Stay on track

Words and pictures by Gerhard Nortjé. Words and pictures by Gerhard Nortjé.

We all know the adage make no new tracks but do we know just how important keeping to this rule is? Gerhard Nortje is busy doing his PhD on wildlife management and has chosen to investigate how vehicle tracks affect the environment.

Have you ever driven off the track? If you have, you might have caused irreparable damage to the soil.

I am currently writing up my PhD thesis in Wildlife Management at the University of Pretoria. My research site is the Pafuri area in the northern Kruger National Park, where I was supported by Wilderness Safaris, part of the Joint Management Board of the Makuleke Contractual Park. I measured two separate but linked aspects that show the impacts of off-road driving on the environment: soil compaction, and the distribution of roots in the soil. Soil compaction was measured with an electronic penetrometer, and root distribution was measured by analysing digital photographs on a specifically-designed software program.

The first time that a standard 4x4 game viewing vehicle drives off-road, it causes damage up to one metre deep and up to one metre wide on either side of the tyre tracks. Think about it: what you see is two narrow tyre tracks but below the surface there is a 3.8 metre-wide swath of physically degraded soil. Further damage by subsequent passes on the same tracks is limited, and often almost insignificant. This might come as a surprise to many operators, land owners and recreational 4x4 drivers who think it’s better to make a new track rather than return on their own tracks. The fact is that the more tracks you make, the more widespread and serious the damage.

The main damage is compaction: the soil is compacted by the weight, but more specifically by the vibrations, of a motor vehicle. Many 4x4 enthusiasts argue that heavy animals like elephants also cause damage and compact the soil; but there is a huge difference in the extent of the damage caused by a car and that caused by an animal of the same weight, and the difference is in the vibrations. Game footpaths are evidence of ‘natural’ compaction, and here is the crux of the matter: underneath game footpaths and elephant tracks the compaction is limited to about 20 cm and is only as wide as the track itself. Compare this with a vehicle of the same weight, which causes damage one metre deep and almost four metres wide.

Soil compaction has profound effects on an ecosystem: plant roots cannot penetrate and so the diversity and vigour of plants are greatly reduced. A day or two after driving off-road, it might look like the grass and shrubs have bounced back and recovered, but it is a limited recovery. Whether full recovery is ever achieved, and how long it takes, depend on the resilience (recovery potential) of a specific ecosystem. To try to determine the recovery potential (soil resilience) of the different soils, off-road driving sites were monitored over time by the use of digital photography.

Normally, we would think that soil compaction recovers naturally over relatively short periods of between a few months, to one to three years, depending on the extent of the damage. But this is where we sometimes make serious mistakes. Studies on soil recovery after compaction by vehicular traffic indicated that recovery can take anywhere between 5 to 1 000 years, depending on the climate and soil type. Soils in South Africa, with large amounts of clay which can swell and shrink during dry and wet periods, and soils of the Northern hemisphere, which are under the influence of freezing and thawing, recover naturally faster than soils which do not have such characteristics.

This means that for certain soil types under a specific climate, no recovery occurs within a human lifespan. Soils of arid climatic areas of the world are much more sensitive to damage and generally have much longer recovery times than soils of the more humid climatic areas. Large areas of South Africa are arid and have soils and vegetation highly sensitive to human disturbance. A second part of the study (of the impact of off-road vehicles on sub-soil compaction) included root density distribution.

Part of the damage by off-road vehicles, and an indirect effect of the soil compaction, is poor root development and root distribution, with the following highly negative consequences: poor water and nutrient uptake, poor vegetative cover, fewer antelope and thus fewer predators. Results showed that the higher the tyre pressure, the less the root distribution. Roots generally also grew horizontal and more shallow where the soil had been compacted by vehicle traffic. More vehicle passes also had similar effects to those of higher tyre pressures.

Another component I studied was the perceptions and attitudes of eco-tourists towards off-road driving. I found wide disparities and contradictions between their attitude towards off-road driving in general and their attitude when it came to their personal participation in it. When asked whether off-road driving damaged the soil and vegetation and had a negative effect on wildlife, most tourists said it did. But when asked whether they would like to drive offroad to get closer to an animal, the majority said yes.

These findings coincide with literature which shows that eco-tourists share the beliefs that the environment should be protected, but are not always willing to act accordingly. Another important finding is that a large percentage of tourists really do not know whether the activities they take part in have negative impacts on the environment. This is especially true where it concerns impact on the soil.

The solution is both scientific and educational. Soil studies should continue to include the impact of off-road vehicles on a wider variety of soil types, and monitoring should continue, but over much longer periods of time. Such results and findings should be made available and acted upon. On the educational side, tourists should be educated by focusing marketing programs specifically on their possible impact on the environment, and specifically on the soil. Respect for the environment should be a main part of this education.

The dilemma is that the problems with regard to off-road driving are not just limited to the privately-managed areas and private nature reserves. It is a very real problem on general public areas in the Kruger National Park.

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