Weed Risk Assessment Research Articles

Running bamboo species pose a greater invasion risk than clumping bamboo species in the continental United States

Bamboo species have been promoted for utility in both biomass and pulp production because of their high productivity. However, some bamboo species are known to be problematic invaders. Our goal was to use a weed risk assessment (WRA) tool to evaluate and compare invasion risk of non-native running and clumping bamboo species, many of which are under consideration as paper pulp and bioenergy crops in the continental United States. WRAs were conducted for 18 running and 29 clumping bamboo species using a version of the Australian WRA modified for the U.S. We tested for differences in scores and the number of questions answered for clumping and running species, the relationship between the WRA score and the number of questions answered, and the questions that differentiated low and high-risk species. Overall, we found that running bamboo species present a significantly higher invasion risk than clumping species. Only one running bamboo species (Chimonobambusa tumidissinoda) was identified as low risk and one clumping species (Bambusa bambos) was high risk for invasion. History of invasiveness elsewhere, the ability to form dense thickets, and unintentional dispersal of viable rhizome pieces were associated with significantly greater predicted risk. Commercial applications of bamboo should focus on the use of low invasion risk clumping bamboo species to reduce the risk of escape and colonization of nearby natural areas. Further, bamboo-specific best management practices (BMPs) should be implemented to reduce the probability of invasion for species used in commercial production.

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.

Two-leaf nightshade (Solanum diphyllum L.)-An addition to the flora of Delhi, India and weed risk assessment of the species

Two-leaf nightshade (<i>Solanum diphyllum</i> L.)-An addition to the flora of Delhi, India and weed risk assessment of the species

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.

First assessment of naturalised Rubus ellipticus Sm. populations in South Africa - A potential invasion risk?

The first naturalised Rubus ellipticus populations are described from KwaZulu-Natal, South Africa. Surveys were undertaken at five sites in Hillcrest, during which site specific distribution data were collected. Plant density estimates were calculated by dividing the number of plants per polygon area at each site. Basic physiological data such as plant height and number of stems were recorded at three of these sites (n=399).We recorded 422 plants in total, and site-specific plant densities were below 30%. Only 6 % of the population sampled had flowers, and the shortest flowering individual measured 0.9m. The tallest individual recorded was 3.5m. Distribution data from the largest population (n=329) were mapped, and results showed that some seedlings occurred more than 10m away from the nearest adult, which could be attributed to dispersal of the seeds by birds, indicating a minimal level of spread. The initial weed risk assessment score of 21 indicates a high potential invasion risk to South Africa, and the bioclimatic modelling map highlighted 2% of the country as being highly suitable climatically for the species. Our study indicates that R. ellipticus can be considered at an early stage of invasion in South Africa (C3 classification), and we support its current legal categorisation as a category 1a plant invader and eradication-target species. We propose that implementation of an eradication programme would entail removal of all existing populations, monitoring and evaluation of clearing efforts, rapid response to new populations detected, and targeted awareness campaigns and surveys in high risk areas identified in the bioclimatic modelling map.

Cardiospermum grandiflorum

Cardiospermum grandiflorum

Comparison of four modeling tools for the prediction of potential distribution for non-indigenous weeds in the United States

This study compares four models for predicting the potential distribution of non-indigenous weed species in the conterminous U.S. The comparison focused on evaluating modeling tools and protocols as currently used for weed risk assessment or for predicting the potential distribution of invasive weeds. We used six weed species (three highly invasive and three less invasive non-indigenous species) that have been established in the U.S. for more than 75 years. The experiment involved providing non-U. S. location data to users familiar with one of the four evaluated techniques, who then developed predictive models that were applied to the United States without knowing the identity of the species or its U.S. distribution. We compared a simple GIS climate matching technique known as Proto3, a simple climate matching tool CLIMEX Match Climates, the correlative model MaxEnt, and a process model known as the Thornley Transport Resistance (TTR) model. Two experienced users ran each modeling tool except TTR, which had one user. Models were trained with global species distribution data excluding any U.S. data, and then were evaluated using the current known U.S. distribution. The influence of weed species identity and modeling tool on prevalence and sensitivity effects was compared using a generalized linear mixed model. Each modeling tool itself had a low statistical significance, while weed species alone accounted for 69.1 and 48.5% of the variance for prevalence and sensitivity, respectively. These results suggest that simple modeling tools might perform as well as complex ones in the case of predicting potential distribution for a weed not yet present in the United States. Considerations of model accuracy should also be balanced with those of reproducibility and ease of use. More important than the choice of modeling tool is the construction of robust protocols and testing both new and experienced users under blind test conditions that approximate operational conditions.

