed in 1976.
Within a 183 m radius of each sample point, the following were recorded: altitude, soil moisture and soil type, aspect, average plant canopy cover, height and density of the native plant community, dominant native species, and post-burn age. Of non-native plants, only alien shrubs and trees deemed as having ‘capacity to alter the fynbos structure and species composition’ were recorded.

Fourteen invasive woody taxa were recorded (4 Pinus species, 3 Hakea species, 5 Acacia species, Eucalyptus spp. and Cape wattle Albizia lophantha) in the sampling sites. Of concern was that Monterey pine Pinus radiata (10% occurrence in 1959/60, 24% in 1989/90) and rooikrans Acacia cyclops (20% occurrence in1959/60, 26% in 1989/90) showed significant increases in frequency. Neither in the past was considered particularly aggressive invasives in the Peninsula Mountains.

Whilst the density of some species was reduced (particularly the most widespread cluster pine Pinus pinaster from 82% to 62% of sites) they still appear a threat. Biocontrol measures for two Australian invasives, silky hakea Hakea sericea (9% occurrence in1959/60, 6% in 1989/90) and long-leaved wattle Acacia longifolia (7% occurrence in1959/60, 9% in 1989/90) appear effective in keeping these species in check.
The 30 year trend suggests that intensive clearing programmes can contain, and might achieve eradication, of these invasives given adequate funding.
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