Weed Risk Assessment System Research Articles

Interpreting expert-judged priorities of invasive alien plant species by ex post weed risk scoring: A study in Japan

Prioritization for the management of invasive alien plants, a serious threat to biodiversity, often relies on judgment by expert scientists. While comprehensive, expert judgment may result in minimal explanations as to why certain species are prioritized over others and consequently may pose challenges for practitioners in justifying targeted species in their projects. In such cases, ex post scoring of weed risk may help uncover the logic behind experts’ comprehensive judgment, since it would enable us to link the assigned priority of species to explicit scores on various aspects of weediness. To rationalize existing expert-judged priorities, we conducted weed risk scoring of listed invasive alien plants in Japan, using the modified criteria of the post-border weed risk assessment system developed in Victoria, Australia. We scored 45 alien plant species with known expert-judged priorities for management (higher or lower) based on the assessment questions on invasiveness and impact. We then analyzed the correlations between the priority category and the questions and characterized the higher-priority species based on the scores of correlated questions. The higher-priority species showed greater total scores than the lower-priority species. The priority category was significantly correlated with specific questions on lifeform, growth rates, reproductive traits and impacts on social, environmental and agricultural assets. The higher-priority species identified by Japanese experts were aquatics causing damage to water flow and quality, and species that have shown superior capabilities for growth and reproduction and are displacing native species. Our results demonstrate that ex post scoring of the invasiveness and impact of listed alien plant species is a useful approach for interpreting the logic behind experts’ prioritization. Practitioners could better justify their targeted species for control by linking assigned priorities to scores of important questions on weediness.

Developing a hybrid weed risk assessment system for countries with open and porous borders: insights from Bhutan

Developing a hybrid weed risk assessment system for countries with open and porous borders: insights from Bhutan

Outbreak of a new alien invasive plant Salvia reflexa in north‐east China

SummaryThe establishment of invasive species is widely recognised as a pivotal issue in the preservation of biodiversity. Salvia reflexa, a species native to the south‐central United States and Mexico, has been widely introduced in Argentina, Australia, New Zealand and Japan. In China, the first population of this plant was found growing adjacent to a grain depot in Shahai village, Jianping County, Liaoning Province, on 25 July 2007. Since the grain depot imported foodstuffs from regions where the plant is native, we infer that S. reflexa was introduced into China via imported foodstuff in the early to mid‐2000s. Based on field observations, at least seven populations of this plant were observed in north‐east China. The plants displayed vigorous growth in midsummer and produced prolific seeds to overcome the cold environment in winter. Salvia reflexa occurred in both dense monocultures and in mixed stands with native plants. In order to validate a system for recognising and categorising non‐native plants in China, the Australian Weed Risk Assessment system was used to assess the invasiveness status of 19 exotic and 16 native plants in north‐east China. Salvia reflexa exhibited a high score of 10, suggesting it is a potentially pernicious alien invasive plant. Although the current distribution of S. reflexa is restricted to Liaoning province and thus far has limited impact on local environments, local regulatory authorities should pay close attention to this plant and take measures to stop its expansion. This is the first time that an invasive plant from the Lamiaceae (mint family) has been documented from cold environments in China.

A test of the Australian Weed Risk Assessment system in China

The Australian Weed Risk Assessment system (AWRA) is an effective pre-border weed-screening tool that has played an active role in preventing the introduction of alien weeds into Australia and has been utilized in several other countries worldwide. Here, we selected 131 species of naturalized exotic plants (including 76 species of given non-weeds and 55 species of given weeds) to evaluate the AWRA in China for the first time. The AWRA performed better for discriminating major weeds than non-weeds and minor weeds, as it correctly rejected 84% of major weeds and did not wrongly accept a major weed. Among non-weeds, 76% were correctly classified with the final outcome of “accept” and 7.9% were wrongly rejected by the AWRA. This system correctly rejected 56% of minor weeds but accepted only 2.8% of minor weeds. The remaining 23% of all alien plants tested were classified as “evaluate further” by the AWRA. The area under the ROC curve (AUC) was 0.944, suggesting that the AWRA would be highly efficient at discriminating alien plants in China. In addition, we compared the scores of seven attributes of the AWRA between prior plant categories and analyzed their correlation with weed status. The average score for each attribute differed significantly between the two prior categories (weed and non-weed), but the average scores of the attribute “undesirable traits” did not significantly differ between any two of the three categories (non-weeds, minor weeds, and major weeds). There was a significant positive correlation between the scores of each attribute of the AWRA and weed status. The correlation coefficient for “dispersal mechanisms” and weed status was the highest and that for “undesirable traits” was the lowest. We believe that the AWRA can serve as an important weed-screening tool for plant introduction management in China.