Testing weed risk assessment paradigms: Intraspecific differences in performance and naturalisation risk outweigh interspecific differences in alienBrassica

AbstractRisk assessments of alien species are usually conducted at species level, assuming that all individuals of a given species pose similar risks. However, this may not be the case if there is substantial within‐species variation that could influence invasion success.We used a seed addition experiment, comprising 25 taxonomically stratified varieties of threeBrassicaspecies introduced to roadside habitats in Canterbury, New Zealand, to quantify variation in performance among species, subspecies and varieties. We aimed to assess if species was the most appropriate taxonomic level at which to evaluate invasion risk.Differences among varieties within species explained approximately 30 times more of the variation in performance (number of individuals/quadrat) than differences among species. Some of the variation among varieties was attributable to differences in seed viability.Nevertheless, differences among taxonomic groups explained only 7% of the total variation in performance; 28% was attributable to differences among plots, reflecting broad‐scale environmental variation, while 65% was attributable to differences among quadrats nested within plots, highlighting the importance of fine‐scale variation in the availability of suitable microsites.Policy Implications. Our seed addition experiment quantified variation in performance of 25 taxonomically stratifiedBrassicataxa introduced to roadside habitats. Varieties (nested within species) differed in performance far more than did species. This suggests risk assessments carried out at species level may overlook important subspecific variation in invasion risk. This is particularly true for conventionally bred and genetically modified species, which may contain taxa posing risks different to that at which the species is assessed. Consideration should be given to subjecting unassessed subspecies and varieties of plants to risk assessments similar to those applied to species.

Integrating invasive species policies across ornamental horticulture supply chains to prevent plant invasions

Abstract Ornamental horticulture is the primary pathway for invasive alien plant introductions. We critically appraise published evidence on the effectiveness of four policy instruments that tackle invasions along the horticulture supply chain: pre‐border import restrictions, post‐border bans, industry codes of conduct and consumer education. Effective pre‐border interventions rely on rigorous risk assessment and high industry compliance. Post‐border sales bans become progressively less effective when alien species become widespread in a region. A lack of independent performance evaluation and of public disclosure, limits the uptake and effectiveness of voluntary codes of conduct and discourages shifts in consumer preference away from invasive alien species. Policy implications. Closing the plant invasion pathway associated with ornamental horticulture requires government‐industry agreements to fund effective pre‐ and post‐border weed risk assessments that can be subsequently supported by widely adopted, as well as verifiable, industry codes of conduct. This will ensure producers and consumers make informed choices in the face of better targeted public education addressing plant invasions.

Contemporary Remotely Sensed Data Products Refine Invasive Plants Risk Mapping in Data Poor Regions.

