EFFECTS OF TEMPERATUEE : THE TIMBER-LINE. 267 



ber is of relatively slower growth and of inferior shape, but the quality 

 in the main is good. 



These differences are often but shades that would at times be scarcely 

 observed, especially in isolated hills; but at other times would be 

 strongly marked, especially where a long trend of hills or mountains 

 gave these influences their full eflect; and would be most apparent when 

 the slopes in this case are north and south, when the differences amount 

 to contrasts that would attract the notice of a casual observer. 



TEIIPERATURE. 



Although particular species of trees have their limits of endurance 

 and zones of greatest development, determined by the prevailing tem- 

 peratures, their extremes, succession, and changes, perhaps quite as 

 much as by the humidity of tbe atmosphere, there are no points witbiu 

 our territory, excepting in Alaska and above the timber-line of our 

 mountains, in which the temperature of itself would forbid the growth 

 of forests.^ There are vast treeless tracts and arid regions, where trees 

 cannot be made to grow, but this is rather from want of moisture than 

 from any excess or deficiency of heat. In fact, in tropical countries 

 where the greatest heats prevail, there is the greatest luxuriance of 

 forests, where the humidity is abundant. 



But the temperatures adverse to one species may be favorable to 

 another, and it is one of the greatest aims of forestry to determine these 

 limits of possibility and zones of best conditions, in order that we may 

 avail ourselves of every chance of success and avoid every risk of 

 failure. 



The effects of temperature depend less upon their annual mean degree, 

 or even upon their extremes, if seasonable and not of long continuance, 

 than upon their fluctuation, especially in winter and early spring. The 

 endurance of frosts in plants and trees depends very much upon the 

 state of vegetation, whether in activity or repose. A multitude of her- 

 baceous plants are killed down by frost, at any time during their grow- 

 ing season, but their roots when perennial will endure the severest cold 

 of winter without injury. It is the same with many trees, which are 



'The " timher-Une," or limit of forest growth among tbe Rocky Mountains, is found 

 at an elevation of from eleven to twelve thousand feet above sea-level. The timber 

 rapidly disappears within a vertical range of four or five hundred feet, and tbe trees 

 along tlie upper margin of their growth are stinted in height rather than in the size 

 and length of their branches, which are commonly bent extremely in the direction of 

 the prevailing winds. The trunks of trees are often found extremely twisted at these 

 great altitudes, and apparently from the same cause. This is more apparent in places 

 where one side of the tree is quite sheltered by rocks while the other side is much 

 exposed to the winds. 



Elevation of the timher-Une in the BocTcij Mountain region and Pacific States. 



[These are mostly from Dr. C. C. Parry's measnrements, as published in Professor Hayden's Report 

 of 1872, p. 751.] 



Feet. 



Bridger's Peak, Montana 9,002 



Mount Delano, Montana 8, 784 



Ward's Peak, Montana 9,156 



Mount Blackmore, Montana 9, 550 



Second Caiion Madison River, Montana 9, 754 



Electric Peak, Wyoming 9, 442 



Mount near Henry's Lake, Idaho 9,368 



Mount Washburn, Wyoming 9, 900 



Cascade Range, Oregon 7,000 



Mount Hayden, Teton Range 11,000 



Wind River Mountains 10, 160 



Feet. 



Mount Shasta, California 8,000 



Gilbert's Peak in Uintas 11,100 



Long's Peak, Colorado 10,609 



Audubon's Peak, Colorado 11, 325 



Mount Engelmanu, Colorado 11,518 



Berthoud's Pass, Colorado 11,816 



Grav'sPeak, Colorado 11,643 



Pike's Peak, Colorado 12,040 



Colorado in general 11,600 to 12,000 



San Francisco Moun tain , Arizona 1 1 , 547 



The elevation is less as the latitude increases, and as we approach the sea-coast. 

 The timber-line in the Himalayas is at 11,800 feet ; and on the Alps it averages G/lOO, 

 but some trees are found at 7,000 feet above sea-level. 



