Urban land transformations and its implication on tree abundance distribution and richness in Kumasi, Ghana

Abstract

Despite the rapid urban transformation in green space in most cities in Ghana, knowledge on urban tree diversity and the evidence of the consequences of built-up expansion on trees is scanty. This article provides a novel contribution to the current urban trees abundance and richness in Kumasi Metropolitan Area, Ghana. Post classification change detection technique was applied to quantify urban land use land cover (LULC) transformations (urban forest, agricultural, riparian vegetation and built-up) from 2007 to 2017. Species rank abundance distribution and richness were quantified using geometric series and individual-based rarefaction models. A total of 858 individual trees belonging to 76 taxa were recorded across the four LULC classes. Species abundance distributions in three LULC types varied substantially, with the exception of riparian LULC (slope [k] 0.08660.12, v2P 19.42, P0.15). Land use pressure led to a 13.56km2 reduction in forest cover, while built-up and agricultural LULC increased by 31.13 and 1.85km2, respectively. These disturbances did not only affect indigenous tree dominance (41.3%) in favour of exotic species (58.7%) in the agricultural and built-up LULC types but also impacted on tree abundance (n126) and richness (n28) in agricultural land compared to abundance (n280) and richness (n67.86) in forest cover. Despite the contribution of LULC transformation to increase in tree diversity, there is the likelihood of future dominance of exotic species in the Metropolis if urban planners do not institute measures to conserve indigenous species.