Growth-form responses to fire in Nama-Karoo escarpment grassland, South Africa

Abstract

Fire is a rare phenomenon in the semi-arid Nama-Karoo region of South Africa, but appears to have become more common in recent years, possibly as a result of climate change. The ecological effects of fire in this vegetation are poorly understood, but are likely to involve changes in structural composition, that of the shrub−grass ratio in particular. A fire burned an area of Karoo escarpment grassland (a mixture of shrubs and grasses) on the Nuweveld Mountains in October 2013. We assessed changes in plant structural composition and fire survival or persistence strategies of perennial shrubs at 2.5 years post fire. The canopy cover abundance of grasses, herbs, and dwarf shrubs increased post fire, while that of large shrubs decreased. Despite all large shrub species (except Elytropappus rhinocerotis [L.f.] Less.) exhibiting post-fire resprouting and reseeding, vigor varied widely within species. Localized post-fire extinctions appeared possible in many large shrub species, including Cliffortia arborea Marloth (Vulnerable; Raimondo et al. 2015). Increases in fire frequency or fire intensity are predicted to result in persistent negative feedbacks (the grass−fire cycle) whereby the herbaceous stratum would increase in dominance at the expense of larger woody growth forms. This process may be hindered by actions to prevent and suppress fires.