Dundas Land System Figures 29-30 (PDF - 418KB)
To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).
Plate 18.-The Dundas land-system is a flat tableland supporting a savannah woodland-usually of red gum.
|Visitors to south-western Victoria who travel from Hamilton to Casterton or Harrow nearly always remark on two things-the impressive stands of spreading red gum and the remarkably flat plateau, sharply dissected in parts. These two features together are the chief characteristics of most of the Dundas land-system, although on its southern fringe, red gum (Eucalyptus camaldulensis) is replaced by other eucalypts. Strictly, the Dundas land-system is the area of the lateritised tableland, where it is not deeply dissected nor predominantly covered with acid white sands.
Nature and Extent
The land-system is restricted to the cast of the Kanawinka fault-line, becquse to the west of the fault the land has been covered by lacustrine and aeolian deposits. It is also restricted to the north-west of a line from Hotspur to Hamilton, because to the south-east of that line, basaltic flows of a later age cover the surface. Dissection of the tableland has been chiefly by the Glenelg and Wannon Rivers and their tributaries, so that the bulk of the land-system lies towards the centre of the huge circle enclosed by those two rivers.
The dissected areas falling away sharply from the plateau constitute two other land-systems, the Glenelg and the Casterton. Both of these land-systems, although radically different in nature from the Dundas land-system, have some degree of inter-dependence with it, particularly in their hydrology; these aspects are considered in more detail in the description of the other two land-systems, but some of the remarks on the land-use of the Dundas land-system apply also to one or both of the other two land-systems.
Dundas is the biggest single land-system in the area surveyed. It covers about 384,000 acres and is almost entirely alienated; only 2 per cent, about 8,000 acres, remain with the Crown. Together with the Glenelg land-system, the Dundas land-system provides the bulk of the data on use, area and production from the County of Dundas.
Average annual rainfall varies from 31 inches on the south-western fringe of the land-system to 24 inches on the north-eastern fringe, with a local area of the Brim Brim Plateau receiving up to 33 inches; the greatest part of the land-system probably has between 26 inches and 29 inches. Evidence on pp. and shows that towards the north of this land-system not only is the average annual rainfall lower but also the temperatures have a wider daily and seasonal range than in the rest of the survey area. This feature probably reduces the total period during which there is plant growth in comparison with that in other parts. The seasonal rate of plant growth is probably less favourable than that presented for the climate at Hamilton in Fig. 9.
Laterite is the chief parent material of the soils on this land-system, apart from swamp deposits and small areas of blown sand. Within the boundaries of the land-system, the laterite is dissected to a slight degree, but, except for the Brim Brim land-unit where shallow drainage lines are formed, the dissection within this landsystem does not go deeper than the base of the laterite; as mentioned before, if dissection be deeper, such areas have been separated out as other land-systems. The laterite profile itself, has horizons of widely differing character. They are an upper reddened and iron-rich zone which is frequently indurated, a mottled red and white zone and a lower pallid zone wherein the clay is rich in kaolin.
The soils vary according to their topographic position, the laterite horizon upon which they are formed, and the nature of the material which was lateritised.
Thus, on the upper, indurated zone of the laterite, and where slight dissection has left this in a well drained position, the soil is a red solodic soil with ironstone gravel throughout. On flatter positions, the most common soil is the Koroite series of Blackburn and Leshe (1958), with abundant ironstone gravel, and the lower parts of profiles of this series probably extend into the mottled zone of the laterite. Lower positions in drainage lines have soils where the mottling is duller and sometimes the subsoil is grey, suggesting the old pallid zone of the laterite.
In the Brim Brim land-unit, the textural boundary of the A and B horizons of most soils is not so sharp, the soils being intermediate between solodic soils and medium-textured leptopodsols. This feature may result from the higher rainfall. Also in this land-unit, there is a more pronounced variation in the soils of different topographic positions owing to the gently rolling topography.
Tableland material has been transported off the tableland itself to form the soils of the upper part of the steep slopes immediately beneath it. In swamps the soil is the Parkwood series, a heavy calcareous soil sometimes showing gilgai features. Apart from the swamps, gilgai soils are very rare in this land-system, except on part of the Dundas land-unit in the extreme north-east of the survey area, near Balmoral. Here, however, they are common, and in fact are co-extensive with large areas of similar gilgaied country in the Shire of Kowree.
Blackburn and Leslie (1958) have described in detail the chief soils of small parts of the Dundas, Glenelg and Casterton land-systems around Coleraine, and their remarks apply to most of those land-systems. This and the Glenelg land-systems are the chief areas of the solodic soils (except the Nornumby family) or shallow sands as contrasting with the deep sands on the one hand and dark clays or "earths" on the other. The remarks made there about such soils apply particularly to these two land-systems and may be summarised as follows : The nutrient status of the soils is moderate, and the chief physical feature of the soils, the presence of an impeding layer near the surface, has an advantage for shallow-rooted species in this climate because it retains the water within the root zone.
