Keith B. Ferdinands

Biodiversity and invasive grass species: multiple-use or monoculture?

Invasive plants are recognised as a major threat to biodiversity conservation worldwide. Despite this recognition, our understanding of the mechanisms controlling the invasion process and its impact on flora and fauna is often poor. We examined the impact of an invasive aquatic grass species, para grass (Urochloa mutica), on seasonally inundated wetlands in tropical northern Australia. Flora and avifauna were surveyed at sites invaded by para grass and in native vegetation. Spatial information systems were used to design surveys and determine environmental correlates of para grass distribution and so predict the potential future spread of para grass and infer impacts in the absence of control. Where para grass was present the median number of plant taxa was ~75% lower. Few birds showed preference for habitats invaded by para grass, and most birds were associated with areas of native vegetation or other habitats with little or no para grass. The study identified several wetland habitats that are at greater risk of invasion, based on the apparent habitat preferences of para grass. The degradation or loss of some of these ‘at-risk’ habitats, including Oryza meriodionalis grasslands that play an integral role in the wetland food chain, has important ramifications for the levels of biodiversity supported by the wetlands.

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.

Measuring benefits of protected area management: Trends across realms and research gaps for freshwater systems

Protected areas remain a cornerstone for global conservation. However, their effectiveness at halting biodiversity decline is not fully understood. Studies of protected area benefits have largely focused on measuring their impact on halting deforestation and have neglected to measure the impacts of protected areas on other threats. Evaluations that measure the impact of protected area management require more complex evaluation designs and datasets. This is the case across realms (terrestrial, freshwater, marine), but measuring the impact of protected area management in freshwater systems may be even more difficult owing to the high level of connectivity and potential for threat propagation within systems (e.g. downstream flow of pollution). We review the potential barriers to conducting impact evaluation for protected area management in freshwater systems. We contrast the barriers identified for freshwater systems to terrestrial systems and discuss potential measurable outcomes and confounders associated with protected area management across the two realms. We identify key research gaps in conducting impact evaluation in freshwater systems that relate to three of their major characteristics: variability, connectivity and time lags in outcomes. Lastly, we use Kakadu National Park world heritage area, the largest national park in Australia, as a case study to illustrate the challenges of measuring impacts of protected area management programmes for environmental outcomes in freshwater systems.

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.