Vegetation dynamics after experimental fire disturbance in the arid Succulent Karoo, South Africa

Abstract

Disturbance by fire in the Succulent Karoo is rare but fire events could increase as a result of an increase in grassiness (alien and indigenous species). This study assessed the effects of fire eight years after an experimentally induced burn in Succulent Karoo vegetation. Post-fire monitoring was conducted using the line intercept method and species counts per plot (1 m²) for each of three fire disturbance treatments: control/unburnt, high and low fuel load. Vegetation cover and abundance were compared across treatments and growth forms. Vegetation cover and abundance on fire-disturbed plots had not returned to pre-fire levels after eight years. Resprouters exhibited a rapid recovery and early dominance on burnt plots. Succulent seedlings established slower, but after eight years occurred at higher densities on the burnt than control plots. Recovery after disturbance of density and cover of long-lived, woody non-resprouter non-succulents was slow relative to resprouting non-succulents and reseeding succulents. This study of vegetation change following fire disturbance in an arid system highlights the slow return of canopy cover, immediate regrowth of only two resprouter species and slower re-establishment by seed of non-resprouter species. In addition, fire disturbance led to the numerical dominance of succulents within the first decade after the fire.

Keywords: disturbance, non-succulents, reseeders, resprouters, succulents