It is often claimed that Prosopis made its appearance in southern Africa via Namibia. An indication of this is the colloquial name of “Suidwesdoring” (Afrikaans: South West thorn). It was, however, only after 1910 that Prosopis was introduced to Namibia.
The earliest documented evidence of Prosopis in southern Africa is that one John Marquard of Vanwyksvlei imported P. glandulosa var torreyana to South Africa from the dry areas of the USA (probably Texas) in 1880. More seeds of this species were subsequently imported on a regular basis to establish the plant in regions such as the Karoo and northern parts of the Cape Province. Even though a precise date cannot be pinpointed for the P. juliflora, there are indications that this species, together with P. velutina and P. pubescens, was also imported to South Africa from the USA and Mexico between 1897 and 1916. Evidence exists that at an early stage there were attempts to cross-pollinate the four species, mainly to improve the yield of pods.
The similarities between the arid regions of the USA, the Karoo, the northern parts of the Cape Province and Namibia are remarkable: rainfall is rare and unpredictable; temperatures can drop to below freezing at night during winter, while they rise to more than 40 degrees Celsius during summer; rivers are ephemeral and surface water is scarce; the soil is poor, brackish and shallow. With the exception of certain species such as camel thorn, shepherd’s tree, Karoo thorn and black thorn there are few other trees in these areas. The pioneers of old required shade, protection and fodder. Therefore they chose to import trees, and Prosopis was one of their choices.
Initially all species of Prosopis in South Africa were referred to as P. glandulosa, and later as P. juliflora. Ignorance was the main reason, aggravated by the fact that it was difficult to distinguish between the two species and the new hybrids which developed by cross-pollination of P. glandulosa var torreyana, P. juliflora, P. velutina and P. pubescens. In the meantime the name Prosopis became a household name and today it is collectively used to refer to all the species and hybrids in South Africa and Namibia.
Several stems, a high pod yield and the velvety hairs on the leaves are typical characteristics of P. velutina. This species is a formidable intruder and easily cross-pollinates with other species of Prosopis. There is no big difference between P. juliflora and P. velutina – and both carry many thorns. P. pubescens differs from the other three species in that it produces curled pods, mostly stands alone, has a bushy appearance and is less inclined to invade.
The name Prosopis chilensis appears for the first time during 1894 in the books of the State Nursery in Hanover in South Africa. There may have been early attempts to test the trees’ adaptability to Karoo conditions but evidence of this does not exist.
P. chilensis, however, was one of the four species which were imported to Namibia in 1912 by Kurt Dinter, the botanist of the German colonial administration. As the name implies, P. chilensis originates from Chile. Dinter imported this species because of its fast growing properties and evergreen crown. Unlike the other species it has few thorns and produces reasonable quantities of pods. Some of the presumably first trees can still be seen today in the vicinity of the State Nursery near Okahandja.
Dinter also brought the P. juliflora, P. glandulosa var. glandulosa and P. pubescens to Namibia, probably not from South Africa but directly from Mexico and Argentina. The aim was to provide sufficient quantities of seedlings to government authorities such as magistrate’s offices, police stations, post offices, military and veterinary control points, hospitals and schools. Seedlings were also made available to farmers and municipalities. Many of these original trees can still be seen in Namibia today, usually in rows where the trees gave shade and shelter to man and beast, and the pods provided fodder.
South African farmers started settling in Namibia from the second decade of the 1900s. Probably they brought the seed of different hybrids into the country. The introduction of Prosopis to Namibia’s plant kingdom was dramatic, in terms of time and space. Today Prosopis is the most widespread and most aggressive alien species. The adapted offshoots multiplied in leaps and bounds and due to interbreeding almost perfectly adapted to the extreme Namibian climate – especially after 1970 and at the expense of original Namibian plant life.
Concerns about the sudden increase in Prosopis date back to the 1950s when complaints were lodged with the Windhoek municipality about the clusters of Prosopis on the banks of the Klein-Windhoek River which were thought to be responsible for the rise in hay fever. The City Council responded by removing some of the trees and by law declared the planting of Prosopis in Windhoek illegal.
Today the intrusion along river courses and on flood plains is disturbing and many landowners are at their wits’ end. Along the Nossob and Auob Rivers in the south-eastern parts of the country alone an estimated 8.000 to 10.000 ha are covered by the alien species. Typical intruders consist of 2-4 m high bushy, multi-stemmed plants of which the stem density can even be more than 8.000 individuals per hectare.
The Gondwana History series is a selection of memorable glimpses of Namibia’s history. Collections of the stories are also published as several small volumes in English, German and Afrikaans. The latest one, Gondwana History III, was released in early June and is available at the offices of the Gondwana Collection in Klein Windhoek (42 Nelson-Mandela-Avenue), all the Gondwana lodges and in bookshops.