Trees for the Western Transvaal selected on the basis of arboretum trials
ENGLISH ABSTRACT: Trees are needed on the semi-arid Highveld of the western Transvaal for shelterbelts, woodlots, fodder, honey, shade and ornament. A brief history of tree planting in the area, more particularly at Lichtenburg and Potchefstroom, is given. Relatively few species can be grown successfully in the western Transvaal because of the unfavourable climate. Hot, dry winds blow almost continuously off the Kalahari between August and October before the first, spring rains; cold winds and frosts are experienced in winter, although the summers are hot; the rainfall is erratic and low, averaging about 600 mm. a year and occurring mainly in the form of heavy thunderstorms during summer; hail is common. The geology of the area is complex. In the north-west an overburden of wind-transported sand obscures the underlying formations. The soils are mostly of a light, sandy or loamy consistency, with a fairly high base-saturation value. Concretions, sometimes forming a continuous hardpan, are characteristic of certain types. Various indigenous trees are found in some localities. These are small,and are mainly confined to rocky hillsides and stream banks. In the past they have been much exploited for rough building timber, fence posts and firewood. Their growth is very slow, and exotics have proved to be more vigorous as well as more useful in cultivation. Possible adaptations of trees to dry climates are discussed. It is concluded that'apparent adaptations observed in the field are of little value in selecting trees for dry areas. No practical alternative therefore exists at this stage to the introduction of species from .areas with a similar climate and testing these under local conditions. Parts of the world having a climate similar to that of the western Transvaal are in.dicated. Summarised results of species trials in the western Transvaal are given in tabular form, and recommendations for tree planting in the area are made. In an appendix, trials of BB species in arboreta at Lichtenburg and Potchefstroom are fully described and discussed.