Abstract:
Proc. Aust. Soc. Anim. Prod. (1972) 9: 381 COMMUNITY PREFERENCE BY FREE RANGING SHORTHORNS IN THE ALICE SPRINGS DISTRICT W. A. LOW* Summary During below average rainfall years, cattle demonstrate a preference for plant communities on flood-on and flood-over areas following significant rainfalls. Distribution of cattle is altered markedly by locally significant rains. Savanna woodland and flood plain areas appear to carry the most consistent densities, about 3.5 cattle per square km. Densities up to 40 cattle per square km have been observed on one minor community. I. INTRODUCTION One serious enigma of the pastoralist operating on the extensive basis common to the Australian arid land cattle industry (Kelly and Williams 1953) is grazing preference and the control of grazing intensity. Average grazing densities are meaningless under extensive, systems, since cattle forage selectively in the variable environment. Inevitably some areas receive heavy grazing pressure and other areas low grazing pressure. At present, there is some data on plant species preferences at the end of a long draught (Chippendale 1968), but information available on preference shown by cattle for different plant communities in arid areas is of a subjective or inferential nature (e.g. Perry 1960; Condon et al. 1969). This study is designed to determine the preference and grazing density, and when related to concurrent studies on the plant communities, to provide objective information on factors affecting distribution and community preference of cattle in the arid lands. It is part of an overall study of rangeland ecosystems being conducted by the Rangelands Research Unit, CSIRO. II. STUDY AREA The study is being conducted on l53 sq. km (59 sq. mi.) Kunoth paddock, adjacent to the north side of the Mac.Donnell Range, 48 km (30 miles) NW of Alice Springs. The area is described as arid (Slatyer 1962). The long term rainfall average is about 25 cm per year, most of it falling in the summer. Droughts occur about 27 years in a hundred (R. A. Perry personal communication). During the 18 months of the study rainfall has averaged 13 cm per year. The area includes Bushy Park, Hamilton and a small section of Boen Land Systems and lies adjacent to Harts and Bond Springs Land Systems (Perry et al. 1962). The paddock was chosen as a study site because its complexity 1s representative of the cattle grazing areas in the centre of Australia. TSIRO, Rangelands Research Unit, Alice Springs, Northern Territory, 5750. The Land Systems have been divided into relatively homogeneous range communities. These will be described in more detail in another paper; however, a brief description is presented in Table 1. There is considerable interdigitation of some of these communities, and ecotones vary from sharp to ill-defined. TABLE 1 Range Communities on Kunoth Paddock 382 383 III. MATERIALS AND METHODS In excess of 500 head of Shorthorn cows, calves, bulls and heifers are allowed to range freely within the paddock. They are mustered about twice a year. Observations of cattle are made at fortnightly intervals from low-flying aircraft. The paddock, excluding the portion in Harts and Bond Springs Land Systems in the MacDonnell Range, has been divided into 65 hectare cells with large alphanumeric plates visible from the air. The aeroplane is flown along every other transect, i.e. at 1.6 km (one mile) intervals, and the pilot calls out the cell numbers. Cattle are observed in a 0.8 km wide transect from both sides of the plane by experienced observers, and their location noted on a map in the appropriate cell and plant community. The distribution is summarized by determining the density of cattle present in each of the communities on the portion of the paddock on which the grid has been established. Cattle grazing in the adjacent Harts and Bond Springs Land Systems in the MacDtonnell Range were calculated as absolute numbers, because the area has not yet been mapped in sufficient detail to merit calculations of density. The data have been examined with reference to significant winter and summer rainfalls. Rainfall was arbitrarily designated as significant if it was over 1 cm in the winter and over 2.5 cm in the summer. This paper reports the results of observations made from February, 1970, to August, 1971. IV. RESULTS The number of cattle seen during the aerial surveys ranged from 57 per cent to 100 per cent (mean 77 per cent) of the cattle released in the paddock. Densities of cattle on each of the important plant communities are shown in Figure 1. The average grazing density for the gridded portion of the paddock was between 1.4 and 3.2 (mean 2.1) cattle per square km. Cattle have not yet been observed grazing in the hard spinifex community. Cattle in the adjacent MacDonnell Range are shown in absolute numbers and not related to area in Figure 1. During the study rain fell on 12 occasions of which 10 were relatively evenly distributed over the paddock (Figure 1). Five of these rains were judged significant. Two falls were concentrated on the calcareous grasslands. It is apparent