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.
Highlights
The Nama-Karoo of South Africa is a semi-arid biome with infrequent historical fire occurrence and perennial dwarf shrubs and grasses considered to be fire independent and fire sensitive (Mucina et al 2006, Le Maitre et al 2014)
Resprouting vigor was high in Helichrysum trilineatum, Diospyros austro-africana and Anthospermum spathulatum, weak in Cliffortia arborea and Euryops annae, and
We found that herbaceous plants and dwarf shrubs increased significantly after fire
Summary
The Nama-Karoo of South Africa is a semi-arid biome with infrequent historical fire occurrence and perennial dwarf shrubs and grasses considered to be fire independent and fire sensitive (Mucina et al 2006, Le Maitre et al 2014). Increased grassiness in arid shrublands promotes fuel continuity, thereby resulting in increased occurrences of fire (D’Antonio and Vitousek 1992, Brooks et al 2004, Nicholas et al 2009). This has been seen in grassy Nama-Karoo, where sufficient grassy fuels may accumulate in high rainfall years to sustain fires (Le Maitre et al 2014), or with the invasion of arid shrublands by alien grasses in the Karoo (Rahlao et al 2009) and elsewhere (Brooks et al 2004, Balch et al 2013, Syphard et al 2017). Given that grasses are usually more tolerant of fire than shrubs, the combination of grasses and fire could initiate a persistent negative feedback called the grass−fire cycle (D’Antonio and Vitousek 1992, Brooks et al 2004, Rahlao et al 2009, Keeley and Brennan 2012)
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