Turkish Journal of Forestry (Jun 2025)
Spatio-temporal analysis of vegetation dynamics in derived savannah, Ogun State Nigeria from 2002 to 2023
Abstract
Vegetation covers is a significant component of biogeochemical cycles. Derived savannah of Ogun State has been affected by vegetation loss and climate change in recent times. There is lack of information on the rate/extent of vegetation loss in the last two decades. This study assessed changes in vegetation cover in derived savanna ecosystem of Ogun State from 2002 to 2023. Landsat images were downloaded from the repository of the United States Geological Survey (USGS). Composites of red, green, blue and near-infra-red spectral bands of study period were obtained and classified using Maximum Likelihood (ML) algorithm into Land Use Land Cover (LULC) categories as follows: bare soil; built-up areas; forest; and grassland. Change in area extent and rate of change of area of classified images were determined for the study period. Confusion matrix of classified images were generated and compared with Google Earth satellite image with accuracy assessed using kappa coefficients. Overall accuracy of the classified images ranged between 79% and 88% with kappa coefficients of between 0.71 and 0.83. Results showed that built-up area increased from 10.3% cover in 2002 to 35.9% cover in 2023. However, there was a significant decline in forest cover from 31.5% to 13.7% for the same period. Significant increase at 4.2 km2 per year in area extent was observed for built-up LULC class while a decline of 2.0 km2 per year in forest cover was recorded for Forest LULC category from 2002 to 2023. The study revealed that urbanization increased as extent of initial forest cover were degraded and replaced with physical infrastructure. Therefore, there is urgent need for policies that promote conservation and sustainable management of forests and grasslands, as well as measures to promote green infrastructure and urban greening initiatives to address the decline in vegetation cover in the derived savanna ecosystem of Ogun State.
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