Most of the Dundas land-system, even now, presents a park-like appearance with spreading red gums scattered over the landscape, and old records suggest that the whole of the tablelands was originally covered with trees. It is likely that the structure of the original vegetation of most of the land-system was a savannah woodland except for the Brim Brim land-unit where it may have been a tall woodland.
Red gum is the chief tree species of these woodlands over about four-fifths of the land-system, with occasional individual manna gums (E. viminalis) and, rarely, swamp gums (E. ovata). Elsewhere in the land-system, eucalypts other than red gum predominate-particularly manna gum and swamp gum. In the Brim Brim land-unit, these last two eucalypts are the chief tree species in the upper and lower positions of the landscape, respectively, with red gum and snow gum (E. pauciflora) fewer in number. On the southern fringe of the land-system, red gum is eliminated completely, whilst some snow gum occurs with the manna gum and swamp gum and, on leptopodsols, peppermint (E. vitrea) and even messmate (E. obliqua).
The map of isohyets shows that the areas of this land-system where red gum is the chief species all have less than about 29 inches average annual rainfall; where the rainfall is higher, red gum is a minor component or is absent, and the other eucalypts predominate. This relationship holds only for the dominant soils of the land-system such as the Koroite or Gritjurk series, and in many parts of the land-system, where the soils have deeper sandy A horizons, manna gum with a heath or bracken understorey is found, whilst soils of existing or former swamps are usually treeless. Major Mitchell (1839) describes heaths as fringing swamps on this land-system. Early accounts and the first parish plans consistently refer to honeysuckle (Banksia marginata) and often to the blackwood or lightwood (Acacia melanoxylon and A. implexa respectively) as prominent trees, but they are very rare now.
Under the original tree cover, the chief ground species were native grasses, chiefly Stipa spp., Themeda spp., Poa australis and Danthonia spp. These were the main grazing species until introduced grasses and clovers were established recently.
Plate 19 - The sparse native pasture of the red gum woodlands was ideal for the grazing Merino sheep, and this was the main enterprise over0the Dundas land-system for almost a century.
(i) Early settlement. - Together with the Casterton and Glenelg land-systems the Dundas land-system was amongst the earliest land taken up in the settlement of the south-west. Because it was interspersed with the treeless or sparsely-timbered rich grasslands of the Casterton and Glenelg land-systems, which were the first pickings, the Dundas land-system was taken into such early runs as Merino Downs, Muntham, Roseneath and Konongwootong. Also, it was itself relatively easy to thin out to a wooded grassland, in contrast to the scrub and heathlands on which grassland could not be developed and which in large measure reverted to the Crown. The rather sparse native pasture of the semi-cleared woodlands was ideal for the grazing of Merino sheep and this was the main enterprise over the Dundas land-system for almost a century.
(ii) Present use and major trends. - About twenty-five years ago, that era ended, with the advent in western Victoria of subterranean clover and superphosphate.
Despite this, however, the change in the nature of the sward has not stimulated the change in the nature of the produce from it here to the same extent as elsewhere, particularly in the generally wetter and milder County of Follett. This is shown by the statistics for the County of Dundas which, for sheep and beef-cattle, can be regarded as reflecting fairly closely the situation on the Dundas land-system.
Thus, in Table 10, where some changes occurring during the period 1955-1959 are shown, the Counties of Follett and Dundas are compared, and it is evident that in the County of Dundas, a particular degree of change in pasture improvement during that period has not been followed by as much change in the type of sheep raising, as in the County of Follett.
Table 10 - Change in pastures and production in the Counties of Follett and Dundas during the period 1955-1959
|Of pastures improved during 1955-1959|
|Swing to meat breeds in lamb production|
|Swing to medium wool from fine wool|
Table 11 - Pastures and type of sheep in the Counties of Follett and Dundas in 1959
|Wool breeds in lamb production||45||82|
|Fine wool breeds amongst wool breeds||34||70|
As well as a greater production of feed, one important result of introducing clovers and grasses and correcting soil deficiencies is the greater flexibility in management. The reason for the relatively little change in land-use following pasture improvement in the Dundas land-system is probably that elsewhere in the survey area the generally more favourable climatic conditions give greater scope for exploiting this flexibility.
(iii) Other trends. - In the Dundas land-system, the increase in improved pastures and the limited swing away from fine wool are the most important current changes in land-use. However, there have been also three other significant changes recently, and two of them have been more pronounced in Dundas than elsewhere.
