The Plant Risk Evaluation Tool (PRE) was developed as a region-specific, rapid risk assessment for ornamental plants (Conser et al. (2015). It is also used for assessing risk of plants that are not ornamental to establish and become invasive. PRE has been peer reviewed and has a 95% accuracy rate for correctly identifying ornamental species as high or lower invasive risk (Conser et al., 2015). It may be used on plant species, subspecies, or cultivars. However, while the tool can evaluate riparian plants, it is not appropriate for fully aquatic species.
PRE consists of 20 questions on impact, reproduction, dispersal, and how well a species’ worldwide distribution matches with the climate in the region of interest. An evaluator answers each question as Yes or No with points awarded for each Yes. The evaluator cites references, which may include published or unpublished information as well as expert observations, and assigns a Confidence Level to each answer based on the quality of available information. (The original PRE used 19 questions; an additional question and the Confidence Level were added when PRE was converted to an online tool based on feedback from early evaluators). At least 16 questions must be answered for a PRE evaluation to be valid. The final PRE score is categorized as High Potential Risk (>15 points), Moderate Potential Risk (13-15 points), or Low Potential Risk (<13 points).
Several PRE questions compare the climate of the region of interest to other regions where the plant is native or invasive using a climate match tool connected to the online evaluation form. The climate match tool originally used a combination of precipitation, USDA hardiness score, and USDA ecozone to determine climate similarity between regions. In 2026, the climate match tool was updated to use new versions of precipitation and USDA hardiness, and replaced USDA ecozones with United Nations global ecological zone ("Ecozone"). A link to the climate match map is attached to each evaluation for reference. Read more details on climate tool methodology.
We recommend that evaluations are reviewed by at least three people with expertise in plant biology, conservation, or horticulture before being made public. Reviewers add “Issues” (comments) for evaluators to address. This peer review improves the accuracy and completeness of PRE evaluations.
Conser C., L. Seebacher, D.W. Fujino, S. Reichard., and J. M. DiTomaso. 2015. The Development of a Plant Risk Evaluation (PRE) Tool for Assessing the Invasive Potential of Ornamental Plants. PLOS ONE 10(3): e0121053. https://doi.org/10.1371/journal.pone.0121053