Alien aquatic plants in wetlands of a large European city (Geneva, Switzerland): from diagnosis to risk assessment

Wetlands often form an important component in the urban matrix, where they are largely disseminated. Despite the abundance of these urban waterbodies, little is known about the spread of alien aquatic plant species in cities. Ponds are frequent in urban parks and domestic gardens where terrestrial alien plant species are common. Therefore, urban ponds are likely to support many aquatic alien species which might disperse to the natural environment. To investigate this potential, we collected data from 178 ponds in a large European city (Geneva, Switzerland), across an urbanization gradient. 17% (23 taxa) of the aquatic flora appears to be non-native, including five species at high risk of invasion. A large proportion of the waterbodies (43%) supported at least one alien taxa. Through the development of a risk assessment tool, the “Geneva-Aquatic Weed Risk Assessment system”, a risk map was created which revealed several alien species hotspots situated in the urban environment, but also in rural areas, including in protected wetlands. This risk mapping included the dispersal potential distance of species around these risk hotspots, and showed that most areas of dispersal seem to be relatively small. Ponds are target sites for deliberate introduction but they tend to be hydrologically isolated in the urban matrix, and these ‘islands’ therefore present a relative low risk of a wider dissemination of alien species. This risk is nevertheless expected to sharply increase in future. Introduction by humans is likely to be the main source of new alien aquatic plants, and so management should primarily aim to prevent the introduction of these species. Sites supporting alien species should also be monitored and, if possible, the species presenting a risk should be eradicated. Sites supporting alien species should also be monitored and, if possible, the species presenting a risk eradicated.

Priority invasive alien plants in the Tuscan Archipelago (Italy): comparing the EPPO prioritization scheme with the Australian WRA

For the first time, we tested the European and Mediterranean Plant Protection Organization (EPPO) prioritization process (EPP) on 212 alien plant species thriving in the Tuscan Archipelago, Central Italy. We compared the results of the EPPO procedure with those of the Australian Weed Risk Assessment (A-WRA) system. The two methods were also tested against the categorization performed at the national and local level by a panel of experts. Our results suggest that both methods accurately predict the invasiveness of species already present in the Tuscan Archipelago. However, the total numbers of species included in the highest risk categories by the two methods differed greatly, with the EPPO prioritization process including fewer species in the highest risk class. The two methods differed in the ability to correctly detect the invasive species, with the A-WRA method being more conservative, but at cost of more species in the highest risk class. Using Generalized Linear Models, we showed that both methods suffer from some degree of dependence from one or more of the tested explanatory variables (life span, year of first record). The results suggest that the choice of a risk assessment method should be driven by the main aim of the assessment, i.e., distinguishing between a more predictive tool (A-WRA) and a prioritization tool (EPP) for already introduced species.

Risk Assessment and Invasion Characteristics of Alien Plants in and Around the Agro-Pastoral Ecotone of Northern China

ABSTRACTTwo risk assessment protocols were adopted to assess the risks posed by alien plants that naturalized or non-naturalized in the agro-pastoral ecotone of northern China (AGENC). In this study the Risk Assessment for Central Europe method revealed that more than two-thirds of the 19 naturalized and four-fifths of the 17 non-naturalized alien plants presented high or moderate risk, and all 36 alien plants were considered to be rejected for their potential agricultural and environmental risks under the Australian Weed Risk Assessment system. On the characteristics of plant invasions, more attention should be given to disturbed habitats rather than these relative natural or closed ecosystems, and also be prudent and careful of the alien plants that are introduced as useful plants from North or South America and unintentional introduction from Europe. Moreover, annuals needed special attention: three-quarters of the alien plants were annual species, only a few were biennial (8.3%), perennial (11.1%), liana and tree plants (2.8%). Plant invasions are not extremely serious in the AGENC, but there are several alien plants that have naturalized and spread themselves in the region. However, attention should be given in the future to predicting and preventing plant invasions in this fragile region.

