Lippia (Phyla canescens) and its response to fire

Lippia (Phyla canescens), a significant invasive weed, is a recognized threat to floodplain woodlands in Australia, particularly in the Murray-Darling Basin. Current control methods include the use of herbicides, which can be costly and environmentally harmful, particularly in riparian areas. 'Environmentally friendly' control mechanisms are yet to be found, with the potential for biological control still being researched. This research explores the use of fire as a potential control method to help slow the expansion and growth of lippia. Lippia response to fire and the effect of fire in lippia-invaded landscapes has not previously been investigated. Half of the St. Ruth Reserve south of Dalby in Southern Queensland was subject to a control burn in November 2013 by the Western Downs Regional Council in an attempt to reduce lippia abundance in this remnant riparian woodland. This research investigates the response of lippia to the burn. The study will compare the cover abundance of lippia and major functional plant groups between burnt and unburnt (control) sites within the reserve; it will also investigate the impact of fire on lippia germination rates in soil samples from burnt and unburnt sites. Additional studies testing lippia seed viability, using tetrazolium staining, will also be conducted after a range of fire mimicking treatments have been applied to seeds and compared to controls from an unburnt area. This research will contribute to evidence-based decision-making for improved management of lippia-invaded remnant ecosystems

Groundwater thresholds for drought resilience in floodplain woodlands: a case study from the northern Murray-Darling Basin

In ephemeral river systems, canopy condition in dominant riparian and floodplain tree species may depend on access to shallow groundwater resources, particularly during drought. However, unsustainable groundwater extraction and chronic groundwater decline, evident in many agricultural landscapes worldwide, effectively decouples tree roots from deep soil moisture resources, increasing the susceptibility of trees to changes in precipitation. In such regions, drought may trigger loss of canopy condition and have long term consequences for the function and survival of trees and the composition, structure and function of ecosystems they dominate. However, critical groundwater depth thresholds have been difficult to identify. This study used a novel approach including boosted regression trees, quantile regression and threshold analysis to explore the relationship between groundwater depth and tree condition for two dominant tree species, Eucalyptus camaldulensis (river red gum) and E. populnea (poplar box); both species occur on the Upper Condamine floodplain, a region experiencing groundwater depth declines of 25+m in the northern Murray-­‐Darling Basin, southern Queensland. Distinct non-­‐linear responses were apparent, with minimum groundwater depth thresholds identified at 12.1m for E. camaldulensis and 12.6m for E.populnea, beyond which canopy condition declined significantly. This approach represents a repeatable method of quantifying ecological response thresholds along groundwater depth gradients. Its application may enable safe operating limits for groundwater resource management to be identified, supporting improved decision making to support resilient floodplain ecosystems. This will be particularly important in regions where groundwater decline driven by increasing water demand and drying climates is predicted

Identifying groundwater thresholds for drought resilience in floodplain tree species in the northern Murray-Darling Basin

Previous research identifies links between groundwater depth and canopy condition in dominant riparian and floodplain tree species associated with ephemeral river systems, particularly during drought. Chronic groundwater decline, evident in many agricultural landscapes worldwide, effectively decouples tree roots from deep soil moisture resources, increasing the susceptibility of trees to changes in precipitation. Drought may trigger loss of canopy condition and, where severe or prolonged, have long term consequences for the function and survival of trees and the composition, structure and function of ecosystems they dominate. However, critical groundwater depth thresholds, which may reflect ecological 'tipping points' in such systems, have been difficult to identify. This study used boosted regression trees, quantile regression and Threshold Indicator Taxa Analysis to investigate the relationship between groundwater depth and tree condition for two dominant tree species, Eucalyptus camaldulensis (river red gum) and E. populnea (poplar box). Both occur on the Upper Condamine floodplain, a region experiencing significant groundwater decline due to unsustainable groundwater extraction in the northern Murray-Darling Basin, southern Queensland. Distinct non-linear responses were found, with groundwater depth thresholds identified at 12.1–22.6m for E. camaldulensis and 12.6–22.6m for E. populnea, beyond which canopy condition declined abruptly. This approach represents a repeatable method of quantifying ecological response thresholds along groundwater depth gradients, application of which may assist in identifying safe operating limits for groundwater resource management to support resilient floodplain ecosystems. It will be particularly important in regions where increasing water demand and drying climates may drive further groundwater decline

How fungi’s knack for networking boosts ecological recovery after bushfires

The unprecedented bushfires that struck the east coast of Australia this summer killed an estimated one billion animals across millions of hectares. Scorched landscapes and animal corpses brought into sharp relief what climate-driven changes to wildfire mean for Australia’s plants and animals. Yet the effects of fire go much deeper, quite literally, to a vast and complex underground world that we know stunningly little about, including organisms that might be just as vulnerable to fire, and vital to Australia’s ecological recovery: the fungi

