Small-scale diversity of plant communities and distribution of species niches on a copper rock outcrop in Upper Katanga, D.R.Congo

Edouard Ilunga wa Ilunga,Michel-Pierre Faucon,Gilles Colinet,Pierre Meerts,Grégory Mahy,Maxime Séleck

doi:10.5091/plecevo.2013.816

Abstract

Background and aims – In Katanga (D. R. Congo), outcrops of bedrocks naturally enriched in Cu and Co ("copper hills"), host unique plant communities. The spatial variation of vegetation has long been attributed almost exclusively to variation in Cu concentration in the soil, but this assumption has not been experimentally tested. We analysed the variation in plant communities and the niches of selected species in relation to edaphic factors within a copper hill. Methods – Forty-eight 1 m 2 plots were sampled for plant community and soil mineral element composition, and classified with Unweighted Pair Group Method with Arithmetic mean (UPGMA) using the Bray-Curtis distance. Plant-edaphic relationships were examined using a Canonical Correspondence Analysis (CCA). Species niches were modelled with Generalized Additive Model (GAM). Mean edaphic factors between the soil of plant communities were compared with one-way Kruskal-Wallis non-parametric ANOVA. Key results – The diversity of communities at the site scale was higher than observed in previous studies at a larger scale. Cu was the most discriminating edaphic factor of plant communities. However, detailed comparisons of mean edaphic factors among communities revealed individual combinations of edaphic parameters for each community, as well as differences in soil Cu content. High covariation appears to be an essential trait of the edaphic factor variation of Katangan Cu-rich soils. This makes it difficult to examine separately the effect of these factors on plant community structures. A bimodal pattern of niche distribution was found for Cu and pH. For physical parameters, niche optima were normally distributed. Conclusions – Global variation in edaphic factors associated with variation in combinations of edaphic parameters generates a highly heterogeneous environment favourable to a high diversity of plant communities over limited areas. Conservation strategies or restoration actions to limit the impact of mining activities on Cu-enriched ecosystems should pay special attention to recreate heterogeneity, taking into account the covariation of edaphic factors.

Highlights

Identification of the factors that control the distribution and abundance of plant communities is a central problem in ecology, which can be addressed at all spatial scales, ranging from continental scales to patchy or highly restricted microhabitats (Keddy 2007)
We address the degree to which small-scale continuous edaphic gradients can contribute to plant assemblage diversity and the consequences for restoration of metallophyte vegetation
The variables that best correlated with PCA1 were Cu, pH KCl, N, C, Zn, Cd, Ca, Pb and P and the variables best correlated with PCA2 were % rock cover,% stones in soil and Co and K, Fe and Mg

Summary

Introduction

Identification of the factors that control the distribution and abundance of plant communities is a central problem in ecology, which can be addressed at all spatial scales, ranging from continental scales to patchy or highly restricted microhabitats (Keddy 2007). Throughout the world, metal-rich soils host highly distinctive plant communities that result from deterministic species selection by environmental filters and random processes in insular habitats (Ernst 1974, Kruckeberg 1984, Bergmeier et al 2009, Bes et al 2010, Saad et al 2012). Small scale variation in edaphic conditions in metalliferous sites have been demonstrated to affect physiological and evolutionary process (Malaisse et al 1983, Bizoux et al 2008, O’Dell & Rajakaruna 2011, Yost et al 2012), species distribution (Rajakaruna 2004) and, variation in plant assemblages (Ernst 1974, Bizoux et al 2004, Tsiripidis et al 2010)

Objectives

Methods

Results

Conclusion