from observations of changes in their distribution, that cattle demonstrate a sequence of plant community preferences that is altered slightly by the season of growth-inducing rainfalls. Following the general summer rain of December 8, 1970, the density of cattle increased on the foothill fans and gilgais within three weeks. A fortnight later, the density on the calcareous shrubby grassland and flood plain coincident with that on the mulga shortgrass increased at the expense of the density on the gilgais and foothill fans. This was followed a fortnight later with an increase in density in the savanna woodland areas. Locally important rains on the calcareous shrubby grasslands and gilgais in March 1971, interrupted the pattern at this stage. Following the two winter rains in June-July, 197 1, cattle densities increased on the gilgais and flood plains, followed by increases on the calcareo.us shrubby grasslands, foothill fans, savanna woodlands and mulga shortgrass. Locally significant rains such as the falls of November 16, 1970 and March 19, 1971 caused marked shifts in cattle distribution. Heavy rains on both these occasions brought on good growth in the calcareous shrubby grassland, and filled a nearby dam, which resulted in an influx of cattle to that area. Average densities of stock on the seven grazed communities on Kunoth Paddock are shown in Table 2. Mean densities afqd standard errors of cattle on, and areas Kunoth Paddock, 1970-71. TABLE 2 of the communities of V. DISCUSSION Variability in numbers of cattle observed on different communities was a result primarily of distribution of the animals. When the majority of animals were in the open areas, the counts approached total counts. However, when cattle moved into the wooded areas and the hills of the MacDonnell Range the proportion of cattle observed declined. Calibration has not yet been done of visibility of cattle in the three wooded communities, but it is certainly less in the mulga-perennial grass areas than in the mulga-shortgrass and savanna woodland areas. The density of animals observed on the gridded portion of the paddock could be altered slightly when correction factors for observability are used. However, concurrent ground surveys indicate that there is no great discrepancy in the aerial observations. The run-on and flood-over communities exhibit the greatest fluctuation in cattle density, and after rains reach densities as high as 36 cattle per square km. The savanna woodland appears to carry consistently the highest density, except during dry periods when animals scatter widely in search of suitable forage. The mulga-shortgrass and mulga-perennial communities have relatively low grazing densities under observed conditions, and following rain most animals leave these areas for the more open areas. It is in the mulga-perennial areas that graziers carry their stock through drought with best survival (T. W. Prior personal communication). A preference' hierarchy has been tentatively designated as shown in Table 3. The plant community preference hierarchy varies slightly from winter to summer due primarily to different plant species growth response. In winter, some forbs 385 and perennial grasses respond to rain; hence gilgaied areas with Eragrostis setifolia and E. xerophylla are sought out initially. Following summer rains, the flood TABLE 3 Hierarchy of cattle preferences for plant communities in the Hamilton, Bushy Park and Boen Land Systems near Alice Springs plains produce annual grasses and appear to be sought out first. A complicating factor here is that perennials tend to respond most quickly after any rain, and cattle initially graze these plants. However, as soon as annual grasses reach grazeable height, the cattle prefer these over perennials. Cattle distribution over extended periods appears to be controlled under free-ranging conditions by several factors : rain, surface water for drinking, and the growth response, palatibility, quantity and quality of the vegetation. The importance of these factors in controlling distribution of cattle is under study at present. VI. ACKNOWLEDGMENTS The co-operation of Mr. R. N. D. Miller, owner, and T. W. Prior, Manager, of Hamilton Downs Pastoral Station, Alice Springs, is gratefully acknowledged. I appreciate the help of Mr. R. M. Hodder and Dr Robin Tassel1 for assistance in collection and analysis of the data, Boyne Carragher for typing, and the officers and staff of the Rangelands Research Unit for general discussions and assistance. VII. REFERENCES Chippendale, G. M. (1968). Primary Industry Branch (N.T.A., Darwin) Technical Bulletin No. 1. Condon, R. W., Newman, J. C., and Cunningham, G. M. (1969). Journal of the Soil Kelly, J. H. and Williams, D. B. (1953). Economic Record. 29: 189. Perry, R. A. (1960). Land Research Series, C.S.I.R.O. Australia. No. 5. Perry, R. A., Mabbutt, J. A., Litchfield, W. H. and Quinlan, T. (1962). Land Research Slatyer, R. 0. (1962). Land Research Series, C.S.I.R.O. Australia. No. 6. Series, C.S.I.R.O. Australia. No. 6. Conservation Service, New South Wales. 25: 225. 386