CHANGE IN RANGE CONDITION WITH DISTANCE FROM

Aust. Rangel. J . 2(1) 1 9 8 0 , 59-66

CHANGE IN RANGE CONDITION WITH DISTANCE FROM WATERING POINT AND ITS IMPLICATIONS FOR FIELD SURVEY B.D. Foran CSZRO, Divisio~zo f Land Resources Management, P. 0. Box 21 11, Alice Sprit~gs,N, T. 5 750.

Abstract The effect of distance from a water point on range condition was examined for two rangeland types in central Australia; an open woodland community and a mulga annual community. Range condition was measured o n a systematic grid pattern around the bore using the STARC method. In open woodland, range condition improved at about 2 km from water, but in mulga annual no change was detected due partly t o a low number of sites close t o the bore. The location of sampling sites adjacent t o station roads did introduce some bias vrhen compared t o the mean score over the whole area. The amount of bias acceptable must be seen in relation t o factors such as time available for survey and the ease with which sample sites can be relocated. Two to four sampling sites located at a distance greater than 2 km, in rangeland preferred by cattle gave a mean score within 30% of the true mean for the whole area with the influence of 'sacrifice area' excluded. A reasonable accuracy of range condition sampling can be achieved in extensive central Australian rangelands. by stratifying the areas sampled with respect t o country preferred by cattle and distance grazed from water.

Introduction The pastoral industry in Australia's rangeland areas has often been criticised because of environmental degradation that becomes apparent following drought periods (Anon. 1901 ; Ratcliffe 1936; Chippendale 1963). This concern for t h e environment now exists widely, b u t in only some areas has it stimulated land management agencies t o develop monitoring methods based on the concept of range condition and trend (Paylie et al. l 9 7 4 ) , which have been adopted and modified from the principles developed by American range workers such as Dyksterhuis (1958). One such method for assessing range condition, STARC, has been developed for central Australian conditions by Lendon and Lamacraft (1976). Thc STARC method compares plant composition of the site t o be assessed with that of the same pasture type that has been well managed. The area of rangeland which surrounds a permanent watering point is seen as a management unit and has been described as a 'piosphere' b y Lange (1969). Within the piosphere there is a tendency for any environmental damage to decrease as the distance from water increases. The changes in vegetation density and cover with distance from water were investigated on rangelands in southern Australia dominated b y perennial chenopod shrubs (Osborn et al. (1932); Barker (1972); Graetz (1978); Graetz and Ludwig (1978)), and it was found that most of the changes took place over the first 2 k m . Craetz and Ludwig (1978) suggested that the ideal place to monitor the reaction of vegetation t o grazing animals (and hence 'ange condition) is where the biggest changes occur over the shortest distance. Vegetation measurements made in this area should be more sensitive t o changes in grazing animal management. GI-azing o f rangeland pastures is seldom uniform; it varies both with the pasture typles that free ranging animals prefer t o graze and with the distance and direction from a watering point that anilnals will move before grazing. Low etal. (1980) and Hodder and Low (1978) have detailed a hierarchy of grazing preference by cattle for a series of central Australian rangelands which can be used t o predict where the majority of the herd will choose t o spend their grazing time. T!lese prefereed rangeland types are responsible for a significant proportion of animal production, and are also most prone t o environmental degradation because of the grazing pressure exerted there. The distance that cattle will walk out from water is determined b y a complex of many interacting factors, but in central Australia, Hodder and Low (1978) found that the majority of cattle grazed within 3 o r 4 km under good and moderate forage supply and forage quality, while o n t h e Barkly Tableland, Yeates and Schmidt (1974) described the n 8 km. usual feeding areas for 'non walkers' between 1.6 k m and 3 k m , and for 'walkers' between 6.4 k ~ and

B.D. Foran

Although the STARC methodology had been developed there was little current information on how t o apply it to the survey of large properties. From the information available o n cattle behaviour and change in vegetation with distance from water it seemed that a reasonably accurate estimate of condition score around a bore could be obtained b y selecting sites adjacent t o permanent vehicle tracks, a t a distance of 3 k m or more from the bore, in a rangeland type that had a high preference for grazing cattle. This paper reports a study designed t o test this hypothesis of sampling methodology around a bore which was typical of rangeland types in central Australia and was grazed by a commercial beef herd.

