It is not easy to assess prevention because it is difficult to measure invasion events that did not occur. Short-term evaluation measures therefore include assessing the strategy design that lead to the preferred outcomes. In addition, the number of new invasions detected and removed each year can provide a measure of the work accomplished.

Additional measures include stakeholder satisfaction, engagement of local citizens, and the number of partnerships formed among multiple-level stakeholders. Long-term measures of success are optimal and include comparing future inventories to baselines to determine if strategies were effective over time. Prevention would be considered effective if high-risk sites remained weed-free over time and ineffective if new weeds establish and persist.