Realized niche of eight endemic plant species of Katangan Copperbelt (D.R. Congo): implications for copper species conservation

South of the Katanga province (D.R. Congo), a unique vegetation grows on soils developed on 100 Cu-Co outcrops among the most important in the world (katangan Copperbelt). These outcrops form of isolated hills in the landscape hosting vegetal communities evolving along the mineralization gradient. More than 600 metallophytes can be found in these communities with some 32 strict endemics solely known from mineralized soils. These species present physiological and biological adaptations allowing them to tolerate toxic levels of metals in soils. The unique characteristics of most endemics are seriously threatened by the intense mining activities in the region thus also threatening the high genetic potential to be used in development of polluted soils’ restoration strategies. In an effort to characterize the ecology of these species, we model ecological niches of eight endemic species along copper-cobalt gradients. For each species, three sites were prospected and transects set. Along these, five plots where the species occurred were selected: at both the extremities of the gradient and at 1st quartile, median and 3rd quartile. In each plot, individuals of the particular species were counted and composite soil samples collected. Available EDTA Cu-Co values were determined and niches modeled for both metals through the kernel density method in R 3.0.1 (package ‘vioplot’). Results show that ecological niches of the selected endemics are distributed between Cu-soil values of 50 and 11 000 mg.kg-1 and between Co values between four and 1500 mg.kg-1. Six species occur in the lower 100 mg.kg-1concentrations of Co. As for the Cu gradient, two species present ecological optimums over 3000 mg.kg-1. This variation of ecological niches along the gradients indicates a need of adequacy between species conservation strategies and soils’ metal contents. Four of the eight studied species should be conserved on soils contaminated with some 500 mg Cu.kg-1 and 30 mg Co.kg-1. For others, precise conservation actions need to be undertaken.