Challenge of weed risk assessment (WRA) for ecological restoration in China: The case of Rhus typhina L. and the new officially released weed risk assessment system

China has conducted many ecological restoration projects to alleviate environmental degradation, with numerous alien species having good adaptability widely used for fast effect. However, unsuitable plant selection may bring negative impacts and even cause biological invasion. Weed risk assessment (WRA) is therefore indispensable, yet it is often contentious especially concerning those species that has been widely utilized before weedy attributes were noted. In this paper, we take Rhus typhina L. as an example to illustrate how scientific researches and social factors can influence the evaluation of alien species and cause challenge to WRA. The evaluation of this species is not only a pure scientific issue but also influenced by many factors such as the introduction history, current utilization status in afforestation, and divergent underlying values varying through persons and sectors. These factors determined the kind of data to be assessed, which lead to different evaluations, therefore, causing challenge to its WRA. We further examined newly officially released WRA system in China from the invasion biology viewpoint, arguing that it had some major flaws in design and validation and need much improvement. Considering the human dimension and biological characters together, we suggest that the “black list” and “green list” approaches with rigorous expert assessment should be adopted simultaneously in alien species management in China.

Risk assessment for invasiveness differs for aquatic and terrestrial plant species

Predictive tools for preventing introduction of new species with high probability of becoming invasive in the U.S. must effectively distinguish non-invasive from invasive species. The Australian Weed Risk Assessment system (WRA) has been demonstrated to meet this requirement for terrestrial vascular plants. However, this system weights aquatic plants heavily toward the conclusion of invasiveness. We evaluated the accuracy of the WRA for 149 non-native aquatic species in the U.S., of which 33 are major invaders, 32 are minor invaders and 84 are non-invaders. The WRA predicted that all of the major invaders would be invasive, but also predicted that 83% of the non-invaders would be invasive. Only 1% of the non-invaders were correctly identified and 16% needed further evaluation. The resulting overall accuracy was 33%, dominated by scores for invaders. While the overall accuracy increased to 57% when the points assigned to aquatic life forms were removed, 57% of the non-invaders required further evaluation rather than were identified as having low probability of naturalizing. Discrimination between non-invaders and invaders would require an increase in the threshold score from the standard of 6 for this system to 19. That higher threshold resulted in accurate identification of 89% of the non-invaders and over 75% of the major invaders. Either further testing for definition of the optimal threshold or a separate screening system will be necessary for accurately predicting which freshwater aquatic plants are high risks for becoming invasive.

Towards a global database of weed risk assessments: a test of transferability for the tropics

Worldwide spread and establishment of alien plant species continues to accelerate and damage ecological and agricultural systems. Early warning and prevention of high-risk introductions is the most cost-effective approach to minimise losses while maximising benefits, and the Australian Weed Risk Assessment (A-WRA) system has been the most well-developed and successful predictive scheme. However, any system would be limited if the results or scores were confined to the locality of assessment. We compiled A-WRA scores conducted in four tropical to sub-tropical regions and tested the accuracy of these scores for predicting naturalisations for a separate well-documented, equatorial, exotic flora where weed risk assessments have never been conducted. Receiver Operating Characteristic (ROC) curves reflect high accuracies of predictions, comparable to those in other studies. No significant differences in accuracy were found between each regional subset and the compiled set of scores. Our results show that A-WRA scores assessed at one locality can be used for others of similar climate, increasing the utility of every species’ assessment. A global database of A-WRA scores would enable rapid local decision-making in border controls on imported plant species. A growing record of species assessments would also facilitate monitoring evolutionary and ecological aspects of invasive species.

