Parkland Trees under Severe Drought: An Assessment of Species Diversity and Abundance across Three Agroecological Zones of Northern Nigeria

The appraisal of tree stand structure on parklands is crucial for sustainable agroforestry management decisions, particularly in the drylands of Nigeria. An assessment of tree species distribution in farm plots across the three driest Agroecological zones (AEZ) within Northern Nigeria was performed to determine diversity and abundance in a changing climate. The AEZ include Sudan savannah (SS), Northern Guinea savannah (NGS) and Southern Guinea savannah (SGS). In each AEZ, 3 transects were laid per village and a total of 4 sample plots were located along each transect. Tree bole diameter of all the sampled woody perennials with dbh ≥ 10 cm was measured and identified to species level. The measurement and computation include basal area, species relative density and dominance as well as the important value index (IVI). Results showed that across the AEZs, Parkia biglobosa trees had the highest IVI but reduces from the driest zone, SS (50.25%) through the transitional zone, NGS (38.45%) to the wettest AEZ, the SGS (35.43%). The lowest IVI recorded were in Gliricidia sepium (0.62%), Psidium guajava (2.89%) and Eucalyptus camaldulensis (1.83) in the SGS, NGS and SGS respectively. Parkia biglobosa and Mangifera indica dominated the landscapes and are classified as the landscapes’ habitat generalists. Despite the low organic matter content, Sudan savannah had more diverse species on its farm landscapes than the two other AEZ but with less tree popuplation density. The potential contribution of agroforestry parkland trees to agrobiodiversity in reducing drought and improving soil fertility is essential for sustainable agricultural productivity and landscape restoration.