Climatic and soil integrant that drive forest tree species diversity and distribution across cross-river state, Nigeria

Awareness of the ecological needs of forest tree species is a necessity for effective and tenable forest management, conservation and restoration. Our study used the modified Whittaker sampling method to assess the diversity and distribution of forest tree species at twenty-two forest sites across northern, central, and southern Cross River State, Nigeria, and to analyse climatic and soil integrant that drive the diversity and distribution of tree species in forests. Only tree species with dbh ≥ 30 cm were identified and recorded. Tree species occurrence points were also marked using Global Positioning System (GPS) software. Maximum Entropy (MaxEnt) species distribution model and principal component analysis (PCA) for each zone were used to study climate and soil integrant that drive forest tree species diversity and distribution, respectively. The results of the survey revealed a great diversity of tree species in the forests, as 398 species belonging to 64 families were recorded. The maxEnt model established six climatic integrants that drive forest tree species diversity and distribution across Cross River State. These are ‘BIO 3 – isothermality’, ‘BIO 4 - temperature seasonality’, ‘BIO 7 - annual temperature range’, ‘BIO 12 - annual precipitation’, ‘BIO 16 - precipitation of wettest quarter’, and BIO 17 - precipitation of driest quarter. PCA revealed that the soil in the northern zone had seven main integrants (iron, Available Phosphorus, manganese, exchangeable cations, silicon, Hydrogen ion and organic matter); ten in the central zone (zinc, organic matter, iron, Total Nitrogen, Sodium, boron, clay, soil pH, exchangeable acids and silicon); and nine in the southern zone (sand, silt, Organic Carbon, Manganese, Hydrogen ion, Calcium, cation exchangeable capacity, Potassium and clay) that drive species diversity and distribution. Our findings can be used as rudimentary details for managing forest and ecosystem preservation at all levels and, characteristically, for forest conservation across Cross River State, Nigeria.