The land / livestock ratio refers to the availability of feed from land relative to the feed requirements of livestock. To some extent the ratio corresponds with ‘carrying capacity’ (Tropical Livestock Units per ha). In general carrying capacity is calculated based on estimated annual biomass production and feed requirements by livestock. These calculations often do not consider seasonal variation in production and feed quality, or if they do, they do not consider the various ways farmers can anticipate this variation. A clear example in this respect is the large difference in production per ha. between mobile and sedentary livestock production systems. Under similar climatic conditions herds from nomads in Mali and Botswana produced twice to three times more per ha than herds on ranches in USA and Australia (Breman and de Wit 1983, referred to in Livestock and the Environment, finding a balance page 19-20). Many farmers practice a kind of rotational grazing, whereby the duration of grazing is the main variable. Short periods with a high stocking rate are alternated with longer periods without grazing. Availability of water and the quality of feed compared with that elsewhere determine more the time, the duration and intensity of grazing than the quantity of biomass available.
In years of scarcity more of the poor quality biomass can be consumed, but an alternative is to move livestock earlier to other areas. Camels and goats, both browsers, and sheep (selective feeders) may still find enough feed in areas where cattle can not. Consequently the effective carrying capacity of a communal pasture in terms of TLU per ha will vary:
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