54 FOREST TREES OF THE PACIFIC SLOPE. 



temperature than Douglas fir or yellow pine, but probably less moisture and higher 

 temperature than Engelmann spruce and alpine fir. Actual climatic requirements not 

 fully determined. 



Tolerance. — Very intolerant of shade, especially when young, but able to persist for 

 a long time (20 or 30 years) in very dense stands or for a shorter period under spe- 

 cially adverse light conditions. Requires and thrives best in full light. Even aged 

 stands with full top light, such as commonly follow complete destruction of the former 

 forest by fire, thrive for many years (50 or 60) in dense stands with little natural thin- 

 ning out, while a thinning of overtopped trees at earlier periods in uneven-aged stands 

 is a proof of its inability to endure long-continued shade. 



Reproduction. — Usually a prolific annual seeder and large numbers of cones are borne. 

 Seed of high rate of germination, and with persistent vitality. Bears fertile seed at 

 from 6 to 10 years of age when in the open. In crowded stands cones are borne by trees 

 from 15 to 20 years old. Small, light seed widely disseminated by wind — to about 200 

 yards from mother trees. Squirrels and birds destroy great numbers of seeds, but the 

 effect on reproduction is inappreciable. Extension by natural seeding is ordinarily slow, 

 scant, and uneven, but with aid of fire is exceedingly thick and even. Full light and 

 exposed mineral soil are requisites of good reproduction. The latter condition is pro- 

 duced by fire, which, when it does not consume the cones, leaves them open or in condi- 

 tion to open and release their seeds. Fire is thus especially instrumental in the repro- 

 duction of this pine. 



Gray Pine; Digger Pine. 



Pinus sabhiiana Douglas. 



DISTINGUISHING CHARACTERISTICS. 



Gray or Digger pine owes its common names to the pale blue-green color of 

 its foliage and to the fact that the large seeds furnish an important food to the 

 California Digger Indians. Its gray, thin-foliaged crown of one or two long 

 upright forks with lower drooping small branches distinguishes it at long dis- 

 tances from associated trees. The meager foliage permits the big, dark cones 

 to be seen half a mile away. Young trees form a rounded or pyramidal crown 

 of upright branches from a short, thick stem. In middle age two or more of 

 the upper branches grow very large and long, forming conspicuous U-shaped 

 forks. Old trees are from 50 to 75 feet high, with a bent or rarely straight 

 trunk from 20 to 30 feet long and from 18 to 30 inches in diameter. Larger 

 trees are sometimes found. The bark of young trees and of branches is a dull 

 gray ; that of mature trunks is about 2 inches thick and very roughly furrowed 

 and ridged. The ridges are scaly, wide, irregularly connected, and of a dark 

 gray-brown, tinged with purple-red in unweathered parts. The thin, drooping 

 clusters of leaves, a light blue or gray-green, occur two in a bundle (fig. 17, a), 

 and are from 8i to about 12 inches long. Those of a year's growth remain on 

 the tree for three or four years. When the tree is planted for ornament in a 

 rich, irrigated soil, within its natural range, the foliage becomes very much 

 stouter, giving the tree an entirely different aspect from one grown in its dry 

 native habitat ; the cones of such cultivated trees are usually smaller. With 

 the exception of the Coulter pine, the gray pine produces the largest and heav- 

 iest cones of any American pine (fig. 17). They mature by September of the 

 second season, remaining firmly attached to the branches for a number of years. 

 The cone scales open very slowly, so that seeds continue to be shed for several 

 months. Indians hasten the opening of the cones by placing them in a small 

 fire. Cones are from 6£ to 10i inches long. The tips of the scales are a red- 

 dish or chestnut brown, later weathered and grayish brown. The seeds (fig. 

 17) and short wings are very dark chocolate or blackish brown. Seed leaves 

 commonly 15, but often 16. Wood, very coarse-grained (the result of scattered 

 or open stands), dark yellowish brown, often tinged with red; locally used for 

 fuel. 



