An Eco-Physiological Investigation of Black Wattle in the Rietvlei Nature Reserve

Project Proposals for 2005 - Group G

The black wattle (Swartwattel, Acacia mearnsii) is an Australian native that was introduced to South Africa in 1864. The black wattle is an unarmed, evergreen tree that can reach heights of up to 30 m and which tends to form extended monocultures in large areas all over South Africa. Nowadays the distribution of the black wattle has expanded in such a way that it has become a major alien invader species, especially in the grassland and savanna biomes. Natural biodiversity, indigenous vegetation and agricultural land are now all threatened by the invasion of Acacia mearnsii. The black wattle also tends to colonize large areas of water catchments and natural river courses and has thus become a very important concern to the Working for Water Program in South Africa.

It is hypothesized that black wattles produce allelopathic chemicals that not only change the chemical composition of the soil and affect the abiotic environment underneath the tree canopy, but also inhibit seed germination and seedling growth.


  1. Does the black wattle produce allelopathic chemicals?
  2. Do these allelopathic compounds change the chemical composition of the soil?
  3. Is seed germination and seedling growth affected by these allelopathic chemicals?
  4. Should the Working for Water Program remove a stand of black wattles, what would the regeneration potential and restoration success of natural vegetation be in that area?

Project Outlay

  1. Fieldwork:
    1. Visit Rietvlei Nature Reserve to collect field data.
    2. Field data include the investigation of the habitat in which the black wattle occurs (ecology), a comparative study between the invaded and natural grasslands (species diversity), and the collection of plant material for laboratory analyses.
    3. Soil samples are collected to determine the influence of allelopathic compounds on seed germination and seedling emergence rates in both the black wattle and the natural grassland sites.
  2. Laboratory work:
    1. Plant extracts are made to examine the chemical composition and test for allelopathic compounds.
    2. Seed germination and seedling emergence rates are investigated using the collected soil samples from the different sites.

Your results will provide knowledge on the restoration potential of natural grassland vegetation after removing black wattle monocultures from an invaded area.


  • Ms. Lizandé Kellerman
  • Ms. Angelique Joubert
Project Proposals for 2005

  Helga Nordhoff
  Last updated: 17 Januarie 2005