Grazing management issues: VRD

Seasonal factors | Grazing pressure | Sustainable grazing rates |  Burning | Tree thickening | Weeds and feral animals |

Seasonal factors

In any discussion of grazing management, the significance of seasonal factors cannot be overemphasized. While areas towards the coast have little climatic fluctuation to contend with, the more fertile areas further inland and to the south are subject to significant seasonal uncertainty. In general, stocking rates have been kept low to account for the uncertainty of seasons. Favourable weather conditions have persisted over much of the 90s, and this in combination with the conservative stocking rates has resulted in generally very good land and pasture condition across most of the VRD.

Grazing pressure

Even after the improvements in infrastructure which came with BTEC, most of the Victoria River District is still characterised by large paddock sizes and limited waters. Paddocks of more than 150 square kilometres are common, although producers are constantly adding fences to create smaller paddocks. Limited fencing cause problems for producers in the VRD in a number of ways. Most importantly, improved fencing would give producers greater control over the distribution of cattle. This has implications for management of land and pasture condition, for within very large paddocks stock are able to overgraze areas of preferred pasture. It is common practice to include some pasture variation within individual paddocks as cattle seem to utiliise different pastures depending on the season. Spelling and rotational strategies are also easier to implement with a larger number of smaller paddocks. Also, herd management and mustering are facilitated by improved fencing.

However, to improve the distribution of cattle, producers must put in new sources of water in addition to fencing. Given that the range of grazing of a herd is largely limited by its proximity to water, more waters will result in more even grazing, and an increase the carrying capacity of land. The sinking and maintainence of bores however is expensive.

In addition, grazing pressure is taken away from river bank environments. Indeed many of the worst affected riparian areas have been fenced off , to protect them from both cattle and from feral donkeys which can contribute significantly to localised grazing pressure.

Other options to manipulate cattle distribution within paddocks include spelling strategies and fire management. The former can be used to maintain optimum pasture community composition, and to allow grasses to recover from patches of heavy grazing. Fire can be used to encourage cattle to graze more evenly, by attracting them to recently burnt areas of 'green pick'.

Sustainable grazing rates

There are still questions regarding exactly what are the most sustainable grazing rates for various native pastures in the region. For example, pastures of the cracking clay soils tend to be resilient to grazing, although with prolonged, heavy grazing some changes in species composition are likely to occur, such as increasing prevalence of Feathertop (Aristida latifolia). It will also result in underdeveloped grass tussocks. Excessively heavy grazing, like that which may occur around watering points, will result in perrenials being completed replaced by annuals which may leave the ground bare at the end of the dry season. Red calcareous soils on the other hand tend to support grassland communities which are far less resilient to grazing pressure. The question for land managers then is, how to determine the carrying capacity of country with both 'red soils' and 'black soils'.

Burning

Fire regimes have undergone major changes in the last 50 or so years. In essence these changes represent the very significant difference between traditional aboriginal burning and contemporary European-style pastoral management practice. While there has been growing acceptance that burning can be beneficial for country, the impacts of different fire regimes is far from clear.

There seem to have been two important changes to the fire regime in the VRD over the last several decades. The first is a decrease in purposefully set early dry season fires. And the second, which is largely an outcome of the first, is an increase in accidental, destructive late dry season fires. An exception to this picture can be found in the more productive black soil plains, which have been actively, and effectively, protected from fire.

Cattle grazing has also no doubt had an impact on the fire regime by reducing the grassey understory which would have carried fire in the past. This has probably been a factor in the 'thickening up' of country, since hotter fires would have limited the extent of tree growth. Indeed destocking to allow fuel build up which will then carry a hot fire is one way of controlling the spread of these trees.

Areas without the cattle density required to significantly reduce fuel loads, such as the rugged sandstone plateaus and areas of lancewood vegetation, are suffering from the opposite problem. That is, a lack of prescriptive burning early in the dry season, and therefore high fuel loads and damaging fires later at the end of the dry. (See Woinarski and Fisher 1995; Russell-Smith et al. 1992)

Tree thickening

There is both scientific and anecdotal evidence that the VRD has seen a thickening up of native tree species over the last fifty years or so. This would seem to have occurred more on heavy, finely textured soils than on sandy loamy soils. The current thinking is that this probably results from changes to the fire regime which would normally keep this vegetation in check. Implications of this for grazing efficiency are very significant, since trials carried out by Katherine DPIF showed that pasture growth under trees is reduced by 60 per cent. These trees can also be an enormous hindrance at mustering time.

You can view images of vegetation thickening in the VRD in Issue 14 of Savanna Links. See below for web link.

Weeds and feral animals

The major introduced weed at present in the Victoria River District is Parkinsonia (Parkinsonia aculeata) , which forms thickets along watercourses making stock access and mustering difficult. Castor oil plant (Ricinu communis) is a tall, spreading shrub which has also caused problems by shading out pasture grasses and therefore decreasing carrying capacities. Noogoora burr (Xanthium strumarium) and devil's claw (Martynia annua) are also present, and both can cause injury to stock. Bellyache bush (Jatropha gossypifolia) is also locally significant.

Riparian strips are currently the areas most affected by weeds in the VRD, although rangeland weeds such as prickly acacia (Acacia nilotica ) and mesquite have the potential to become major problems if not kept in check.

Donkeys and horses have been extremely significant in the VRD in the past, and until recently were thought to be under control. However, donkey numbers have been growing of late in some areas, and producers are being encouraged to control numbers on their properties.