Papers by Samantha Setterfield
Background/Question/Methods The social, economic and environmental impacts of invasive plants are... more Background/Question/Methods The social, economic and environmental impacts of invasive plants are well recognized. However, the social and economic costs of managing and eradicating invasive plants 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 reinvasion. Our framework extends recent approaches to systematic prioritization of weed management to account for spatially variable environmental, social and cultural assets that are threatened by weed invasions. We apply our method to the Daly catchment in the Northern Territory which has significant conservation and development values which are threatened by gamba grass (Andropogon gayanus), a highly invasive species recognized by the Australian government as a Weed of National Sign...
Financial mechanisms such as offsets are one strategy to abate greenhouse gas emissions. However,... more Financial mechanisms such as offsets are one strategy to abate greenhouse gas emissions. However, in the case of carbon offsets, if the carbon is released due to intentional or unintentional reversal through environmental events such as fire, the finan-cial liability to replace lost offsets will likely fall on the provider. In order to manage this risk, an understanding of the spatial and temporal distributions of threats is needed. We use the case study of savanna burning, an approved greenhouse gas abatement methodology under the Carbon Farming Initiative in Australia, to examine the risks posed by high biomass invasive grasses, such as gamba grass (Andropogon gayanus Kunth), to carbon markets in northern Australia. We focus our analysis on the threat of gamba grass to savanna burning due to its documented impacts of increased fuel loads and altered fire regimes. We build on an initial assessment of the spatial and financial extent to which gamba grass poses a risk to savanna burn...
Frontiers in Plant Science, 2015
Comparative studies of plant resource use and ecophysiological traits of invasive and native resi... more 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 (15)N 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.
Ecological Applications, 2015
The social, economic, and environmental impacts of invasive plants are well recognized. However, ... more 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.
Remote Sensing, 2015
The spread of an alien invasive grass (gamba grass-Andropogon gayanus) in the tropical savannas o... more The spread of an alien invasive grass (gamba grass-Andropogon gayanus) in the tropical savannas of Northern Australia is a major threat to habitat quality and biodiversity in the region, primarily through its influence on fire intensity. Effective control and eradication of this invader requires better insight into its spatial distribution and rate of spread to inform management actions. We used full-waveform airborne LiDAR to map areas of known A. gayanus invasion in the Batchelor region of the Northern Territory, Australia. Our stratified sampling campaign included wooded savanna areas with differing degrees of A. gayanus invasion and adjacent areas of native grass and woody tree mixtures. We used height and spatial contiguity based metrics to classify returns from A. gayanus and developed spatial representations of A. gayanus occurrence (1 m resolution) and canopy cover (10 m resolution). The cover classification proved robust against two independent field-based investigations at 500 m 2 (R 2 = 0.87, RMSE = 12.53) and 100 m 2 (R 2 = 0.79, RMSE = 14.13) scale. Our mapping results provide a solid benchmark for evaluating the rate and pattern of A. gayanus spread from future LiDAR campaigns. In addition, this high-resolution mapping OPEN ACCESS Remote Sens. 2015, 7 5118
Pacific Conservation Biology
Assisted Colonization (AC) has been proposed as one method of aiding species to adapt to the impa... more Assisted Colonization (AC) has been proposed as one method of aiding species to adapt to the impacts of climate change. AC is a form of translocation and translocation protocols for threatened species, mostly for reintroduction, are well established in Australia. We evaluate the information available from implementation of translocations to understand how existing policies and guidelines should be varied to plan, review and regulate AC. While the risks associated with AC are potentially greater than those of reintroductions, AC is likely to be the only available method, other than germplasm storage and establishment of captive populations, of conserving many taxa under future climate change. AC may also be necessary to maintain ecosystem services, particularly where keystone species are affected. Current policies and procedures for the preparation of Translocation Proposals will require modification and expansion to deal with Assisted Colonization, particularly in relation to risk management, genetic management, success criteria, moving associated species and community consultation. Further development of risk assessment processes, particularly for invasiveness, and guidelines for genetic management to maintain evolutionary potential are particularly important in the context of changing climate. Success criteria will need to respond to population establishment in the context of new and evolving ecosystems, and to reflect requirements for any co-establishment of interdependent species. Translocation Proposals should always be subjected to independent peer review before being considered by regulators. We conclude that consistent approaches by regulators and multilateral agreements between jurisdictions are required to minimize duplication, to ensure the risk of AC is adequately assessed and to ensure the potential benefits of AC are realized.
