Performance of Tree Species Growing on Tailings Dam Soils in Zambia: A Basis for

Abstract: To facilitate the development of the basis for the selection of plants for re-vegetating tailings in Zambia, an as sessment of the performance of tree species growing on tailings dams was conducted. The performance of species was determined in terms of relative density, frequency and importance value for each species. The study reveals variations in performance of species; for example in terms of importance values, Acacia polyacantha (33.5%), Toona ciliata (21.4%), Acacia sieberana (9.9%), Bauhinia thonningii(9.1%) and Peltophorum africanum (8.3%) were the most dominant species. The dominance of these species on tailings dams demonstrates tolerance to tailings dams conditions. The study recommends that emphasis must be placed on these species in re-vegetating tailings dams.

Key words: Tailings, tree performance, re-vegetation, importance values.

1. Introduction

Most of the abandoned mine tailing sites in Copperbelt remain un-vegetated for extended periods of time and are subject to eolian dispersion and water erosion. As the viability of mines begins to decline, mine closures and the liabilities associated with mine closure become more and more eminent. One of the liabilities is the re-vegetation of areas with tailings. The use of vegetation to stabilize metal mine wastes impacted areas has been attempted in many parts of the world with both failures and successes [1-3]. Other studies [4, 5] have reported specific plant species with a high degree of resistance to metal toxicity. Metal tolerance tends to evolve in some members of common species found growing on mineralized soils[6]. These individuals may adapt internal mechanisms which may either limit the uptake of metal ions or detoxify these ions within their tissues [7]. The use of plants through either natural or artificial re-vegetation in stabilizing tailings dams have been employed in the zambian Copperbelt region. However, no studies have been made to determine the performance of these species on tailings dams. Such information would provide an understanding on how individual species develop on tailings sites which will in turn guide the species selection for re-vegetation of tailings dams. This study, therefore, aimed at developing an understanding of the performance of various tree species growing on tailings dam soils to guide species selection for use in rehabilitating tailings dams in Copperbelt. The key questions were: (1) what plant species grow on tailings? (2) What are the diameters of individuals of each plant species growing on tailings dams?

2. Materials and Methods

2.1 Study Area

The study was conducted on tailings dam No. 25 in

Nkana, east of Kitwe District, Zambia. The tailings dam which covers an area of about 105 ha was established between 1941 and 1946. It contains about 27 metrics of tonnes of tailings, which fall into either Sulphide ore or Oxide ore tails [8]. The site is of low nutrients and water retention capacity. 2.2 Data Collection

Five transects at 200 m from each other were established across the tailings dam. In each transect a number of 30 m diameter circular sample plots were established depending on the length of the transect. The sampling technique gave 20 circular plots. In each sample plot, both the heights and diameters were measured using the hypsometer and the calliper for each species.

2.3 Data Analysis

The collected information was used to determine: species list, ecological density, abundance, frequency, relative dominance, relative density, relative frequency, size class distribution for trees, and importance value of tree species. The importance value is defined as follows:

For plants of ≥ 5 cm Dbh IV = (RF + RD + RBA)/3 where:

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