Virus identification and development of long-term management strategies for the rhubarb industry

The purpose of this report is to present the final results of all activities conducted under HAL Project VG05053 ‘Virus identification and development of long-term management strategies for the rhubarb industry’. The report provides a summary of project findings, a description of technology transfer activities, and recommendations arising from the outcomes of the project. The overall objective of this project was to devise a strategy for the control of rhubarb decline disease through 1) knowledge of the viruses present and their epidemiology, 2) production of virus-free planting material via tissue culture, and 3) formation of a national grower group to represent industry.

Impacts of a fuel oil spill on seagrass meadows in a subtropical port, Gladstone, Australia - The value of long-term marine habitat monitoring in high risk areas.

We used an established seagrass monitoring programme to examine the short and longer-term impacts of an oil spill event on intertidal seagrass meadows. Results for potentially impacted seagrass areas were compared with existing monitoring data and with control seagrass meadows located outside of the oil spill area. Seagrass meadows were not significantly affected by the oil spill. Declines in seagrass biomass and area 1 month post-spill were consistent between control and impact meadows. Eight months post-spill, seagrass density and area increased to be within historical ranges. The declines in seagrass meadows were likely attributable to natural seasonal variation and a combination of climatic and anthropogenic impacts. The lack of impact from the oil spill was due to several mitigating factors rather than a lack of toxic effects to seagrasses. The study demonstrates the value of long-term monitoring of critical habitats in high risk areas to effectively assess impacts.

The effect of long-term repeated burning and fire exclusion on above- and below-ground Blackbutt (Eucalyptus pilularis) forest vegetation assemblages

We used a long-term fire experiment in south-east Queensland, Australia, to determine the effects of frequent prescribed burning and fire exclusion on understorey vegetation (<7.5 m) richness and density in Eucalyptus pilularis forest. Our study provided a point in time assessment of the standing vegetation and soil-stored vegetation at two experimental sites with treatments of biennial burning, quadrennial burning since 19711972 and no burning since 1969. Vegetation composition, density and richness of certain plant groups in the standing and soil-stored vegetation were influenced by fire treatments. The density of resprouting plants <3 m in height was higher in the biennially burnt treatment than in the unburnt treatment, but resprouters 37.5 m in height were absent from the biennial burning treatment. Obligate seeder richness and density in the standing vegetation was not significantly influenced by the fire treatments, but richness of this plant group in the seed bank was higher in the quadrennial treatment at one site and in the long unburnt treatment at the other site. Long unburnt treatments had an understorey of rainforest species, while biennial burning at one site and quadrennial burning at the other site were associated with greater standing grass density relative to the unburnt treatment. This difference in vegetation composition due to fire regime potentially influences the flammability of the standing understorey vegetation. Significant interactions between fire regime and site, apparent in the standing and soil-stored vegetation, demonstrate the high degree of natural variability in vegetation community responses to fire regimes.

Standard yet unusual mechanisms of long-distance dispersal: Seed dispersal of Corymbia torelliana by bees

Mellitochory, seed dispersal by bees, has been implicated in long-distance dispersal of the tropical rain forest tree, Corymbia torelliana (Myrtaceae). We examined natural and introduced populations of C. torelliana for 4 years to determine the species of bees that disperse seeds, and the extent and distance of seed dispersal. The mechanism of seed dispersal by bees was also investigated, including fruit traits that promote dispersal, foraging behaviour of bees at fruits, and the fate of seeds. The fruit structure of C. torelliana, with seed presented in a resin reward, is a unique trait that promotes seed dispersal by bees and often results in long-distance dispersal. We discovered that a guild of four species of stingless bees, Trigona carbonaria, T. clypearis, T. sapiens, and T. hockingsi, dispersed seeds of C. torelliana in its natural range. More than half of the nests found within 250 m of fruiting trees had evidence of seed transport. Seeds were transported minimum distances of 20-220 m by bees. Approximately 88% of seeds were dispersed by gravity but almost all fruits retained one or two seeds embedded in resin for bee dispersal. Bee foraging for resin peaked immediately after fruit opening and corresponded to a peak of seed dispersal at the hive. There were strong correlations between numbers of seeds brought in and taken out of each hive by bees (r = 0.753-0.992, P < 0.05), and germination rates were 95 ± 5%. These results showed that bee-transported seeds were effectively dispersed outside of the hive soon after release from fruits. Seed dispersal by bees is a non-standard dispersal mechanism for C. torelliana, as most seeds are dispersed by gravity before bees can enter fruits. However, many C. torelliana seeds are dispersed by bees, since seeds are retained in almost all fruits, and all of these are dispersed by bees.

