To reduce introductions, prevention actions in WPAs target weed spread as a factor of human activity. Examples of human-related pathways include vehicular transportation, recreation, and importation of contaminated forage, crop seed, soil, gravel, and other materials. The prevention practices in WPAs are also specific to the behavior of the invading plants in the invasion process. For instance, exhaustive monitoring is conducted along roads for weeds, such as spotted knapweed (right), that rely on transportation corridors to gain access to new regions (below).