Soil damage caused by 4×4 vehicles is an underestimated impact of tourism. It can cause long term – between 5 and 1000 years – damage, mostly irreversible. Due to this negative environmental impact, vehicles should not be allowed to do off-road driving in protected areas. Strict legal measures should be applied to regulate 4×4 use in such areas, while very sensitive areas such as wetland areas should be classified as absolute no-go areas.

So says Dr Gerhard Nortjé, based on findings from his doctoral research in wildlife management, which he did through the University of Pretoria’s Centre for Wildlife Management. This soil scientist will receive his PhD degree on 15 April during the University’s Autumn Graduation Ceremonies.

“While it may not seem that off-road driving has negative impacts on the environment, especially on the soil and vegetation, the risk of damage is real,” says Dr. Nortjé. “It is not an ecologically sustainable practice and should therefore not be allowed.” He says increased soil erosion, damage to vegetation and habitat destruction are just some of the visible negative impacts of this popular so-called “eco-tourism” activity.

New guidelines needed

Dr Nortjé, who focused his research in the Makuleke Contractual Park in the northern Pafuri section of the Kruger National Park (KNP), argues that SANParks should reconsider its management strategies for off-road driving in protected areas altogether.

SANPark’s best practice guidelines currently recognise the potential of off-road driving to negatively impact natural resources, but do not explicitly refer to soil damage. Some of the current off-road driving guidelines have up until Dr Nortjé’s study never been tested or scientifically validated. One guideline, for instance, states that vehicles may not drive in each other’s tracks when going off-road. This is exactly the opposite of what Dr Nortjé’s research has shown, namely that up to 90% of damage is caused the first time a vehicle passes over an area, irrespective of soil type or tyre pressure. Driving on the same tracks a few times is therefore much less damaging than driving only once on different tracks.

Some of his other findings include:

• Wet soils are more prone to off-road vehicle damage than dry soils, although both are affected.
• Off-road driving causes three forms of soil degradation: the dense compacting of the subsurface layer because of wheel traffic; the forming of a dense, thin soil crust under te tracks; and soil erosion caused by increased runoff from the hardened soil crust.
• Soil compaction due to off-road driving can be up to 60 cm deep in places.
• It causes soil to be dry, because of poor water infiltration and high run-off. The soils are also poorly aerated, which further hampers seed germination and root development and functioning.
• In all, soil crusting makes plants more vulnerable to drought and influences their ability to absorb water due to shallower and poor developed root systems. Plants in these disturbed areas are often nutrient deficient and poor growers, the research shows.
• The effects are not just confined to strips under the wheel tracks – the so-called wheel pan. It also has a much wider lateral effect on both sides of the vehicle tracks. Even lower tyre pressures cause damage and degradation, although less soil compaction occurs than with higher tyre pressures.
• Off-road driving has negative impacts on vegetation recovery, soil resilience and root density distribution.
• Vegetation degradation worsens over time due to predisposition to further damage. Vehicle tracks acts as rill into which water is channeled, therefore predisposing the soil to erosion

Word of advice

The results indicate a need for improved visitor education on the possible negative impacts of off-road driving, as well as the rigorous enforcement of legal, scientifically based measures to control this practice.

“Vehicles should be driven in the same tracks when driving off-road as a form of traffic control, and that lower tyre pressures should be used,” advises Dr Nortjé.

He says that in game reserves off-road driving is often done on virgin, undisturbed soils. Wild animals tend to concentrate in areas with the most nutritious en palatable vegetation. Consequently these are also the areas where predators are most likely to be found, and the areas with the highest frequencies of off-road driving to bring tourists close to wildlife.

“Tourists’ ignorance and lack of consideration for the environment – or the soil for that matter – combined with operators’ and land owners’ need to make money is normally the reason for allowing off-road driving,” says Dr Nortjé.

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More about Dr Gerhard Nortjé

Dr Nortje is a technical manager at the South African Subtropical Growers’ Association. He received a BSc in Soil Science in 1997, a BSc (Hon) degree in the same discipline in 1999, and an MPhil degree in Wildlife Management in 2005 – all from the University of Pretoria. In 2007, he also completed a Master’s degree in Sustainable Agriculture form the University of the Free State.

For more information, please contact:

Dr Gerhard Nortjé
PhD graduate of the Centre for Wildlife Management, University of Pretoria
+27 083 501 8680
nortjegpn@absamail.co.za

For more information on the University of Pretoria, please contact:

Nicolize Mulder
Senior Media Practitioner
Department of University Relations
University of Pretoria
+27 (0) 12 420 3023
+27 (0) 83 709 3041
nicolize.mulder@up.ac.za