'Phyla canescens' (Kunth) Greene, lippia, (Verbenaceae) is an important invasive species in the Murray-Darling Basin, Australia. The general lack of quantitative information on aspects of the life-history of 'P. canescens' is a substantial impediment to the sustainable management of this species and the communities it invades. Complementary laboratory and field experiments investigated 'P. canescens' germination. A thermogradient plate was used to examine its germination response to a variety of temperature regimes. Recruitment in the field was investigated at four sites across two catchments following four season disturbances. In the laboratory trials, seeds required temperatures that alternated by at least 5°C, light, and to be covered by a thin film of water. Field germination occurred only at the one site that experienced a flood, despite periods of high rainfall that stimulated germination of other species. In this site seedling density and survivorship were reduced in the presence of existing vegetation. A survey of 'P. canescens' following flooding of a temporary billabong revealed recruitment from both seed and vegetative fragments. This recruitment was almost exclusively restricted to the area that had been flooded. The results suggest that 'P. canescens' requires inundation for successful recruitment and that these germination requirements are typical of species from disturbance-prone environments.

We examined the effects of grazing exclusion over a period of 14 years on the species richness and community composition of three plant communities with different dominant species and water regimes in the Gwydir Wetlands in eastern Australia. Responses to grazing exclusion varied among the three plant communities, and were most likely to be evident during dry periods rather than during periods of inundation. In frequently flooded plant communities, there was an increase in phytomass following exclusion of domestic livestock, but changes in plant community composition and species richness due to livestock exclusion varied depending on the morphological attributes of the dominant plant species. In a plant community where tall sedge species were dominant, livestock exclusion further increased their dominance and overall species richness declined. In contrast, where a prostrate grass species such as 'Paspalum distichum' was dominant, species richness increased following livestock exclusion, due to an increase in the abundance of taller dicotyledon species. However, livestock exclusion in a community where flooding was less frequent and native grass species have been largely replaced with the introduced species 'Phyla canescens', resulted in no significant changes to phytomass, species richness or community composition among the grazing exclusion treatments over time. Our results indicate responses to exclusion of domestic livestock are dependent upon the dominant species within the plant community and will likely vary over time with the extent of wetland inundation. Grazing exclusion alone, without increased flooding, is unlikely to restore floristically degraded floodplain plant communities.

Vegetated buffer strips have been recognized as an important element in overall agro-ecosystem management to reduce the delivery of non-point source pollutants from agricultural land to inland water systems. A buffer strip experiment consisting of two tree species ('Eucalyptus camaldulensis' and 'Casuarina cunninghamiana') with two planting densities and a pasture treatment was conducted to determine the effectiveness of NO₃-N removal from a cattle feedlot effluent disposal area at Tullimba near Armidale, NSW Australia. Different management methods were applied for the buffers where grass and weeds were mowed 2-3 times during the second and third years and were not managed during the rest experimental years for the tree buffer, while grass was harvested 1-3 times per year for the pasture buffer. The differences between tree species and planting density significantly affected tree growth, but the growth difference did not significantly affect their capacities to reduce NO₃-N in soil surface runoff and groundwater. On average for all the tree and pasture treatments, the buffer strips reduced NO₃-N concentration by 8.5%, 14.7% and 14.4% for the surface runoff, shallow and deep groundwater respectively. The tree and pasture buffer strips were not significantly different in NO₃-N reduction for both shallow and deep groundwater while the pasture buffer strips reduced significantly more NO₃-N concentration in surface runoff than the tree buffer strips. Both buffer strips reduced more than 50% of surface runoff volume indicating that both the tree and pasture buffer strips were efficient at removing water and nutrients, mostly through a significant reduction in soil surface runoff volume.

This study examined if one grazing strategy (namely seasonal rest) was effective in the control of the invasive forb 'Phyla canescens' (Kunth) Greene (hereafter lippia). We examined if rest from grazing could increase the competitiveness of native palatable species by allowing time to recover from defoliation, thereby altering competitive interactions between native species and lippia. In a field trial, we manipulated cattle grazing to determine its effects on the biomass of lippia and native species. We compared rest from grazing at different times of the year with year-long grazing (low intensity continuous and high intensity short duration) and no grazing (permanently excluding large grazing animals). Experimental plots were stratified into different hydrological areas (approximately annual flooding and flooded less than once every 5 years) to include flood dynamics in the management scenarios. We detected no negative impacts of seasonal rest on lippia, but some positive effects on native species. We found that complete exclusion from grazing in areas that already have substantial lippia invasion (and no flooding) may actually favour the expansion of lippia (at certain times). This study does not suggest that grazing management cannot be used as a tool for lippia control - simply that seasonal resting had no effect over a 3-year period. This is likely due to the dynamics of a boom-and-bust landscape in which if the abiotic conditions are not suitable for growth, then native species will not grow whether grazed or rested.