GEOSPATIAL ASSESSMENT OF URBAN GREEN INFRASTRUCTURE IN YENAGOA, BAYELSA STATE, NIGERIA

Abstract

The rate of urban green infrastructures degradation is increasing rapidly in most countries of the world, especially in developing countries like Nigeria. Thus, this research is aimed at assessing the pattern, distribution and characteristics of urban green infrastructures (UGIs) in Yenagoa with a view to enhance green space planning and management for sustainable city development. The objectives were to evaluate the pattern of urban growth in Yenagoa between 1989 and 2016, assess the characteristics of urban green infrastructures in Yenagoa and predict the status of urban green infrastructures in Yenagoa by 2030. This study made use of both field measurement of vegetation parameter (names of sampled trees, their height and diameter at breast height) and three multitemporal Landsat Satellite imageries for the years 1989, 2002 and 2016. The images were preprocessed and classified into four categories (builtup areas, vegetation, bareland and waterbody). The pattern of urban growth in the study area between 1989 and 2016 was evaluated using Maximum Likelihood classification algorithm. Also, the characterization of Urban Green Infrastructures (UGIs) in the study area was mainly base on an on-site identification of individual species name, measurement of height (>2m for trees) and diameter at breast height (1.35m above ground level). The result obtained from the classification of the imageries was then used as basis to predict the landcover of 2030 using Markov chain and Cellular automata in Idrisi Selva software. The study revealed that between 1989 and 2016, there was a significant decrease in vegetation cover in the study area, while builtup area increased steadily. In 1989, vegetation occupied a greater portion 106.51km2 (87.36%) of the total land area. By 2002, vegetation had decreased to 89.56km2 (73.46% of the total land area) and 42.11km2 (34.54% of the total land area) in 2016. Based on the field measurement of UGIs in the study area, a total of 333 individual trees belonging to 25 different genera were encountered identified in the 82 sample plots during the field work. Many important tree species were recorded, some of which are Mahogany (Khaya ivorensis), Iroko (Chlorophora excelsa), Afara (Guarea cedrata), Opepe (Nauclea dederrichii) etc. Finally, based on the major findings of the study, it was discovered that some of the observed threats to the structural characteristics of the green spaces in the study area are the increasing demand for land both for residential and commercial purposes and the rise in population. Thus, strategies aimed at improving urban green infrastructures conservation and management in the study area are urgently needed.