Abstract
The Greater Cape Floristic Region (GCFR) of South Africa is a biodiversity hotspot threatened by the impacts of habitat transformation and invasive alien species. Cape Flats Sand Fynbos (CFSF) is a critically endangered vegetation type occurring within the GCFR, and its largest remaining fragment is the focus of a large-scale invasive plant control and biodiversity restoration project. Acacia saligna is a highly problematic invasive in CFSF and the main target of the control. To mitigate damage caused by this species, stands are removed and burned, which stimulates both the large invasive seed-bank and the indigenous seed-bank in the soil. Although there are no clear methods on how to manage the re-invasion at this stage without damaging indigenous plant recovery, three post-burn removal methods have the potential to be effective: (1) cutting the Acacia saplings below the coppicing point, (2) cutting the saplings and applying herbicide to the stumps, and (3) foliar herbicide spray. The aims of this study were to (i) find the most effective post-burn A. saligna control treatment, (ii) find the treatment that causes the least harm to indigenous plant recovery, (iii) determine the most cost-effective treatment, and (iv) establish which treatment is the most suitable for large-scale use. Cutting below the coppicing point of the A. saligna provided the most effective removal and was also the least damaging to indigenous vegetation recovery. The foliar spray treatment, however, saved the most time and costs. The best method is therefore dependent on the project goals, scale, and density of the A. saligna invasion. These results may be applicable to other types of fynbos and to other fire-stimulated invasive Acacia species.
Highlights
Invasions by non-indigenous species have become a global issue; they are a leading cause of biodiversity loss, drive habitat degradation, and affect functional processes that provide ecosystem services (D’Antonio et al, 2001)
This study was conducted at Blaauwberg Nature Reserve, Cape Town, in densely alien-invaded Cape Flats Sand Fynbos (CFSF), a vegetation type located on the acidic sands in the lowlands of Cape Town
The quantity of herbicide used in the herbicide treatments ‘cut and poison’ and ‘foliar spray’ was not calibrated to a specific quantity per plot or per plant, the amount used per treatment could not be determined
Summary
Invasions by non-indigenous species have become a global issue; they are a leading cause of biodiversity loss, drive habitat degradation, and affect functional processes that provide ecosystem services (D’Antonio et al, 2001). Warm-temperate and sub-tropical areas account for much of the world's biodiversity but are prone to invasions (Holmes and Cowling, 1997). One such area is the Cape Floristic Region (GGCFR) in South Africa which is a botanical biodiversity hotspot severely threatened by invasive species (MacDonald and Richardson, 1986; Van Wilgen et al, 2001). Much of the biodiversity in the GCFR is not adequately protected or managed, those vegetation types adjoining areas of development and urbanization, such as the Cape Flats Sand Fynbos (CFSF) (Rebelo et al, 2006, 2011).
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