The replacement of natural fynbos vegetation with pine plantations in the southern Cape and the subsequent invasion of surrounding land by invasive pine trees significantly increased the severity of the 2017 Knysna wildfires.
This was among the findings of a study published in the journal Fire Ecology by a research team from the Centre of Excellence for Invasion Biology at Stellenbosch University, Nelson Mandela University, SANParks, and the Council for Scientific and Industrial Research.
The aim of the study was to assess the climatic, weather and fuel factors that contributed to one of the region’s worst fires ever recorded.
Over four days in June 2017, the Knysna fires burnt 15 000 hectares, claiming the lives of seven people and destroying more than 5 000ha of commercial pine plantations and over 800 buildings.
The experts say events of this nature can become more frequent as the climate of the southern Cape becomes more hot.
The researchers used satellite imagery to compare the landscape before and after the fire, including the type of vegetation covering the different areas. This information enabled them to estimate the amount of biomass consumed by the 2017 fire.
One of the main findings was that the severity of the fire was significantly higher in plantations of invasive alien trees, and in fynbos invaded by alien trees, than in non-invaded fynbos.
And while the weather conditions were extreme, they were not unprecedented, as similar conditions occurred in the past at a rate of approximately one day every three years.
The severity of the 18- to 24-month drought that preceded the fires, on the other hand, was higher than ever recorded in the historical weather record, and this contributed significantly to the impact of the fire.
One of the co-authors, fire ecologist Professor Brian van Wilgen, said large tracts of natural vegetation in the southern Cape had been systematically replaced with plantations of pinus and eucalyptus species.
It was estimated that pine trees had invaded more than 90% of the Garden Route National Park’s fynbos vegetation at various densities. Additional invasions by Australian acacia and eucalyptus species covered a further 29% and 14% respectively.
“By increasing the amount of fuel available to burn, the fires become more intense and more difficult to control,” Van Wilgen explained.
“The conditions will occur again. People need to stay vigilant and implement fire-wise practices, and, more importantly, steer away from placing developments in high-risk areas in the long inter-fire periods.”