28 



LONGEVITY. 



The giant Douglas firs of the coast forest are known to have 

 attained great age. More than TOO rings have been counted on a 

 single stump. The vast majority of trees, however, succumb to fire, 

 windfall, insects, or fungous diseases at a much earlier age. The 

 average length of life of the merchantable stand has not been deter- 

 mined, but it is safe to say that in the coast region the larger trees 

 have taken upward of four hundred years to attain their present size. 

 The Rocky Mountain forest contains relatively few trees more than 

 400 years old. By the end of the second century diameter growth is 

 very slow and height growth has practically ceased, and from that 

 point on the tree continues to grow very slowly until it falls a victim 

 to the numerous destructive agencies that surround it. 



SIZE. 



Closely related to longevity is the maximum size attained by the 

 trees. The tallest Douglas fir of the coast form for which there is 

 record was 380 feet high, which is also the maximum height recorded 

 for redwood. Trees 15 feet in diameter have been observed, and some 

 of the largest Douglas firs of the coast forest have scaled as much a^ 

 60,000 board feet. Whole forests are found in which the trees average 

 250 feet in height and 5 feet in diameter. Such trees are usually clear 

 for a long way up the stem, since their rapid growth in competition 

 for light does not permit the formation of large side branches, and 

 such small ones as are formed soon die under the shade of the crowns 

 and are broken off. 



In striking contrast to the enormous dimensions of the coast fir 

 are the relatively small sizes of the mature mountain form. Even 

 under exceptionally favorable conditions this form rarely exceeds 150 

 feet in height or 4 feet in diameter. In the northern and central 

 Rocky Mountains, and under conditions of altitude and exposure in 

 which it attains its best development, it reaches an average height of 

 from 100 to 120 feet, with a diameter of from 15 to 30 inches, at an 

 age of 200 to 300 years. In the Gila, Datil, and Magdalena National 

 Forests, New Mexico, it reaches a merchantable diameter of 18 inches 

 at breastheight in from 100 to 150 years, and trees 150 feet high have 

 been reported. At the upper altitudinal limit of its merchantable 

 range in Colorado and Utah it remains for the most part below 70 

 feet in height, with a breasthigh diameter of about 27 inches. Its trunk 

 maintains a pronounced taper from the stump up, and a tree of these 

 dimensions would not cut over 480 board feet (Scribner rule). In 

 contrast to this, a coast fir of the same diameter w^ould be from 145 

 to 170 feet tall and would yield from 1,000 to 1,250 board feet, while 



[Cir. 150] 



