Grasslands of the World.pdf - Disasters and Conflicts - UNEP

Australian grasslands 359
Animal production depends on the herbage layer, the composition of which
varies widely, depending on the timing of the unreliable rainfall in these arid
areas. Winter rain produces a flush of ephemerals with forbs (particularly
members of the Asteraceae) prominent; summer rain favours perennial and
annual grasses and is responsible for the bulk of the herbage.
Xerophytic tussockgrass
Communities dominated by Mitchell grass (Astrebla species ) are widespread
(40 million hectares) on heavy, cracking clay plains of inland northern
Australia , particularly in Queensland. Many of these are true grasslands,
with no trees, but large areas also have scattered trees and shrubs. Some
areas have been invaded by the exotic tree Acacia nilotica (see Plate 9.3).
The perennial Astrebla plants provide stability and drought reserve feed, but
animal production is closely related to the growth of short -lived, nutritious
inter-tussock species, mainly annual grasses (particularly Iseilema spp. , but
also Dactyloctenium spp. and Brachyachne convergens ) and forbs (species
of Boerhavia , Sida , Portulaca and Ipomoea ). Cattle can gain weight on dry
annual herbage, but lose weight when depending on dry Mitchell grass . Other
perennial grasses may also be important – Panicum decompositum , Aristida
latifolia , Eragrostis spp., Bothriochloa spp. , Dichanthium spp. , Eulalia aurea
and Chrysopogon fallax .
The Mitchell grass lands are the most productive of the semi -arid and arid
grazing lands in Australia . They have been stable, withstanding prolonged
heavy grazing, although there is concern about invasion by Aristida latifolia
in some areas.
Xerophytic hummockgrass
These communities – characterized by perennial species of Plectrachne and
Triodia (“spinifex ”) – occupy large areas of sandy soils with annual rainfalls of
200 to 400 mm, and shallow skeletal soils in higher rainfall areas. Plectrachne
and Triodia plants form hummocks or mounds from 1 to 6 m in diameter,
and there are sparse populations of shrubs and small trees (Acacia spp. and
Eucalyptus spp.) throughout much of the area. These areas have low and erratic
rainfall and include waterless deserts of little or no value for grazing . Although
the spinifex grasses are generally unpalatable to stock except after fire , and
the mature herbage is very low quality, these lands provide important grazing
(mainly for breeding cattle ), especially if other, more palatable, perennial
species (e.g. Chrysopogon fallax , Eragrostis spp.) are present. After rain, annual
grasses and forbs provide valuable grazing.
SOWN PASTURES
Pasture improvement in Australia has been and continues to be, based on the
use of selected, exotic species, with particular emphasis on legumes. Many