ABSTRACT Background/Question/Methods Tropical savannas are the dominant vegetation across norther... more ABSTRACT Background/Question/Methods Tropical savannas are the dominant vegetation across northern Australia, covering approximately ¼ of the continent. The region is characterised by frequent fire, with approximately 50% burnt each year. During the 20th Century, hundreds of grass cultivars were introduced to northern Australia for the purpose of improving agricultural potential. Many of these species are now major weeds with some species of particular concern due to their effects on fire behaviour. The most serious is Andropogon gayanus Kunth. (gamba grass), which was introduced from Africa for pastoral production but has now invaded significant areas of the Australian savanna region, including land managed for conservation, rural/residential purposes, agriculture, defence and mining. The objective of this research was to quantify the changes in fire regimes following broadscale invasion, and document environmental, cultural and economic consequences. Results/Conclusions Compared with native grasses, gamba grass forms substantially taller and denser stands that cure later in the dry season. The large fuel loads resulting from gamba grass invasion support fires 5 to 10 times more intense than those fuelled by native grasses. The change in fire fuel properties means that flame height is significantly increased and we have recorded the first passive crown fires in the region in the gamba invaded areas. The change in fire regime caused a major decline in woody vegetation, which results in a major loss of above-ground carbon store. Fire risk has increased dramatically and this presentation describes the transformation in changes in fire management practices required to mitigate this threat, resulting in a 10 times increase in the cost of fire-management resources.
Effective fire management relies on the ability to assess the potential risk that a fire event po... more Effective fire management relies on the ability to assess the potential risk that a fire event poses to the community so that fire managers can ensure sufficient resources are available to respond to unplanned fires. Fuel loads are a major contributor to fire risk and any significant changes to fuel load should be incorporated into fire risk models. An example is the invasion of Australia's tropical savannas by the high biomass African grass Andropogon gayanus Kunth (gamba grass). Fine fuel load (grass and twigs <6 mm) in a heavily invaded landscape has increased from 6 to 10 t ha −1 . Consequently, in 2010, the Bureau of Meteorology created two 20 km 2 radius 'primary response zones', which are defined areas of dense invasion in the greater Darwin region in which fire risk is assessed using an estimate of increased fuel load. In this paper, we quantify the effect of the increased (invaded) fuel load on the assessment of fire risk. We do this by modelling the daily McArthur Mark 4 Grassland Fire Danger Index (GFDI) for the fire seasons in 2012 and 2013 using both native (6 t ha −1 ) and invaded fuel loads. We show that the number of days with GFDI >50 (the threshold for fire weather warnings and fire bans) has increased and the length of the severe-risk fire season has extended, resulting in substantial increases in fire management costs. This has safety and resource implications for fire management agencies as the area of invasion increases across northern Australia.
Para grass (Urochloa mutica (Forssk.) T.Q.Nguyen) is an environmental weed that forms dense monoc... more Para grass (Urochloa mutica (Forssk.) T.Q.Nguyen) is an environmental weed that forms dense monocultures on Australia's tropical floodplains. It is a weed of particular concern for Kakadu National Park managers and the Indigenous Traditional Owners. To inform the design of a large-scale management program of para grass in Kakadu, we collected distribution and control data. This information will be incorporated into a weed risk and management model for Kakadu. Here we report on the initial data collection findings.
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Papers by Samantha Setterfield