Mountains are fragile with diverse flora and fauna species habited in different Attitudinal Gradients (AG). Up-to-date information are lacking on flora species diversity and distribution in mountain forests ecosystem of southwestern Nigeria. Hence, this study assessed species structure along AG and Digital Elevation Modeling (DEM) of Idanre Forest Reserve, Southwestern Nigeria. The forest was stratified into three AG: Upper (>600m), Middle (301m-600m) and Base (≤300m). In each AG, data were collected from 25m x 25m Temporary Sample Plots (TSP) alternately laid along the AG. In each TSP, all living trees with diameter at breast height (dbh) ≥ 10cm were identified to species level and measured. The results from the study revealed that at the base gradient, there were high diameter at breast height (dbh) (81.4 cm), stem height (33 m), basal area (8m2/ha), volume (91m3/ha), aboveground biomass (121904.68kg/ha) and Albizia zygia as the most abundant species (14/ha). The DEM for the study area was produced from the elevation data using the interpolated natural neighbour algorithm of the Quantum Geographic Information System. At 50m between each extraction, topographic maps were retrieved from the DEM. The study area's elevation was found to vary from 226 m to 1030 m. Therefore, this study provided baseline information and tools for management of Idanre forest.
Key words: Altitudinal gradients, DEM, forest structure, Albizia zygia, Idanre forest