TITLE:
Success Indicators of Progressive Ecological Rehabilitation of Sites around a Tropical Highland Open Pit Mine
AUTHORS:
Lefranc Busane Basima, Jean-Berckmans Bahananga Muhigwa, Alfred Kabagale Cubaka
KEYWORDS:
Mining, Ecological Rehabilitation, Plant Growth Pattern, Soil Improvement
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.13 No.4,
April
25,
2025
ABSTRACT: The plant species involved in the progressive rehabilitation around the Twangiza open gold mine in DR Congo were inventoried to establish their abundance and diversity. Their spatial growth patterns were mapped and described through NDVI on a 10 m Sentinel satellite imagery. Field data collection was based on transects and relevés. Soil physico-chemistry was evaluated. Multivariate cluster analysis was computed to describe associations. Tree species were planted in 2012 on barren land. Five years later, in 2016, the very dense vegetation class already reached 10.8% and a twofold increment in 2023 (22%). The moderately dense vegetation category was already very high in 2016 and similarly in 2023 (24.1% - 25.9%). Results show that Brachypodium retusum, Muhlenbergia capillaris, Cynodon dactylon, and Melastoma malabathricum were the most frequent herbaceous plant species (5% - 10% cover). Among the planted trees, the highest cover was performed by Pinus patula (30%). Casuarina equisetifolia and Grevillea robusta achieved about 10% - 12% cover. Hagenia abyssinica, a native plant, was among the species that achieved a moderate cover. Prunus africana, Jacaranda mimosifolia and Acacia mearnsii achieved a relatively lower cover. Ficus thonningii is the largest tree (max 280 cm collar diameter). Acacia melanoxylon and Maesopsis eminii were large trees as well (163 - 175 cm). The tallest trees were respectively Maesopsis eminii, Cedrela serrulata and Acacia melanoxylon (35 - 45 m) followed by Ficus thonningii. Among the shrubs, the highest cover was achieved by Erica scoparia (26%) followed by Sambucus canadiensis, Pycnostachys erici-rosenii, Blechnum cordatum, and Quercus lusitanica. The vegetation encountered at Twangiza during the baseline study back in 2008 was generally disturbed and secondary. Evidences of soil improvement are given too: Organic carbon, total nitrogen, exchangeable magnesium, absorbable potassium, exchangeable sodium, calcium and absorbable phosphorus are strongly boosted. Animal recolonization is successfully proven separately (Basima et al., 2025a). Grazing land for cattle is the main ecosystem service in the rehabilitated zone (66%). Most cattle are composed of cows, goats and ships which graze on grass (Muhlebergia capillaris, Cynodon dactylon, Brachypodium retusum) that was planted for erosion control and soil cover as part of the rehabilitation exercise from the vicinities.