Vanessa H. Chewings

A leakiness index for assessing landscape function using remote sensing

The cover, number, size, shape, spatial arrangement and orientation of vegetation patches are attributes that have been used to indicate how well landscapes function to retain, not ‘leak’, vital system resources such as rainwater and soil. We derived and tested a directional leakiness index (DLI) for this resource retention function. We used simulated landscape maps where resource flows over map surfaces were directional and where landscape patch attributes were known. Although DLI was most strongly related to patch cover, it also logically related to patch number, size, shape, arrangement and orientation. If the direction of resource flow is multi-directional, a variant of DLI, the multi-directional leakiness index (MDLI) can be used. The utility of DLI and MDLI was demonstrated by applying these indices to three Australian savanna landscapes differing in their remotely sensed vegetation patch attributes. These leakiness indices clearly positioned these three landscapes along a function-dysfunction continuum, where dysfunctional landscapes are leaky (poorly retain resources).

Ecological impacts of buffel grass (Cenchrus ciliaris L.) invasion in central Australia - does field evidence support a fire-invasion feedback?

Buffel grass (Cenchrus ciliaris L.) has invaded extensive areas of arid and semi-arid Australia following its introduction as a pasture species and for erosion control. It has been suggested that buffel grass has initiated a positive fire-invasion feedback in central Australia, disrupting existing fire regimes, encouraging further buffel grass invasion, and disadvantaging the native woody flora in particular, but this hypothesis has not been tested quantitatively. This study investigated recently burnt woodland areas near Alice Springs for evidence of a fire-invasion feedback, including the impact of changing fire behaviour (intensity) on the native woodland overstorey flora. Despite the limitations inherent in a short study of ecological processes in a highly heterogeneous environment, substantial field evidence was found to support the existence of a buffel grass-initiated fire-invasion feedback. Buffel grass invasion was significantly correlated with increased fuel loads. Increased fuel loads were significantly correlated with increased burn severity, although the direct relationship between the proportion of buffel grass and increased burn severity was marginally non-significant. High field variance resulted in inadequate power to test whether or not the relative abundance of buffel grass had increased in the post-fire community. Burn severity was significantly correlated with the mortality of woodland overstorey species, and with the proportion of fire survivors that were reduced to basal resprouts. Seedling density of canopy species was low. It appears likely that future recruitment of canopy species will be hindered by the dense post-fire reestablishment of buffel grass cover at some sites. The overstorey flora is thus likely to be adversely affected by increased severity of fire associated with buffel grass invasion. As a result, there may be major change in the structure and composition of some woodlands.

A Synthesis of Current Approaches to Traps Is Useful But Needs Rethinking for Indigenous Disadvantage and Poverty Research

Indigenous disadvantage and poverty have persisted and are set to continue into the future. Although a large amount of work describes the extent and nature of indigenous disadvantage and poverty, there is little evidence-based systems understanding of the mechanisms that keep many indigenous people in their current dire state. In such a vacuum, policy makers are left to make assumptions about the causal mechanisms. The persistence of inequality and poverty suffered by indigenous people is broadly consistent with the existence of dynamical traps as described in both the resilience and development literature. We reviewed and synthesized these bodies of literature on traps and found that although they give a good lead to a systemic and parsimonious way of exploring traps, the mechanisms suggested need significant rethinking for the indigenous context. Specifically, we recommend extending the concept of traps to encompass the possibility that they are highly resilient but undesirable states, in contrast to current notions of traps as low resilience states. We also highlight the need for close scrutiny of the boundaries of indigenous systems because of the historically public nature of indigenous lives as well as the possible conjoint existence and causal linkage between poverty- and rigidity-traps in the indigenous context.

A framework for assessing regional biodiversity condition under changing environments of the arid Australian rangelands

Rangelands support many ecosystem services important to humans, including climate regulation. They also have a significant role to play in the mitigation of greenhouse gases. However, the capacity of any rangeland to do this depends foremost upon the condition of biodiversity, and the functioning of its ecosystems. Considerable research has been undertaken on rangeland condition but it has not yet included the assessment of biodiversity (plants, animals and microbes) as a primary focus. Rangeland managers have struggled to assess biodiversity condition because it is rarely defined, is everywhere (so what do you assess?), is always changing in response to natural and human disturbances (so how do you know when it has changed?) and what amount signals management action. Here we present a framework that addresses these issues, and apply it to select surrogates and indicators that are scientifically defensible in biological and planning terms for assessing biodiversity. An arid Australian rangeland region is used as a case study to develop and apply our approach. We were not able to illustrate interpretation of condition because of the absence of long-term monitoring data in Australian rangelands, but we do provide guiding principles about sampling design and analytical methods for interpretation that use raw data rather than multimetrics. We discovered that different management outcomes expected to be informed from assessing biodiversity condition affected surrogate and indicator choice, and that a number indicators were not robust when assessed on conceptual relevance, measurement qualities, feasibility of implementation and policy and management relevance for four different management outcomes. Our work highlights the importance of stating the expected outcomes of biodiversity condition assessments up front, so that indicators relevant to future management are chosen. It also shows that critical thought on the robustness of indicators is warranted, especially as condition assessments under climate change will require information on the functional traits of species. We conclude by assessing the strengths and weaknesses of our framework in relation to environmental planning.

How can we identify socio-regions in the rangelands of Australia?

The Australian rangelands are divided into regions for statistical reporting, cultural identification or administrative and bioregional management purposes. However, many of these divisions do not reflect the characteristics of inland towns. In this study we used the Urban Centre/Locality (UCL) structure (for settlements with at least 200 people) as the smallest unit of analysis to build preliminary socio-regions based on demographic (e.g. Median Age and percentage of Indigenous people in UCL), socio-economic (dependency ratio and unemployment rate) and a few environmental indicators (e.g. Normalised Difference Vegetation Index (NDVI) and Rainfall variability). A key finding of the study is that there are strong differences among UCLs in the rangelands. A threshold of around 5000 people is apparent with some indicators across all UCLs around which variability changes. There is much greater variability in the indicators among UCLs with fewer than 5000 people than there is among UCLs with over 5000 people. This confirms the need to consider statistical units smaller than those commonly used such as Statistical Local Areas (SLAs) as these and other regionalisation techniques mask the detail within areas that contain socio-economically and culturally different settlements. The high variability of indicator values observed for UCLs with smaller populations suggests that they have more diverse research, policy and investment needs than larger urban centres. We used a non-traditional approach and grouped UCLs into socio-regions based on their social characteristics instead of their geographic location. This created clusters of similar UCLs rather than contiguous regions. Some of these socio-regions cross administrative and statistical borders. The regionalisation presented in this study is likely to be valuable when selecting case-study areas for research projects and, in the long-term, when developing policy and investment initiatives.