Methods Stud-v site Brumby Bore o n Milton Park Station, 8 0 k m north-west of Alice Springs, was chosen as the study area (see Fig. 1). T w o major rangeland types were represented: open woodland occurring o n coarse textured alluvial soils with an overstorey of scattered palatable shrubs and trees and a field layer of nutritious short grasses and forbs; -

mulga annual on l o a n ~ ysoils with mulga (Acacia atzeuva) over a predominantly annual field layer of grasses and forbs.

Mounta~n Floodplain Open Woodland

Fig. 1. Location map. There were six minor rangeland types represented with Cottonbush Flat, a floodplain rangeland type with cottonbush (Maireana aphplla) on texture contrast soils, being the most important. This bore was flanked by two other watering points which were available t o free ranging livestock: Ildirika Dam, 9.3 k m t o the east and Cattle Creek Bore, 8.5 km t o the north-west. The grazing area was restricted to the ~ 0 ~ 1 bt hy mountain ranges and was adequately served b y station roads. Samplilzg Procedure Range condition was assessed using the STARC method (Lendon and Lamacraft 1976) which relates species composition (measured b y biomass) of a particular site, t o that of a benchmark of relict site, and expresses the results as STARC units with a maximum total of 100. Tests made during the development of STARC showed that there were only minor differences between properly trained observers in the scoring of plant composition. The

Change in range condition ~ v i t hdistance from watering point

observers in this trial had been ~lsingSTARC in the field for one year and were consistent in their estimations. They were divided into two groups (Group A - 2 observers; Group B - 3 observers), with one group assessing sites east of the bore, and the other group sites west of the bore. Vegetation types were mapped from 1 :25,000 aerial photos and then a 1 km grid was imposed on the whole area. Distance of the sites from Brumby Bore varied from 0.44 km t o 6.24 km. A total of 9 3 sites were surveyed of which 4 3 were in open woodland, 3 6 were in mulga annual and the remaining 1 4 were in minor rangeland types. In addition t o the STARC condition score each site was graded 'typical' or 'not typical' of the rangeland type in question. This is an assessment of whether the site is true to type (soil type, woody plant composition, ground strata); if a site lay in the interzone between open woodland and mulga anliual with some characteristics of each rangeland type but retaining a dominant open woodland character it was classified as 'open woodland - not typical'. This classification resulted in two types of data: - 'not restricted' containing sites that were 'typical' and 'not typical'; - 'restricted' containing only 'typical' sites.

Statistical analysis The scores for open woodland and mulga annual were separated into distance classes with a class interval of 1 km. These groups were subjected t o an analysis of variance using a two-way classification with unequal numbers in the cells with means adjusted for non-orthogonality.

Results The mean score for open woodland was 56.4 t 2.3 (Table 1). There was a significant increase in condition score with distance from water, with scores of 42.5 t 3.1 and 46.3 t 2.5 for the first two distance classes, rising t o 62.9 t 3.6 for the next class and being maintained beyond 4 km (Table 2). The effect of including t!ie 'not typical' sites in the analysis was to increase the experimental error; for example, the residual variance increased from 78.8 for the restricted data t o 114.3 for the unrestricted data. There was a significant difference in mean condition score between sites east and west of the bore (16.3 ? 3.5 STARC units). Since there was n o interaction between sites and distance from bore the distance means were averaged over the t w o groups o f sites.

Table 1. Mean STARC condition scores of different rangeland types around Brumby Bore.

Type of rangeland

Mean and S.E. (mean)'

Open woodland

56.4 i 2.3

Mulga with an annual understorey

64.9 1 2 . 3

Other rangeland types3

Coefficient of variation %2

No. of sites

-

Total 1 . S. E. (mean) =

2. C.V.

Standard deviation J I1

- Standard deviation -

mean

x 100%

3. There were six ottiei langeland types of which "cottonbush flat" with five sites was the most important.

Table 2. Mean condition score for each distance class from water for open woodland Distance class from water (km)

Mean

Data restricted* N S.E. (mean)

Mean

Data not restricted* N S.E. (mean)

'Not restricted' contains sites that have been classified 'typical' and 'not typical' of the rangeland type being assessed, while 'restricted' contains only 'typical' sites. Means adjusted for non-orthogonality

unequal nlurnbers within each distance class.

