The Development of a Plant Risk Evaluation (PRE) Tool for Assessing the Invasive Potential of Ornamental Plants

Abstract

Weed Risk Assessment (WRA) methods for evaluating invasiveness in plants have evolved rapidly in the last two decades. Many WRA tools exist, but none were specifically designed to screen ornamental plants prior to being released into the environment. To be accepted as a tool to evaluate ornamental plants for the nursery industry, it is critical that a WRA tool accurately predicts non-invasiveness without falsely categorizing them as invasive. We developed a new Plant Risk Evaluation (PRE) tool for ornamental plants. The 19 questions in the final PRE tool were narrowed down from 56 original questions from existing WRA tools. We evaluated the 56 WRA questions by screening 21 known invasive and 14 known non-invasive ornamental plants. After statistically comparing the predictability of each question and the frequency the question could be answered for both invasive and non-invasive species, we eliminated questions that provided no predictive power, were irrelevant in our current model, or could not be answered reliably at a high enough percentage. We also combined many similar questions. The final 19 remaining PRE questions were further tested for accuracy using 56 additional known invasive plants and 36 known non-invasive ornamental species. The resulting evaluation demonstrated that when “needs further evaluation” classifications were not included, the accuracy of the model was 100% for both predicting invasiveness and non-invasiveness. When “needs further evaluation” classifications were included as either false positive or false negative, the model was still 93% accurate in predicting invasiveness and 97% accurate in predicting non-invasiveness, with an overall accuracy of 95%. We conclude that the PRE tool should not only provide growers with a method to accurately screen their current stock and potential new introductions, but also increase the probability of the tool being accepted for use by the industry as the basis for a nursery certification program.

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

“…When evaluating the predictive power of the 56 questions of the final PRE tool, Conser et al (2015) detected that only 11 of them showed statistical significance in separating invasive from non-invasive species. Four were the result of merging two similar questions, where both were significant or near significant (e.g., different methods of vegetative reproduction, various biotic and abiotic propagule dispersal mechanisms).…”

“…Four were the result of merging two similar questions, where both were significant or near significant (e.g., different methods of vegetative reproduction, various biotic and abiotic propagule dispersal mechanisms). Similarly to Conser et al (2015), we evaluated the predictive power of the 38 questions of the USAqWRA scheme for each region and for each species, demonstrating that 8 of them are the most powerful in separating invasive from non-invasive species. These questions were classified into groups because was the result of merging similar questions: (1) Ecology and habitat of the species (questions 2, 4, 6); (2) seeding ability (question 20) and (3) potential of impact and damage to natural areas (questions 24-26, 29).…”

“…This method is widely used for assessing the performance of a screening test. A ROC curve represents test specificity (accuracy for correctly categorising non- (Conser et al, 2015).…”

“…An AUC value closer to 1.0 would indicate that the scheme perfectly discriminates between invaders and non-invaders. On the contrary, values near 0.5 indicate an inability to discriminate (Conser et al, 2015). Threshold USAqWRA score was calculated by the point of the ROC curve closest to the point on the axes that maximises the true positives and minimises the false positives.…”

Predicting invasiveness of exotic woody species using a traits‐based framework

“…Effective screening tools have long been sought to assess the potential invasiveness (i.e., potential for spread and/or impact) of exotic species (e.g., the Australian Weed Risk Assessment; Pheloung et al 1999, He et al 2018; and the Environmental and Socio-economic Impact Classification of Alien Taxa (EICAT/SEICAT) tools; Blackburn et al 2014, Bacher et al 2018. Most existing screening tools, however, are based primarily on a priori assumed importance of individual traits and naturalization history beyond native ranges (Gordon et al 2008, Koop et al 2012, Conser et al 2015.…”