Measuring conservation value at fine and broad scales: implications for a diverse and fragmented region, the Agulhas Plain

摘要

This study explores the implications of spatial scale for conservation planning in the Agulhas Plain, South Africa. Regional planning relies on broad-scale data but fine-scale data are usually required for implementation at local level. This study addresses the implications of broad-scale planning for fine-scale implementation. Two original systems of notional reserves were developed for this region using C-plan, a decision support system for systematic conservation planning. The first conservation plan was derived using broad scale data (1:250,000) and consisted of nine broad habitat units (land classes based on topography, geology, and climate), remote sensing mapping of habitat transformation and large-planning units defined by 1/16th degree squares (average size 3900 ha). The second system was identified at a finer scale (1:10,000) using 36 vegetation types (mapped in the field), ground survey mapping of habitat transformation and cadastral boundaries as planning units (average size 252 ha). Using classification trees, this study compared reserve-design efficiency (the area required to achieve conservation targets), the spatial patterns,of conservation value (the irreplaceability value of planning units), biodiversity features, and habitat transformation at both scales. A similar amount of land was required to meet all conservation targets (identified using minimum set analysis) at the broad and fine scale. There was considerable overlap between the two conservation plans as most of fine-scale conservation targets could be achieved under the broad-scale conservation plan. However, irreplaceability values, which measure the likelihood of selecting planning units for achieving representation targets, were much higher at the fine scale. The use of broad-scale biodiversity features underestimated irreplaceability value at a fine scale in heterogeneous and fragmented portions of the landscape. The implications of moving from broad- to fine-scale conservation planning, as well as their respective benefits are discussed. Maximising biodiversity conservation while minimising cost and resources might be achieved by a combination of broad-scale assessments for relatively homogeneous and untransformed areas and fine-scale ones for heterogeneous and fragmented areas.