Answer the following question given this paragraph: 

As pictured below ( Figure below ), some grazing animals, especially sheep and goats, eat grass right down to the roots. They may even pull the grass entirely out of the ground. Grazing animals can kill the grass. They may thin it out so much that it offers little protection to the soil. If animals are kept in the same place too long, the soil may become completely bare. The bare soil is easily eroded by wind and water.


Q: By pulling out grass by its roots and over-grazing, livestock contribute to what negative process?


A:
erosion