One change is the increase in the acreage given over to meadow hay, a 163 per cent increase over the four-year period ending in 1959, producing a threefold, i.e. 200 per cent, increase in yield. The actual proportion of land so treated is as yet small - 3 per cent in 1959 - -but if the trend continues, it may increase the carrying capacity considerably.
The importance of the trend is connected with the chief climatic limitation in the Dundas area which, is the restriction of the growing season of the chief pasture species because of summer dryness. The effect of such restriction is that there is no green feed in the shallow rooted pastures from about the middle of November until the autumn break over most of the Dundas and Glenelg land-systems, except for the wetter Brim Brim or Tahara land-units where green feed may persist until the middle or end of December.
There is not much opportunity for flexibility under these conditions. If stock are to be carried solely on standing dry feed during the summer without the risk of losing too much condition, then the number of stock carried during spring cannot use fully the nutritious lush growth of that season, and much of its value is lost during the summer. On the other hand, heavier stocking during spring may result in summer stocking raised to the point where, not only is the safety margin so small that an extended or dry summer may mean financial loss when disposing of stock, but also, that the land is brought much nearer to a state conducive to erosion. This bottle-neck under good farming, and hazard under bad farming can be lessened in two ways. The first is by extending the growing season. This can be done with deep-rooted perennials which tap a greater volume of soil-water reserves (see Figs. 7, 8 and 9), or with summer fodder crops which have been sown late on prepared fallows wherein moisture has been conserved and which are then in a position to respond to summer showers. The other way is by conserving fodder from the period of flush production. Relatively small areas used for such purposes have a disproportionately big effect in alleviating the difficulties of the dry period. Therefore in the drier land-systems, such as Dundas, Glenelg and Casterton, increases in the acreage of meadow hay or of cereal grains for stock-feeding are important.
Another significant change in land-use in the Dundas and Glenelg land-systems is the increase in acreage under oats-for-grain, the grain being used as a stock supplement, during both the winter and dry periods. Higher stock maintenance requirements resulting from the low winter temperatures, together with the relative abundance of wet succulent feed, create a need for dry nutritious stock-feed particularly when lambing time is during the winter. Indeed, the climate of the Dundas area, as far as stock are concerned, goes from one extreme to another, and conserved grain or hay is a valuable supplement for both winter and an extended summer.
Finally, a change more pronounced in Dundas than elsewhere is the larger numbers of beef cattle; these are increasing at the rate of 11 per cent per annum. Cattle, on account of their feeding habits, are more adversely affected by drier conditions than are sheep, and the increase in cattle numbers makes an expansion of fodder conservation more important.
(iv) Potential. - The differences of potential within the land-system are largely a matter of average annual rainfall. Where this is below about 29 inches, that is, over the greater part of the land-system, improved pastures of late annual species mainly, with some perennials, can be established, and can form the basis of supplementary enterprises like grain crop production for stock feed and some summer fodder crop production. In the land-units with more than 29 inches average annual rainfall, particularly Brim Brim, farming can be based on perennial pastures, with greater possibilities for diversifying the system to include summer fodder crops, oats, roots, pulses-in fact any late annual cash or fodder crop-and specialised cash crops like seed production.
Erosion and Salting
Erosion in the Dundas land-system is slight. Except for the Brim Brim and Winyayung land-units, there is only incipient sheet erosion, which is confined to those few parts which are shallowly dissected. There is, too, salting in depressions, particularly in certain areas.
Cope (1958) has suggested that four conditions are needed for catchment salting. These are a catchment sufficient to concentrate any mobile salts into a small proportion of the area over which they were originally distributed, soils showing a sudden increase of texture, that is, soils of the solodic general group, the replacement of the original cover by one which is sparser or transpires over a shorter period of the year, and average annual rainfall of less than 30 inches. In the occasional shallow drainage lines within the Dundas land-system, the first three conditions are satisfied where the red gum has been cleared, but only towards the north-east is the climatic requirement fully met. The tendency to salting, therefore, is more marked towards the north-east, so that in the shallow drainage lines of the Cavendish land-unit, there is almost always some salting, sometimes severe ; this is the chief reason for separating out this particular land-unit.
In the Brim Brim land-unit, drainage lines are deeper and sheet erosion and some shallow and moderately deep erosion occur ; here also, despite the higher rainfall, there is some salting because of the more pronounced drainage lines. Sheet erosion and shallow gullying occur also on the Winyayung land-unit too, where there are some gentle slopes on the eroded surface of the laterite plateau.
