A MULTIPLICATIVE LANDSCAPE PRESSURE INDEX FOR DIAGNOSING URBAN SPRAWL IN A WEST AFRICAN SECONDARY CITY: THE CASE OF SAKI, NIGERIA

Abstract

Secondary cities in Sub-Saharan Africa are expanding rapidly, yet diagnosing ecological consequences is difficult due to limited spatial data and analytical capacity. We present an integrated approach combining a multiplicative Landscape Pressure Index (LPI) with landscape metrics to identify synergistic stressors in a rapidly urbanizing secondary city. We apply it to Saki, Oyo State, Nigeria, a representative West African settlement within the Guinean Forest-Savanna mosaic. Using Landsat imagery (2013-2021) and CA-Markov projections to 2025, we quantified urban sprawl, vegetation fragmentation, and their spatial coupling. Results reveal heterogeneity in sprawl-population dynamics, with the western trade corridor experiencing the highest relative pressure (LPI = 0.78 in 2013 to 1.00 by 2025). We found no support for a widely assumed 30% nonlinear fragmentation threshold; fragmentation rates decelerate as built-up cover increases. The LPI mapped persistent hotspots along cross-border trade routes, though the "speculative eastern periphery" remains an untested hypothesis because land-tenure and vacancy data are unavailable. Because spatial units were too few for reliable local regression, the analysis is limited to LPI, landscape metrics, and descriptive statistics. For policy, findings provide spatially explicit evidence for moving beyond uniform zoning in Saki while identifying implementation barriers: limited municipal capacity, funding constraints, land-tenure complexity, and weak enforcement. The LPI workflow offers a replicable, low-cost toolkit for planners in other data-scarce Nigerian cities. The LPI measures relative landscape structural pressure, not ecological health; future work must validate it against field data.