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Impacts of browsing on woody plants in African savannahs Peter F Scogings Department of Livestock & Pasture Science, University of Fort Hare, Alice 5700, South Africa Abstract Little is known about the responses of woody plants to browsing in savannahs. Most of what is known is from African savannahs. Literature on the responses of woody plants to browsing in African savannahs is therefore reviewed here to look for general patterns and provide a framework for research in savannah systems. The emphasis of this review is placed mostly on browsers other than African elephant, for which a large body of literature already exists. Problems with experimental designs are identified and recommendations are made for future research. For most woody species reviewed here, especially the Acacia species, summer browsing stimulates browse production during the growth season because the rate of recovery is quickest then. Anything more than light (25%) defoliation of Acacia during the leaf flush phase at the beginning of the growth season does not stimulate shoot production. Winter browsing generally has no effect on production. This contradicts observations in boreal systems. Frequent, heavy browsing of woody plants in African savannahs does not stimulate shoot production, but infrequent, heavy browsing does. Prolonged browsing, however, reduces plant growth and increases mortality rate. The stimulatory effect of browsing subsides sooner than the recovery of plant growth rate after cessation of browsing. Nothing is known of the effect of browsing on root growth, but browsingstimulated shoot production is likely at the expense of root production and plant growth. Increased spinescence accompanies browsing-induced changes in shoot morphology and demography. In many cases, changes in the components of nutritional quality have not been detected, but when changes do occur, they are variable, depending on many factors, and have been explained in terms of the carbon/nutrient balance of the plant. Increases in carbon-rich secondary metabolites in palatable, deciduous species are related to browsing intensity, while decreases in evergreen and unpalatable, deciduous species are not. Reduced concentrations of these compounds may be accompanied by increased nutrient concentrations and they persist for longer than the increased concentrations do. Nitrogen-rich secondary metabolites in woody plants have not been well-studied in African savannahs. Repeated browsing reduces canopy cover of woody plants well before plant populations are affected. Plant population densities are unaffected, increase or decrease, depending on many factors. Altered plant populations lead to plant community changes. The most studied demographic processes in relation to browsing are seedling survival, mature plant recruitment and mature plant mortality. Seedlings are most sensitive to browsing that decapitates the seedling below the cotyledons. When clipped above the cotyledons, seedlings are most sensitive at the time when they are switching dependence for nutrients from the cotyledons to the roots. Otherwise, seedlings are quite tolerant of browsing and are more susceptible to drought than browsing. Browsing alone, unless it involves the felling of the plant at the base, seldom causes the direct mortality of woody plants in African savannahs, but can cause mortality indirectly. The ability to coppice after felling is important for woody plant survival in savannahs subjected to many disturbances. An integrated approach, that uses multifactorial experiments to understand the physiological 76
functioning of the whole plant and the dynamics of plant populations, in response to browsing and resources, is essential for a better, predictive understanding of the browse-browser interaction in African savannahs. 77
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Research and Training Strategies fo
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Goat breeding and reproduction 1. R
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Welcoming address NH Casey Head: De
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understandable that the efficiency
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Winrock International, 1992. Assess
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3. Investigate the potential benefi
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The Australian goat industries Barr
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The farming systems approach: the c
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expose others in the community to t
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Table 2 Total slaughtering during 1
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In the Northern Province a major co
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history of communal land use. The v
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Table 2 The livestock ownership pat
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Data analysis Data was analysed usi
Page 29 and 30: Dyamala Melani Univ. of Fort Hare R
Page 31 and 32: Illius, A.W. and O' Connor, T.G., i
Page 33 and 34: achieved in other parts of the worl
Page 35 and 36: The main disease identified was coc
Page 37 and 38: Table 2 Milk yields and milk compos
Page 39 and 40: supplementation in the form of luce
Page 41 and 42: Results Mean weights of goats from
Page 43 and 44: productivity of ruminants, is furth
Page 45 and 46: Anindo, D., Toe, F., Tembely, S., M
Page 47 and 48: project and driven by effective des
Page 49 and 50: profit from skins on the farm. It m
Page 51 and 52: Year n Kidded n Born n Weaned n Bor
Page 53 and 54: Table 6 Most preferred grass, tree
Page 55 and 56: the hair) of the various breeds is
Page 57 and 58: The down fibre diameter profile of
Page 59 and 60: Biological constraints and opportun
Page 61 and 62: development, although there is evid
Page 63 and 64: Feeding behaviour of free range goa
Page 65 and 66: habits of goats have demonstrated a
Page 67 and 68: R. lucida, 203.8 230.0 146.1 186.5
Page 69 and 70: Provenza, F.D., Burritt, E.A., Clau
Page 71 and 72: Treatments involved different combi
Page 73 and 74: programme following chemical bush c
Page 75 and 76: Potential of some agroforestry shru
Page 77 and 78: Jones, R.J. Value of Leucaena leuco
Page 79: Table 4 Total supplement intake (kg
Page 83 and 84: - on native pastures. - The use of
Page 85 and 86: Communal goat production In communa
Page 87 and 88: Rwandan goats (21 months). The dela
Page 89 and 90: 30 25 20 15 10 5 0 Graph 3 Seasonal
Page 91 and 92: Cervical insemination of indigenous
Page 93 and 94: ovulated. Only a trial with control
Page 95 and 96: taken that females are not pregnant
Page 97 and 98: producing a pregnancy and a live ki
Page 99 and 100: Management of goats at pasture Barr
Page 101 and 102: 1 Cradock Experimental Station, PO
Page 103 and 104: Table 2 Percentage raw combed cashm
Page 105 and 106: Our current ability to select, mani
Page 107 and 108: 103 farming operations in Southern
Page 109 and 110: UNIVERSITY OF FORT HARE CURRENT AND
Page 111 and 112: MARA RESEARCH STATION, DEPARTMENT O
Page 113 and 114: The billy goats also received light
Page 115 and 116: Goat research at Medunsa EF Donkin
Page 117 and 118: 4. New Research Projects Using the
Page 119 and 120: UNIVERSITY OF PRETORIA Computerised
Page 121 and 122: Expected Benefits * The research re
Page 123 and 124: 119 of healthy and nutritious produ
Page 125 and 126: 121 farming systems. The following
Page 127 and 128: LIST OF PARTICIPANTS Surname First
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