The success of diffuse knapweed must be attributed to a combination of several mechanisms. Its invasiveness is due to a mix of allelopathy, the enemy release hypothesis (ERH) and superior resource competition. However, the most importance must be attributed to the ERH because diffuse knapweed, while a very effective invasive species in its novel environment, is non-invasive and doesn't establish monocultures in its native range. It is the differences, biotic and abiotic, between its novel and native surroundings that cause it to be invasive.