Nature's Notes * * * * * 107 



people. Timberline is something that changes with the latitude. In the 

 Arctic circle, timberline is not far above sea level. At the Equator it is 

 said to be about three miles high. It varies in a very definite ratio be 

 tween altitude and latitude. One mile straight up in the air is the 

 equivalent of eight hundred miles north or south from the Equator. Of 

 course, exception must be made to the rule to allow for warm or cold 

 currents of the ocean, or other conditions which may change the tem 

 perature materially in certain parts of the earth. The angle of a moun 

 tain slope is a factor. Timberline is higher on a southern slope which re 

 ceives the sun's rays than it is on a northern slope which is in the shade. 



This can best be illustrated by an unusual condition in Yosemite 

 Valley, where the steep southern wall is constantly in the shade and the 

 north wall is in the sun all winter long. In the valley, the condition of 

 life zones is unique. The south side of the valley is the home of flowers 

 and trees which ordinarily grow a hundred miles or more to the north. 

 The north wall is the home of flowers and trees found far to the south 

 of Yosemite Valley. The equatorial side of the valley is the colder. 

 Incidentally, this condition has given Yosemite Valley a remarkably 

 rich flora and made it the happy hunting ground of the naturalist. To 

 the cold shade of the south wall of Yosemite Valley trees have migrated 

 from the north and from higher altitudes. In the warm sunlight of the 

 north side of the valley, where there is reflected warmth from the cliffs 

 of that side, are found plants which are known to have thrived in regions 

 as far south as Mexico. People enjoy the climate of the north side of 

 the valley as much as the plants do, and they live there in the reflected 

 sunlight and warmth of the valley wall, but they only have to go a short 

 distance into the shadow of the south wall to find arctic conditions, cold 

 snow, winter sports. 



Timberline is five hundred feet higher on the south slope of Mount 

 Washburn and other high Yellowstone peaks than it is on the north 

 slope. In Yellowstone, timberline ranges 

 from ninety-five hundred to ten thousand 

 feet. The top of Mount Washburn is in 

 the Arctic-Alpine zone, well above timber- 

 line. It is here that one finds the gorgeous 

 gardens of flowers growing right against 

 snow banks. These little plants thrive a 

 while in the intense sunlight unfiltered by 

 the heavy atmosphere of the lower levels. 

 The sun's rays bring them out in gorgeous 

 carpets that blanket the higher peaks of 

 Yellowstone, Rocky Mountain, Glacier, 

 and Rainier National parks. 



