This volume is concerned with those parts of the earth's surface where semiarid to subhumid climate determines that the potential vegetation is characterized by a more or less continuous layer of grasses and other associated herbs. These grasslands have been modified to a very considerable degree by the activities of man and his domesticated animals. The authors of the various chapters have evaluated the effect of these stresses in modifying ecosystem structure and activities of organisms.The book provides an intensively referenced and indexed synthesis and review of knowledge concerning the natural grasslands of the world in as uniform a style as possible. Because of its length, it is published in two parts. The first part deals with the grasslands of the Western Hemisphere, and the Eastern Hemisphere and the resumé compose this second volume.