Nkhuhlu Exclosure Burnt to Mimic External Conditions

Fire is not a popular phenomenon in the Lowveld at the moment, but in the Kruger National Park (KNP) it is used under controlled conditions as part of a long-term ecosystem experiment.

The fire team from Scientific Services in Skukuza has been using fire as part of an ongoing experiment in the Nkhuhlu exclosure in the south of the KNP.

The Nkhuhlu vegetation exclosure, which is 139ha in size, is visible across the Sabie River from the Nkhuhlu picnic site and was set up in 2002. The main purpose of this exclosure is to determine the effect of different combinations of fire, elephants and other herbivores on the vegetation.

It was fitting that this exclosure be named after the Tsonga word for the Natal mahogany, a beautiful tree seen along the Sabie riverbanks. The exclosure will be maintained and managed as such for the next 20-25 years during which time close monitoring of the vegetation changes will be done.

The exclosure also provides ideal opportunities for other research, such as soil – plant relationships, soil nutrient and population dynamics studies. There are nine research projects on the go in the exclosure, including ant monitoring, an analysis of the impacts of elephants on woody vegetation and a baseline rodent survey.

The last fire in the exclosure was put in during October 2002. This year the fire treatments were applied in August as the rest of the area had naturally burnt already and the aim of the experiment is to simulate the natural frequency of fire regime in the area. Navashni Govender, fire ecologist, and Dr Holger Eckhardt, vegetation ecologist, together with a dedicated fire team from scientific services, burn sections in the full exclosure, where all herbivory (from duiker to elephant) is excluded by a strong fence.

It is vital that the fire does not jump into the area where fire is excluded from the vegetation as part of the experiment, as this would have a negative effect on the research projects that are currently being done in this exclosure. Grass samples are taken from the veld before the team gets to work. 

These are used to work out the moisture content of the grass. Safety is of paramount concern and Navashni briefs the team on the plan for the fire and all safety procedures. The first part of the procedure is to burn a firebreak along the fence. This prevents the fence being damaged by the hot head fires that are applied later and reduces the risk of the fire jumping the fence and getting into the veld.

The fire is started along the fence by a drip torch with a petrol and diesel mix. The team quickly douses any flames that get too close to the fence. Once the perimeter has been secured by firebreaks, the rest of the block is burnt with a hot head fire that has huge, crackling flames. The fire quickly dies down as it reaches the firebreak and has no more fuel to burn.

The team has to work together closely and be aware of each other as the fire is dangerous and can turn with the wind very quickly. "Always keep one foot in the black (burnt area)" says Navashni. Raptors and smaller birds are attracted to the smoke as insects flee the oncoming flames.

The fire creates its own energy and noise as it burns through the vegetation. "Some grasses burn better than others" says Navashni "some grasses have chemicals in them that make them unpleasant for animals to eat and they accumulate in biomass, such as turpentine grass.

Another interesting point is that black smoke indicates very dry grass while white smoke shows there is more moisture in the grass" explained Navashni. Fire is viewed as a natural phenomenon in savanna ecosystems and understanding its effects on the vegetation and ecosystems processes forms an important component of the research that is undertaken by scientific services.

Learn more about different grasses in our Africa Grass Guide

By Michele Hofmeyr

Kruger National Park - South African Safari