Developing a Multi-Criteria Decision Framework for Forest Protected Area Network Expansion in Nigeria

Nigeria's protected area network is widely acknowledged as inadequate in both coverage and representativeness, yet formal frameworks for prioritising network expansion that integrate biodiversity data, ecosystem service values, social equity, and cost-efficiency into a transparent decision process have not been developed for the Nigerian context. This study develops and validates a multi-criteria decision framework for forest protected area network expansion in Nigeria, integrating spatial biodiversity data, ecosystem service mapping, social equity considerations, and land tenure analysis. Biodiversity data included species distribution models for 320 forest-specialist species modelled under current and 2050 climate projections. Ecosystem service layers for carbon storage, watershed protection, and non-timber forest product provisioning were derived from InVEST modelling outputs calibrated against field-collected data. Social equity criteria incorporated indigenous land claim mapping, community forest dependence indices, and conflict risk scores derived from historical land tenure dispute records. Cost estimates for gazette process, management, and community compensation were developed for 1,200 candidate expansion parcels. A Marxan with Zones optimisation algorithm identified efficient protected area network expansion portfolios under alternative weighting scenarios for the four criteria categories. The biodiversity-optimal solution requires designation of 6.3 million hectares of additional forest, primarily in the Oban-Obudu corridor and the Middle Belt forest mosaic. Incorporating equity constraints reduced biodiversity return by 11% while improving social legitimacy scores by 43%. The study presents an operational toolset directly applicable by the National Park Service and State Forestry Commissions to guide evidence-based expansion planning. Keywords: protected area expansion, multi-criteria decision analysis, Marxan, Nigeria, conservation planning