Aaron M. Petty

Adding fuel to the fire: the impacts of non-native grass invasion on fire management at a regional scale

Background Widespread invasion by non-native plants has resulted in substantial change in fire-fuel characteristics and fire-behaviour in many of the worlds ecosystems, with a subsequent increase in the risk of fire damage to human life, property and the environment. Models used by fire management agencies to assess fire risk are dependent on accurate assessments of fuel characteristics but there is little evidence that they have been modified to reflect landscape-scale invasions. There is also a paucity of information documenting other changes in fire management activities that have occurred to mitigate changed fire regimes. This represents an important limitation in information for both fire and weed risk management. Methodology/Principal Findings We undertook an aerial survey to estimate changes to landscape fuel loads in northern Australia resulting from invasion by Andropogon gayanus (gamba grass). Fuel load within the most densely invaded area had increased from 6 to 10 t ha−1 in the past two decades. Assessment of the effect of calculating the Grassland Fire Danger Index (GFDI) for the 2008 and 2009 fire seasons demonstrated that an increase from 6 to 10 t ha−1 resulted in an increase from five to 38 days with fire risk in the ‘severe’ category in 2008 and from 11 to 67 days in 2009. The season of severe fire weather increased by six weeks. Our assessment of the effect of increased fuel load on fire management practices showed that fire management costs in the region have increased markedly (∼9 times) in the past decade due primarily to A. gayanus invasion. Conclusions/Significance This study demonstrated the high economic cost of mitigating fire impacts of an invasive grass. This study demonstrates the need to quantify direct and indirect invasion costs to assess the risk of further invasion and to appropriately fund fire and weed management strategies.

Linking humans and fire: a proposal for a transdisciplinary fire ecology

Human activity currently plays a significant role in determining the frequency, extent and intensity of landscape fires worldwide. Yet the historical and ecological relationships between humans, fire and the environment remain ill-defined if not poorly understood and an integrative approach linking the social and physical aspects of fire remains largely unexplored. We propose that human fire use is ubiquitous and evidence that historical fire patterns do not differ from non-anthropogenic fire regimes is not evidence that humans did not practice fire management. Through literature review and the presentation of two case studies from the south-eastern USA and tropical Australia, we discuss how the study of fire ecology can benefit from paying attention to the role of humans in three thematic areas: (1) human agency and decision processes; (2) knowledge and practice of landscape fire and (3) socioecological dynamics inherent in the history of social systems of production and distribution. Agency, knowledge of fire ecology and social systems of production and distribution provide analytical links between human populations and the ecological landscape. Consequently, ignitions ultimately result from human behaviours, and where fire use is practised, ignitions result from decision process concerning a combination of ecological knowledge and belief and the rationale of livelihood strategies as constrained by social and ecological parameters. The legacy of human land use further influences fuel continuity and hence fire spread.

Distribution, demography and dispersal model of spatial spread of invasive plant populations with limited data

1. Invasive weeds are a major cause of biodiversity loss and economic damage world-wide. There is often a limited understanding of the biology of emerging invasive species, but delay in action may result in escalating costs of control, reduced economic returns from management actions and decreased feasibility of management. Therefore, spread models that inform and facilitate on-ground control of invasions are needed. 2. We developed a spatially explicit, individual-based spread model that can be applied to both data-poor and data-rich situations to model future spread and inform effective management of the invasion. The model is developed using a minimum of two mapped distributions for the target species at different times, together with habitat suitability variables and basic population data. We present a novel method for internally calibrating the reproduction and dispersal distance parameters. We use a sensitivity analysis to identify variables that should be prioritized in future research to increase robustness of model predictions. 3. We apply the model to two case studies, gamba grass and para grass, to provide management advice on emerging weed priorities in northern Australia. For both species, we find that the current extent of invasion in our study regions is expected to double in the next 10 years in the absence of management actions. The predicted future distribution identifies priority areas for eradication, control and containment to reduce the predicted increase in infestation. 4. The model was built for managers and policymakers in northern Australia working on species where expert knowledge and environmental data are often lacking, but is flexible and can be easily adapted for other situations, for example where good data are available. The model provides predicted probability of occurrence over a user-specified, typically short-term, time horizon. This output can be used to direct surveillance and management actions to areas that have the highest likelihood of rapid invasion and spread. Directing efforts to these areas provides the greatest likelihood of management success and maximizes the return on investment in management response.