Riparian woodland dysfunction is driven by groundwater decline in a northern Murray-Darling intensive production landscape

Altered hydrological regimes are significant drivers of ecosystem change in riverine, riparian and floodplain ecosystems. This study has found that declining condition in Eucalyptus camaldulensis/E. tereticornis riparian woodlands of the highly-modified Upper Condamine floodplain, southern Queensland, is predominantly linked to falling groundwater levels associated with extraction for irrigation. Evidence of dieback in this species complex increases with groundwater depth falling below 13-16m, and community composition (functional group diversity) is strongly associated with both groundwater depth and tree condition. These findings contrast with studies in Murray River floodplain woodlands where poor tree health is associated with soil salinisation associated with rising water tables and/or altered flood regimes. Results from this study are summarized in a semi-quantitative State-and-Transition resilience model, identifying critical thresholds for the persistence of this essentially groundwater-dependent ecosystem. Such systems, currently existing close to ecological thresholds, contribute significantly to our understanding of how ecological systems respond to change, and of how major disturbances such as climate change may play out across landscapes

Using stable isotopes to identify soil moisture sources of key species in drought-stressed riparian woodlands

Remnant riparian woodlands on the Upper Condamine floodplain of the northern Murray-Darling Basin are characterised by the dominant canopy species Eucalyptus camaldulensis (river red gum), a facultative phreatophyte which preferentially accesses shallow groundwater sources during drought conditions. Phyla canescens (lippia), a perennial clonal herb, is also dominant in these ecosystems. Lippia is an invasive alien species, readily dispersed by flooding, with potential to spread throughout much of the Murray-Darling system with significant economic and environmental impact. Recent research indicates that trees may facilitate the persistence of lippia, enabling it to survive and reproduce under drought conditions, and that lippia may in turn contribute to dieback severity in canopy eucalypts in these woodlands. Greater understanding of the intensity and direction of interactions between these two species will contribute to the management of both lippia and tree condition in this landscape. This research uses natural abundance stable isotopes to investigate the relative importance of water sources utilised by E. camaldulensis and P. canescens under low ambient soil moisture conditions. This approach will elucidate potentially important interactions between E. camaldulensis and P. canescens. It will also contribute to better understanding of the role of shallow groundwater resources in ecosystems subject to seasonal and long-term drought, and/or potentially at risk due to floodplain development and increasing climate variability

Impact of altered flow regimes and weed invasion on riparian communities in the Condamine catchment, south-east Queensland

Recent vegetation management legislation in Queensland protects the extent of native woody vegetation types, but does little to ensure that fundamental ecological values will be retained within remnants. Those remnants embedded in landscapes that have undergone major land use change are particularly at risk. This project aims to look at (i) the role of major landscape change on the health and function of Eucalyptus camaldulensis/tereticornis riparian woodland communities occurring on the Darling Downs, an intensive cropping area in southern Queensland, and (ii) the potential for restoration of these ecosystems through moves to re-establish 'environmental flows' and control ecologically-significant weed species. The study will take a multi-dimensional approach including time-series landscape analysis (GIS-based), field assessment of current community composition and condition, experimental investigation of interactions between lippia (Phyla canescens) and Eucalyptus species involving both competition for moisture and chemical (allelopathic) suppression, and an investigation of landholder responses to eucalypt dieback and lippia infestation

Modelling riparian woodland response to altered and novel disturbance regimes in production landscapes

Understanding native ecosystem responses to altered and novel disturbances is a crucial foundation for policy development and management aimed at maintaining and enhancing biodiversity and ecosystem services in production landscapes. Remnant riparian woodland ecosystems in an intensively-farmed landscape in the northern Murray-Darling Basin are subject to significant changes in hydrological regimes and land use intensity, and exhibit dieback and limited recruitment of the dominant canopy species complex, Eucalyptus camaldulensis/tereticornis, widespread invasion by the introduced perennial herb Phyla canescens, and altered floristic composition and function. Current land and water management fails to address critical changes in this landscape, and hence curb ongoing degradation. This study indicates the importance of systems-based empirical research to developing better understanding of the dynamics of remnant ecosystems in highly-modified landscapes. It uses a resilience-based state and transition modelling approach to synthesise results, highlighting key drivers of stability and critical change in the condition and function of these riparian ecosystems. Such research is vital to understanding the ecology of remnant native ecosystems and their role in the provision of important ecosystem services in production landscapes. Representation of this understanding in a simple conceptual model provides an important link to support evidence-based policy and adaptive management