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.