Invasive weeds are a serious problem worldwide, threatening biodiversity and damaging economies. Modeling potential distributions of invasive weeds can prioritize locations for monitoring and control efforts, increasing management efficiency. Forecasts of invasion risk at regional to continental scales are enabled by readily available downscaled climate surfaces together with an increasing number of digitized and georeferenced species occurrence records and species distribution modeling techniques. However, predictions at a finer scale and in landscapes with less topographic variation may require predictors that capture biotic processes and local abiotic conditions. Contemporary remote sensing (RS) data can enhance predictions by providing a range of spatial environmental data products at fine scale beyond climatic variables only. In this study, we used the Global Biodiversity Information Facility (GBIF) and empirical maximum entropy (MaxEnt) models to model the potential distributions of 14 invasive plant species across Southeast Asia (SEA), selected from regional and Vietnam’s lists of priority weeds. Spatial environmental variables used to map invasion risk included bioclimatic layers and recent representations of global land cover, vegetation productivity (GPP), and soil properties developed from Earth observation data. Results showed that combining climate and RS data reduced predicted areas of suitable habitat compared with models using climate or RS data only, with no loss in model accuracy. However, contributions of RS variables were relatively limited, in part due to uncertainties in the land cover data. We strongly encourage greater adoption of quantitative remotely sensed estimates of ecosystem structure and function for habitat suitability modeling. Through comprehensive maps of overall predicted area and diversity of invasive species, we found that among lifeforms (herb, shrub, and vine), shrub species have higher potential invasion risk in SEA. Native invasive species, which are often overlooked in weed risk assessment, may be as serious a problem as non-native invasive species. Awareness of invasive weeds and their environmental impacts is still nascent in SEA and information is scarce. Freely available global spatial datasets, not least those provided by Earth observation programs, and the results of studies such as this one provide critical information that enables strategic management of environmental threats such as invasive species.

Predicted versus actual invasiveness of climbing vines in Florida

Climbing vines cause substantial ecological and economic harm, and are disproportionately represented among invasive plant species. Thus, the ability to identify likely vine invaders would enhance the effectiveness of both prevention and management. We tested whether the Weed Risk Assessment (WRA) accurately predicted the current invasion status of 84 non-native climbing vines in Florida. Seventeen percent of the species require further evaluation before risk of invasion can be determined. Of the remaining 70 species, the WRA predicted that 70% were at high risk for invasion, but only 50% of the 84 species are currently invasive in Florida. The status and risk prediction were inconsistent for 27% of the species: 15 non-invaders were predicted to be of high risk for invasion (i.e., false positive) and 4 invaders were predicted to be of low risk (i.e., false negative). Longer residence time in the flora was significantly correlated with higher invasion risk. Further investigation is necessary to identify whether residence time explains inconsistencies between risk and status conclusions, or whether the WRA over-predicts invasion risk. Nevertheless, the effects of invasive vines on native systems coupled with the influence of time on invasion status, suggest a precautionary approach is warranted when considering the introduction and management of non-native vines.

Traits related to biological invasion: A note on the applicability of risk assessment tools across taxa

Biological invasions are occurring frequently and with great impact to agricultural production and other ecosystem services. In response to this, the Australian Weed Risk Assessment (AWRA) was created to assess the potential ‘weediness’ of plants based on answers to questions related to biogeography, undesirable attributes, and biology or ecology. This basic model has been expanded and adapted for use on other taxa, often without adequate validation. Since invasive insect crop pests are a major economic cost to agricultural production, there is interest in using an expanded model for insects. Here, we review traits related to invasiveness of insects based on a systematic review of the literature. We then compare the identified invasive traits of insects with those identified for plants in the AWRA. Using insects as a case study, we illustrate that although there is some overlap in invasive traits, there are many unique traits related to invasion for both insects and plants. For insects, these traits relate largely to social behaviour. This lack of congruence may also be the case for other taxa. To increase predictive power, a taxon-specific risk assessment tool and deliberate verification are required.

Native and non-native aquatic plants of South America: comparing and integrating GBIF records with literature data

The Global Biodiversity Information Facility (GBIF) is at the moment one of the largest and most widely used biodiversity databases. Nevertheless, there are still some limitations, e.g. in terms of plant species status (native vs. non-native) and geographic resolution of records. At the same time, it is well known that alien plant invasions in inland freshwaters can alter community structure, ecosystem functions and services with significant negative impacts on biodiversity and human activities. We assessed if the GBIF database has a geospatial homogeneous information for native and non-native aquatic plant species for South America and whether or not literature resources not yet digitalized (floras, checklists and other papers) could provide additional information. We selected a set of 40 native and 40 non-native aquatic species. These 80 species included a sub-set of 40 alien species previously evaluated with the USAqWRA scheme (US Aquatic Weed Risk Assessment). Species with non-reliable identification, duplicates of the same collection, records poorly georeferenced were removed from the dataset. New records were manually compiled through classical literature research. All the georeferenced records (GBIF + literature) were used for the mapping and the comparative analysis. As a result, we can conclude that the two datasets provide quite significantly different information and the combination of the two offers new information that would not exist in a single data source. Nevertheless, a careful quality evaluation of the primary information, both in the case of literature and GBIF should be conducted, before the data is used for further analyses.

