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

Transdisciplinary environmental research: trial and evaluation. Final report

A group of four NESP Northern Australia Environmental Resources Hub projects operating in the Fitzroy River catchment (Western Australia) used a transdisciplinary (participatory, interdisciplinary and outcomes-focused) approach by having water resource management as a common theme. The projects partly integrated their research processes and outputs and developed strong links with research users. The transdisciplinary project team included researchers from four projects, who integrated their research processes and outputs in pairs: 1.3.3 (Environmental water requirements) and 1.5 (Indigenous water requirements); 1.6 (Multi-objective planning) and 5.4 (Showing and sharing knowledge). Project 6.2 (this research) aimed to support the development of a transdisciplinary research (TDR) approach in the Fitzroy catchment and contribute to the emerging body of knowledge on transdisciplinarity more broadly. We achieved that aim by conducting a formative evaluation (i.e. during project implementation) of the collaboration between the four projects above. This involved: (1) the development of the Theory of Change of this collaboration, (2) a literature review, (3) interviews of research users, and (4) researchers’ reflection on the previous steps. The team identified different research impacts occurring because of people’s participation in, or access to the outputs of research. Research impacts, on both researchers and research users, included: • learning and increased understanding of scientific information • development of new skills or social learning (i.e. learning from working together with other stakeholders) • empowerment (e.g. meeting and deliberating with peers regarding collective action because of the projects) • enhancing communication with other groups and a better understanding of their perspectives • creating new contacts (e.g. meeting new people) and strengthening existing relationships. Two projects (Environmental water requirements and Indigenous water requirements) have directly contributed to the Fitzroy catchment water allocation plan and to stakeholders’ submissions on the draft water plan consultation (i.e. Western Australian Department of Water and Environmental Regulation [DWER] Discussion Paper). The Multi-objective planning and Showing and sharing knowledge projects contributed with less tangible outcomes such as enhancing communication, and strengthening relationships and Indigenous institutions. Researchers identified processes or outputs that contributed positively to knowledge uptake by research users, for example, the use of videos and interactive maps, which can help users such as Traditional Owners to assimilate and use project information. They also identified things that hindered the use of project outcomes, such as confusion between the roles of research and government planning, and the limited capacity of some organisations to use research outputs

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