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   Manejo de pastagens

      MANAGEMENT INTERVENTIONS TO OVERCOME SEASONAL QUANTITY AND QUALITY DEFICITS OF NATURAL RANGELAND FORAGES
       
  12/8/2008  

K.P. Kirkman1 and P.C. de Faccio Carvalho2

1University of Natal, Private Bag X01, Scottsville, South Africa. E-mail: kirkmank@nu.ac.za
2Universidade Federal do Rio Grande do Sul, Postal 776, Porto Alegre, Brasil. E-mail: paulocfc@ufrgs.br

1. INTRODUCTION
Rangelands essentially comprise geographical regions dominated by grass with or without scattered woody plants.
Rangelands are often considered to function primarily as feed for livestock. In this view, conservation and biodiversity issues are secondary. The alternate view involves recognising rangelands as a biome without a specific function, but where there is an implied responsibility for inventory, maintenance and conservation (Blench & Sommer 1999). Most of the world’s rangelands support grazing or browsing animals in a variety of systems ranging from commercial
livestock enterprises on privately owned or controlled land, through commercial enterprises on communally owned and controlled land to subsistence farming, either sedentary or nomadic. On many areas of rangeland on several continents livestock are kept for purposes other than just commercial gain, and objectives of livestock owners vary tremendously as a consequence. Large tracts of rangeland have been formally set aside for conservation purposes, and contain a
variety of indigenous herbivores, which are managed largely for conservation purposes with maintenance of biodiversity often a primary objective. An increasing number of private landowners, particularly in Africa, are converting from commercial livestock farming to commercial game farming. While commercial game farming is often seen as a form of conservation, it may differ from classic conservation, as the focus tends to be on utilising game
species that generate an income rather than conservation for the sake of conservation in an altruistic sense. Also, the focus tends to be on selected game species rather than the diverse array of fauna and flora present in what is often a highly manipulated system. Irrespective of the livestock production system, game production systems or conservation objectives, any herbivore system on rangeland is dependant on the forage produced by the rangeland.
The quality and quantity of rangeland forage production (both graze and browse) varies tremendously depending on climate and a range of other environmental factors. These factors also influence seasonal fluctuations in growth rates, dormancy periods and seasonal variations in quality. These inter- and intra-seasonal quality and quantity fluctuations result in nutrient deficits that severely limit livestock production potential, particularly where animal movement is
restricted by artificial boundaries. While wild herbivores are probably better adapted than domestic livestock to survive these deficits, restriction of movement enhances the effect of the fluctuations and may consequently compromise condition, reproduction rates and survival rates of wild herbivores.
These limitations to livestock production should be seen in the context of increasing world population, urbanisation and
rising incomes with consequent increasing demand for food, particularly protein. Urban populations tend to consume
more animal products than rural populations and there is also a positive relation between level of income and consumption of animal protein (Steinfeld, de Haan & Blackburn 1997). Both the human population and the livestock sector in developing countries are growing at an unprecedented rate (Steinfeld et al. 1997). Current population growth estimates require a global increase in food supply of 2% (Nolan et al. 2000). Coupled to the increasing population and
livestock sector is a decline in rangeland area as the demand for arable land increases. Degraded cropland is often allowed to fallow and converts to a poor form of pasture (Steinfeld et al. 1997). This, as well as the impact of grazing pressure, points to a perceived decline in condition of rangelands around the world with concomitant decline in production potential and quality.
Rangeland managers have a wide range of options available to overcome these deficits. These options include high input strategies such as ameliorating soil fertility (Tainton et al. 2000), modifying species composition by including more productive grasses or legumes (Tainton et al. 2000), establishing forage trees (agro forestry), incorporating crop residues where available, replacing rangeland with cultivated pastures or low input strategies such as burning humid grassland to improve quality (Barnes & Dempsey 1992, Zacharias 1994) or to stimulate unseasonal growth and thus
improve quality (Trollope 1999). Management of animals on rangeland involves manipulating three variables, namely
animal movement (within and between seasons), animal numbers (stocking rate) and animal type (ratios between types),
as well as reproductive patterns, which influence seasonal forage demand.
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Proceedings of the VIIth International Rangelands Congress 26th July – 1st August 2003, Durban, South Africa
Editors: N. Allsopp, A.R. Palmer, S.J. Milton, K.P. Kirkman, G.I.H. Kerley, C.R. Hurt, C.J. Brown ISBN Number: 0-958-45348-9
Proceedings produced by: Document Transformation Technologies Congress Organised by: SB Conferences
 
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