Prioritizing plant eradication targets by re-framing the project prioritization protocol (PPP) for use in biosecurity applications

The eradication of newly detected alien plant species is often prescribed, but rarely successful. Eradication programs fail for many reasons, however, for eradication to remain a cost-efficient management option it is clear that good decisions must be made at the outset. Here we re-frame the project prioritization protocol (PPP), a tool widely used in conservation biology, for use with the metrics typically used by a biosecurity agency. We then use existing methods to estimate the cost-efficiency of eradicating 50 hypothetical species incursions and compare the reduction in weed risk achieved by allocating resources using the PPP framework with the allocation based on risk ranking. By allocating resources to plant eradication programs using the PPP our analysis indicated that it is possible to improve the return on public expenditure by 25% compared to investing based solely on weed risk assessment scores. We also demonstrate how the cost-efficiency of the overall portfolio is influenced by the choice of planning horizon; including the decline in overall portfolio performance that arises when attempting to eradicate individual species too quickly. Finally, we discuss the logistical benefits to a management agency that arise from the use of a generic overarching framework such as the PPP. We believe that the PPP has considerable potential for use in biosecurity and can help focus attention on those species where management can make the biggest difference.

Big troubles are already here: risk assessment protocol shows high risk of many alien plants present in Portugal

Invasion by alien plants results in serious adverse impacts on biodiversity, ecosystem services, economy and social welfare, and is an ever-increasing challenge for nature conservation. Control of established invasive species is frequently very difficult and costly. Therefore, predicting which species have risk of becoming invasive is crucial both to prevent introduction of new invaders and to target high risk species already present in order to avoid their spread, particularly to areas with high conservation value. In Portugal more than 600 alien plant species are present as casuals or naturalized, and decision support tools are needed to discriminate which of these have higher probability of becoming invasive. We aimed to assess the effectiveness of the Australian Weed Risk Assessment, adapted to the Portuguese conditions (P-WRA), by evaluating 172 plant species: 49 considered as invasive; and, 123 as non-invasive species. The results showed that the P-WRA correctly identified all invasive species. As for non-invasive species, 17% were accepted, 78% rejected and 5% required further evaluation. Receiver Operating Characteristic (ROC) curve reflected high accuracy of predictions despite lower than that found in other regions. The best cutoff level for P-WRA score, maximizing the ability for classification of the protocol, was 13 resulting in more non-invasive species accepted (46%). In the end, this assessment informed that in addition to the 49 species already invasive, a high number (66) of alien plant species have invasive risk. Amongst these, a list of 20 species is proposed for targeted priority management aiming to prevent their spread. Comparison of the scores obtained with A-WRA for other regions with Mediterranean climate revealed that 17% of the species compared (78) reached different outcomes, signaling the need to be careful when extrapolating the use of previous scores. The P-WRA can be a promising screening system post-border for predicting invasive species already present in Portugal and contribute to the targeting of species for priority intervention, particularly in natural areas with high conservation value.

Determination Of Priority Species For Invasive Plant Management In Wetlands Of Wasur National Park Merauke

