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31/01/2019

In June 2017, one of the worst wildfires on record in the Knysna region of the Western Cape burned 15000 hectares – from Knysna to Sedgefield in the west, and to Plettenberg Bay in the east – destroying more than 800 buildings, 5000 hectares of forest plantations, and claiming the lives of seven people.

 

One-third of the area that burned was in natural vegetation (mainly fynbos shrublands), and more than half was in plantations of invasive alien (non-native) pine trees, or in natural vegetation invaded by alien trees.

“This called for research on the factors that contributed to the fire, a fire of such severity that it could happen again if preventive measures are not taken to limit the fuel loads,” says Dr Tineke Kraaij from Mandela University's School of Natural Resource Management, whose field of interest is fire ecology in South African vegetation types, particularly fynbos. “It’s like living in an earthquake prone area; it is not a question of whether it will happen again, it is a question of when, as the average natural frequency of fires would be 20 to 30 years in fynbos vegetation, many species of which need fire to stimulate germination,” she explains.

In a paper accepted by the journal Fire Ecology, published in August 2018, titled “An assessment of climate, weather and fuel factors influencing a large, destructive wildfire in the Knysna region, South Africa”, Dr Kraaij and her co-authors researched the factors that contributed to the severity of these fires. Her co-authors are Johan A. Baard from the South African National Parks, Garden Route Scientific Services, Jacob Arndt from the Department of Geography, Environment and Society, University of Minnesota Twin Cities, Lufuno Vhengani from the Meraka Institute, Council for Scientific and Industrial Research, and Prof Brian W. van Wilgen from the Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University.

“Natural fires had been largely suppressed for over 50 years in the Knysna area because of the commercial timber plantations and development in and around Kynsna,” says Dr Kraaij.

“Much of the fynbos in the Knysna coastal area had therefore become moribund and partially encroached by thicket and forest species or invaded by alien trees and shrubs. Historically, mega-herbivores, such as elephants, rhinos and hippos, no longer present in the area, would also have helped to reduce fuel build-up between the natural fire occurrences.” Adding to the fuel loads was the presence of alien invasive plants, including commercial pine plantations close to the town and also invasions of pine, wattles and eucalyptus trees in the coastal vegetation and mountain catchments. Fire intensity is not only affected by the amount of fuel, but also by the moisture and chemical content of fuels.

To measure the severity of weather conditions in relation to fire risk, researchers and fire managers use a system called the Fire Danger Index, where blue and green is safe, yellow or orange is moderate and red is very high danger. The index is based on weather parameters that include temperature, relative humidity, wind speed and rainfall – which includes factors such as whether it rained the day(s) before.

Weather conditions equivalent to (or worse than) those experienced on the day that the Knysna fires started occurred on approximately 0.1%–0.2% of days since the 1940s. “On average, you thus get one day every three years in the Knysna area where the weather conditions are as extreme as those experienced during the fire,” Dr Kraaij explains. The fire danger conditions during these fires were therefore very high, but not unprecedented in recorded history. “However, what we found was that the drought conditions over the 18 months preceding the fire were the worst in the recorded history for the southern Cape (Knysna, George) and Port Elizabeth regions.”

The rainfall was also the lowest in recorded history during that 18-month period, and the drought indices – including factors such as the extent to which the soil has dried out and what amount of rain it would take to moisten the soil – were also the worst in recorded history. The vegetation was therefore extremely dry and much had died off as a result of the drought, providing large amounts of dry fuel.

“This time around when the fires started – with two distinct fires at the outset – they could not be controlled, such was their severity, with extreme berg wind conditions fuelling the rapid spread of the fires, so they even jumped the Knysna estuary.”

The fires wreaked havoc in the commercial timber plantations, mostly pine, which are only flammable under very dry hot weather conditions. When this happens, they burn with high severity, exacerbated by the large amounts of biomass.

“The amount of biomass consumed during the fire – which may be interpreted as a proxy for fire intensity or severity – was significantly higher in plantations of invasive alien trees, and in fynbos invaded by alien trees, than in uninvaded fynbos, providing support for the contention that invasion by alien trees increases the impact and difficulty of control of wildfires,” says Dr Kraaij, who presented these results at a meeting of the Southern Cape Landowners Initiative.

“Our results show that commercial plantations and alien invasions comprised 50% of the total burnt area, and these results support calls to control invasive alien plants, reduce commercial planting of invasive alien trees, ensure that there are proper, well-maintained firebreaks in key areas and strictly regulate development in areas of high fire risk, as well as maintaining awareness of the need for fire wise practices.

“We need to think critically about the timber industry, as the commercial plantations around Knysna are situated in former fynbos areas, which means they are located in the fire-exposed and fire-prone parts of the landscape, situated in the fire paths. The fire risk is really high and plantation companies need to think of fires as something that will happen, and not as unexpected disasters when they do happen.

“The region’s municipalities need to closely consider fire in their town planning and look closely at the location of developments in relation to berg wind-driven fire paths. The recent fires burnt many areas with very poor residential planning, including informal settlements, as well as low-density estate developments situated on hilltops with plenty of alien-invaded fynbos around them.

“Overall, it calls for the need to look at the control of alien invasives, reduction of plantations in fire-prone areas, particularly those neighbouring urban areas, the reintroduction of prescribed burning programmes, particularly in the urban–wildland interface, and the strict regulation of town development in areas of high fire risk. Far better town planning is required and it needs to include the insurance companies, which should not insure properties that are situated in very fire-exposed parts of the landscape, in the same way they shouldn’t ensure properties built below the flood line.”

Many of the houses across the socio-economic spectrum are being rebuilt in exactly the same places where they burnt down. Owners also need to focus on managing the vegetation around their properties to keep down the fuel loads immediately surrounding their assets.

As the authors concluded in the Fire Ecology paper: “Growth in the human population has been accompanied by development in rural areas and an increase in the urban–wildland interface, increasing the risk of exposure to wildfires. These factors, combined with very high fire danger weather conditions, preceded by an unprecedented drought, and vast amounts of alien invasive plants, led to the destructive wildfires of 2017. Events like these are infrequent and people can quickly lose interest in implementing fire-wise practices and become increasingly willing to place developments in high-risk areas in the long inter-fire periods.”

“People cannot afford to become complacent in this area,” says Dr Kraaij. “As I said at the outset, it is not a question of whether it will happen again, it is a question of when.”

Contact information
Tineke Kraaij
s211211583@mandela.ac.za