Reforestation in Northern Arizona 99 



cause the surface soil to dry out so readily that a large percentage 

 of the seed fails to germinate, and the few seedlings that do come 

 up usually die for lack of moisture. After the beginning of the 

 rainy season in late summer the seed germinates, but early frosts 

 commonly kill many of the seedlings. During the winter seed- 

 lings on the heavy soils are liable to be "heaved out" of the 

 ground by constant freezing and thawing of the top layer of 

 the soil. 



The forest types are determined largely by precipitation, 

 altitude and exposure. The Woodland type occurs between the 

 elevations of 4,000 and 6,200 feet, where purely semi-arid cli- 

 matic and soil conditions prevail. The principal species are : 

 One-seed Juniper (Juniperus monosperma (Engelm.) Sarg.). 

 Alligator Juniper (Juniperus pachyphloea Torr.) and Pinon 

 (Finns ednlis Engelm.), which occur scattering and in rather 

 open stands. In some parts of this region thickets of Arizona 

 Cypress (Cupressus arizonica Greene) occur. 



The Western Yellow Pine type, composed of nearly pure 

 stands of Western Yellow Pine (Pinus ponderosa Laws.) is 

 found at elevations extending from 6,200 to 8,500 feet. Near its 

 lower altitudinal limit there are scattered specimens of Pinon, 

 while the Gambel Oak, (Quercus gambelii Nutt.) and Alligator 

 Juniper are found scattered over the entire area. The climatic 

 conditions approach the semi-humid, the annual precipitation av- 

 eraging about twenty-two inches. The characteristic nature of 

 this type is that the trees occur in open continuous stands inter- 

 spersed with many open parks. 



The Transition type is a narrow and irregular belt occurring 

 at elevations of 8,500 to 9,800 feet. The climatic and soil con- 

 ditions are excellent for tree growth. In this type are found 

 Douglas Fir (Pseudotsuga taxifolia Britton), White Fir (Abies 

 concolor Parry), Limber Pine (Pinus ftexilis James), scattering 

 Western Yellow Pine, Aspen (Populus tremuloides Michx.), 

 and Engelmann Spruce (Picea engelmanni Engelm.). 



The Sub-alpine type occurs at elevations of 9,800 to 12,000 

 feet, which embraces a region of considerable rainfall. The 

 chief species found in this type are : Engelmann Spruce, Bristle- 

 cone Pine (Pinus aristata Engelm.), Foxtail Pine (Pinus bal- 

 fouriana Murr), and Aspen. The trees are stunted and scat- 

 tered as timber line is approached until finally they become mere 

 shrubs. 



