There're mainly two harmful effects road construction has on our environment. The first one is that roads help some plants to move from one area to another. And the migrant plants then become a trouble for the existing plants in the area because the new-comers will compete with the local species for resources. A good example is the yellow star thistle in California. When there were cars driving down the road, the seeds of yellow star thistle got stuck in the tires and were then carried to new areas. They then competed with local species, which made it harder for local species to survive. Another is that the busy highways have become barriers for animals, and they divide up animals' habitat into smaller ones, where there usually isn't enough food to support the animal population. For example, the kit fox that feeds on mice and squirrels now get shut in smaller areas by highways and cannot get their food that is spread out over open grassland. As a result, its population has decreased. (173 words)
In the lecture, the professor talks about two ways that roads can do harm to the environment. The first way is that it contributes to the movement for plant species from one place to another. This is harmful because the new plants would compete for resources with the native plants. For example, the seeds of starthistles always got stuck in tires and they are often distributed to new areas. Then they compete with the native plants for water, which makes it harder for native plants to survive. Another way is that roads become barriers for animals, making it difficult and dangerous for animals to cross and look for food over a large expansion of land. For example, Kit Foxes hunt mice and squirrels for a living. However, since the roads are constructed, it become really difficult for them to get enough food, leading to a decrease in number.