Mpumalanga Biodiversity Conservation Plan Handbook - bgis-sanbi

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Box 4.2 Continued The MBCP used relatively small planning units, dividing the Province into a honeycomb of 65 000 hexagons of 118 hectares each. The biodiversity features were then overlaid and the amount of each feature occurring in a planning unit was calculated. The software then identified the required portfolio of planning units that best meets all biodiversity targets in the smallest possible area. Thus each planning unit is assessed in terms of whether it is needed to meet targets and what the likelihood is of other planning units being selected to protect the same biodiversity feature (a measure of irreplaceability). Sites with truly unique biodiversity are crucial in meeting targets. No alternative units will be offered because there are none, i.e. they are irreplaceable. Other sites may offer various alternative planning units to meet a target and thus have a lower irreplaceability value. INTEGRATING TERRESTRIAL AND AQUATIC ASSESSMENTS IN A SINGLE BIODIVERSITY PLAN The MBCP started from the premise of trying to be as inclusive and integrated as possible. This led to the decision to integrate the aquatic and terrestrial analyses into a single biodiversity plan. The general approach that underlies this process may be summarised as: Recognising the priority to conserve aquatic biodiversity within healthy subcatchments; Assessing the biodiversity importance of high value subcatchment areas and influencing the selection of terrestrial priorities towards these areas; Assessing future land-use pressures and influencing the terrestrial assessment to avoid these areas; Using spatially intelligent software (Marxan) to combine freshwater and terrestrial assessments in a single biodiversity plan; Producing a practical, meaningful output, useful at both provincial and municipal scales; Providing land-use guidelines for biodiversity conservation at the strategic or planning level. CHAPTER 4 - BIODIVERSITY SPATIAL ASSESSMENT INCORPORATING BOUNDARY COST Just selecting planning units on their biodiversity features alone may result in a very fragmented and dispersed portfolio of planning units. Marxan is ‘spatially intelligent’ in being able cluster units, usually in a connected portfolio (i.e. lower boundary cost). INCORPORATING PLANNING UNIT COST Marxan can also assign a cost to the actual planning unit and use this value to influence selection. Many factors can be used as a cost, including financial value, habitat transformation, and ecosystem health. Marxan selects planning units which minimise these costs while still meeting the required biodiversity targets. This can be used, for example, to minimise land-use conflicts by avoiding areas with high development potential. In developing MBCP, ecosystem health for each subcatchment was used as a cost surface in the aquatic biodiversity assessment. A summary of the aquatic assessment was then used as a cost surface for the terrestrial assessment. The terrestrial cost surface includes areas likely to be subject to future land-use pressures, thereby allowing them to be avoided to minimise land-use conflict. SETTING CLUMP TARGETS Marxan can also set select clumps of biodiversity features so that they meet clump targets. So, for example, it is possible to select at least three large grassland patches of 10 000 ha. One is able to set a minimum clump size, a required minimum distance between clumps and the number of clumps required. CALCULATING ‘IRREPLACEABILITY’ USING MARXAN Based on the number of runs, the frequency of selection of planning units can be used to derive an irreplaceability value. If 100 runs are chosen, irreplaceability will range from 0 (never selected) to 100 (always selected – i.e. irreplaceable). This is, however, different from the irreplaceability measure calculated in C-<strong>Plan</strong>, which is a statistical measure. 23 SPATIAL ASSESSMENT
MPUMALANGA BIODIVERSITY CONSERVATION PLAN HANDBOOK Thus the process started with the aquatic analysis, which was then integrated into the terrestrial analysis to produce the final product, using the following steps: Aquatic assessment preparation: collate spatial data on 24 biodiversity features, aquatic processes and high water production areas; Identify healthy subcatchments; Set targets for aquatic biodiversity features (Table 4.1); Do aquatic assessment using Marxan and identify priority sites within the healthy subcatchments needed to protect aquatic features; Convert the identified priority subcatchments into a GIS layer (cost surface) which will bias the selection of terrestrial planning units towards these important areas; Terrestrial assessment preparation: collate spatial data on biodiversity, ecological processes and protected areas; Set targets for terrestrial biodiversity features (Table 4.2); Develop a GIS-layer for biodiversity/land-use conflict (and convert to cost surface); Combine output of the aquatic assessment with the land-use conflict layer; Do terrestrial assessment to meet targets for all terrestrial features, while combining cost layers (favouring aquatic priorities and avoiding areas of land-use conflict); Sort output into meaningful biodiversity categories; Create land-use guidelines applicable to these categories. Various analyses and trials were conducted to integrate the aquatic and terrestrial assessments to produce the overall biodiversity plan. Through this process, various products were generated, including: Assessment of the health and integrity of subcatchments (Figure 4.1); Assessment of aquatic biodiversity (Figure 4.2); Assessment of future land-use pressures on biodiversity (Figure 4.3); Assessment of terrestrial biodiversity (Figure 4.4); Guidelines for land-use planning for biodiversity conservation (Chapter 6). AQUATIC ANALYSIS The MBCP aquatic assessment is a first-of-its-kind in South Africa. It incorporates several novel aquatic biodiversity features: use of subcatchments as planning units; biasing the selection of required units to healthy subcatchments; and using Marxan to assess the required subcatchments to meet targets. PLANNING UNITS Rivers are linear features driven largely by flow dynamics. They are not well suited to analysis by two-dimensional GIS based procedures. Wetlands are ecologically and functionally linked to rivers and the two need to be treated as interdependent. This indicates the suitability of small subcatchments as planning units. These were modelled from the 90m SRTM DEM (digital elevation model). BIODIVERSITY FEATURES Rivers can be recognised for their unique biodiversity and their functional types. They were thus classified according to both these characteristics using Ecoregion Level 2 criteria (as surrogate categories for biodiversity) and River Signature classifications respectively (Driver et al. 2005). Wetlands include pans and were split into four functional types: perennial and nonperennial pans; seepage wetlands; and valley bottom wetlands. Other features include peat wetlands and four threatened fish species. Important aquatic processes that were mapped include important pan and wetland clusters and high water-production areas for continuity of flow. Table 4.1 summarises the aquatic biodiversity features used. M P U M A L A N G A <strong>Biodiversity</strong> CONSERVATION PLAN HANDBOOK
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Mpumalanga Biodiversity Conservation Plan Handbook - bgis-sanbi

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