Listen to part of a lecture in an Environmental Science class.
Roads, paved roads are everywhere and sometimes seem like part of the natural landscape. But, of course, roads are not part of nature and, in fact, road construction can have harmful effects on the environment and seriously impact both animal life and plant life. One harmful environmental effect of roads is that they contribute to the movement of plant species from one area to another. This causes problem for existing plants, plants already growing in that area because when a new plant species gets introduce into an area where it wasn't growing before, the new plants compete for resources with existing plant life. For example, this happened in California with a weed called the yellow star thistle. What happened was the star thistle's seeds got stuck to the tires of cars driving down the road and the seeds were distributed to new areas.