Results

For each scenario, maps displaying the network meeting the biodiversity targets for the least cost (i.e. the run with the lowest objective function value) were produced.

Within this chapter, we discuss the network resulting from the best runs using the input parameters for each scenario to consider current land use and potential management and to demonstrate how we might use the biodiversity data generated through this project to identify an optimal site network for conservation of freshwater species. As noted above, when applying this method in practice it will be important to include other data sets, such as existing land management, legal and customary ownership and tenure, concessions and national spatial planning strategies, to come up with an optimal network employing the systematic conservation planning approach demonstrated here.

First, let us consider Scenario A, in which no planning unit cost was specified. Some 122 planning units were identified as being the minimum set of planning units required to meet the species targets (Table 10.1). This scenario does not account for the area or the human footprint within those planning units. The total area required by these planning units was 125,958 km² and the nominal cost was 4.9 (Table 10.1). Scenario B accounted for the area and human footprint within the planning units by using a planning unit cost (Equation 10.2, Figure 10.1). In this scenario, 65 planning units were retained from Scenario A; including 30 ‘irreplaceable’

planning units that were required in each instance to meet the targets (see section 10.3.1). Some 57 planning units from Scenario A were ‘dropped’ and 64 planning units were added in. This resulted in a network which meets the species

Scenario Cost

C A PAs 1,486 41 1,582 96 16.9 19.9 3.0 852,607 931,217 78,610

D A PAs and

KBAs 1,710 67 1,797 87 19.6 21.6 2.0 973,780 1,027,141 53,361

Table 10.1 Results of Marxan analysis for scenarios A–D. Source: Compiled by the report authors.

targets but which covers a smaller area of 87,254 km² and a lower cost of 3.3 (Table 10.1). By selecting slightly more planning units with a lower total area and human footprint (i.e.

a lower cost), Scenario B represents a more efficient network for including the targets for representation of threatened freshwater species in western Africa.

Next, we consider scenarios C and D, in which planning units with existing management are ‘locked in’. Scenario C used the same parameters as for Scenario B, except that 1,486 planning units representing protected areas were

‘locked in’ to the network. These planning units covered an area of 852,607 km² and the targets for 41 of the 194 freshwater species were already met within these planning units (Table 10.1). The best solution for Scenario C resulted in an additional 96 planning units being selected in the optimal sites network, covering an area of 78,610 km² and at a cost of 3.0, in order to meet all species targets.

Scenario D used the same parameters as for Scenario C, except that an additional 224 planning units representing KBAs were locked in to the network. These combined 1,710 planning units covered 973,780 km² and the targets for 67 of the 194 freshwater species were already met within these planning units (Table 10.1). The best solution for Scenario D resulted in an additional 87 planning units being selected in the optimal sites network, covering an area of 53,361 km² and at a cost of 2.0, in order to meet all species targets. Several of these planning units included eight of the 13 CEPF freshwater KBAs discussed in Chapter 9 (excluding Rhombe Swamp, Upper St Paul River, Lower Volta Eastern Catchment, South East Niger Delta and São Tomé), as well as other potential freshwater KBAs and including all of those planning units containing potential AZE sites (which are irreplaceable sites in these scenarios).

10.3.1 Irreplaceability

The target for each species was presence in at least two planning units, except for 37 species occurring only in a single planning unit, for which the target was presence in one

planning unit. These 37 species were distributed between 22 planning units, and these planning units were effectively

‘locked in’ by definition of the target requiring their inclusion in any given solution (Figure 10.5). Most of these planning units represent the only known locality for these 37 species globally, of which 35 species are assessed as EN or CR, and therefore by definition have potential to yield AZE sites (meeting KBA criterion A1e). Confirmation of AZE sites in these planning units will require field surveys to confirm species’ presence (see Chapter 9).

An additional 12 species each occurred in only two planning units. Therefore, there was also only one option to meet these species’ targets i.e. inclusion of both of the planning units for each of these species. This resulted in an additional eight planning units being implicitly locked in to the network.

Ultimately, 30 ‘irreplaceable’ planning units representing 49 restricted range species occur in every network where the targets are met.

10.3.2 Gaps in the current network

Based on Scenario D, the target of one or two planning units per threatened freshwater species was already met by the existing protected area and KBA networks for 67 of 194 species. The presence and importance of any freshwater species known to occur at these sites should be communicated to the site managers, and management strategies aimed at these freshwater biodiversity elements should be developed and implemented. An additional 87 planning units (with a combined area of 78,610 km²) are outside of the KBA and PA networks (Figure 10.4), and these sites represent the most important gaps, with respect to the conservation of threatened freshwater species, in the current network of sites. We advise that this network of gap sites be used in conjunction with other KBA scoping methods (Spiliopoulou, 2021) as a scientific basis for the development and expansion of the existing KBA and protected and conserved area network, including OECMs, in order to ensure that freshwater biodiversity is better represented and protected.

Figure 10.3 Scenario A vs Scenario B spatial conservation prioritisation networks. Source: Compiled by the report authors.

Figure 10.4 Scenario D spatial conservation prioritisation network. Source: Compiled by the report authors.

Figure 10.5 Planning units representing the only known localities for 37 freshwater species in western Africa. Source: Compiled by the report authors.