&lt;p&gt;Threats on biodiversity in a conservation area can originated from outside or inside the area. One of the outsiders that rarely noticeable is invasion of exotic species, which usually alters the stability of natural processes within the area. Wasur National Park has some wetland ecosystems that overcome the issues of deterioration in function and benefits due to exotic plant invasion in recent days. This research was carried out to determine priority species that need immediately managements in Wasur National Park. Field survey and inventory followed by scoring and evaluation methods using Weed Risk Assessment by Exotic Species Ranking System were taken in this research to obtain the priority species. The scoring and ranking steps placed encountered invasive plant species into four categories of management priority based on Significance of Impact and the Feasibility of Control. The result identified 49 species of invasive plants from three wetlands in Wasur National Park, which 75% (or 36 species) of them are species of Priority 3 (lesser threat and easy to control), 4 species of Priority 4 (lesser threat – hard to control) and at least 9 species of Priority 2 (serious threat-hard to control). Priority 2 species consist of &lt;em&gt;Carex&lt;/em&gt; sp., &lt;em&gt;Eleocharis indica&lt;/em&gt; (Lour.) Druce, &lt;em&gt;Hanguana malayana&lt;/em&gt; (Jack.) Merr., &lt;em&gt;Imperata cylindrica&lt;/em&gt; (L.) Beauv., &lt;em&gt;Ludwigia oktovalvis&lt;/em&gt; (Jacq.) Raven, &lt;em&gt;Melaleuca cajuputi&lt;/em&gt; Powell, &lt;em&gt;M. leucadendron&lt;/em&gt; (Linn.), &lt;em&gt;Paspalum&lt;/em&gt; &lt;em&gt;conjugatum&lt;/em&gt; P. J. Bergius, and &lt;em&gt;Stachytareta jamaicensis&lt;/em&gt; (L.). These invasive plants need to be managed properly and thoroughly further.&lt;/p&gt;

Prioritisation of aquatic invasive alien plants in South America with the US Aquatic Weed Risk Assessment

Forty South American aquatic plant species were selected and categorised in four a priori status classes (alien naturalised, alien invasive, native and absent) according to expert opinion, for 16 South American regions (Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Falklands Islands, French Guiana, Galapagos, Guyana, Paraguay, Peru, South Georgia and South Sandwich Islands, Suriname, Uruguay and Venezuela). The 40 aquatic plant species were assessed using the US Aquatic Weed Risk Assessment (USAqWRA) scheme for each of the 16 South American regions, for a total number of 644 assessments and for South America (153 assessments). The method was benchmarked against expert opinion (invasive, non-invasive). We ranked 17 of them as naturalised, and 15 as invasive species in at least one South American region. The USAqWRA distinguished between non-invaders and invaders with an overall accuracy of 84.9% in South America and 54.1% in the 16 regions, with areas under the curves equal to 0.893 and 0.853, at a threshold score of 51.5 and 43.5, respectively. The study highlights that the USAqWRA could represent a suitable screening protocol to prioritise aquatic species that have the potential to cause negative impacts, prevent attempts of introduction and to manage risky aquatic plants in South America.

Assessing the invasiveness of Berberis aristata and B. julianae (Berberidaceae) in South Africa: Management options and legal recommendations

The detection of two alien species spreading in natural ecosystems, namely Berberis julianae and Berberis aristata, prompted investigation into the risk that they pose as invasive plants to South Africa. Here we determined their distribution in South Africa, assessed population structure and reproductive size, determined seed germinability, evaluated the risks posed by the species by conducting weed risk assessments, and provide recommendations for control. We also assessed the extent of current and historic cultivation. B.julianae was found to be widely cultivated while but B. aristata was not found in cultivation. Only a single naturalized population was found for each species, with B. julianae occupying an area of 14ha (0.02ha condensed canopy) and B. aristata occupying an area 180ha (1.58ha condensed canopy). Given its very limited known distribution, there is an opportunity to eradicate B. aristata, although this would need to be reviewed if further surveys find new populations; we recommend that it be classified as category 1a invasive according to the National Environmental Management: Biodiversity Act. We do not yet recommend that B. julianae be regulated particularly given its horticultural popularity. However, it is clearly a species that needs to be monitored.

Weed Risk Assessments Can Be Useful, But Have Limitations

An abstract is not available for this content so a preview has been provided. Please use the Get access link above for information on how to access this content.

Weed Risk Assessments Are an Effective Component of Invasion Risk Management

An abstract is not available for this content so a preview has been provided. Please use the Get access link above for information on how to access this content.