Terrestrial weeds

The environmental and economic impact of terrestrial weeds in terms of productivity activity from land are:

• Loss of native flora and fauna and ecosystem services
• loss of production due to reduction of grass cover and carrying capacity, leading to reduced fodder production;
• increased costs for mustering;
• toxicity to stock;
• adverse impact on human health (e.g. Parthenium ).

Rangelands

Weed infestations are widespread in the rangelands. Eucalypt savannas, acacia scrubs and dry rainforests of the region have been seriously invaded by

Exotic shrubs such as:

• Lantana ( Lantana camara ) and
• Rubber vine ( Cryptostegia grandiflora ), and
• Prickly acacia ( Acacia nilotica )

Existing grasses and forbs such as

• Grader grass ( Themeda quadrivalvis )
• Guinea grass ( Panicum maximum ) and
• Parthenium weed ( Parthenium hysterophorus ).

Weed infestations displace indigenous species, leading to a decline in species composition of pastures and a loss of biodiversity. Invasion of rangelands by weeds is closely linked with grazing management, drought and fire regime.

Riparian zones - frontage country

“Riparian” refers to vegetation along streams, wetlands, waterholes and estuaries. It is often known as “frontage country”. Riparian vegetation is important, not only as a different habitat type in itself, but also for aquatic ecosystems. Leaf litter provides an important food source for many aquatic animals, riparian vegetation provides shade, which controls water temperatures and other water quality processes. The physical habitat provided by tree roots and snags is important to many aquatic animals, and riparian vegetation acts as a filter to trap nutrient and other contaminants before they enter streams. Riparian ecosystems support plants and animals that do not occur anywhere else in the landscape. They also have a greater biodiversity than many surrounding ecosystems. During dry periods, animals from surrounding woodlands move into riparian ecosystems for refuge.

Riparian zones are especially susceptible to colonisation by certain weeds. This is presumably because water and nutrients are in greater supply in these areas. Rubber vine ( Cryptostegia grandiflora ) is an obvious example from the Burdekin rangelands of a weed species that thrives in riparian zones. While occurring in other parts of the landscape, plants of this species are larger, grow more densely and produce more seeds in riparian zones ( Roth et al. 2002 ).

• Other species that develop particularly serious infestations in riparian zones are: Castor oil bush ( Ricinus communis ),
• Guinea grass ( Panicum maximum ),
• Parkinsonia ( Parkinsonia aculeata ),
• Chinee apple ( Ziziphus mauritiana ),
• Bellyache bush ( Jutrepha gossypiifidia ),
• Giant rat's tail grass ( Sporobolus pyramidalis and Sporobolus natalensis ),
• Giant Parramatta Grass ( Sporobolus fertilis ) and
• American Rats Tail Grass ( Sporobolus jacuemontii ).

Parkinsonia represents a serious and growing threat to swamps, billabongs and wetlands in the Desert Uplands bioregion ( Morgan 2001 ) .