Flood-induced recruitment of the invasive perennial herb 'Phyla canescens' (lippia)
'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.
Germination response to temperature of 'Phyla canescens' (lippia)
'Phyla canescens' (Kunth) Greene (Verbenaceae) is an introduced invasive herb of floodplain pastures and wetlands in the Murray-Darling Basin. Its germination response to 81 constant and alternating temperatures was studied using a two-way thermogradient plate. The experiment was repeated for seed aged four months and 16 months, as well as seed collected from a population in another catchment. Germination prediction surfaces were generated using Geographical Information Systems-based techniques. All seed batches exhibited a 'homothermophobic' response, in which virtually no seed germinated at constant temperatures. The ecological significance of the homothermophobic germination response is discussed.
Nitrate-nitrogen reduction by established tree and pasture buffer strips associated with a cattle feedlot effluent disposal area near Armidale, NSW Australia
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.
The use of saline mine water and municipal wastes to establish plantations on rehabilitated open-cut coal mines, Upper Hunter Valley NSW, Australia
Commercial forestry plantations as a post-mining land use in the Upper Hunter Valley NSW, Australia, have productivity limitations and are restricted by the poor nutrient quality of mining substrates and low regional rainfall. However, municipal waste products and saline groundwater from coal mining operations can assist in establishing and improving plantation growth rates. The aim of this study was to investigate the establishment and growth of four potentially commercial species in a saline irrigation and nutrient amendment experiment over 2 years. The experiment was designed as a split–split plot with irrigation being the main plot effect, nutrient amendments (overburden, fertiliser, biosolids, compost and topsoil) as the subplot effect and species ('Corymbia maculata' Hook, 'Eucalyptus botryoides' Smith, 'E. tereticornis' Smith and 'E. occidentalis' Endl.) as the sub-subplot effect. Survival, height, diameter, above-ground biomass, tree form and weed competition in each treatment were measured along with substrate electrical conductivity. Tree survival after 24 months improved with irrigation (89.8%) compared to the rain-fed treatment (78.6%). Irrigation did not significantly improve tree growth responses but there was an increasing trend after 24 months with irrigation producing better overall growth. Biosolids, compost and fertiliser produced significantly better growth than the topsoil and overburden treatments. However, weed growth was higher in biosolids and compost and was correlated with reduced tree growth but not less than topsoil and overburden treatments. 'Eucalyptus occidentalis' performed significantly better than other species in relation to height (1.89 m), diameter at 30 cm (3.1 cm) and standing crop biomass (982 kg ha⁻¹) after 2 years. Surface substrate EC1:5 (0–10 cm) increased significantly following irrigation events but reduced over time by leaching from rainfall. Electrical conductivity in the lower horizon (10–30 cm) was not significantly different from the upper horizon in the irrigation treatment but was significantly higher in the rain-fed treatment after 2 years. Biosolids and compost increased EC1:5 over the first 6 months but thereafter compost and overburden produced higher values during the second year of the study. These results show that saline mine water irrigation can be used to establish plantations without impacting deleteriously on tree growth and substrate EC1:5. However, further research is required to determine whether growth rates will reach a commercial standard and that the long-term impacts of using saline irrigation water are avoided.
Divergent responses to long-term grazing exclusion among three plant communities in a flood pulsing wetland in eastern Australia
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.
Phyla canescens: multiple introductions into Australia as revealed by ISSR markers and nuclear ribosomal DNA internal transcribed spacers (ITS)
Lippia ('Phyla canescens' (Kunth) Greene: Verbenaceae) is a very invasive weed in wetlands and riparian zones in Australia and especially in the Murray Darling Basin. The use of chemicals as a control method is inappropriate in such environmentally sensitive areas, particularly the Macquarie Marshes and Gwydir Wetlands. Biological control will be the only option in many areas. We investigated genetic diversity in 12 populations of lippia from four different catchments in Australia, eight populations from the native range in South America and five populations from France where the species is non-native and invasive. Low levels of genetic diversity were detected within some Australian regions in contrast to the Argentinean and French populations. In the analyses the Australian material segregated with two disjunct regions in Argentina, suggesting that Australia has experienced multiple introductions of lippia.
Riparian Vegetation Assessment along the Estuary-River Transition Zone: Hastings River, NSW. November 2002 - January 2004
A study was undertaken of the health and condition of riparian vegetation along the estuary-river transition zone of the Hastings River after observations noted that trees and understorey species were stressed and appeared to be dying as the drought worsened in late 2002, river flows declined significantly and the river ceased to flow over short periods, and salinity concentrations increased as the salt wedge pushed upstream. The principal causal factors likely tn be involved in vegetation decline include salinity, drought and subsequent soil moisture stress.