Invasive Plants in the Floodplains of Australia's Kakadu National Park

Kakadu National Park is Australia’s premier protected area and one of the few World Heritage areas listed for both its natural and cultural heritage values. Kakadu National Park encompasses vast areas of seasonally inundated wetlands that support an outstanding abundance of biodiversity, particularly birds and fish. The wetlands provide critical resources for the Indigenous landowners and are also a major tourist attraction. The international importance of Kakadu National Parks’ wetlands is also reflected by their listing under the Ramsar Wetlands Convention. Unfortunately, these wetlands are under substantial threat from a range of high impact invasive alien plants. The response of managers to different invasive alien plants has varied substantially. For example, the response by Kakadu National Park managers to the threat from the alien shrub Mimosa pigra has widely been used as a case study of best practice. The response was rapid, appropriately resourced, consistent over time and well-monitored. In contrast, the response to two aquatic invasive alien grass species, Hymenachne amplexicaulis and Urochloa mutica, has been relatively poor. Subsequently, whereas M. pigra remains under control, with a limited number of small infestations, the alien grasses have spread extensively in recent years and now pose a substantial threat. This chapter explores the history, invasion and management response to invasive alien grass management in Kakadu National Park. We suggest actions that should commence immediately to avoid wasting the past efforts made to save Kakadu National Park’s wetland ecosystems from M. pigra, and prevent their conversion into invasive alien grass dominated systems.

Scale relationships and linkages between woody vegetation communities along a large tropical floodplain river, north Australia.

Riparian vegetation varies according to hydrogeomorphic processes operating across different scales over two didmensions: transversely (across-stream) and longitudinally (parallel to stream). We tested the hypothesis that vegetation patterns reveal the scale and direction of underlying processes. We correlated patterns of dominant woody vegetation with environmental variables at 28 sites located within four geomorphologically distinct regions along the length of the South Alligator River catchment of Kakadu National Park, northern Australia. Across the catchment there existed a strong transverse boundary between upland savanna vegetation and two zones of riparian vegetation: Melaleuca-spp.-dominated closed-forest vegetation along stream channels and mixed open-woodland vegetation adjacent to closed forest. We surmise that there is hierarchic constraint on smaller-scale catchment processes due to fire incursion into the riparian zone and access to water during the dry season. Within the closed-forest zone, vegetation did not vary transversely, but did longitudinally. Riparian woodlands also varied longitudinally, but in the upper reaches varied independently of stream variables. By contrast, in the lower reaches woodland was strongly correlatedwithstreamvariables.Theobservedpatternofweaktransverselinkagesinheadwatersbutstronglinkagesin lowerreachesisanalogoustomodelsdevelopedforin-streampatternsandprocesses,particularlytherivercontinuum and flood-pulse concepts.

Cultural Uses and Impacts of Fire: Past, Present, and Future: Analysis, Integration and Modeling of the Earth System (AIMES), Fourth Young Scholar's Network (YSN) Workshop; Boulder, Colorado, 14–18 July 2008

Fire is a global phenomenon transcending social, economic, and political boundaries. Effective decision making regarding fire policies requires integrating knowledge of human, ecological, and climatic components of fire research over a range of spatial and temporal scales. The Analysis, Integration and Modeling of the Earth System (AIMES) fourth Young Scholars Network workshop brought together early-career researchers representing anthropology, archaeology, atmospheric science, climate modeling, ecology, fire management, geography, paleoclimate, political science, and remote sensing. Goals of the workshop were to explore the drivers, impacts, and feedbacks of human use of fires and to contextualize the management of fires.