The impact of native large herbivores and fire on the vegetation dynamics in the Cape renosterveld shrublands of South Africa: insights from a six‐yr field experiment

Abstract

Question Renosterveld – a vegetation complex within the Fynbos Biome of South Africa – occurs in multiple structural states, including shrublands and various types of grasslands, lawns and herb‐lands. Uncertainty exists over whether the present unpalatable shrubland state might have replaced a historical grassland state. Settled agriculture characterized by fixed burning cycles and overgrazing by livestock has been blamed for this putative change. However, the disappearance of native large herbivores has also been implicated. Understanding the drivers responsible for putative state changes is of importance for conservation of this critically endangered vegetation type. Location Renosterveld shrublands and grasslands of the De Hoop Nature Reserve, Western Cape Province, South Africa. Methods Three structural states of renosterveld (grazing lawn, tussock grassland and shrubland) were subjected to an experiment involving fire (burned/unburned) and herbivory (grazed/ungrazed by native mesoherbivores). Using animal exclosures and experimental burning, we measured the responses of the biomass of major plant functional types over 6 yrs to test whether switches between states occur in order to discern the drivers of these changes. The data were analysed using permutational manova, Fisher's exact contingency tests and NMDS. Results Herbivory (but not fire) had significant effects on lawn and tussock grassland biomass. Palatable shrubs proliferated in tussock grassland protected from herbivory. Unpalatable shrubs invaded burned lawn habitats exposed to herbivory. The vegetation composition of the shrubland state was affected by fire, herbivory and by the interaction between the two. Burned and grazed shrubland reverted to a dense canopy unpalatable state, while shrubland plots protected from grazing became palatable shrubland with a grass understorey. Palatable shrub species increased in the unburned and ungrazed shrubland plots, while the biomass of unpalatable shrubs declined in both the unburned grazed and exclosure plots. Conclusion We found no evidence supporting the hypothesis that the disappearance of native large herbivores led to the conversion of tussock grassland into unpalatable shrubland. Instead, the removal of native browsers caused palatable shrubs to dominate tussock grassland areas. Unpalatable shrubland is retained through a combination of fire and herbivory, but how this state established and persisted historically remains undetermined. Temporary relief from large herbivore grazing after unpalatable shrubland has been burned is recommended if a more open grassland state is the desired target.

Two dung beetle species that disperse mimetic seeds both feed on eland dung

“…Eland dung was found at all six sites whereas bontebok dung was found at all but the last two fynbos sites (sand plain fynbos and limestone fynbos). Previously, Radloff et al 3 noted that bontebok avoid fynbos whereas eland are found throughout fynbos, including limestone fynbos. To reduce chances of pseudoreplication, we sampled only a single pellet of bontebok or eland dung from a dung pile; only dung piles greater than 5 m apart were sampled and, as judged by colour, only relatively fresh samples were collected until a total of 10 pellets had been sampled from within each vegetation type.…”

“…2,3 The two dominant grassland/ renosterveld grass species at Potberg are Cymbopogon popschilli (Andropogoneae) and Cynodon dactylon (Chloridoideae), 3 to which can be added the relatively widespread Themeda triandra (Andropogoneae). All three species utilise the C4 photosynthetic pathway rather than the C3 pathway.…”

Towards an integrated ecological restoration approach for abandoned agricultural fields in renosterveld, South Africa

“…10 Secondly, a study on natural recovery concluded that vegetation recovery is occurring naturally in mountain renosterveld (Table 2). 4,19 Lastly, studies on restoration benefits have confirmed that restoring abandoned agricultural fields improves hydrological and soil retention services. 20,21 The above three outcomes are an indication that ecological restoration initiatives in renosterveld are yielding mixed results.…”

“…This is possible where grazing and browsing animals are allowed to utilise palatable species, leaving unpalatable species to dominate abandoned agricultural fields. 4 Besides, grazing has also been reported to disperse seeds of invasive alien grasses rather than those of native shrubs. 12 Secondly, natural succession will only be successful where remnants of renosterveld are close to the abandoned agricultural fields so as to allow seed dispersal to take place.…”

“…[1][2][3] Similarly, acknowledgement of heavy transformation (over 80%) and fragmentation (approximately 5% intact remnant patches remain) of renosterveld vegetation has been well documented. 4,5 Renosterveld -a shrubby vegetation type dominated by Elytropappys rhinocerotis (L.f.) Less -has been heavily transformed and replaced by agriculture, mostly vine, olive and wheat cultivation. 6 The fragmented renosterveld remnants remain under threat of being cleared for new agricultural lands or being subjected to disturbances like overgrazing, fire and invasion by alien plants.…”