Frequent burning maintained a stable grassland over four decades in the Drakensberg, South Africa

Abstract

The mesic temperate montane grasslands of the Drakensberg, located within the broader Drakensberg Alpine Centre in southern Africa (Carbutt and Edwards 2003), are productive and ancient (Ellery and Mentis 1992; Bredenkamp et al. 2002; Bond and Parr 2010). Covering more than 42 000 km 2 of the upland area in KwaZulu-Natal (KZN), with only >2 500 km 2 in formal protected areas (Carbutt et al 2011), these closed-canopy grasslands were shaped by conditions during the late Miocene, which facilitated the spread of grassland dominated by C 4 grasses that benefitted from increasing aridity, low atmospheric CO 2 concentrations, and recurrent natural fires (Manry and Knight 1986; Meadows and Linder 1993; Keeley and Rundel 2005; Scheiter et al. 2012). Fire has played an important role in the evolutionary development of the structure and floristic composition of the Drakensberg grassland, with constituent productive grasses that promote fire (Bond et al. 2003) and a diverse assemblage of endemic resprouting forbs with underground bud banks and energy storage units that allow them to withstand frequent burns (Uys 2006; Bond 2016). Fires also maintain the Drakensberg grassland largely free of trees, except for scattered protea species and woody plants in refugia (Adie et al. 2017). A pronounced dry winter together with slow decomposition rates of sourveld grass leaves, result in high loads of cured above-ground biomass (Everson et al. 1988a), which fuel the fires that remove accumulated moribund foliage and litter, allowing sufficient light to reach the soil surface to sustain basal-tillering caespitose grasses (Everson et al. 1985; Everson et al. 1988b; Bond et al. 2003; Neumann et al. 2014) and initiate spring flowering in numerous obligate fire-stimulated grassland forbs (Lamont and Downes 2011). Together, the afore-mentioned appear to indicate a fire regime naturally occurring outside the main growing season of montane grassland plants, but at a time when swards are most susceptible to fire. The frequency and seasonal timing of historical fire regimes in the Drakensberg is unknown and likely variable (Gordijn et al. 2018). Before San hunter-gatherers employed fire to attract wildlife after they settled in the Drakensberg approximately 8 000 to 5 000 BP (Hall 1984; Mazel 1989), lightning was the main natural source of ignition in the

Mountain Watch: How LT(S)ER Is Safeguarding Southern Africa’s People and Biodiversity for a Sustainable Mountain Future

“…Management objectives aimed at maintaining the stability of montane grasslands therefore need to incorporate their dynamic nature in response to fire [67]. Application of fire at the correct frequency and season is essential for optimising grassland biodiversity and condition, which minimises erosion and sediment losses to maintain a steady supply of clean water and maximise storage of soil organic carbon to mitigate climate change [68,69].…”

“…To understand these dynamics long-term, the Brotherton Fire Experiment (1981-1992 and 2015-present; South Africa; Figure 2) at Cathedral Peak in the Maloti-Drakensberg was established as a small-scale mesocosm-type fire experiment using 1-, 2-, 5-, and 12year fire-return interval treatments to complement the larger research catchment-scale fire experiment discussed previously [69][70][71]. The experiment is generally sampled biennially, but occasionally on an ad hoc basis [71][72][73].…”

“…In 2004, a multi-disciplinary team of scientists used the fire experiment to convince the management authority of its importance by including a broader suite of biodiversity elements and the potential for climate change research [73]. The original aim was to assess the effects of pyrodiversity (varied fire frequency and seasonality treatments) on mesic montane grass structure (basal cover) and composition (diversity) [72], but has been expanded to test the effects of fire on forb species composition and diversity [66], soil properties and landscape functioning [74], invertebrate diversity and abundance [75], and multi-decadal changes in grass and forb species composition in concert [69,70]. It also hosts a warming experiment using open-top chambers [76].…”

“…All of these metrics are important indicators of grassland health [77] and biodiversity value [66]. Data from the long-term fire experiment are used to inform optimal burning practices in the Maloti-Drakensberg, established as regular biennial burning in the dormant season [69], supplemented with smaller patch burns at slightly longer fire-return intervals [70]. Biennial burns in late winter or early spring maintain grass bud banks and important grass species at desired levels of abundance [69,78] to ensure a long-term desired state of grassland equilibrium and stability that can resist change and maintain healthy and resilient grassland communities [69,78,79] and water towers [67,69].…”

Limits to resilience of Afroalpine vegetation to grazing and burning: a case study of grasses from the Drakensberg Mountain Centre, southern Africa

“…Despite these threats, Afroalpine grasslands of the DMC remain understudied regarding their response to human influence, with most ecological, paleoecological and floristic research focused on lower-elevation Afromontane grasslands of southern Africa (e.g. Joubert et al, 2017;Lodder et al, 2018;Breman et al, 2019;Morris et al, 2021) and Afroalpine grasslands found in East and Central Africa (e.g. Gehrke & Linder, 2014;Johansson et al, 2018;Lézine et al, 2019;Vidal & Clark, 2020).…”