Assessment of the application of the mitigation hierarchy on a road improvement project in Western Uganda

Abstract

The mitigation hierarchy is vital for preventing and managing environmental impacts of infrastructure development, yet empirical evidence of its effectiveness in safeguarding biodiversity remains limited, particularly in developing countries. This study assessed the application of the mitigation hierarchy following upgrade of the 66 km Fort Portal-Kamwenge road, specifically the 13 km section traversing Kibale National Park in western Uganda. The objectives were to: 1) assess extent of mitigation hierarchy principle application; 2) analyze spatial-temporal land use and land cover changes along the road corridor; and 3) evaluate vegetation composition within the established road corridor. Data were collected using systematic vegetation surveys, multi-temporal LANDSAT satellite image analysis (2015, 2017, 2023), and comprehensive document review following PRISMA guidelines. Stratified random sampling established 36 plots (10m × 10m) at three distance strata (0m, 50m, 100m) from both road sides across six equal segments. ArcGIS was used to perform spatial-temporal LULC analysis within a 500m buffer zone of the road corridor within the national park. The Community Analysis Package was used for the Analysis of Similarity (ANOSIM) and Non-metric Multidimensional Scaling (NMDS). Vegetation community structure and diversity indices were analysed using R software. Environmental and Social Impact Assessment reports were reviewed to evaluate compliance with mitigation hierarchy requirements. Implementation was assessed using indicators derived from international standards (BBOP) and scored on a standardized numerical scale. Results showed differential implementation across mitigation hierarchy stages: complete avoidance and minimization (100% compliance), partial restoration (67%), and absent offset/compensation measures (0%), yielding 62% overall implementation. Land cover analysis revealed initial tree cover loss (-3.6%) during construction (2015-2017), followed by significant recovery (+4.9%) by 2023, with concurrent grassland expansion. Vegetation assessment documented 94 plant species from 45 families. There were no significant differences in species composition or woody stem density relative to road proximity, suggesting minimal road edge effects on forest structure eight years post-construction. These findings suggest that the mitigation hierarchy framework, when properly implemented, may contribute to biodiversity protection as indicated by the forest recovery and limited road edge effects on vegetation structure. We recommend prioritizing complete implementation of all hierarchy sequences, particularly establishing robust offset/compensation mechanisms and comprehensive restoration protocols, to achieve optimal environmental protection outcomes.