The Copperbelt is studied for fifty years. This area represent a significant curiosity in geological and pedological point of view. It extends from the Democratic Republic of Congo (before the Kundelungu) to the North of Zambia. Successions of geological eras permit at the highest mineralized rocks (normally at hundred kilometers depth) to be at earth surface. Several rocks units contribute to the diversity of geological formations an contains notably, carbonates, sulfurs, silicates, grey and clay. Metals are commonly linked with carbonates and sulfurs.
This geological history is responsible of the presence of high concentration of metal (total and available) in soil, notably Cu, Co, Mn, Zn and U.
The Upper-Katanga (Democratic Republic of Congo) includes some of the largest ore bodies of copper and cobalt in the world. This area of 50 km large extends from Kolwezi to Lubumbashi (300 km) and named The Katangan Copperbelt
Basically, few plant species are able to tolerate more than 1000 ppm of available Cu or 100 ppm of avalable Co in soil. Metals, when they are absorbed by roots in excess, disrupt the mechanisms of cells. Taxa or species able to tolerate metal concentrations a higher threshold than other is called a metallophyte. Two tolerance strategies can be identified for metallophyte (Baker, 1987):
Flora of the katangan Copperbelt includes metallophytes. The ore comes to the surface in open deciduous forest (Miombo woodland) in the form of hills covered by herbaceous vegetation. Soil covering ores of the hills present high levels of metals concentration (Available [Cu] in soil exceeds 10.000 ppm and [Co] 1.000 ppm). This flora is stable for thousand years like tropical forests (Veldman et al. 2015).
At the landscape scale, plant communities are scattered in the open deciduous forest (Miombo) and the spatial configuration of Cu-Co hills is of primary importance for Cu-Co species richness (A on figure below).
At hills scale (B and C on figure), Cu and Co concentrations are a primary determinant of plant species richness since vegetation varies in physiognomies on Cu-Co outcrops from the top to the bottom along a topographical gradient corresponding roughly to the Cu-Co gradient.
At the top of hills, chasmophytic vegetation colonize the cracks and fissures of low mineralized rock (i.e. with Cu concentration comprises between 250 and 900 ppm). Then steppe vegetation (C on figure) colonizes the upper part of the outcrop slopes with highest Cu soil concentrations (ranging from 3,500 to 10,000 ppm). Finally, steppic savanna vegetation (B on figure) develops on the intermediate and foothill slopes at the bottom of the outcrops, characterized by lower Cu soil concentration (i.e. with Cu concentrations varying from 100 to 3,500 ppm). The available concentration of Co in soil is ten lower than Cu.
These plant communities contain more than 550 recorded taxa having various tolerance to Cu or Co included in more than 60 families(Leteinturier et al. 2002). The half is available on the official eFlora. The Katangan copper hills are recognized as a hotspot for biodiversity with 10% endemism, or 56 endmic taxa (Faucon et al. 2010).
Among the 56 endemic taxa:
This question is related to evolution ecology. After Kruckeberg (1984), the process of new species creation on metal-rich soil takes several generations.
This kind of ecosystem presenting spots having Cu/Co-rich soil (i.e., hills), scattered in matrix with dominant vegetation is subject to strong selective pressure leading to distinctive flora with a great diversity of taxa, sub-species, variety and ecotype. Phenotypical variations between populations occuring on two distinct hills exists according to the taxa.
Due to their copper-cobalt toxicity and their geographical isolation, Katanga copper hills host highly distinctive flora and vegetation. The figure below represents a typical transect of vegetation on a copper hill where an increase of the total copper concentration is observed from down the slope to up the slope. On this figure, 11 habitats can be distinguished (10 + the miombo open forest).
A & B) The natural sward (~3500-10000 ppm): Open vegetation on colluvial soils, mainly made up of perennial grasses, Cyperaceae, annual and perennial dicotyledons with woody stump and monocotyledons with corms or bulbs. The sward is rich in cuprohytes reflecting the high contamination level of this habitat (on left)(3500-100 000 mg/kg). A variant is the natural Xerophyta sward with Xerophyta spp. as dominant species (on right).
C) Sward on mineralized rock debris (~10000-100000 ppm): secondary habitat colonized by cuprophytes and where copper-cobalt concentrations are extremes.
D & F) The steppic savanna or steppe-savanna (~1000-3500 ppm): closed vegetation characterized by the dominance of two biological types, i.e. caespitose grasses 50-100 cm high and dicotyledons with woody stems (geofrutex). This type of vegetation can be found on three types of ecological conditions:
E) The steppe on rocky outcrops (~600-900 ppm): this is a variant of the steppic savanna located on the crest in between compact siliceous rocks (RSC, RSF) and composed of grasses, suffrutex and little scrubs.
G) The chasmophytic vegetation on rocky outcrops (~250-900 ppm): vegetation made up of plants growing in low mineralized rocks (RSC), rooted in the crevices.
H) The shrubs on rocky outcrops (~250-800 ppm): dense vegetation located on the crest, made up of little trees, shrubs and scrubs, high grasses and suffrutex.
I)Uapaca fringe (~500-1000): edge habitat showing the limit of the copper-cobalt contamination and where the shrub Uapaca robynsii is dominant.
J) Transition shrub savanna (~500 ppm): edge habitat with diverse species of shrubs where the last cuprophiles can be found.
K) Miombo open forest (~50 ppm)