Assessing the invasive potential of biofuel species proposed for Florida and the United States using the Australian Weed Risk Assessment

Twelve taxa under exploration as bioenergy crops in Florida and the U.S. were evaluated for potential invasiveness using the Australian Weed Risk Assessment system (WRA) modified for separate assessment at the state and national scales. When tested across a range of geographies, this system correctly identifies invaders 90%, and non-invaders 70% of the time, on average. Predictions for Florida were the same as for the U.S. Arundo donax, Eucalyptus camaldulensis, Eucalyptus grandis, Jatropha curcas, Leucaena leucocephala, Pennisetum purpureum, and Ricinus communis were found to have a high probability of becoming invasive, while Miscanthus × giganteus, Saccharum arundinaceum, Saccharum officinarum, and the sweet variety of Sorghum bicolor have a low probability of becoming invasive. Eucalyptus amplifolia requires further evaluation before a prediction is possible. These results are consistent with reports on other tests of these taxa. Given the economic and ecological impacts of invasive species, including the carbon expended for mechanical and chemical control efforts, cultivation of taxa likely to become invasive should be avoided.

Evaluation of the Australian weed risk assessment system for the prediction of plant invasiveness in Canada

The Australian Weed Risk Assessment system has been tested in a number of countries and geographical areas since its introduction in 1997, and is widely considered to be an accurate method of predicting the risk of invasiveness of new plant introductions. We evaluated the system against 152 plant species with at least a 50-year introduction history in Canada, including major and minor weeds and species which have not naturalized. Four questions that referred explicitly to Australian conditions were replaced with appropriate equivalent questions for Canada. The weediness of each species was independently rated by a panel of Canadian agricultural, botanical, and conservation experts. Using the standard cut-off scores, the system correctly rejected all major and 86% of minor weeds. However, it also incorrectly rejected 44% of non-weedy species. The diagnostic power of the system, as measured by the receiver operating characteristic curve, was similar to but somewhat lower than that found in other regions where the system has been evaluated. Answers to 23 of the 49 questions were not significantly associated with experts’ weediness ratings, indicating that a simplified system could give equally reliable results for Canada. Experts’ ratings were strongly related to cold-hardiness, suggesting that the system could be improved by making better use of data on climatic tolerances. We suggest that performance would also be improved by combining likelihood- and consequence-related scores in a multiplicative rather than additive way.

Assessing risk across the spectrum of weed management.

Abstract A range of risk assessment systems has been applied to the field of weed management globally to address the ever-growing problem of plant invasions. Here, we review the development of risk assessment and management systems across the spectrum of weed management, spanning pre-border (quarantine), post-border (generally aimed at eradication and containment) and the protection of environmental assets. These systems have been developed using broader risk management frameworks, enabling consistency with a range of other agreements and strategies (e.g. pre-border with international phytosanitary measures). While a weed risk assessment system (pre-border) has been developed and widely tested/adopted, post-border systems, especially for established weed species, have been more varied in their nature and application. For example, a triage system has been outlined only recently for managing the current risks of established or widespread weeds to native species. This review also highlights a range of other weed management areas in which risk assessment systems have been applied (e.g. invasion pathways) and where further progress is needed in the current systems to make them more robust. By assessing risk across the spectrum of weed management, we have demonstrated the role of each system and how they link together to address the majority of the spectrum. The application of risk assessment procedures has helped to create systems that aim to prevent, eradicate, contain and protect assets from the effects of weed invasions, the legacy of which will be long lasting, globally.

