Acacia nilotica ssp. indica (L.) Willd. ex Del. (Mimosaceae)

Prickly acacia, a Weed of National Significance or WONS, is a serious problem in Queensland particularly the Mitchell grass downs where it was once planted to provide shade for livestock. The chapter summarises current knowledge about the taxonomy, biology, distribution, ecology, impacts and biological control of the weed. Queensland has been trying to achieve biological control of prickly acacia since 1980 when it began foreign exploration in Pakistan. Since then further exploration was undertaken in Kenya, South Africa and presently India. Six insects have been released in Queensland but only two of these are established. Greater emphasis is being placed on climate matching, plant response to herbivory and genotype matching in present work and it is hoped that this approach will allow more rigorous evaluations of agent performance and better understanding of reasons for success or failure of agents.

Demography of three perennial grasses in a central Queensland eucalypt woodland.

The population dynamics of the palatable, perennial grasses Bothriochloa ewartiana (Domin) C.E.Hubb. (desert Mitchell grass), Chrysopogon fallax S.T.Blake (golden beard grass) and Heteropogon contortus (L.) P.Beauv. ex Roem. & Schult. (black speargrass), were studied in an extensive grazing study conducted in a eucalypt woodland within the Aristida-Bothriochloa pasture community in central Queensland between 1994 and 2000. Treatments were three grazing pressures based on light, medium and heavy utilisation of forage available at the end of summer and two timber treatments (trees intact and trees killed). Seasonal rainfall throughout this study was generally favourable for plant growth with no severe drought periods. Grazing pressure had a greater overall impact on plant dynamics than timber treatment, which had minimal impact. Grazing pressure had a large impact on H. contortus dynamics, an intermediate impact on B. ewartiana and no impact on C. fallax. Fluctuations in plant density of both B. ewartiana and C. fallax were small because both species were long lived with low levels of seedling recruitment and plant death, whereas fluctuations in H. contortus density were relatively high because of its relatively short life span and higher levels of both recruitment and death. Heavy grazing pressure increased the recruitment of B. ewartiana and H. contortus in some years but had no impact on that of C. fallax. Heavy grazing pressure reduced the survival of the original plants of both B. ewartiana and H.contortus but not of C. fallax. For H. contortus, the size of the original plants was larger where trees were killed than where trees were left intact and plants of the 1995 seedling cohort were larger in 1998 at heavy compared with those at light and medium grazing pressure. Grazing had a minor negative impact on the soil seed bank of H. contortus. Populations of all three species remained stable throughout this study, although the favourable seasonal rainfall experienced and the short duration of this study relative to the life span of these species may have masked longer term, deleterious impacts of heavy grazing pressure.

Lagarosiphon major (Ridley) Moss ex Wager (curly water weed)

Curley water weed is a southern African submerged macrophyte that has become a serious water weed in several countries including New Zealand after its introduction by the aquarium industry. It has been recorded in Australia, including Queensland, but is not considered to have established. The chapter describes the ecology and management of this weed. Control of further dispersal is considered critical to its management. It has also been considered for classical biological control and manipulation of grass carp densities has also been studied. Issues relating to the use of herbicides in freshwater systems are also discussed.