A grazing study was conducted in a semi-arid mulga (Acacia aneura) woodland to determine the relative importance of variables controlling sheep production in this environment. The study was based on six sheep stocking rates (0.3-0.8 sheeplha) with the exclusion of other large herbivores including kangaroos and feral goats. The availability of forage and its components, together with the wool growth and live weight of the sheep were measured every three months for seven years from October 1986. Annual rainfall accounted for 60% of the annual variation in live weight gain per head and 79% of the variation in wool growth per head. Stocking rate accounted for an additional 10% of the variation. Rainfall accounted for this large proportion of variation by its strong influence on the yield of green leaf which accounted for 78% of the variation in live weight gain and 66% of the variation in wool growth. Green leaf was a determinant of sheep production because of its superior crude protein content and digestibility compared to dry leaf and stem. The species comprising this green leaf had an influence on sheep production only during drier years when the presence of palatable perennial grasses became important to sheep production. The frequency and yield of perennial grasses were greatly diminished at high stocking rates. This change in forage composition caused a decline in sheep productivity as detected by a loss of linearity in the relationship between stocking rate and live weight gainlhead. We conclude that adjusting stocking rates is required in this environment for maintenance of long-term sheep productivity and landscape function. The loss of palatable perennial C, grasses over much of the region has reduced livestock productivity and increased the variability in forage availability. Stock numbers should be adjusted at critical times to avoid losing perennial grasses that are important for sheep production in drier years. New grazing strategies are required to restore these grasses to the region.
Methods for measuring long-term changes in vegetation and soil condition were evaluated in terms of recording error, efficiency and value in meeting management objectives. The evaluation was made on 4-5 sites for each of six vegetation types across the semi-arid rangelands of South Australia and New South Wales. In the semi-arid woodlands the lowest errors of measurement (C.V. = 12-14%) were associated with point measures of canopy cover, while in the chenopod shrublands the most precise measure in most situations was the density of shrub clumps (C.V. = 12-16%). Measures of herbaceous and litter cover had a high error of measurement (e.g. C.V. = 60%) and observers were significantly different. The point measurement of the area of degraded soil surface was reliable on duplex soils, but not on gradational soils. The results are discussed in terms of their application for the monitoring of change in range condition. It is concluded that the most appropriate measure of the shrub layer is foliar cover in woodlands and clump density in chenopod shrublands.
Seeds of annual and perennial grasses were planted in the field in fall, winter, and spring to test the rapidity of their germination at low temperatures. They were brought from the field into the laboratory at frequent intervals and germinated at 10°C. In general, the longer the exposure to field conditions, the more rapid the subsequent germination. After 1 month of exposure to the winter environment, the ranking of species in order of decreasing rapidity of germination (at 10°C) was as follows: cheatgrass (Bromus tectorumj, medusahead (Taeniatherum asperumj, crested wheatgrass (Agropyron desertorum), Siberian wheatgrass (Agropyron sibiricum), bluebunch wheatgrass {Agropyron spicatum), and smooth brome /Bromus inermis). The order in which seedlings emerged was the same, except that medusahead emerged earlier than cheatgrass. When seedlings are exposed to drought or to competition with other species, rapidity of germination at low temperatures may be important to their survival.
Australia must be regarded as a world leader in the development of grazing production systemsthe yearlong gra7ing of sheep and cattle on grass. Not only have these production systems developed greatly in extent in the postwar period, but they have also developed in productive and economic efficiency. This development has been linked with, and has also financed, considerable scientific investigation of the grazing process.This has been aimed at seeking better animal nutrition and higher production from the land available. Australian scientists in this field are also world leaders, and the whole process, including the science, is now being exported t o developing countries.
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