Review of approaches to evaluate the effectiveness of weed biological control agents

We review key issues, available approaches and analyses to encourage and assist practitioners to develop sound plans to evaluate the effectiveness of weed biological control agents at various phases throughout a program. Assessing the effectiveness of prospective agents before release assists the selection process, while post-release evaluation aims to determine the extent that agents are alleviating the ecological, social and economic impacts of the weeds. Information gathered on weed impacts prior to the initiation of a biological control program is necessary to provide baseline data and devise performance targets against which the program can subsequently be evaluated. Detailed data on weed populations, associated plant communities and, in some instances ecosystem processes collected at representative sites in the introduced range several years before the release of agents can be compared with similar data collected later to assess agent effectiveness. Laboratory, glasshouse and field studies are typically used to assess agent effectiveness. While some approaches used for field studies may be influenced by confounding factors, manipulative experiments where agents are excluded (or included) using chemicals or cages are more robust but time-consuming and expensive to implement. Demographic modeling and benefit–cost analyses are increasingly being used to complement other studies. There is an obvious need for more investment in long-term post-release evaluation of agent effectiveness to rigorously document outcomes of biological control programs.

Applying a simulation model to the management of an infestation of Miconia calvescens in the wet tropics of Australia

A simulation model that combines biological, search and economic components is applied to the eradication of a Miconia calvescens infestation at El Arish in tropical Queensland, Australia. Information on the year M. calvescens was introduced to the site, the number of plants controlled and the timing of control, is used to show that currently there could be M. calvescens plants remaining undetected at the site, including some mature plants. Modelling results indicate that the eradication programme has had a significant impact on the population of M. calvescens, as shown by simulated results for uncontrolled and controlled populations. The model was also used to investigate the effect of changing search effort on the cost of and time to eradication. Control costs were found to be negligible over all levels of search effort tested. Importantly, results suggest eradication may be achieved within several decades, if resources are increased slightly from their current levels and if there is a long-term commitment to funding the eradication programme.

Collation, analysis and research of thermal benefits of green life in the urban landscapes

This project reviewed international research conducted on the possible role of plants in alleviating high temperatures in our living spaces. The literature review served to identify the work that has already been carried out in the area and to highlight the gaps to be filled by experimental research. A pilot study then investigated the thermal properties of six of the most common landscaping materials. This project clearly shows that plants can play a significant role in modifying the thermal conditions of urban environments. Tall trees can shade nearby buildings and allow for reductions in cooling costs. In addition to basic shading, the dispersal of heat via the plant’s natural transpiration stream has long been recognised as an important component of the urban energy balance. It has been shown that urban temperatures can be up to 7°C higher than nearby rural areas, illustrating the impact of plants on their environment. These benefits argue against the idea of removing plants from landscapes in order to save on water in times of drought. Similarly, the idea of switching to artificial turf is questionable, since artificial turf still requires watering and can reach temperatures that far exceed the safe range for players. While vegetation offers evaporative cooling, non-vegetative, impervious surfaces such as concrete do not, and can therefore cause greater surface and soil temperatures. In addition, the higher temperatures associated with these impervious surfaces can negatively affect the growth of plants in surrounding areas. Permeable surfaces, such as mulches, have better insulating properties and can prevent excessive heating of the soil. However, they can also lead to an increase in reflected longwave radiation, causing the leaves of plants to close their water-conducting pores and reducing the beneficial cooling effects of transpiration. The results show that the energy balance of our surroundings is complicated and that all components of a landscape will have an impact on thermal conditions.

A case study on the economics of overhead irrigation in the lower Burdekin

Converting from an existing irrigation system is often seen as high risk by the land owner. The significant financial investment and the long period over which the investment runs is also complicated by the uncertainty associated with long term input costs (such as energy), crop production, and the continually evolving natural resource management rules and policy. Irrigation plays a pivotal part in the Burdekin sugarcane farming system. At present the use of furrow irrigation is by far the most common form due to the ease of use, relatively low operating cost and well established infrastructure currently in place. The Mulgrave Area Farmer Integrated Action (MAFIA) grower group, located near Clare in the lower Burdekin region, identified the need to learn about sustainable farming systems with a focus on the environment, social and economic implications. In early 2007, Hesp Faming established a site to investigate the use of overhead irrigation as an alternative to furrow irrigation and its integration with new farming system practices, including Green Cane Trash Blanketing (GCTB). Although significant environmental and social benefits exist, the preliminary investment analysis indicates that the Overhead Low Pressure (OHLP) irrigation system is not adding financial value to the Hesp Farming business. A combination of high capital costs and other offsetting factors resulted in the benefits not being fully realised. A different outcome is achieved if Hesp Farming is able to realise value on the water saved, with both OHLP irrigation systems displaying a positive NPV. This case study provides a framework to further investigate the economics of OHLP irrigation in sugarcane and it is anticipated that with additional data a more definitive outcome will be developed in the future.