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The use of rangeland inventory and condition surveys

D.G. WILCOX *

(*) D.G. Wilcox, Senior Adviser, Rangeland Management Section, Department of Agriculture, Western Australia, 6151.


Introduction
Methodology in western Australian surveys
Estimation of stocking rate on grazing areas
Conclusions
Appendix
Bibliography

SUMMARY

Rangeland evaluation techniques used in Western Australia for assessing pasture condition and erosion status are described. The land system approach to land classification and the use of relic or benchmark sites are basic in the methods used. Continuous traverse records of pasture condition, wind erosion, and water erosion can be sorted and converted into statements of range condition and erosion status for areas of up to 100,000 sq. km.

The data obtained during the surveys are used to produce range condition guides which can be used to determine management techniques appropriate to the condition of the country.

Introduction

A number of rangeland workers have undertaken studies of range condition in Australia. Jessup (9) reported a survey of chenopodiaceous shrublands in South Australia and introduced the concept of condition and departure from the pristine state to the maps he produced. He attempted the quantification of range condition over 130,000 sq. km. in that State. Condon et al. (4, 5) reported on range condition in Central Australia. Beadle (1) completed a study of erosion in the Western Division of New South Wales where he described and delineated the areas of erosion on natural grazing land.

These studies have produced maps at scales of one to one million or smaller. While these have been useful in the reporting sense, they cannot contribute to the field management situation without amendment or enlargement of scales. Attempts are being made to survey rangelands in Australia in terms of inventory and condition, at scales which are meaningful to the field worker, property owner, and land administrator. Some of these, notably those of Skinner et al. (11) and Robinson (10) have dealt with specific areas of erosion hazard. In a more general way, the Soil Conservation Service of New South Wales and the Department of Agriculture of Western Australia are preparing reports and maps of range condition at scales of 1: 250,000 and larger. These scales lend themselves to the planning of management strategies for rangeland use and can be used to determine proper courses of action for rangeland rehabilitation.

This paper will deal with the approach to range condition that has been adopted in Western Australia, and with the methods used to put the results of survey into action.

Methodology in western Australian surveys

Range inventory and condition surveys in Western Australia are based upon the concept of the land system defined by Christian and Stewart (2) as an area or group of areas with a recurring pattern of topography, soils, and vegetation. The land system and its component elements are the basic descriptive units used to define the large areas being surveyed.

While inventories of the present status of the area could be made without reference to the relic site or benchmark, it is considered that the surveys achieve more meaning if the variability in condition can be expressed against a definite standard. Clements (3) introduced the concept of relic site to rangeland evaluation, and Dyksterhuis (6) developed the principle further in his description of the Quantitative Climax approach to range condition assessment. He later (7) suggested that departures from climax may be desirable if maximum productivity is to be achieved. Hacker (8) stated that the attainment of maximum productivity commensurate with landscape satisfies the aims of proper range management. He observed that in most instances in the truly arid environment, this requirement is achieved only when the climax or pristine situation is obtained. Since most Western Australian rangeland is arid, the principle of climax condition was adopted as the optimum for ranking purposes.

Preliminaries to survey

Land systems recognisable as distinct, recurring photographic patterns are delineated on aerial photographs at 1:40,000 or 1:80,000 prior to the commencement of the survey. Traverses are then planned and sites selected for examination during a ground reconnaissance of the area. During reconnaissance the accuracy of the interpretation is assessed and preliminary descriptions of the units of the proposed land systems are made.

Descriptions are made of relic sites or sites not far removed from climax, where these can be found, and form an essential part of the technique. Data obtained from long-established benchmark exclosures contribute substantially in this respect.

Species lists of desirable, intermediate, and undesirable species together with precise ground condition statements are compiled where the information is available.

Survey techniques

The field work of the survey falls naturally into two classes. The first deals with definition of each of the elements comprised in the land systems of the area. The other is concerned with the assessment of rangeland condition or departure from the pristine state in respect of each land system, each property or grazing area, and lastly, the whole of the survey area.

