Fighting fire with fire – Kruger nearing 70 years of testing fire regimes

Standing between two plots of 150 by 350 metres near Skukuza, Tercia Strydom, an abiotic scientist in the park, explained that it was one of the world’s largest, long-term fire experiments.

“The reason why this experiment was started was to test the role of different fire regimes (different fire frequencies and intensities) on savannah vegetation.

“What we see here are just two plots. It is repeated in the landscape across the park, and there are 208 of these plots that we have been maintaining for the last almost 70 years.”

Strydom said the KNP has a long history of fires that translates to a system of fire management and research.

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“Our management strategy has gone through many eras over the past decades and we have learned a lot along the way as research improves and we get the latest technology.

These days we make use of satellite imagery to monitor our fires across the park, so we have come a long way to where we are today.”

She said it is important to note that fires are an important part of the system. Both animals and trees are able to cope with fires, said Strydom.

“Many of these tall trees have very thick bark that allows them to cope with a fire.

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“Only once a tree is compromised, for example when a marula tree is debarked by an elephant because he is eating, a fire comes through and the heat penetrates into the inner cambium of the tree; that is the part that transports nutrients and water from the roots to the leaves. That is often how we lose our big trees; it is not just because of a fire.

“What is quite interesting and shows how these animals have evolved with fires, is that when we are burning and putting in controlled experimental burns, birds come and flock because they know insects will be trying to get away from the fire.”

Animals are seen grazing on the side of the veld that has burnt as well. Strydom said this shows that there is something they want and need in that area.

When it comes to the experiment, there are two plots next to each other. One is scheduled to burn at a specific time, while the other serves as a control plot that does not get burned at all.

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These two are then compared to see what the effects are on the vegetation. To the untrained eye the plots might not look very different, but Strydom pointed out that one is “more woody with a lot more grass, where the other is a more open area”.

“There is one plot that we burn every year in August, then there is one that also gets burned in August, but only once every three years. There is then three years’ worth of ‘fuel load’, so the intensity is slightly different. It will be more intense, because there is three years’ worth of grasses that we are burning.

“Then we have one that burns once every three years in December, which is a much cooler fire, because the grasses are starting to green up. Then there is one every three years October, and every three years April.

“We burn five times a year and then there are various frequencies. Every year, every two years, every three years and up in Satara, and at Mopani we burn every four and six years as well, and then there is one plot where fires have been kept out.”

Strydom said this experiment was started during a time when the thinking was that fires are bad for the system. National policy at the time prohibited prescribed burning because of the perceived effects it had on soil.

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“The thinking was that fires are bad for the soil and that they will lead to soil erosion and degradation, and that is bad for farming. That was when we thought we need to have an experiment to see if fires have a detrimental role or are a positive for the savannah. And after the last decades of research, we have seen and shown that fires are very important for the system.”

Strydom did her masters on these burn plots and is busy with her doctorate. She is taking a look at the effect of fires on soil hydrology: do they cause erosion, do they cause a reduction in the filtration rates and are they bad for soil nutrients?

Initial findings suggest that when it comes to soil, a fire does not make that big of a difference.

“Fires do have an initial effect on soil. With regards to infiltration, they will slow it down initially, especially when there is still ash on the surface. And then, over time, like within a year, there is no difference between one plot and the other; the hydrology is very similar.”

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The experiment also has collaborators from different countries. Strydom mentioned the involvement of the European Space Agency. With the satellites currently available, they are able to pick up fires on these plots, which was not possible with older satellites.

One of the few disadvantages of such a large-scale, long-term experiment is the funding and logistics it requires.

“Although this is one of our champion research infrastructures in the park, maintaining it takes a lot. Two-hundred and eight burn plots burned five times a year at various frequencies does take a lot.

“Somehow we have managed it for the last 60-plus years. We have maintained the integrity of the experiment. We make sure that if it is scheduled to burn every year August, we will burn it.

“So far, so good; we have not had major issues with regards to maintaining it.”