City of Cape Town Biodiversity Network by Patricia Holmes

(Extract article from the volume 2008/1 Newsletter)

Biodiversity Management Branch, Environmental Resource Management Department,
City of Cape Town

Cape Town lies in the extreme south west of the Cape Floristic Region (CFR), an area of global biodiversity significance. However, we have lost extensive areas of natural habitat to urbanization, agriculture, mining and alien plant invasion, and Cape Town is now considered an international ‘hot spot’ of biodiversity. A biodiversity hotspot is an area under threat that harbours a high proportion of endemic species.
The transformation of natural environments in Cape Town has severely impacted lowland vegetation types and their associated habitats. The World Conservation Union recommends that a minimum of 10% of each vegetation type be conserved. This target is not sufficient to conserve biodiversity in regions with high levels of species endemism and a high turn-over in species composition between one area and another, such as in the CFR. In South Africa, conservation targets sufficient to conserve 70% of biodiversity in each vegetation type typically lie between 20-35%.

A desk-top conservation planning study was initiated in 2002, resulting in the first systematic conservation plan for the City in 2004: the Biodiversity Network. This network of sites is the minimum required to conserve a representative sample of the City’s terrestrial biodiversity and thus promote sustainable development. It includes all the nature reserves and core flora sites. We updated the plan in 2006 using more recent aerial photography to decipher remaining natural vegetation remnants. Also, we aligned City biodiversity conservation planning to the national planning under the National Environmental Management Biodiversity Act (NEMA No. 100 of 2004). Council adopted this plan subject to more detailed investigation of the sites and recommended that the Biodiversity Network be declared a Bioregional Plan under the NEMA.

In 2007-8, after we extensively ground-truthed habitat condition, the biodiversity remnant layer was updated and the systematic conservation planning analyses were re-run . Biodiversity informants used in the analyses were local vegetation units that are subtypes of the national vegetation types, plant species locations from three data sources (Protea Atlas Project (SANBI); Custodians of Rare and Endangered Wildflowers (SANBI); Sites and Species database (Coastec). Species were used in conjunction with the vegetation types in assessing sites on the basis of irreplaceability values (i.e. unique biodiversity features).

The widely used conservation planning analysis programme “C-plan” was used to calculate the most efficient set of remnants to meet biodiversity targets, but this time using 100 ha polygons as the maximum remnant size to improve efficiency. In addition, remnants of highest habitat condition were selected first. Remnants of high and medium condition selected on the Biodiversity Network are of the highest priority. Restorable remnants of vegetation types with insufficient habitat left to meet targets are also considered to be a high priority.

In order to improve connectivity among remnants, the programme “Marxan” was next applied, to select additional remnants needed. Corridors and connectivity sites help to conserve ecological processes, which include the dispersal and migration of plants and animals, necessary to conserve healthy populations in the long-term.

The City has been a leader amongst municipalities in local conservation planning, but up until now this has not translated into implementation on the ground. The Biodiversity Management Branch now has stronger ties to other conservation partners, such as CapeNature, and together we have moved into the implementation phase to secure critical biodiversity areas on the ground. An important milestone has been the integration of the 2008 Biodiversity Network into the Strategic Development Frameworks and Environmental Frameworks for the City.

Detailed desktop mapping of the City’s wetlands was completed in July this year, and we have just begun the ground-truthing of these wetlands. Before we can publish a Bioregional Plan, we need to prioritize the wetlands and coastal habitats and select additional ones to be included in the Biodiversity Network. This will be ongoing work during 2008 - 9.

Further reading: City of Cape Town Biodiversity Report 2008. 
This will shortly be available in municipal libraries and a low resolution electronic copy will be placed on the City’s website www.capetown.gov.za/environment