The effects of past management practices for invasive alien plant control on subsequent recovery of fynbos on the Cape Peninsula, South Africa
Integrated control aimed at reducing impacts of alien woody plant invasions on biodiversity is underway in many parts of the Cape Floristic Region. However, the kinds of control measures applied may themselves affect the recovery of the natural vegetation. In view of this, we investigated the effects of past management practices, viz: 'bulldozing and aerial-spraying', 'aerial-spraying', 'boom-spraying' and 'foliar-spraying' aimed at clearing invasive alien woody plants on subsequent fynbos recovery in the Table Mountain National Park. Changes in soil (pH and depth) and vegetation (species cover, richness, diversity, evenness) properties, the total cover of species representing different dispersal guild, regenerative mode, and life form categories were compared between the differently treated and control plots at three different sites in the reserve. Only partial recovery of fynbos was observed in the 'boom-sprayed' and one of the 'foliar-sprayed' plots where measured species richness was significantly lower than that in control plots. However, marked changes in community structure were observed following 'boom-spraying' and 'foliar-spraying' at one site where a significant reduction in long-lived obligate reseeding species and an increase in the graminoid component was measured, though high fuel loads with possible post-fire erosion may also have aggravated the effects of foliar-spraying. Growth form structure changed the least following 'aerial-spraying' and 'foliar-spraying'. Multivariate analysis of plant functional types indicated a greater similarity between the control plots than the differently treated plots, implying a treatment effect on subsequent fynbos recovery. However, past land use and residual effects of the alien woody invaders may also have contributed to the differential recovery in the treated plots. It is concluded that re-introduction of species in the under-represented guilds may speed up fynbos recovery. The recommendation is a comprehensive seed mix containing the major guilds, and an initial seed mix of fast-growing indigenous species to stabilise the soil.