Human population the primary factor in exotic plant invasions in the United States - EurekAlert (press release) | population growth |

The invasion of invasive plants in the United States hasnt come on its own, the plants had to have been carried here.  As more humans are born and as the worldwide population grows people have brought exotic plants from foreign places to te United States to try to create diversity.  But all they have done is gotten the plants to overgrow and take over the native plants.  So the more humans their are and the more plants they bring over the more invasive the exotic plants will become.