Risk analysis of potential invasive plants in Spain

Once non-native species become established in a new region, they are extremely difficult to eradicate or control, suggesting an urgent need for the development of early warning systems to determine the probability of a given species becoming invasive. Risk assessment schemes are valuable tools to diminish the risk of invasion and to concentrate resources on preventing the entrance and spread of those species with higher risk of invasion. For many European countries, plant species not yet introduced to the country and with high invasive potential have not been identified. The present study aims to identify and rank non-native plant species that could potentially become invasive in Spain if introduced. As a first step, a plant data set was pre-selected for screening, containing invasive plants in neighbouring countries and in other Mediterranean regions of the world but not present in Spain. A preliminary list of 80 species was obtained, Leguminosae being the most represented family (15%) and gardening (62%) the most common pathway of introduction. As for the potential European Nature Information System (EUNIS) habitats to invade, heath land and scrubland habitats types (F; 19%), followed by constructed, industrial and artificial habitats (J; 14%) and woodland and forest habitats (G; 13%) seem to be the habitats most at risk despite F and G habitats currently being the least invaded in Spain. We ranked these potential invasive species using the Australian Weed Risk Assessment system and a Risk Assessment for Central Europe developed by Weber & Gut (2004) [Weber, E., & Gut, D. (2004). Assessing the risk of potentially invasive plant species in central Europe. Journal for Nature Conservation , 12, 171–179]. Most species received intermediate values in both tests. The species with higher scores were mainly aquatic plants and should be prohibited or kept out of trade. Chromolaena odorata (Asteraceae) obtained the highest score in both tests and therefore is the species with the highest risk to become invasive in Spain if introduced.

Evaluating the invasiveness of Acacia paradoxa in South Africa

We present the first detailed survey of a population of Acacia paradoxa DC. (syn. Acacia armata R.Br.), Kangaroo Thorn, in South Africa. The species is listed under the Conservation of Agricultural Resources Act as a category 1 invasive plant and, until 2008, was being managed as part of Working for Water's general alien clearing operations. Acacia paradoxa is currently restricted to a small population (~ 11,350 plants over ~ 295 ha) on the northern slopes of Devil's Peak, Table Mountain National Park in the Western Cape. Its distribution is highly clumped, and at a local scale it has formed thick stands of up to 20 plants m − 2 . Using a bioclimatic model we predict that it has a large potential distribution in South Africa, especially along the southern coast. We confirmed the categorisation of A. paradoxa as a potential landscape transformer that requires immediate control by conducting a formal risk assessment using the Australian Weed Risk Assessment system. However, the population appears to be spreading slowly, and, while there is a significant seed-bank in some places (~ 1000 seeds m − 2 ), this is largely restricted to below the canopy of existing plants. Therefore, the population has not and likely will not rapidly spread in area, and so containment is feasible. Dedicated and thorough annual follow ups are required because plants can produce seeds when they are 1 year old and standard clearing operations have missed flowering plants.

Assessing Biofuel Crop Invasiveness: A Case Study

BackgroundThere is widespread interest in biofuel crops as a solution to the world's energy needs, particularly in light of concerns over greenhouse-gas emissions. Despite reservations about their adverse environmental impacts, no attempt has been made to quantify actual, relative or potential invasiveness of terrestrial biofuel crops at an appropriate regional or international scale, and their planting continues to be largely unregulated.Methodology/Principal FindingsUsing a widely accepted weed risk assessment system, we analyzed a comprehensive list of regionally suitable biofuel crops to show that seventy percent have a high risk of becoming invasive versus one-quarter of non-biofuel plant species and are two to four times more likely to establish wild populations locally or be invasive in Hawaii or in other locations with a similar climate.Conclusions/SignificanceBecause of climatic and ecological similarities, predictions of biofuel crop invasiveness in Hawaii are applicable to other vulnerable island and subtropical ecosystems worldwide. We demonstrate the utility of an accessible and scientifically proven risk assessment protocol that allows users to predict if introduced species will become invasive in their region of interest. Other evidence supports the contention that propagule pressure created by extensive plantings will exacerbate invasions, a scenario expected with large-scale biofuel crop cultivation. Proactive measures, such as risk assessments, should be employed to predict invasion risks, which could then be mitigated via implementation of appropriate planting policies and adoption of the “polluter-pays” principle.

