Planning for biodiversity and cereal production in the Gariep Basin : a conservation perspective

[摘要] ENGLISH ABSTRACT: Biodiversity feature richness and cereal production potential increase west to eastacross South Africa's Gariep basin, the regional focus area in the Southern AfricanMillennium Ecosystem Assessment. lrreplaceability, developed for measuring biodiversityvalue, provides a unit free, spatially explicit measure that can be used to measure an area'simportance in terms of cereal production. It provides a common currency to measurecompeting land-uses. This study models cereal production potential for four cereal types(maize, millet, sorghum, wheat) and sets three cereal production targets, based on minimumnutritional cereal demands and models of actual consumption rates.Chapter 2 uses C-Plan to determine irreplaceability and compares the irreplaceabilityvalues for cereal production potential and biodiversity. Higher cereal production targetsincrease the irreplaceability of sites for cereal production and increase the number of siteswith high irreplaceability for both biodiversity and cereal production. These sites thus havehigh potential for conflict between these land-uses. Areas of conflict occur primarily acrossthe central eastern region, largely in the grassland biome. The biodiversity features and cerealproduction potential of these sites are known, thus making potential trade-offs involved in theconservation of these sites explicit.Sites with conflict potential can be avoided using area selection algorithms thatmaximise conservation target achievement while minimising the cost to cereal production. CPlan's simple iterative heuristic approach to minimising costs succeeds in avoiding someareas of conflict potential but more complex algorithms provide better solutions. Thesimulated annealing algorithm available in another conservation planning software platform,MARXAN, offers a more complex consideration of penalties and costs associated withmeeting conservation targets and minimising cereal production costs. Chapter 3 finds that thebalance between the penalties for not achieving all biodiversity targets and those forexceeding the cereal cost thresholds in MARXAN are critical, impacting the achievement ofcertain biodiversity feature targets. Important penalties include the conservation featurepenalty factor, the cost threshold, and the cost threshold control parameter. MARX.ANgenerates numerous solutions for a single problem, providing a measure of a site's selection frequency over a number of runs. The central eastern region has highest variability inselection frequency where both cereal production and biodiversity irreplaceability are high.As cereal production targets increase, sites in this region become more difficult to avoid andtrade-offs are unavoidable.Comparing the software, chapter 4 concludes that the relationships between the inputsand planning parameters on outputs are crucial for effective conservation decision making. CPlan's sensitivities are restricted to the combination size and site selection rules. MAR.XANrequires numerous input parameters that collectively provide more variable outputs. Furtherdocumentation on best and current practices in MARXAN, sensitivities of conservationoutputs to input parameters, and awareness of these sensitivity in capacity building exercisesare required to guide decision makers. Irreplaceability allows the comparison of two differentobjectives and the potential trade-offs that might exist. Explicit inclusion of cereal productionpotential into systematic conservation planning frameworks generates more cost effective andsocially acceptable reserve solutions that strengthen the partnership between conservation andcivil society.Key Words: conservation planning, biodiversity, cereal production, irreplaceability, tradeojfs,opportunity costs, MARXAN, C-Plan.

[发布机构] Stellenbosch University