The Restoration of Degraded Landscapes along the Urban–Rural Gradient of Lubumbashi City (Democratic Republic of the Congo) by Acacia auriculiformis Plantations: Their Spatial Dynamics and Impact on Plant Diversity

Abstract

This study examines the spatio-temporal dynamics of Acacia auriculiformis in Lubumbashi city, southeastern Democratic Republic of Congo, in the context of rapid urbanization following the liberalization of the mining sector. The city has experienced significant demographic growth and unplanned spatial expansion, resulting in a decrease in vegetation cover. The introduction and proliferation of A. auriculiformis, an exotic tree species, have occurred without strategic planning or monitoring. Utilizing digitized remote sensing imagery from 2006, 2014, and 2021, we quantified the expansion of A. auriculiformis along the urban–rural gradient. Additionally, a floristic inventory conducted in 2021 provided insights into tree diversity within A. auriculiformis plantations. Our findings indicate a substantial increase in the number and area of A. auriculiformis patches, predominantly in urban zones. However, the patch values, highest in 2006, were shown to decline by 2021, especially in urban areas. The floristic inventory identified 39 tree species within A. auriculiformis plantations, including predominant species such as Albizia lebbeck, Albizia alba, and Leucaena leucocephala. Notably, 20 of these species are exotic, with half being invasive. In contrast, the 19 indigenous species were primarily found in peri-urban areas. While a greater number of tree species were observed in urban zones, larger average diameters were recorded in peri-urban zones. The persistence and expansion of A. auriculiformis in a landscape characterized by declining tree cover suggest its potential sustainability in this setting. However, A. auriculiformis plantations have facilitated the establishment of predominantly exotic and potentially invasive species. These findings highlight the need for the strategic management of A. auriculiformis and associated exotic flora to mitigate their spread and to consider their role in the restoration of degraded lands.