An Economic Assessment of Management Programs for Land Degradation on a Regional, Farm and Paddock Basis
This study is concerned with the economic assessment of programs to manage land degradation at a regional, farm and paddock level in New South Wales. It has been undertaken within an interdisciplinary framework by combining economic and environmental factors. The overall objective is to improve information for decision-making relating to the management of land degradation, through the integration of economic and bio-physical information. Despite increased funding support at Federal and State levels and a significant rise in the number of Landcare groups across Australia, land degradation continues to be a serious environmental problem. There is a lack of reliable information at various scales of management on the impact of land degradation on agricultural productivity, and the economic viability of land-management programs. Furthermore, few attempts have been made elsewhere to integrate economic and biophysical data to provide prescriptive information to improve management decisions. ... On the basis of the initial success of methods developed in this project, further research that incorporates economic and bio-physical information in models is recommended.
Germination and early survival of 'Eucalyptus blakelyi' in grasslands of the New England Tablelands, NSW, Australia
Establishing native eucalypts in grasslands developed by the historical clearing of forests and woodlands has to overcome significant difficulties brought about by past land use activities and associated environmental changes. Options for establishment include natural regeneration from remnant trees, direct sowing or tree planting. 'Eucalyptus blakelyi' is a significant species on the New England Tablelands, being just north of the central part of its ecological range and is potentially useful for ecosystem rehabilitation, agroforestry and farm forestry. The aims of this series of studies are to determine the effects of cold temperatures resulting from microclimate changes on germination and early survival of 'E. blakelyi', the level of seed predation by ants, and the effectiveness of site preparation techniques on survival and growth of seedlings planted in grasslands. Germination of local seeds collected from the New England Tablelands was tested under constant and alternating temperatures, either in the dark or under 12 h light/dark cycle. 'E. blakelyi' exhibited optimal germination between 15 and 25°C with the maximum occurring at 15°C under constant temperatures, and at 15–25°C under alternating temperatures. Light had a significant and positive effect on germination under both constant and alternating temperature regimes, although this difference was not significant at temperatures around the optimum. Seedling survival decreased significantly as temperature decreased from −5 to −10°C, as exposure time to low temperature increased from 1 to 4 h, and as seedling age increased from 1 to 8 weeks. Ant predation was high with 73% of the seeds removed within 7 days. Four site preparation techniques (grazing exclusion, cultivation, burning and fertiliser) were used in a factorial arrangement to examine their interactions and influences on seedling survival and height growth 30 months after establishment. Grazing significantly reduced seedling survival and height, whereas soil cultivation and burning significantly increased them. Survival and height were consistently lower when fertiliser was added to grazed plots across all cultivation treatments including the control. When grazing was excluded, fertiliser significantly reduced survival with cultivated treatments, and increased height only with shallow cultivation (to a depth of 5 cm) while it significantly reduced height with deep cultivation (20 cm). The interactions amongst the various treatments identified that seedling survival and growth were best when grazing was excluded and the site was deep cultivated without the broadcast application of fertiliser. Fire has an additive effect on seedling survival and height growth. The main benefits of this combination of treatments lie in preventing browsing and trampling damage by livestock, reducing competition from the herbaceous layer, removing litter, and possibly alleviating potential allelopathic effects.
Estimating the Unknown Components of Nutrient Mass Balances for Forestry Plantations in Mine Rehabilitation, Upper Hunter Valley, New South Wales, Australia
Commercial forestry plantations as a post-mining land use in the Upper Hunter Valley of New South Wales, Australia are restricted by both the poor nutrient availability of mining substrates and low regional rainfall. An experiment was conducted to investigate whether municipal waste products and saline groundwater from coal mining operations could improve early tree growth without impacting on the environment through salt accumulation and/or nutrient enrichment and changes in groundwater quality. Potential impacts were investigated by quantifying the nutrient cycling dynamics within the plantation using an input–output mass balance approach for exchangeable calcium (Ca²⁺), exchangeable magnesium (Mg²⁺), exchangeable potassium (K⁺), exchangeable sodium (Na⁺), nitrogen (N), and phosphorus (P). Measured inputs to and outputs from the available nutrient pool in the 0–30 cm of the overburden subsystem were used to estimate the net effect of unmeasured inputs and outputs (termed 'residuals'). Residual values in the mass balance of the irrigated treatments demonstrated large leaching losses of exchangeable Ca, Mg, K, and Na. Between 96% and 103% of Na applied in saline mine-water irrigation was leached below the 0–30-cm soil profile zone. The fate of these salts beyond 30 cm is unknown, but results suggest that irrigation with saline mine water had minimal impact on the substrate to 30 cm over the first 2 years since plantation establishment. Accumulations of N and P were detected for the substrate amendments, suggesting that organic amendments (particularly compost) retained the applied nutrients with very little associated losses, particularly through leaching.