Population Patterns and Environmental Determinants of Warburgia ugandensis (Sprague) in Northern Tanzania

Abstract

Warburgia ugandensis is a valuable medicinal tree native to East Africa, yet its populations are declining due to unsustainable harvesting and habitat degradation. Despite its ecological and socio-economic importance, there is limited information on its current population status and the environmental factors shaping its distribution across different landscapes in northern Tanzania. This study assessed the population density and distribution patterns of W. ugandensis across selected mountainous regions (Mt. Kilimanjaro, Mt. Ketumbeine, Mt. Monduli, Mt. Gelai, and Mt. Longido) in northern Tanzania, and determined how these are affected by land use, elevation gradients, and environmental factors. Data collection involved stratified random sampling across elevation ranges (1000–2500 m a.s.l), encompassing diverse land-use types (national parks, forest reserves, croplands, grazing lands, and settlements). Population density significantly varied among land-use types, with forest reserves showing the highest densities (6.485 ± 1.628 stems/ha), significantly higher than grazing lands (1.833 ± 1.369 stems/ha). Elevation positively correlated with density, where the highest elevations (2001–2500 m a.s.l) supported the greatest density (6.937 ± 1.837 stems/ha). GLM analysis highlighted that elevation, temperature, soil organic carbon, soil pH, and nitrogen significantly influenced W. ugandensis densities. Spatial mapping revealed population hotspots around Mt. Kitumbeine and Mt. Kilimanjaro, highlighting these as priority areas for conservation. Management strategies should prioritise high-elevation forest reserves, considering the critical environmental and soil parameters influencing W. ugandensis distribution.