Mulga annual had an average score of 64.9 -+ 2.3 which was higher than that for open woodland (Table 1). Sites were not evenly distributed among distance classes with the greater proportion present in the classes beyond 2 k n ~and , there was no sigliificant change in condition score with distance (Table 3). nor was there significant difference between the areas east and west of the bore. The inclusion of the h o t typical' sites in the analysis again resulted in an increase in experimental error with the residual variance increasing from 128.8 in the 'restricted' data t o 169.7 for the 'unrestricted' data. These variances are larger than those for sites in open woodland and tend t o suggest that nlulga annual is nime difficult to score or is, in itself, more variable.

Table 3. Mean condition score for each distance class from water for mulga annual. Distance class from water (km)

* +

Mean

Data restricted* N S.E. (mean)

Mean

Data not restricted* N S.E. (mean)

'Not restricted' contains sites that have been classified 'typical' and 'not typical' of the rangeland type being assessed while 'restricted' contains only 'typical' sites. Means adjusted for non-orthogonality

-

unequal numbers within each site

111 order t o investigate a strategy for sub-sampling b y stratifying sampling sites into areas of easy access, a comparison was made of scores obtained over the whole area and those !ying adjacent t o station tracks (Table 4). For open woodland the differences were not significant for the unrestricted data, b u t significant for the restricted data. The reverse was true for the mulga annual rangeland type.

The level of precision obtained by a specific mode of field sampling (position of sites, numbers of sites) determines the extent to which the result can be generalised. The number of sites required for sampling t o give a score within a certain percentage of the true mean is given for different coefficients of variation (Table 5). The C.V. for the restricted data in the open woodland and mulga annual is 19% and 21% respectively. At this level

Change in range condition with distance from watering point

two to five sites are needed to give an 80% probability that the sample mean lies within 30% of the true mean. A sample mean within 10% of the true mean would require a greater number of samples than would be feasible given the cost constraints of this type of range survey.

Table 4. A cornparison of condition scores for the whole bore area and those adjacent to roads for open woodland and mulga annual.

Type of rangeland

Type of data used -

Open Woodland

Mulga Annual

Data from the whole area Mean and S.E. (mean)

Test for significance

N

Data adjacent to roads Mean and S.E. (mean)

N

-

-

N.s.'

Not restricted2 A11 distances from bore

56.4 1 2 . 3

43

53.5 5 5.7

7

Restricted2 All distances from bore

55.8

12.4

37

45.0 5 2.8

5

Not restricted2 All distances from bore

64.9 + 2.3

36

76.4 5 2.7

7

sig.5%'

Restricted2 All distances from bore

64.6

28

74.0

+ 4.8

5

N.s.'

f 2.5

~ i ~ . 5 % ~

--

-

Both a 'one way AOV' with 'F test', and a two sample 't test' was used t o test these groups.

'Not restricted' contains sites which have been classified 'typical' and 'not typical' of the rangeland type being assessed. while 'restricted' contains only 'typical sites'. Modified 't test' used because of unequal variances.

Table 5. The number of sites needed to give a STARC condition score within a certain percentage of the true mean (95% confidence interval) with an 80% probability of being correct (after Cochran and Cox 1957). Desired Confidence Interval as percentage of the mean (5 %j

Open Woodland - not restricted Open Woodland - restricted Mulga Annual not restricted Mulga Annual - restricted -

Coefficient of Variation

15

20

Coefficient of Vaiiation % 27 19 21 21

25

B.D. Foran

Discussion The 'piosphere effect', or the environmental damage caused by grazing animals returning I-epeatedly to a permanent watering point is only one of the many factors which contribute t o the alteration of vegetation by free ranging domestic herbivores in the rangelands of Australia. The heavy utilization by sheep of Astvehla grasslands near Blackall in Queensland was attributed to wind direction and shade availability as well as position of watering facilities (Orr 1979). In the rangelands of central Australia grazed by predominantly British breed cattle. the type of rangeland community and its palatability is one of the dominant factors affecting animal distribution in the long term, and climatic effects such as forage availability and greenness produce only short term alterations to the established pattern (Low et al. 1980). I

