The Critical Biodiversity Areas (CBA) map for the Overberg District Municipality aims to guide sustainable development by providing a synthesis of biodiversity information to decision makers. It serves as the common reference for all multi-sectoral planning procedures, advising which areas can be lost to development, and which areas of critical biodiversity value and their support zones should be protected against any impacts. As part of the C.A.P.E. fine scale biodiversity planning, a systematic biodiversity assessment of the Overberg DM was undertaken, and a critical biodiversity area (CBA) map was produced. This district-wide biodiversity assessment is used to inform Spatial Development Frameworks (SDFs), Biodiversity Sector plans, Environmental Management Frameworks (EMFs), Strategic Environmental Assessments (SEAs) and the Environmental Impact Assessment (EIA) process. This biodiversity assessment, through the development of a CBA map for the district, is aimed at assisting biodiversity and land use managers and decision makers in this demanding task. This report summarizes the results of the biodiversity assessment conducted.

The CBA map indicates areas of land as well as aquatic features which must be safeguarded in their natural state if biodiversity is to persist and ecosystems are to continue functioning. Land in this category is referred to as a Critical Biodiversity Area. CBAs incorporate: (i) areas that need to be safeguarded in order to meet national biodiversity thresholds (ii) areas required to ensure the continued existence and functioning of species and ecosystems, including the delivery of ecosystem services; and/or (iii) important locations for biodiversity features or rare species.

Ecological Support Areas (ESAs) are supporting zones required to prevent the degradation of Critical Biodiversity Areas and Protected Areas. An ESA may be an ecological process area that connects and therefore sustains Critical Biodiversity Areas or a terrestrial feature, e.g. the riparian habitat surrounding and supporting aquatic Critical Biodiversity Areas.

Those areas of natural vegetation identified on the map as Other Natural Areas are sufficiently extensive at this stage that they may withstand some loss through conversion of their natural state, and undergo development. It is important to note that in the future, such areas will be increasingly converted or impacted, and it is possible that they will eventually be reclassified as Critical Biodiversity Areas. Therefore, in all decision making, the precautionary principle needs to be applied.

Biodiversity Overview

Biogeographically, the Overberg DM contains the western portions of the Southwest Phytogeographical Centre and Agulhas Plains Phytogeographical Centre of the Cape Floristic Region (CFR) (Goldblatt and Manning, 2000), the former being the most species diverse and endemic rich Phytogeographical Centre of this global biodiversity hotspot (Myers et al., 2000).

The Overberg DM can conveniently be divided into three broad habitat types:

• The higher altitude Table Mountain Sandstone areas support the fynbos vegetation group, which contains the greatest number of taxa and highest levels of endemism, as well as the highest number of threatened species. The Kogelberg-Hottentots Holland Mountain axis forms floristic heart of the CFR, may further act as a climatic refugia (cf. Cowling and Lombard, 2002)
• The mid-altitude rolling hills of the Rûens, with their rich shale derived soils contain the remains of the much transformed and fragmented Renosterveld vegetation group, now mostly under wheat. These highly threatened broader Renosterveld habitat types are in urgent need of effective conservation planning, to protect the few remaining viable fragments.
• The southern portion of the Overberg DM contains the lower altitude littoral sand and limestone deposits of the western portion of the Agulhas Plains Phytogeographical Centre. This western area has the highest richness and endemism of the Agulhas Plains Phytogeographical Centre, and includes the distinct TMS Potberg fynbos. The area also contains a large number of important wetalnds.
  

Biodiversity data

• The habitat map developed is a biodiversity proxy map (i.e. not a true fine-scale vegetation map) and is based on the refinement of the national vegetation map using finer scale habitat delineation from overlapping fine scale plans where available. A total of 114 habitat types were delineated in the district.
• A wetlands dataset was specially commissioned for the district.
• Special species data such as distribution of endangered species (e.g. CREW), and special habitats know to have high biodiversity (intact Renosterveld) were included in the analysis.
• Expert-mapped information was collected, comprising important complimentary information to the habitat map.
• Nationally listed threatened ecosystems (under NEMBA) were incorporated.
• Other protected habitat types (Wetlands, Forests) not protected by NEMA were also incorporated.

Land cover data/Transformation

• A dedicated land cover map was produced for this study. This layer combined data from the Western Cape Fields layer and 1:50 000 topographical data for features such as roads. Additional finescale transformation mapping from the Agulhas Plain was incorporated. These base products were then supplemented by an extensive head-up digitizing process based on the SPOT5 satellite imagery (2005).
• At the district level, 45.9% is still natural vegetation (mostly montane fynbos), 5.7% is degraded, 41.3% is transformed by cultivation, and 4.83% is transformed by urban and infrastructure (urban, roads and dams). However, the situation is far more dire for the Rûens Renosterveld, which occupies 36% of the planning domain. Only 6.5% remains in a natural state with an additional 6.1% being degraded. 81% of this area has been transformed agriculture.

Ecosystem status and threats

• Agriculture and to a lesser extent urbanization are likely to be the principal drivers of biodiversity loss in the district, especially in the mid and low altitude areas, at present about 54.1% of the area of the district’s ecosystems are transformed or degraded.
• Currently, of the 114 vegetation types described in the study, 23 are Critically Endangered, 11 are Endangered, 15 are classified as Vulnerable, while the remaining 65 are Least Threatened. Thus, the Overberg DM contains a very high proportion of threatened habitats compared to elsewhere in South Africa.

Protected area network

• The protected area (PA) network is not fully representative of the biodiversity in the district. At present, protected areas cover 18.4% of the district (formal and informal), however almost all of this is in mountain fynbos or along the coast. Much of the midland areas are very poorly represented with for example only 0.44% of Rûens Renosterveld being protected.

Critical biodiversity areas

• The biodiversity assessment for the Overberg District Municipality is designed to identify an efficient set of Critical Biodiversity Areas (and Ecological Support Areas) that meet the targets for the underlying biodiversity features in as small an area as possible and in areas with least conflict with other activities. Of fundamental importance is that these areas are identified in a configuration that deliberately facilitates the functioning of ecological processes (both currently and in the face of climate change) which are required to ensure that the biodiversity features persist in the long term.
• A critical biodiversity area (CBA) map has been developed for the district.
• This CBA map is intended to act as the biodiversity sector’s input into multi-sectoral plans and assessments (e.g. SDF, EMF EIA, IDP, etc.).
• The CBA map product is aligned with national standards for bioregional plans in terms of terminology and methods.
• Land use guidelines have been developed for each CBA category and aligned with land use categories commonly used in SDFs.