An Evaluation of the Changes in some Physiognomic Characteristics of Vegetation in Iseyin, in the Nigerian Guinea Savanna Belt

Abstract

This study examined physiognomic parameters affected by vegetation changes from 1984 to 2014 in Iseyin, Southern Guinea Savanna Belt of Oyo State, Nigeria. Ten plots of (10m by 10m) plots in size were randomly laid in selected farms, maturing guinea savanna and degraded plots for vegetation enumeration of species level. The results showed no significant differences (at ≤ 0.05) in the species diversity (Simpson’s species diversity) 0.8, 0.83 and 0.86 for the farms, degraded plots and maturing grassland areas, respectively. In the overall, tree height, girth, basal area, crown cover, tree abundance, species diversity and tree volume also varied with mean tree height, 4.31m- 4.60m; mean girth, 0.42m – 1.55m  ; 0.024m² -0.22m² , mean basal area; 19.1- 72.0%, mean crown cover; 1.60- 2.67, mean tree abundance, 0.80-0.86, and Simpson’s index of diversity and mean tree volume 1.8m³ – 10.4m³, respectively. The NDVI (Value of Normalised Difference Vegetation Index) indicated rapid fluctuations in the vegetation health status between 1984 (NDVI = -0.002), 2000 (NDVI = -0.12) and 2006 (NDVI = 0.07) and 2014 (NDVI = -0.09) have decreased significantly between 1982 and 2014
(F ≥ 23.3; p ≤ 0.05), it was -0.002 for 1984; -0.12 for 2000; 0.07 for 2006 and -0.09 for 2014. The study concluded that vegetation parameters that were affected as a result of vegetation changes were tree height, basal area, crown cover and tree girth.