Ponderosa pine (Pinus ponderosa) is the most widely distributed conifer in North America, and one of the most valuable. Commercial stands of the species are found in all of the 15 States which lie wholly or in part west of the 102d merinian, and in all but one it rank among the most important lumber producers. In the Southwest, ponderosa pine is of particular importance since this one species makes up 88 percent of the standing saw-timber volume in the two States of Arizona and New Mexico.