Element definition and land system inventory

Rangeland inventory sites are selected on traverse routes through the survey area in order that as many representative examples as possible of each photo pattern may be visited on each property or grazing area. At each site detailed information on geology, geomorphology, soils, vegetation, and soil disturbance are collected for each of the elements of the pattern. The location of the site is pricked onto the aerial photograph and each element of the land system is photographed. The data are processed on computer programmes specifically designed to accept the type of information peculiar to the area being surveyed.

The land systems are described and then mapped at 1: 250,000 scale, as shown in Figure 1. The locations of detailed recording sites and traverse data are also shown. Placed onto cadastral base plans, these maps can be used on a property or grazing area to determine appropriate management techniques. The management systems for each pasture type or land system are set out in range condition, and management guides prepared. In practice these guides are formulated in preliminary form before the survey, but are refined and modified during its course. The practice of continuing detailed observation provides a constant check for the assessors concerned with allocating condition classes to the area being traversed.

Figure 1 - Reproduction at reduced scale of land systems on Mt. Phillips 1: 250,000 base plan from Western Australia. Traverse records and range evaluation sites are shown. Cadastral information includes grazing lease boundaries, homesteads and roads.

Condition assessment

As the areas being surveyed are as large as 100,000 sq. km., the method of condition assessment is related to the size of the areas involved. A continuous traverse record is compiled from a vehicle travelling at 40 km/hr. on traverses planned to sample representative sections of all land systems occurring on the grazing area or property. Visual assessments are made of pasture condition and erosion status as each land system is entered and left, and at each 1.5 km within the land system. For simplicity the definitions described here are those from the survey of the West Kimberley area, and are shown in the Appendix. The erosion assessments are made independently for wind and water effects in four categories. Pasture condition is assessed in five classes derived from reconnaissance information, local knowledge, and the continuing element definition. Two observers are used to reduce bias and drift in the assessments made.

In the survey of the West Kimberley, over 4,500 recordings of pasture condition and soil erosion were made in 45 land systems extending over 90,000 sq. km. The data accumulated were sorted, using a programme designed for the Cyber 72 computer, into the following categories: land systems on each property; each property as a whole; each land system in the survey area; and the survey area as a whole.

Range condition of the area was determined by grouping the traverse results into logical sections based upon a combination of the wind and water erosion and pasture condition statements obtained for each land system. The wind and water erosion data were grouped into a series of four categories of total erosion as shown in Table 1, in order to simplify the process.

Range condition statements for each land system or pasture grouping on every grazing area were established by this technique. Subsequent management of the pastures was related to the recommendations for use contained in the Range Condition Guides. The range condition assessments can be supplied as overlays on individual properties at 1: 100,000 scale.

Table 1 - The derivation of total erosion

Wind erosion

+ Water erosion

= Total erosion

Rating

Nil

+ Nil

= Nil

0

Nil

+ Minor



Minor

+ Nil

= Minor

1

Minor

+ Minor



Nil

+ Moderate



Minor

+ Moderate



Moderate

+ Nil

= Moderate

2

Moderate

+ Minor



Moderate

+ Moderate

= Severe

3

Nil

+ Severe



Minor

+ Severe



Moderate

+ Severe



Severe

+ Nil

= Severe

3

Severe

+ Minor



Severe

+ Moderate



Severe

+ Severe



Range condition or "health" of the basic resources of the range was derived from the total erosion figures described above and the pasture condition statements. Three levels of range condition were selected and determined as shown in Table 2.

Table 2 - Derivation of range condition

Range condition

Total erosion

+ Pasture condition

Good

Nil

+ Excellent

Nil

+ Good

Minor

+ Excellent

Minor

+ Good

Fair


Nil

+ Fair

Nil

+ Poor

Minor

+ Fair

Minor

+ Poor

Moderate

+ Excellent *

Moderate

+ Good *

Bad





Nil

+ Very poor +

Minor

+ Very poor +

Moderate

+ Fair

Moderate

+ Poor

Moderate

+ Very poor

Severe

+ Excellent *

Severe

+ Good*

Severe

+ Fair *

Severe

+ Poor

Severe

+ Very poor

* These conditions were not encountered in the field.
+ These conditions were very rarely encountered in the field.

