Tumbleweeds are adapted for life in the desolate regions of Russia, but those adaptations served them well when the were introduced in the United States in the 19th century. While the root stays alive, the upper part of the plant dies after it goes to seed. As the wind rolls it along, it drops seeds along the way. In areas with dry, poor soil, that makes it more likely that some of the seeds will wind up in a place where they can grow.