Survey of Invasive Plant Species and Their Ecological Impacts in Sambisa Forest Reserve, Borno State

Biological invasions by non-native plant species represent an escalating but underappreciated threat to the ecological integrity of Nigerian forest reserves, particularly in areas subject to past disturbance and reduced management attention. Sambisa Forest Reserve in Borno State has experienced prolonged management disruption, creating conditions potentially conducive to invasive plant establishment. This study surveys the distribution, abundance, and ecological impacts of invasive and naturalised alien plant species within accessible sections of Sambisa Forest Reserve. Belt transects were surveyed across five habitat types within the reserve, with all non-native species identified, mapped, and assessed for cover and frequency. Species origin and invasion history were verified through herbarium records and published checklists. Impact assessments were conducted for the three most abundant invasive species using paired native-invaded and uninvaded plots to compare native plant richness and cover. A total of 28 alien plant species were recorded, of which 14 are classified as invasive. Chromolaena odorata showed the most extensive distribution and was associated with a 54% reduction in native herbaceous species richness in invaded plots. Prosopis juliflora dominated degraded woodland fringes near water points. Invasion intensity was highest along roads and in areas with documented historical disturbance. The study recommends targeted mechanical and chemical control programmes for Chromolaena and Prosopis as priorities, integrated with post-conflict forest restoration planning. Keywords: invasive plants, Chromolaena odorata, Sambisa Forest, biological invasion, restoration