The support of a piosphere theory does not therefore accept that distance trailed to water is the only factor involved in grazing utilization, but it is one that is under the control of management and easily quantified. The use of range condition concepts and methodology is an attempt to integrate changes to tlie environment which are caused by management, and t o separate them from those effects which are purely seasonal. The STARC methodology underwent a considerable amount of development in central Australia, and the testing procedure which was used to differentiate between sites in varying range condition, isolated change in plant composition as the factor most useful in range condition definition, and the one least prone to observer error provided there was sufficient observer training. The acceptance of STARC as an environmental monitoring tool in rangelands grazed by cattle does not constitute therefore a step into the unknown, but is merely an extension of a developed methodology into a practical field situation. Stratification procedures such as those tested in this study, were seen to be an integral part of STARC use, in order to allow the time available for sampling to be used in those rangeland types susceptible to degradation and/or important for animal production. This study showed that for open woodland the environmental damage caused by grazing anima!s (measured by STARC condition score) decreased significantly after 2 km from the watering point. This agrees with vegetation studies in other rangeland types by Graetz (1978), Graetz and Ludwig (19781, Barker (1972), Osborn et al. (1932), and Leys (1977). The reasons for the relationship between environmental damage and distance ranged by cattle out from permanent water, have been detailed by Yeates and Schmidt (1974), Hodder and Low (1978) and Low et ul. (1978). If the vegetation on this study area was perfectly uniform, then the zones of different condition scores might form annuli around the watering point. This is not the case however, due to the differential preferences that grazing animals exhibit for different rangeland types. The community preference hierarchy reported by Hodder and Low (1978), suggested the animals watering on Brumby Bore tended to graze cottonbush flat, the open woodland, and then mulga annual. This was reflected in their relative range condition scores with cottonbush flat 40.0 (results not presented due to small number of sites arid minor area), open woodland 56.4, and mulga annual 64.9. Graetz and Ludwig (1978) showed a sigmoid relationship between distance from a watering point and vegetation change. They suggested that two permanent monitoring sites be established to characterise the effects of management on any watering point. The first should be in the area where condition changes most rapidly, and should be used to monitor condition change with time, that is to provide an estimate of range trend. The other should be as far away from water as is possible so that it has a relatively low grazing pressure and will give an appreciation of changes due to season. Both these aims are valid, and are comparable to the accepted basis of range condition theory, that is, separating out the management from the seasonal effects. However, the initial aim of condition assessment in central Australia is to define the condition of the majority of the country as an aid to modifying long term stocking capacities, and then using permanent survey sites to assess condition change with time (G. Bastin and G. Pearce, pers. comm.). This aim requires that condition be monitored, not where it is most sensitive to change (around 2 km for open woodland) but at a distance of 3 km or more from the watering point where condition score has been stabilized, and where the effect of the 'sacrifice area' close to the watering point has diminished. The amount of country available for the grazing animal increases by the square of the distance from water, and so condition assessment sites placed further from the bore, are representative of a greater area of country and also representative of those areas that can carry large numbers of stock when forage is green and abundant (Hodder and Low 1978). The distance from water at which change in condition score for mulga annual was most sensitive is not possible to define in this study, because there were few areas represented near to Brumby Bore and only two sites were assessed within the 2 km range. Since mulga annual has a lower preference than open woodlands in the grazing

Change in range condition with distance b o r n watering point

hierarchy (Low et al. 1980), the sensitive area for condition change in mulga annual is probably closer than 2 1:m since it receives less grazing pressure throughout the year. In order to assess range condition of mulga annual over the watered area available for grazing animals, a distance of 3 km or more would still apply since the score at this distance has stabilised. The significant difference that existed between the areas of open woodland east and west of the bore was due to the effects of site rather than differences between the two groups of observers, who had trained and worked together for the previous year on smilar types of country. Because of the expected agreement between observers and practical constraints imposed by the field design of the experiment, between and within observer variability was not included as a consideration. Studies of cattle behaviour around Brumby Bore indicated that areas to the east and north-east of the bore received heavy usage at particular times during the year 1976-77 (R.M. Hodder, pers. comm). If this is a reflection of long term use it could help to explain the distribution of lower condition sites on the eastern side of the study area.

