Detection of Seasonal Trends in Vegetation Cover in Kogi State: Guinea Savannah Region of Nigeria Using Time Series MODIS NDVI Data

摘要

Natural vegetation is an important source of livelihood for rural communities living in the savannah region of Nigeria. Apart from the direct benefit derived from vegetation exploration, vegetation also is of vital importance in environmental processes such as protecting soil against erosion and maintaining the carbon cycle. Due to human perturbation and inherent climate variability, there has been an increasing decline in vegetation productivity over the last decades in the guinea savannah region of Nigeria. Hence, there is an urgent need to carry out research on seasonal trends of vegetation pattern using reliable techniques, especially in Nigeria where population is growing at a fast rate, and the dependency on vegetation for means of livelihood is high. This paper analyses the trends in vegetation greenness in Kogi state, Nigeria, using seasonal trend analysis (STA) to extract information from the monthly MODIS NDVI (Terra) data from 2000 to 2010 in four different locations. The results show considerable variations in the period of greening (start and end of greening) from the four different locations in Kogi state, a situation which implies that there is a shift in vegetation types in this ecological zone. This is taken to be a consequence of human interference due to the pattern of agricultural intensification and urban expansion over the years. Although, seasonal trend analysis is a robust means of analyzing trends in vegetation, this paper suggests that other indicators such as soil aridity, climatic data and land-use pattern should be included for further analysis in order to uncover human-induced loss of vegetation cover in the guinea savannah region of Nigeria.