A PLANT RISK EVALUATION TOOL FOR ASSESSING THE INVASIVE POTENTIAL OF ORNAMENTAL PLANTS^©

Weed Risk Assessment (WRA) methods for evaluating invasiveness in plants have evolved rapidly in the last two decades, but none were specifically designed to screen ornamental plants prior to being released into the landscape. For a WRA tool to be accepted as an evaluation tool by the nursery industry, it must be able to accurately predict non-invasiveness without falsely categorized them as invasive. We used a science-based and systematic process to develop a new Plant Risk Evaluation (PRE) tool for screening ornamental plants as part of a prevention strategy. The final PRE tool included 19 questions, which was narrowed down from 56 original questions obtained from other 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 19 question PRE tool was further evaluated for accuracy using 57 additional known invasive and 37 known non-invasive ornamental plant 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 our new PRE tool (Table 1) should provide growers with a method to accurately screen their current stock and potential new introductions. It is our hope that the tool will be accepted for use by the industry as the basis for a nursery certification program.