The Sudwala Caves are situated in Pre-cumbrian dolomites of the eastern Malmani Group, formed over 3000 million years ago. The dolomite is a carbonate sedimentary rock consisting mainly of the mineral dolomite. The dolomite is a marine deposit formed from Chemical precipitation when the Lowveld area was covered by warm shallow seas in the Pre-cumbrian time.
For more information about the caves you can visit
the Sudwala EarthCache by GPS Storm, GC1R07F at Link or
the Sudwala Caves website at Link
The Sudwala Rainforest grows at the base of a unique geological formation which manifests in a gigantic cliff face close to the Caves, clearly visible from the R539 (on the left as you pass Sudwala on route to the town of Sabie). A gorge with stinkwood trees (Ocotea bullata) is part of the rain forest. The rare aloe, Aloe aloöides, is found here. The Rainforest has been declared Natural Heritage Site #167. Since the formation of the cliff face and certainly for as long as local people can recall, a ridge of fountains has been providing water that falls from the top of this cliff.
Basal shales from the Daspoort Formation of the Pretoria Group (Early Proterozoic Transvaal Supergroup) underlie the catchment area. The shales in the catchments are highly arenaceous, with bands of sandstone and quartzite grading into shale. A number of diabase dykes run across the catchments with a predominant strike of northeast to southwest. The shale beds dip gently 2-4” west. The bedrock is generally broken, semi weathered and permeable to roots and water. This is necessary for plant growth for the soil is only a few centimeters deep. Deep drilling in the catchment area revealed that the shales are broken to 30 m below the surface and rooting is thought to be possible for much of this depth. The original vegetation of the catchments is sub-climax grassland, Acocks’ Veld Type 8, North-Eastern Mountain Sourveld.
In 1969 the catchment along a part of the Houtbosloop near the Sudwala Caves and Rainforest was afforested with Eucalyptus grandis (Bloekom/Bluegum trees) and Pinus patula (Pine trees) as an experiment (the Mokobulaan experiment) to study the effects of these exotic plantations on this ever flowing river which originates near Lydenburg. As a result, there was a statistically significant decrease in stream flow in the third to fourth year after planting and the stream dried up completely in the ninth year after planting. The eucalypts were clear felled when 16 years old but full perennial stream flow did not return until five years later. This was rather surprising, and points to something exceptional in the catchment area. The clear felling of a pine plantation at the nearby Witklip research catchment, also on the Mpumalanga escarpment, led to an immediate stream flow. Similarly, cleat-felling of mature Pinus radiata plantation in the Western Cape Province led to stream flow increases which were noticeable once a third of the plantation had been cleared and were sustained for five years. These results agree with many other research from other countries, except the Mokobulaan catchment.
Deep drilling within the catchment revealed that the shale substrate was weathered and carried water reserves to depths of up to 45m below the surface, without being saturated, i.e. without being below a water table. Citing several studies that record eucalypt rooting at depths from 5.6 to 28m, the experiments postulated that eucalypt roots were able to penetrate the fractured substrate of the catchment to considerable depths below the normal soil profile, and tap the deep, unsaturated soil-water reserves. These deep soil-water stores would have to be replenished before the catchment could be restored to its pre-afforestation hydrological behavior.
The conclusion of this experiment was that the complete afforestation of these grassland catchments with Eucalyptus grundis and Pinus patula led to the catchments drying up nine to twelve years after planting respectively.
The problem facing the Sudwala Caves and Rainforest is that in the late 1980’s a section of the grassland on the plateau behind the Sudwala Caves and the rainforest cliff was planted with timber.
As should have been anticipated, these now mature plantations are exerting unsustainable pressure on the water resource, and compounded by the drought conditions is leading to the complete drying out of the unique rainforest and cave eco-systems. The Sudwala Cave has become extremely and unusually dry – even the fair late summer rains had failed to percolate through the deep cave system and certain parts of the natural rain forests are also dying because of these conditions.
Experiments all over the world concluded that these trees are drying out the soil on which they were planted and extracting water from deep under the regolith. In an eco sensitive environment, as in the case of the Sudwala Caves and Rain Forest, it can have devastating effects.
Reference:
CSIR Link
Geasphere Link
To claim a find for this cache you need to answer the following and sent it to me:
1.) Describe the rock features and give a short explanation on how it was formed. Not the same as for the EarthCache GC1Y2R7.
2.) Do you see any water flows from the mountain or places where the water uses to flow? Describe your findings.
3.) What are your views in regard to the afforestation of exotic trees in catchment areas? Your comments will be confidential.
NOTE: You can sent me your answers in either Afrikaans or English.
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