A review of alternative cost layers for spatial prioritization tools

Systematic Conservation Planning (SCP) seeks to optimize biodiversity outcomes under real-world constraints, including limited financial and social resources. Integrating cost data into spatial prioritization tools is essential for effective conservation, yet current applications lack consistent guidance on the selection and use of cost metrics. This study aims to develop a structured roadmap for cost integration in SCP and assess how alternative types of cost data are used to inform spatial prioritization. We focus on the classification of cost metrics and the ways they are implemented and aggregated in spatial prioritization tools. We developed a structured roadmap for cost integration in spatial prioritization tools, based on a systematic analysis of 139 peer-reviewed studies. From these, we examined the alternative layers of information and aggregation methods used to achieve conservation targets. Costs were classified into two main categories: monetary (i.e. opportunity, acquisition, management, and transaction costs) and proxy metrics. Six proxy approaches were identified: area-based, distance-based, anthropogenic uses and activities, human pressures, ecological impacts, and other unclassified metrics. Aggregation methods range from single-layer to cumulative and multi-layer approaches. Cost inclusion often remains simplistic, overlooking synergies and uncertainties. Gaps include limited use of spatially explicit socio-economic and ecological data, aggregation methods, and metrics for emerging threats. This roadmap offers evidence-based guidance for cost selection and implementation in spatial prioritization tools, and insights that support more socially equitable and operationally effective conservation planning. Addressing current gaps will be critical to designing socially and ecologically sound conservation strategies in the face of climate change.