The influence of Pechuel-Loeschea leubnitziae (wild sage) on grass sward and soil seed bank composition

  • MJ Tedder
  • KP Kirkman
  • CD Morris
  • WSW Trollope
  • MC Bonyongo

Abstract

Soil seed banks provide not only a historical record of vegetation composition but also the potential for post-disturbance revegetation. Pechuel-Loeschea leubnitziae (wild sage) is a multistemmed, aromatic shrub, occurring in Namibia, Botswana, Swaziland, Zimbabwe and the northern regions of South Africa, that colonises disturbed regions on sandy, alkaline soils. The influence of differing levels of P. leubnitziae cover on soil seed-bank characteristics and aboveground herbaceous species composition was determined by examining aboveground species composition, recorded in the field, and soil seed-bank species composition, determined by recording germinations from topsoil samples collected at each of 104 sites in the southern Okavango Delta. No correlation was observed between aboveground and soil seed-bank composition (p = 0.209). Cover of P. leubnitziae did not affect soil seed-bank species composition (p = 0.31) or the grass:non-grass ratio within the seed bank (p = 0.308). It did, however, affect aboveground grass composition (p = 0.018), with increasing P. leubnitziae cover associated with increasing abundance of poor-quality, shade-tolerant grass species. This confirms the observations that encroachment of P. leubnitziae may be associated with a decrease in veld quality and carrying capacity, and highlights the necessity for further study to facilitate a better understanding of the species for management purposes.

Keywords: Okavango Delta, rangelands, semi-arid savanna, shrub encroachment

African Journal of Range & Forage Science 2012, 29(3), 101–107

Author Biographies

MJ Tedder
Grassland Science, School of Life Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, Pietermaritzburg, South Africa
KP Kirkman
Grassland Science, School of Life Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, Pietermaritzburg, South Africa
CD Morris
Agricultural Research Council, c/o School of Life Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, Pietermaritzburg, South Africa
WSW Trollope
Research and Development, Working on Fire International, Nelspruit, South Africa
MC Bonyongo
Okavango Research Institute, University of Botswana, Private Bag 385, Maun, Botswana
Published
2013-01-11
Section
Articles

Journal Identifiers


eISSN: 1727-9380
print ISSN: 1022-0119