The unique vegetation of the Southeastern DRC

The Copperbelt, a geological and pedological anomaly

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

The katanga copper belt

The Copper Flora, a vegetation on extreme soil conditions

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):

  • Excluders only tolerate metals in the substrate by restricting the uptake of metals into the root and tissue. The majority of metallophytes are excluders.
  • (Hyper)accumulators present specialized mechanisms allowing them to accumulate or even “hyperaccumulate” metals in their above ground biomass (mainly leaf cells) at concentrations that can exceed 2 % of their dry weight.

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.

Copperbelt Ecosystems

legend plant communities

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.

Species diversity and endemism in Cu-Co communities

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).

Species diversity

Among the 56 endemic taxa:

  • 32 are strict endemic or absolute metallophyte: All individuals of these taxa occur on Cu/Co rich soils. Most of these taxa are found in the Steppes or in the metal-rich Steppic savanna.
  • 24 are broad endemic or facultative metallophyte: More than 75% of the populations of these taxa occur on Cu/Co rich soils. These taxa constitute mostly the steppic savanna.

Why a vegetation can develop on metal-rich soils?

This question is related to evolution ecology. After Kruckeberg (1984), the process of new species creation on metal-rich soil takes several generations.

  • The species occurring on normal soil (non-tolerant species - Species 1 on figure) produce individuals in which some are preadapted to higher concentrations of metals in soil than other ones and are reproductive (i.e., can accomplish all the plant life circle).
  • These individuals continue to colonize the metal-rich and produce descendants that are able to tolerate the soil conditions. Due to their ability, descendants constitue new population than have distinct habitat conditions (metalliferous soils) than the Species 1 but are always interbreedable (= ecotype).
  • After some generations, both populations (Species 1 and the new one) cannot be crossed and evolve distinctly (in genetic point of view). A new species or taxon, metallophyte is created (Species 2).

Speciation process

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.

Speciation process


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).

natural sward

C) Sward on mineralized rock debris (~10000-100000 ppm): secondary habitat colonized by cuprophytes and where copper-cobalt concentrations are extremes.

secondary sward

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:

  • On soils from Kalahari sands located in the high plateau (Marungu, Biano, Kundelungu, etc.) in DRC.
  • On dembos which are flat valleys, poorly drained and situated at the head of streams.
  • On copper-cobalt deposits from the Katangan Copper Arc and from the Zambian copperbelt. The number of cuprophytes is lower than in the natural sward. Three types of steppic savanna may be distinguished according to their position on copper-cobalt sites:
  • The summit steppic savanna: on the summit of bare hills, in cases of absence of rocky crest.
  • The slope steppic savanna: the most frequent.
  • The dembo steppic savanna: on the hill’s piedmont where the metal contamination extends to the edge.

steppic savanna

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.

Steppe on rocky outcrops

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.

chasmophytic vegetation

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.

uapaca fringe

J) Transition shrub savanna (~500 ppm): edge habitat with diverse species of shrubs where the last cuprophiles can be found.

transition savanna

K) Miombo open forest (~50 ppm)