Floristic Checklist and Conservation Status of Woody Species in Relation to Gradient in Osomba Hills of Cross River National Park, Nigeria

Abstract

Extant floristic data checklist and conservation status of woody species were determined in relationship with elevation gradient in Osomba hills of the Cross River National Park, Oban division. A total of 78 species of woody plants in 31 families were identified. The family Fabaceae recorded the highest number of species (13) followed by Malvaceae with 8 species, Annonaceae and Euphorbiaceae had 6 species each, Apocynaceae had 5 species, Irvingiaceae, Ochnaceae, and Olacaceae had 3 species each, Buseraceae, Clusiaceae, Combretaceae, Ebenaceae, Moraceae, Myristicaceae, Rubiaceae and Sapotaceae had 2 species each, Anacardiaceae, Anisophylleaceae, Asteraceae, Bombacaceae, Cecropioaceae, Gentianaceae, Hyperiaceae, Lecythiddaceae, Meliaceae, Passifloraceae, Polygalaceae, Rhizophoraceae, Rutaceae, Simaroubaceae and Violaceae had 1 species each. The investigation of the conservation status of the species using the IUCN redlist data revealed that 1 species (Berlinia korupensis Mackinder& Burgt) is critically endangered (CR), 6 species are near threatened (NT), 7 species are vulnerable (VU), 7 species are not evaluated (NE) and 54 species are of least concerned (LC). Life forms identified included 14 shrubs and 64 tree species in the study area. In the dry season, a total of 29 species including 5 shrubs and 24 trees were identified, while in the rainy season, a total of 57 species including 10 shrubs and 47 trees were identified. Plant diversity along elevation gradient was generally heterogeneous and could be influenced by many factors such as climate, spatial heterogeneity, biotic processes, and evolutionary history. Overall species richness of both shrubs and trees decreased along the elevation gradient whereas the tree species increased with the elevation. Anthropogenic factors and accessibility to the mountainous terrain could also contribute to the patterns of the plant diversity and tree community structure in the study area. Common anthropogenic activities observed were timber harvesting, firewood collections, and harvesting of plants for food and medicinal uses.