1909] PHILLIPS A STUDY OF PINON PINE 219 



shade of older trees. After the seedling stage is passed it prefers the 

 open, and is one of the most intolerant of forest trees. This gives an 

 orchard-like appearance to most stands of this species. Occasionally 

 stands of 0.7 density were noted, although few stands have more 

 than 0.6 density. 



On the best sites the trees reach a maximum height of 12 to 13 . 7 m 

 (40 to 45 feet) and a diameter of 60 to 75 cm (2 to 2.5 feet) at breast 

 height, but ordinarily the mature individuals range from 3 to 10.5 

 (10 to 35 feet) in height and from 15 to 45 cm (o. 5 to i . 5 feet) in diam- 

 eter. A difference in development was apparent on different sites. On 

 exposed sites the tree is globular, very scraggly when mature, and 

 has little or no clear length. On favorable sites trees in the open 

 have a very short clear length and a fairly regular globular or egg- 

 shaped crown. If grown in stands, the trees have a greater clear 

 length and a flat or vase-shaped crown. Young trees on favorable 

 sites are conical or globular in shape and usually very regular in 

 form. 



On the most exposed sites, shrublike trees were found which 

 were fifty to eighty years old, and only 1.8 to 3 m (6 to 10 feet) in 

 height, with a crown diameter reaching a maximum of two to four 

 times the height of the tree. On such trees it was impossible to dis- 

 tinguish the leader from the branches, and the general appearance 

 of the tree was much like that of the dwarf mountain pine (Pinus 

 monticola). The foliage is more densely clustered on these dwarf 

 trees than it is on trees in the open, with shorter and apparently 

 thicker leaves. Practically all trees, whether growing on poor or 

 good sites, are characterized by dead and half-dead branches, which 

 are retained on the tree for several years. This is characteristic of 

 nearly all species in the southwest and is due to the small amount of 

 growth that is made, the necessity of retaining only a small amount 

 of living tissue, and the dry nature of the climate, which allows the 

 retention of dead branches for a longer period than would a moist 

 climate. In exceptional stands, such as occur to the west of Servil- 

 leta, New Mexico, where a clear length of 4. 5 to 7 . 6 m (15 to 25 feet) 

 is not exceptional, the branches are shed largely because the density 

 of stand prevents the formation of as large branches as are found in 

 those trees which enjoy full sunlight. 



