Nursery and Establishment Techniques as Factors in Productivity of Man-made Forests in Southern Africa

SUMMARY The effects of silvicultural practice, both in nursery and field establishment, on the survival and growth of man-made forests are discussed. In the nursery the production of trees which survive is considered more important and more likely to succeed than trying to influence the long-term growth of the stand. The nursery-man should concentrate on increasing his efficiency without reducing the survival rate of his plants. The use of containers, particularly polythene sleeves, is still the most important method of producing seedlings. Bed-raised, bare-rooted plants which have been thoroughly conditioned are becoming increasingly important, however. Conditioning, the under-cutting and wrenching of a tree's roots which produces a compact fibrous root system and a dormant state in the shoot, has created the greatest possibility for change in nursery practice in Southern Africa. Mycorrhizal inoculation in the nursery using ground sporophores or spores of Rhizopogon and/or Pisolithus has been shown to be more effective than the traditional system of using infected forest soil. Fertilizer application combines well with mycorrhizal inoculation to produce a well balanced plant with a high root regeneration potential. Fertilizer application reduces the nursery period and increases the plants' survival potential but is unlikely to have a lasting effect on its growth when field-planted. Changes in site preparation involving ripping and the use of a glyphosate herbicide have significantly reduced the cost of establishment without serious loss of growth. There is some evidence that with pines adequate growth can be achieved with the herbicide alone and no site cultivation, at least on high-altitude sites. Reduction in the use of fire for slash removal has created favourable conditions for tree growth following re-establishment. The thick mulch of slash retains moisture in the soil well into the winter drought, supresses initial weed growth and stimulates seedling development through a slow but steady mineralisation of the organic matter. Rapid increase in costs and the current oversupply of markets have forced the silviculturist to examine his nursery and establishment techniques critically.

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