Predicting plant invaders in the Mediterranean through a weed risk assessment system

Risk assessment schemes have been developed to identify potential invasive species, prevent their spread and reduce their damaging effects. One of the most promising tools for detecting plant invaders is the weed risk assessment (WRA) scheme developed for Australia. Our study explores whether the Australian WRA can satisfactorily predict the invasion status of alien plants in the Mediterranean Basin by screening 100 invasive and 97 casual species in Spain. Furthermore, we analysed whether the factors taken into account in the WRA are linked to invasion likelihood (i.e., invasion status) or to impacts. The outcome was that 94% of the invasive species were rejected, 50% of the casual species were rejected and 29% of them required further evaluation. The accuracy for casuals is lower than in other studies that have tested non-invasive (i.e., casuals or non-escaped) alien species. We postulate that low accuracy for casual species could result from: (1) an incorrect “a priori” expert classification of the species status, (2) a high weight of the WRA scores given to potential impacts, and (3) casual species being prone to becoming invasive when reaching a minimum residence time threshold. Therefore, the WRA could be working as a precaution early-warning system to identify casual species with potential to become invasive.

Screening new plant introductions for potential invasiveness: a test of impacts for the United States

AbstractThe economic, health, and environmental costs of invasive plant species suggest the need for screening systems to reduce the probability of importing new harmful invaders. We assessed 105 plant species introduced to the United States since 1995 using the Australian Weed Risk Assessment system and a secondary screen to evaluate the proportion of species that would have been prohibited from import were such a screening system implemented. These tools are likely to result in correct decisions to accept or reject species of unknown invasive potential over 80% of the time. The species tested spanned temperate and tropical locations of origin and represented all vascular plant life forms with the exception of aquatic plants. We had insufficient data to complete assessment of 4% of the species. None of the remaining 101 species were predicted to become invasive: 88% were predicted to be noninvasive and 12% required further evaluation. On average, we required 8 hours to assess each species. These results, in combination with the savings incurred when likely invaders are identified and prohibited prior to import, suggest that this screening system could be implemented to protect the economy and environment and would be unlikely to significantly preclude opportunities for the horticultural industry.

Risk Assessment of Potential Biofuel Species: An Application for Trait-Based Models for Predicting Weediness

To avoid major negative impacts of the widespread adoption of biofuel species, whether they are exotic species, natives, or novel constructs, we need a system for screening their weed potential. Australia is an important global center of biodiversity and also has major cropping industries to protect. Prevention of the entry of further weeds is therefore a major national priority. The Weed Risk Assessment (WRA) system was developed and implemented for importation decisions in 1997; it has since been introduced into other countries and is probably as good as any system currently in operation. However, we need to be aware of the limitations of any system, to address these, and to work toward improved or alternative systems. WRA is a very simple spreadsheet requiring answers to questions about a species' life-history traits, dispersal, habitat suitability, impacts on other species, and history overseas, which are then added together and compared with numerical decision criteria. Its predictive powers are limited by this simplicity and by the complexity of human attitudes toward risk and impact. Alternative risk-management methods are available but, even so, the capacity for improvement is limited. It is quite possible, therefore, that in using any trait-based system to assess the negative risks of importation or interstate translocation of biofuel species, we will wrongly reject a valuable species or approve a species that turns out to be a major weed. It is suggested that, rather than attempting to improve a single-tiered decision-support system (the quarantine “sieve”), a multitiered system (nested sieves) would lead to a more effective system and greater cost-effectiveness. The key to this would be a postentry screening process for those species that have successfully passed through the WRA system.

Developing a pre-entry weed risk assessment system for use in Japan

We evaluated the applicability of the Australian Weed Risk Assessment (AWRA) system in Japan. Native weeds (n = 117) and introduced plants (n = 142), whose weed status was classified by 20 plant experts, were assessed using a slightly modified version of the AWRA system designed to fit Japanese conditions. A receiver operating characteristic (ROC) curve for the system, when classifying two-thirds of the 259 taxa as weeds or non-weeds, was plotted and the area under the ROC curve was calculated. The area was 0.88 and significantly greater than 0.5. Thus, the validity of the system to classify plants was proven. The best cut-off level for the WRA score using Youden’s index was 10. When taxa whose AWRA scores were greater than 10 were regarded as weeds, the sensitivity and specificity were 0.88 and 0.78, respectively. These values were verified with the remaining one-third of the taxa. From these findings, the modified AWRA system was considered to be effective for use in Japan. However, further studies are required to set the best cut-off level in terms of maximising the benefits gained from using the system. A second screening test associated with the cut-off level also needs to be developed.