Bush-Control Studies in the Drier Areas of Kenya. II. An Evaluation of the Holt IXa 'Bush Breaker' in Tarchonanthus/Acacia Thicket

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Abstract
The effects of the Holt IXa bush-control machine on land rendered unproductive by a mature stand of Tarchonanthus/Acacia thicket were studied. The Holt treatments were factorially combined with grass seeding and subsequent burning treatments. Data are presented on the primary effects of the Holt machine and on grass establishment (including the effects of seeding on the woody plant population), followed by a final assessment based on the physiognomy of the plots, the effect of treatments on woody plant populations, and the composition of the grass cover. The machine is probably most useful in denuded areas of relatively high rainfall, where it is necessary to flatten the thicket canopy before further advance can be made. It is potentially dangerous when used indiscriminately, while under low rainfalls the Holt corrugations form an unsatisfactory seed-bed. Studies of individual species show that the population of Tarchonanthus was largely unaffected by the treatments, while Acacia brevispica and Dichrostachys cinerea increased markedly in numbers after Holt-treatment and could only be held within bounds by seeding and burning. The former was more sensitive to seeding and the latter to burning. The treatments generally improved the grass cover. Burning significantly decreased the frequency of Harpachne schimperi (a dominant of the natural flora) without affecting the main sown species, Rhodes grass (Chloris gayana). It is thought that the sequence of Holt treatment, seeding and burning increased grass productivity 6-fold.

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