Another connection between allelopathy and the ERH is the fact that concentrations of allelopathic chemicals were found to increase when diffuse knapweed was planted in North American soil as opposed to Eurasian soil. This effect is probably due to the absence of unfavorable soil conditions or soil microorganisms that exist in its native environment. As a result, the allelopathic chemicals will be able to reach higher concentrations, spread farther and therefore be more effective. By effecting more neighboring plants, the favorable changes in soil condition contribute to the success of diffuse knapweed.