Average rainfall for Olifants Camp is 478 millimetres, 523 millimetres for Shingwedzi Camp, and only in the months from November to February does more than 50 millimetres fall in any one month. The extreme aridity of this region - which is located near to ample sources of oceanic moisture - is attributed to the Limpopo high pressure system, which causes air to descend and therefore acts as a barrier to air moving in from the coast.
Mopane Tree Growth
Of all the regions of Kruger, the vegetation in the north is the least diversified and much of the region is blanketed in shrub mopane (Colophospermum mopane). The distribution of this tree in South Africa, Mozambique and Zimbabwe coincides with hot, semi-arid, low-lying valleys, and the mopane thrives under these conditions. Mopane leaves hang vertically and during the heat of the day very little shade is cast, which helps to minimise evaporation.
Where soils are deep and adequate water is available this tree can grow into a fine specimen, but where soils are shallow or poorly drained the mopane grows as a multi-stemmed shrub. Not many browsers feed on its leaves, but Mopane forms an important part of Elephants' diet. Caterpillars of the emperor moth (Imbrasia belina), also known as mopane worms, feed on the leaves and are considered a delicacy by many African tribes.
Although water use beyond the Park's boundary has reduced its flow, the Letaba remains one of the most enchanting of Kruger Park's seven major rivers. Across this almost homogeneous expanse of mopane, the Olifants, Letaba, Shingwedzi, Tsendze and Mphongolo rivers carve corridors of botanical diversity.
Along their banks, tall apple-leaf, sycamore fig, nyala (Xanthocercis zambesiaca), tamboti (Spirostachys africana) and jackal-berry trees form narrow corridors that differ markedly from the surrounding stunted mopane. Apart from the Olifants and Letaba, these rivers hold water mainly in the form of large pools. The Olifants River is the largest in Kruger and its considerable catchment, extending over 54 300 square kilometres, generates four per cent of the total river flow in South Africa.
During the severe drought of the mid-1940s, the Letaba stopped flowing for two short spells at the end of winter. The Letaba and Olifants rivers are home to 60 per cent of the Park's hippo, and in the past large numbers of hippo died in times of drought. In 1970 the American industrialist, Charles Engelhard, financed the construction of a large dam on the Letaba River downstream of Letaba Camp.
The completion of major reservoirs has helped create suitable habitat for both hippos and waterbirds. Since the completion of the Engelhard Dam, three other dams have been built on the Letaba and the completion of the Kanniedood Dam on the Shingwedzi River in 1975 pushed back water in the riverbed for six kilometres.
While these reservoirs are artificial structures, and not entirely in keeping with the principles of a national park, in an arid region where the supply of water from outside has become erratic (nowadays, surface flow ceases in early May in most years), these dams at least make it possible to retain the many water-dependent species that would otherwise die out.
These relatively lush river corridors are the favourite habitat of many species of mammals and birds. Waterbuck, bushbuck, impala and kudu are common, but the riverine vegetation is also the haunt of the exquisite nyala. Herds of elephant and buffalo depend on the rivers for water, and predators such as lion, leopard and hyaena concentrate where prey is abundant. The Northern Region is home to half of Kruger's Elephants. Breeding herds favour the country bordering the Olifants River, and elephant herds also gather along the Letaba, Shingwedzi and Mphongolo rivers.
Elephants on the Increase
Since the proclamation of the first conservation area in the Lowveld in 1898, the elephant population has enjoyed a phenomenal increase. In 1905 Stevenson-Hamilton estimated that there were only 10 elephants in the Park; by 1932 there were 170, and at the time of his retirement in 1946 the population had reached 450. The current estimate of just less than 9 000 represents a remarkable recovery.
In addition to the fact that elephants have been able to raise their young in the safety afforded by the Park, Elephant immigration from Mozambique, where poaching has been rife, has also played a major contributing role in this increase in the Park's population.
As game in the region is concentrated near water, tourist camps and roads also tend to be located near rivers or major dams. Olifants, Letaba and Shingwedzi camps all border on rivers of the same names, and the Shimuwini, Bateleur and Sirheni bushveld camps are all positioned near large dams. In this sunburnt region where summer temperatures of 45°C are not uncommon, wildlife is drawn to the rivers, and any exploration of these picturesque river roads, especially along the Olifants and Shingwedzi rivers, can produce some of the best game-viewing in the Park.
Apart from the concentrations of game that are present, the towering shade trees and refreshing pools of fast-flowing water, adjacent to sunbaked mopaneveld, create some of the most appealing habitats in all of Kruger. Apart from the sizeable herds of elephant and Buffalo that inhabit the mopaneveld, the eastern basalt plains are the chosen habitat for several rare antelope species. Of the 20 species of antelope that occur in the Park, a number of species are restricted to the Northern Region. Broad, grass-covered drainage lines are a common feature of the shrub mopaneveld.
These grasslands are formed when clay soil formed on basalt coincides with a deeper layer of impervious calcareous substrate. Trees cannot take root and elongated, narrow grasslands are formed that provide an optimum habitat for tsessebe, sable, roan, eland and reedbuck. But in times of severe drought, grass cannot obtain sufficient moisture to grow, and barren areas of exposed soil result. In areas where dry spells have killed off the grass, major declines in these rare antelope species occur.
Pools of fast-flowing water, adjacent to sunbaked mopaneveld, create some of the most appealing habitats in all of Kruger. Apart from the sizeable herds of Elephant and Buffalo that inhabit the mopaneveld, the eastern basalt plains are the chosen habitat for several rare antelope species. Of the 20 species of antelope that occur in the Park, a number of species are restricted to the Northern Region. Broad, grass-covered drainage lines are a common feature of the shrub mopaneveld.
Following the severe drought of 1992/1993, Sable antelope decreased by 85 per cent and Tsessebe by 70 per cent in the Northern Region. As these antelope are rare in South Africa, park managers are concerned and have taken steps to arrest the decline. Recovery in populations is normally fairly rapid in the wet cycle that follows a long drought, however, providing that long-term changes in the habitat were not caused by the drought.
Variable Occurrence of Bird Species
Many species of birds have a preference for a specific habitat, and a number of unusual birds can be found in the Northern Region. The mourning dove has a distinct preference for rest camps and is common in Letaba and Shingwedzi camps. Arnot's chat is restricted to tall mopane forest, and in Kruger the greyrumped swallow and brownthroated martin occur only along the Olifants and Letaba rivers.
Where the Olifants cuts a gorge through the Lebombo, goliath heron, Cape Parrot, Yellowbellied Bulbul, Yellow-spotted Nicator and Black Stork build nests, and shrub mopaneveld can reveal Dickinson's Kestrel, Marsh Owl, Rock Kestrel, Cloud Cisticola and Broadbilled Roller.