Seasonal factors | Grazing pressure |
Sustainable grazing rates | Burning |
thickening | Weeds and feral animals |
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
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
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
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'.
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'.
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.
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.
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
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
Tropical Savannas: not what they used to be
Many landscapes of the tropical savannas gradually being transformed. From Savanna Links, Issue 14, April - June 2000 [read more...
Vegetation structure and function
The results of a study conducted to answer: Have trees thickened in the VRD? How 'tough' is the country? How well does it recover from damage?
Effect of woody vegetation increase in the Victoria River District
An article about the encroachment of native trees and shrubs into open grasslands and woodlands in the VRD