Table 3 - Range condition - Myroodah Land System

Wind erosion %

Water erosion %

Total erosion %

Pasture condition %

Range condition %

Nil

45.8

Nil

55.0

Nil

34.8

Excellent

1.8

Good

19.1

Minor

34.8

Minor

30.9

Minor

38.5

Good

17.5

Fair

53.4

Moderate

16.5

Moderate

13.1

Moderate

18.6

Fair

46.9

Bad

27.5

Severe

2.9

Severe

1.0

Severe

8.1

Poor

27.0









Very poor

6.8



Summary statements of range condition for each land system were available from the computer sort of the data. The condition of one land system is shown in Table 3.

Using area data, the amount of each land system in specified classes of condition could be determined.

The assessment of erosion status

One of the functions of the survey team was to provide maps of erosion for the information of land administrators. There were a number of difficulties associated with the presentation of wind and water erosion data gathered on the traverse in a form which would give an index of erosion status. The total erosion data provided a breakdown of the various classes of erosion in each land system on each property. At the scale of mapping used (1: 250,000) it was necessary to convert this information to single units.

Figure 2 - A combination of land systems map and erosion index overlay for a station in the West Kimberley area of Western Australia. Severe erosion is shown by dark open stipple, moderate by medium stipple, minor by light stipple. Traverse records are shown together with range evaluation sites.

The Erosion Index was expressed as a value which would place the particular land system in one of four erosion classes, as follows:

EI < 50 nil

erosion,

EI 50-150

minor erosion,

EI 150-400

moderate erosion,

EI > 400

severe erosion.

The Erosion Index for Camelgooda Land System on one grazing area was derived as follows:

An erosion index for each land system was therefore derived from an empirical formula using the total erosion data.

The Erosion Index was defined as:

EI = (x1 + x2 + x3) + (0x0 + 1x1 + 2x2 + 6x3)

where:

x0 = % nil total erosion,
x1 = % minor total erosion,
x2 = % moderate total erosion,
x3 = % severe total erosion.

Rating

No. of observations

% in class

Nil

216

83.1

Minor

38

15.0

Moderate

4

1.5

Severe

1

0.4


EI

= 2(15) + 3(1.5) + 7(0.4)


= 37.3

Nil Erosion.

Figure 3 - Showing a relationship between pasture condition and grazing capacity (cattle units per sq. km year long) in several pasture types in the Kimberley Division of Western Australia.

The erosion index indicating the erosion occurring on each land system on each property was transferred to clear overlays, which were placed on the land systems maps. Figure 2 shows the erosion map prepared during the survey for Margaret River Station. Areas of severe erosion (dark open stipple), moderate erosion (medium stipple), minor erosion (light stipple) and nil erosion can be clearly seen.

Because of the interrelationship between range condition and erosion in all but the most resistant land forms, such overlays record range condition on a property scale.

Estimation of stocking rate on grazing areas

Provided that there is adequate background information, the survey data can be used to derive stocking rates on specific grazing areas. In the West Kimberley area, production data are available for a number of pasture types at various levels of range condition. These are shown in Figure 3, where grazing capacity in terms of cattle units per sq. km is related to pasture condition.

Cattle unit capacities were determined on the basis of an annual consumption by adult cattle of 4,000 kg dry matter, assuming a 40 % utilisation of standing grass crop (Payne and Ryan, priv. comm.). The pasture condition scores for each land system or pasture type can be expressed as a mean value, and the appropriate stocking rate read off the graph.

These are admittedly approximations only to proper use levels, but are considered satisfactory in an area where there is a dearth of information on proper stocking rates.

Conclusions

The method of survey outlined has been used in several field operations which have involved the description and mapping of over 200,000 square kilometres of rangeland in Western Australia. It has proved to be a reliable method for establishing range condition and erosion status in broad terms. More intensive sampling has revealed that minor alterations to the presentation may be necessary under special circumstances. The discrepancies have not detracted from the overall view nor from the usefulness of the techniques as a stimulus for effecting change in the management of overused rangeland pastures.

Appendix

Erosion

Wind and water erosion incidence were recorded in the following fashion.

Wind erosion

Severity

Rating

 

Nil

0

No erosion.

Minor

1

Litter build-up and small scalds.
Small isolated scalds, on which the surface showed some degree of polishing. Re-distribution of soil to the margins of the scald, or minor build-up of soil material around obstacles.

