Shrubland fire regime scenarios in the Swartberg Mountain Range, South Africa: implications for fire management

Abstract

Over the last seven decades, the Mediterranean-type shrublands of the Swartberg Mountain Range (170 856 ha), South Africa, have been subject to divergent fire management policies. Management objectives sequentially focused on grazing, fire control, water and biodiversity conservation during successive fire management periods. The aim of the present study was to explore the factors that determined the prevailing fire regime patterns during these fire management periods. This was considered particularly relevant in view of the ongoing debate on the relative role of fuel characteristics versus weather and ignition rates in shaping fire regime patterns. The extent of burning followed climatic cycles of alternating periods of relatively high temperatures and summer rainfall with cooler periods and increased winter rainfall. Accordingly, fires occurred more extensively during the former and were largely unaffected by the absence or presence of fire control measures. Fire return intervals were strongly inversely related to productivity of the vegetation. Long-term means between 30 and 55 years were found to apply in low-altitude xeric shrubland types. Corresponding fire return intervals were generally shorter in mesic shrublands at mid to high altitudes (15–30 years). Proteoid shrublands younger than 6 years were practically non-flammable. Two basic fire regime scenarios were identified. Fire regime patterns in xeric shrublands at lower altitudes were largely controlled by the rate of fuel accumulation, whereas climatically controlled ignition frequencies and fire climate constituted the dominant controls in proteoid shrublands at mid to high altitudes. The spatiotemporal distribution of fire regime parameters (fire frequencies, season, size and intensity) as recorded in the present study for the Swartberg Mountain Range under natural fire zone management (predominance of lightning fires since 1980), appeared to be conducive to the maintenance of biodiversity according to our current understanding of the fire–vegetation system.