Land-use patterns and plant community structure in the peri-urban environs of Lokoja, Kogi state, Nigeria: an integrated field and NDVI assessment, 2015 to 2025

Abstract

Rapid urbanisation is transforming natural vegetation on the fringes of medium sized Nigerian cities, yet the flora of these zones is rarely documented. This study assessed plant community structure in relation to land use in the peri-urban fringe of Lokoja, Kogi State, by combining field surveys at three sites, namely Zango, Ganaja and Banda, with a dry season Landsat 8 NDVI record spanning 2015 to 2025. Along one transect of 2 km at each site, trees and shrubs were counted in twenty plots of 10 m by 10 m and herbs and grasses were recorded with a point intercept frame of 1 m by 1 m on six visits, in April to June and October to December 2025. Shannon diversity and Pielou evenness were calculated, area normalised densities of each growth form were compared among sites by one way analysis of variance with the Duncan test, differences in composition were tested by permutational multivariate analysis of variance on Bray-Curtis dissimilarities, and NDVI trends were tested with the Mann-Kendall test and the Sen slope estimator. Seventy four taxa were recorded, comprising 13 trees, 8 shrubs, 14 grasses and sedges and 39 herbs, in 31 families. Woody plants averaged 187 stems per hectare, and two introduced trees, Cassia fistula and Azadirachta indica, made up 71 percent of tree stems, while the herb layer was dominated by ruderal species such as Hyptis suaveolens and Cynodon dactylon. Ganaja was the richest and most even site, with 44 taxa, a Shannon index of 3.19 and an evenness of 0.84; Banda had the fewest taxa at 24 and Zango the lowest evenness at 0.71. Tree and herb densities differed among sites, at p = 0.004 and p < 0.001 respectively, whereas shrub and grass densities did not. Composition differed clearly among sites, with a pseudo F of 7.19, an R2 of 0.49 and p = 0.001. Across the eleven year record, moderate vegetation condition covered between 69.1 and 87.6 percent of the land area in every year and no monotonic trend in dry season NDVI was detected. The findings indicate a flora already reshaped by disturbance, in which the dominant woody component is introduced and the herb layer is ruderal, and in which compositional difference between neighbouring sites is large.