In the condition assessment of large areas of extensively managed cattle station the location of assessment sites adjacent to station tracks is seen as a necessary aid to rapid survey in the first place, and as an aid to easier relocation of sites on subsequent sueveys. Two of the four analyses performed showed no significant difference between sites located on tracks and the sites spread over the whole area. The other analyses of unrestricted data for mulga annual and restricted data for open woodland showed significant differences of 11.5 and 10.8 STARC units respectively. This is difficult t o explain. In both rangeland types, using the classification of sites into 'typical' and 'not typical', the process of stratification by locating sites adjacent to roads or tracks seems justified, bearing in mind that the first step in range survey is to interpret aerial photographs, on which relatively homogeneous areas, representing different rangeland types, are delineated. Sites are then marked in these areas before ground survey is undertaken. The number of sites assessed for each watering point is limited by the availability of personnel and time. Two to four sites per watering point (200 km2 available for grazing with an 8 km radius), stratified by rangeland type and distance from water, would seem to be the maximum that can be achieved for central Australian conditions. At this level of sampling there is an 80% chance that the mean score will be within 30% of the true mean of that rangeland type with the influence of the sacrifice area excluded.

Acknowledgements

I would like to thank the following: Mr. Milton Willick, the owner of Milton Park Station for his permission t o survey Brumby Bore; my colleagues from the Division of Primary Industry, Northern Territory Government, who made up the survey team, G. Bastin, D. Petty, G. Pearce and S. Liebolt; and K. Cellier of the Division of Mathematics and Statistics who helped with the statistical analysis. References Anon. (1901). Royal cornmission to inquire into the condition of Crown tenants. Western Division of New South Wales. (Govt. Printer: Sydney.) Barker, S. (1972). Effects of sheep stocking on the population structure of arid shrublands in South Australia. Ph.D. thesis, University of Adelaide, S.A. Chippendale, G.M. (1963). Pasture deterioration in central Australia. J. Aust. Inst. Agn'c. Sci. 29(2), 8 4 - 9 Cochran, W.G. and Cox, G.M. (1957). Experimental designs. 2nd Ed. (John Wiley: New York.) Dyksterhuis, E.J. (1958). Ecological principles in range evaluation. Bot. Rev. 24,253-72. Graetz, R.D. ( I 978). The influence of grazing by sheep on the structure of a saltbush (Atriplex vesicaria Hew. ex Benth.) population. Aust. Rangel. J. 1 , 1 17-25. Graetz, R.D. and Ludwig, J.A. (1978). A method for the analysis of piosphere data applicable to range assessment. Aust. Rangel. J. 1, 126 -36.

B.D. F o r a n

Hodder, R.M. and Low, W.A. (1978). Grazing distribution of free-ranging cattle at three sites in the Alice Springs district, central Austraha. Aust. Rangel. J. 1,95-105. Lange, R.T. (1969). The piosphere, sheep track and dung patterns. J. Range. Manage. 22,396-400 Lendon, C. and Lamacraft, R.R. (1976). Standards for testing and assessing range condition in central Australia. Aust. Rangel. J. 1 , 4 0- 8 . Leys, D.M. (1977). Pasture utilization by free-ranging cattle in central Australia. B.A.(Hons.) thesis, A.N.U., Canberra. Low, W.A., Hodder, R.M. and Abel, D.E. (1978). Watering behaviour of British breed cattle in central Australia. In 'Studies of the Australian arid zone. 111. Water in rangelands'. (Ed. K.M.W. Howes) (CSIRO: Melbourne.) Low, W.A., Muller, W.J. and Dudzinski, M.L. (1980). Grazing intensity of cattle on a complex of rangeland communities in central Australia. Aust. Rangel. J. 2, 76-82 -

Orr, D.M. (1979). Effect of sheep grazing Astrebla grassland in central western Queensland. M.Agr.Sci. thesis, Department of Agriculture, University of Queensland. Osborn, T.G.B., Wood, J.G. and Paltridge, T.B. (1932). On the growth and reaction to grazing of the perennial saltbush, Atriplex vesicarium. An ecological study of the biotic factor. h c . Linn. Soc. N.S. W ,57,377-402. Payne, A.L., Kubicki, A. and Wilcox, D.G. (1974). Range condition guides for the West Kimberley area, W.A. (West Aust. Dept. Agric.: Perth.) Ratcliffe, F.N. (1936). Soil drift in the arid pastoral areas of South Australia. C.S.I.R. Pamphlet No. 64. Yeates, N.T.M. and Schmidt, P.J. (1974). 'Beef cattle production'. (Butterworths: Sydney.) (Manuscript received 3 January 1980)

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