Killer drought that ravaged SA’s bush the worst in decades
Disturbing new data shows it killed off a quarter of the Kruger Park's buffalo and nearly half of its hippos
The recent drought that gripped SA will be remembered in the big cities as one of the worst in living memory – but what happened out in the bush and remote communal lands while attention was fixed mainly on the “Day Zero” water shortages?
In the Kruger National Park it killed off more than 25% of the park’s buffalo population, about 45% of the hippos and up to 40% of trees and shrubs in some parts of the park.
At least one heavily stocked private game reserve lost 75% of its herbivores, while some communal farmers in the Giyani district of Limpopo lost up to 33% of their cattle.
In the northern parts of KwaZulu-Natal the losses were even more severe, with communal farmers losing 43% of their cattle and nearly 30% of the goats.
Writing in the latest edition of the SA Journal of Science, a group of ecologists conclude that the low-rainfall and high-temperature drought of 2014-17 was not the worst drought of the century when measured on a national scale.
But, for the northeastern parts of Mpumalanga, northern KZN and eastern parts of the Free State, it appeared to have been the most severe in many decades – worse than the droughts of the early 1960s, early 1980s and early 1990s.
“A key feature of the drought which distinguished it from former ones was high temperatures, with an unprecedented number of locations experiencing record-breaking monthly mean maximum temperatures during 2015 and 2016,” said lead author Dr Tony Swemmer of the SA Environmental Observation Network (SAEON).
Swemmer suggests that despite significant death levels in certain animal and plant species, drought can also play a “positive” ecological role.
“Drought impacts on commercial farmers are relatively straightforward to assess through quantification of crop yields, but ecological impacts are less tangible, particularly as many of these may only manifest years after the drought has ceased.
“They may have some positive impacts in ecosystems, such as reducing herbivore numbers (thus preventing overgrazing in the long term), reducing the densities of trees (thus combating bush encroachment) and providing an opportunity for ‘drought-adapted’ flora and fauna to thrive.”
During a recent SAEON workshop to measure the ecological effects of drought, some experts suggested that droughts open up savannas by killing trees, while others argued that grasses can take decades to recover their productive potential.
“Does each successive drought transform an ecosystem, pushing it towards a new state from which recovery to an original state eventually becomes impossible? Alternatively, are our fauna and flora so well adapted that they can recover comfortably before the next drought strikes?
“This question is particularly pertinent, considering the prediction that global climate change will result in droughts becoming more severe and possibly more frequent,” says Swemmer.
SA National Parks ecologist Dr Izak Smit told the workshop that in some respects, the effects of the most recent drought were not as severe in the Kruger Park, partly due to the fact that animal distribution patterns changed after several artificial waterholes were closed in recent decades and because boundary fences with several adjoining private reserves had been removed.
Nevertheless, nearly 26% of the Kruger buffalo population died between 2015 and 2017, compared to 48% during the drought of 1992-1993.
Hippos suffered heavy losses, with 45% of these water-loving animals dying in four major Kruger rivers because they were unable to access enough food close to rivers.
“Against expectations, elephant numbers in Kruger increased by 13% between 2015 and 2017. This suggests that the elephant population is still far from being resource limited, and prompted the question of whether drought impacts on the tree layer might have been more pronounced if elephant densities were two or three times higher.”
Kudus and other browser species were also not as badly affected as grass-grazing herbivores such as buffalo.
Though the grass layer across the park was severely reduced, as expected, researchers also noticed some “interesting and unexpected patterns” in the composition of grass species and other vegetation in the months following the drought.
In the Satara area, where the drought was particularly severe, grass species recovered very quickly when the drought broke.
In the Hluhluwe-Imfolozi Park less than 1% of the trees died during the recent drought, whereas the death of trees in the southern parts of Kruger was quite significant.
In some parts of Kruger, up to 40% of trees and shrubs were killed and led to savannah areas being transformed into open grassland in some areas.
“However, such impacts were not widespread, and mortalities only occurred in certain regions and only affected certain species.”
Swemmer said more data was needed to help predict the impacts of future droughts on trees and the spread of alien plant species.
“Trees can starve to death if they are unable to store carbon as a result of insufficient carbon gain over multiple summers of low rainfall.”
Alternatively, trees could also die when moisture dropped to below a critical level, in which case a single year (or even a few months) of severe drought could kill them.
The full article can be read at www.journals.assaf.org.za