Plate 20 - The Brim Brim land-unit, on the Brim Brim plateau, is the highest part of the Dundas land-systems. (It is undualting, with a higher rainfall than the rest of the Dundas land-system, and supports manna and swamp gum, with some red gum.)
Control measures for salting have been listed and discussed by Cope (1958 p. 81), together with species suitable for use on both salted areas and surrounding catchments (ibid. pp. 80, 61). A general recommendation for the control of incipiently salted areas on the Dundas land-system is to sow Wimmera ryegrass, cluster and strawberry clovers with Bacchus Marsh sub clover on the salted areas in the autumn, with a heavy dressing of superphosphate and sulphate of ammonia, and to fence off for two years. For severely salted patches, drainage and mulching together with gypsum may be required. To establish a full and actively growing cover for as long a period of the year as possible - that is, a cover which will obtain maximum transpiration - is, however, the chief means of preventing an extension or aggravation of the salting, not only on the tablelands, but also in parts of the adjoining Glenelg land-system. This is best done by pasture improvement provided that it does not then deteriorate to short-lived annuals, and by reestablishing trees. In this connection, it is interesting that Murray and Mitchell (1962) have found a higher level of fertility under remaining red gums than where they have been removed and they believe that removal of the gum trees has prevented the circulation of fertilising elements from the deep root-zone into the leaf litter. On account of both increased evapo-transpiration and fertility circulation, the re-establishment of red gums should be encouraged.
A brief description of each of the various land-units follows. It is based upon three groups, termed subsystems, into which they conveniently fall.
The first, the Brim Brim sub-system, contains the Brim Brim land-unit and occupies the undulating Brim Brim Plateau, that is, a lateritised tableland block-faulted above the rest of the Dundas Tablelands. It has shallow drainage lines, which are the headwaters of the valleys forming the surrounding Glenelg land-system. Average annual rainfall varies from 29 to 33 inches, soils are chiefly those intermediate between solodic soils and medium-textured leptopodsols and they originally supported a tall woodland of manna gum, swamp gum, red gum and snow gum. There is some salting and gullying of drainage lines, but perennial pastures, cash crops and fodder crops can be grown. The land-unit is more dissected than the rest of the land-system and its shallow valleys could logically have been mapped together with the Stapylton land-unit of the Glenelg land-system. However, the whole area was mapped as a unit because of the higher rainfall and different vegetation common to it, and its separation on the map illustrates the flexibility of the method of survey.
The Brit Wit, Cavendish, Corndale, Dundas, Grassdale and Tahara land-units together form the Dundas subsystem and all are lateritised tablelands at roughly the same elevation (500 to 650 feet) with their surfaces only very slightly dissected and with occasional swamps. Chief soils are solodic soils of the Koroite series, with the Follett series and meadow soils as minor groups. For the four land-units mentioned first, with average annual rainfalls less than about 29 inches, the native vegetation was probably a savannah woodland of red gum and native grasses with a little manna gum and swamp gum; these land-units can support annual or perennial improved pastures instead of the native pastures on which fine wool has been produced. Cavendish land-unit has salting, sometimes severe, in the drainage lines, whilst the others show incipient salting in the depressions. The Brit Brit, Corndale and Dundas land-units are separated on the basis of average annual rainfall, Brit Brit having the highest and Dundas the lowest of the three. The other two land-units in this sub-system, Grassdale and Tahara, with average annual rainfalls exceeding 29 inches, originally supported savannah woodlands of manna gum, swamp gum and some snow gum and native grasses. Because of their higher rainfall, they may have a potential approaching that of the Brim Brim land-unit, but they are flatter, have been more denuded of timber and are more exposed.
Winyayung is the only land-unit in the third sub-system on the south-western extremity of the lateritised tableland, and is somewhat eroded to generally below tableland level. It has an average annual rainfall above 30 inches and the soils are leptopodsols which support a tall woodland of manna gum, peppermint and occasional messmate. This land-unit can grow perennial pasture and possibly pines (P. radiata) but it is mostly under native forest now.
The characteristic feature of the Dundas land-system is that it is a lateritised tableland with only very shallow drainage lines. The exception is the Brim Brim land-unit where slightly deeper dissection may produce a locally gently rolling topography. The original vegetation was a savannah woodland, of red gum chiefly, and most of it even now has a park-like appearance. Solodic soils predominate and under the climatic and topographic conditions in which they occur, can be easily improved to support introduced late annual pastures and, where the rainfall is higher, perennial pastures, with scope for cash cropping or specialised crops. Generally, the erosion hazard is low except for some gullying in the Brim Brim land-unit. There is salting in the north-easterly areas, and changes in the hydrology may affect adjacent land-systems which have been exposed by dissection of the tablelands.