It has been long believed that when trees or shrubs replace pastures or grasslands, there is an automatic increase of Carbon stocks. Today, it is becoming increasingly clear that this does not happen all the time.For example, in a study conducted by Jackson et al. (2002) in the United States, it was shown that the invasion of grasslands by shrubs increased Carbon in vegetation although to a much lower extent than expected. On the other hand, soil Carbon increased only on the drier sites and actually decreased in the wetter sites.