Moderate

2

Large isolated scalds and hummocks.
Stripping of the soil surface and build-up against obstacles associated with large but generally discontinuous scalds; or numerous small scalds scattered throughout the site.

Severe

3

Major deflation of soil surface.
Active stripping resulting in large continuous scalds with polished and sealed surfaces. Frequent large hummocks against obstacles. In sandy systems major dune drift. Plant cover very sparse to absent.

Water erosion

Severity

Rating

 

Nil

0

No erosion.

Minor

1

Rilling.
Patchy rifling and small gullies affecting small areas of the site. Much undisturbed ground between these areas.

Minor

2

Thin sheeting.
This sheeting (1 to 2 cm) and breaking of the surface seal on parts of the site. Some redistribution of soil and litter down slope.

Moderate

3

Gullies and sheeting on lower slopes.
Gullies on the lower slopes or more susceptible parts of the site, these being capable of extension to less susceptible areas. The gullies may be associated with extensive but discontinuous disturbance of the soil surface by sheet erosion and redistribution of soil material.

Severe

4

Terracing or extensive gullies.
Severe sheeting or terracing affecting nearly all of the site. Redistribution of soil and exposure of sub-soil or rock material. The sheeting may be associated with or replaced by very extensive Bullying over most of the site.

Pasture condition

Using information obtained from the Range Evaluation Sites, reconnaissance trips, prior knowledge of the area and experimental data, it was possible to assess pasture condition in the following terms.

Rating

1 Excellent pasture condition.

Nearly all plants present are desirable species, and ground cover is optimum for the site.

2 Good pasture condition.

Most plants present are desirable, with intermediate perennials and annual types increasing in frequency; a few undesirable species may be present.

3 Fair pasture condition.

Intermediate value species usually predominate; desirable and undesirable species occupy similar proportions of the available ground space. Small patches of bare ground may be present.

4 Poor pasture condition.

Undesirable and intermediate species predominate in the stand; desirable species are very infrequent and may occur only in small patches. The overall stand may be sparse or patchy with frequent small areas of bare ground.

5 Very poor pasture condition.

Undesirable species or bare ground predominate; there are few intermediate species and virtually no desirable species in the stand.

Bibliography

1. BEADLE, N.C.W. - The vegetation and pastures of Western New South Wales, with special reference to soil erosion (New South Wales Conservation, Dept. of). Sydney, Govt Printer, 1948. 281 p.

2. CHRISTIAN, C.S. and STEWART, G.A. - Methodology of integrated surveys. In " Aerial Survey and Integrated studies". 1968. Proc. Conf. UNESCO. Toulouse, 1964. pp. 233-280.

3. CLEMENTS, F.E. - The relict method in dynamic ecology. J. Ecol., 1934, 22: 39-68.

4. CONDON R.W., NEWMAN, J.L. and CUNNINGHAM, G.J. - Soil erosion and pasture degradation in Central Australia, Part III, The assessment of grazing capacity. J. Soil Conserv. Serv. N.S.W., 1969, 25: 225-295.

5. CONDON, R.W., NEWMAN, J.L. and CUNNINGHAM. G.J. - Soil erosion and pasture degradation in Central Australia. Part. IV. J. Soil Coursers. Serv. N.S.W., 1969, 25: 295-321.

6. DYKSTERHUIS, E.J. - Condition and management of rangeland based on quantitative ecology. J. Range Mgmt., 1949, 2: 104-115.

7. DYKSTERHUIS, E.J. - Ecological principles in range management. Bot. Rev., 1958, 24: 253-272.

8. HACKER, R.B. - Some concepts in rangeland management. J. Agric. W. Aust., 1974, 15 (4th ser.): 76-80.

9. JESSUP, R.W. - The soils, geology and vegetation of North Western South Australia. Trans. r. Soc. S. Aust., 1951, 74 (2): 189-273.

10. ROBINSON, C.S. - Ecology of the Hardman Basin. Darwin, Animal Industry and Agriculture Branch, N.T. Admin., 1971. (Tech. Bull. n° 6).

11. SKINNER, A.F., GILLIES, C.C. and MILTON, L.F. - An erosion survey of the Upper Nogoa Catchment. Div. of Land Util. Queensland Dept. Prim. Ind., 1972. (Tech. Bull. n° 6).


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