Fire as a novel disturbance and driver of vegetation change in Nama-Karoo rangelands, South Africa

Abstract

Nama-Karoo vegetation is fire naïve and therefore vulnerable to transformation by fire. This study investigated the effect of fire, a novel disturbance, on the composition and structure of shrub communities in semi-arid Eastern Upper Karoo rangelands. Nine sites across a rainfall gradient had been burnt between eight years and six months before time of sampling, whose grazing history ranged from heavy or lenient to no grazing. Fire markedly changed the composition and structure of Karoo shrublands, the nature and extent of which depended on climate regime. Non-sprouting species, including some dominant species, were extirpated by fire and replaced by previously non-dominant sprouter species. Replacement of non-sprouter by sprouter species was conspicuous for palatable and unpalatable dwarf shrubs. Under conditions that closely resemble climate change forecasts for the region, fire transformed Nama-karoo shrublands. The possibility of larger more frequent fires in the Nama-Karoo threatens to transform the vegetation, ecosystem functioning, and economy of the region. Fire has emerged as a novel agent of vegetation change in the eastern Nama-Karoo owing to a directional increase in annual rainfall over the past three decades, that may cement a state change from shrubland to grassland in an ampliative, positive feedback manner.