Edaphic and topographic gradients have differential influence on woody species assemblages on serpentine and non-serpentine soils in an African Savanna

Abstract

Abstract Background and aims Understanding the determinants of plant species associations on unique serpentine substrates is crucial for restoration ecology yet understudied. We investigated the influence of local edaphic and topographic gradients on woody species associations on serpentine and non-serpentine soils along the Zimbabwe great Dyke. Methods Vegetation attributes were assessed in 62 plots located on serpentine and adjacent non-serpentine patches at varying slope magnitude and orientation. Plant community comparisons and relationships with soil and topographic variables were analyzed using ANOVA and ordinations. Results Aspect had more influence on woody composition, species associations and densities on- compared with off-serpentine soils. Lower species richness, tree/shrub densities were observed on-serpentine than non-serpentine patches. Soil Mg, Mg/Ca ratio, total Ni, Cr and Mn, and available Ni were significantly higher on-Serpentine than off-serpentine patches. All parameters (pH, Ca, Mg, Mg/Ca ratio; available Ni, Cr, Mn and total Mn) were similar between Serpentine east- and west-facing slopes, but only total Cr and Ni were higher on east-facing slopes. Only available Ni and Mn were higher on Serpentine piedmont than on slopes. Tree/shrub density and species richness were positively correlated to available Mn and Cr while negatively correlated to total and available Ni, pH, Mg/ca ratio and herbaceous plant cover. Conclusion Vegetation patterns on serpentine substrates are partly driven by intra-site edaphic (metals and Ca/Mg ratios) and topographic gradients. Aspect has differential influence on woody vegetation assemblages on serpentine and non-serpentine substrates. Combinations of species and environmental determinants observed can be used in mine site rehabilitation planning.