Optimal dynamic control of invasions: applying a systematic conservation approach

The social, economic, and environmental impacts of invasive plants are well recognized. However, these variable impacts are rarely accounted for in the spatial prioritization of funding for weed management. We examine how current spatially explicit prioritization methods can be extended to identify optimal budget allocations to both eradication and control measures of invasive species to minimize the costs and likelihood of invasion. Our framework extends recent approaches to systematic prioritization of weed management to account for multiple values that are threatened by weed invasions with a multi-year dynamic prioritization approach. We apply our method to the northern portion of the Daly catchment in the Northern Territory, which has significant conservation values that are threatened by gamba grass (Andropogon gayanus), a highly invasive species recognized by the Australian government as a Weed of National Significance (WONS). We interface Marxan, a widely applied conservation planning tool, with a dynamic biophysical model of gamba grass to optimally allocate funds to eradication and control programs under two budget scenarios comparing maximizing gain (MaxGain) and minimizing loss (MinLoss) optimization approaches. The prioritizations support previous findings that a MinLoss approach is a better strategy when threats are more spatially variable than conservation values. Over a 10-year simulation period, we find that a MinLoss approach reduces future infestations by ~8% compared to MaxGain in the constrained budget scenarios and ~12% in the unlimited budget scenarios. We find that due to the extensive current invasion and rapid rate of spread, allocating the annual budget to control efforts is more efficient than funding eradication efforts when there is a constrained budget. Under a constrained budget, applying the most efficient optimization scenario (control, minloss) reduces spread by ~27% compared to no control. Conversely, if the budget is unlimited it is more efficient to fund eradication efforts and reduces spread by ~65% compared to no control

Resource-use efficiency explains grassy weed invasion in a low-resource savanna in north Australia

Comparative studies of plant resource use and ecophysiological traits of invasive and native resident plant species can elucidate mechanisms of invasion success and ecosystem impacts. In the seasonal tropics of north Australia, the alien C4 perennial grass Andropogon gayanus (gamba grass) has transformed diverse, mixed tree-grass savanna ecosystems into dense monocultures. To better understand the mechanisms of invasion, we compared resource acquisition and usage efficiency using leaf-scale ecophysiological and stand-scale growth traits of A. gayanus with a co-habiting native C4 perennial grass Alloteropsis semialata. Under wet season conditions, A. gayanus had higher rates of stomatal conductance, assimilation, and water use, plus a longer daily assimilation period than the native species A. semialata. Growing season length was also ~2 months longer for the invader. Wet season measures of leaf scale water use efficiency (WUE) and light use efficiency (LUE) did not differ between the two species, although photosynthetic nitrogen use efficiency (PNUE) was significantly higher in A. gayanus. By May (dry season) the drought avoiding native species A. semialata had senesced. In contrast, rates of A. gayanus gas exchange was maintained into the dry season, albeit at lower rates that the wet season, but at higher WUE and PNUE, evidence of significant physiological plasticity. High PNUE and leaf 15N isotope values suggested that A. gayanus was also capable of preferential uptake of soil ammonium, with utilization occurring into the dry season. High PNUE and fire tolerance in an N-limited and highly flammable ecosystem confers a significant competitive advantage over native grass species and a broader niche width. As a result A. gayanus is rapidly spreading across north Australia with significant consequences for biodiversity and carbon and retention

When to Use Transdisciplinary Approaches for Environmental Research

Transdisciplinary research (TDR) can help generate solutions to environmental challenges and enhance the uptake of research outputs, thus contributing to advance sustainability in social-ecological systems. Our aim is to support investment decisions in TDR; more specifically, to help funders, researchers, and research users to decide when and why it is most likely to be worth investing in TDR approaches. To achieve our aim, we: 1) define TDR and use a decision tree comparing it with alternative modes of research (i.e., basic, applied, disciplinary, multi-disciplinary, and interdisciplinary research) to help researchers and funders distinguish TDR from other research modes; 2) identify features of the research problem and context (complexity, diverse knowledge systems, contestation, power imbalance, and disagreement on the need for transformative change) where a TDR approach could be more appropriate than the alternative research modes; and 3) explore the idea that the intensity of the contextual features in (2), together with the problem at hand, will help determine where a research project stands in a continuum from low- to high-TDR. We present five studies exemplifying lower- to higher-TDR approaches that are distinguished by: 1) the number and variety of research participants engaged; 2) the strength of involvement of non-academic actors; and 3) the number and variety of disciplines and knowledge systems involved in the research

Approaches to strategic risk analysis and management of invasive plants: lessons learned from managing gamba grass in northern Australia

Given the environmental damages caused by invasive species, it is critical to allocate limited management budgets carefully. To address this need, there are a variety of approaches for analysing invasive species risk and designing management strategies; these range from pre-border risk assessment through to local-scale prioritisation of management actions. Risk assessment can be broadly characterised into three components: risk analysis, risk characterisation and risk management. For each component we give a brief review of current approaches and then present innovative tools being developed and applied in northern Australia. We use gamba grass (Andropogon gayanus Kunth.) as a case study to contrast the benefits of the different approaches presented. With our case study, we demonstrate the practical application of novel risk management tools, with results from these tools that are being used locally to prioritise management actions. Lastly, we note that for even greater benefit to be achieved, the new spatial prioritisation approaches presented must be accompanied by further development of data and methods to accommodate planning for multiple weed species and incorporation of further human dimensions (e.g. social and cultural values)