12 THE FORESTS OF ALASKA. 



In many places in the interior the post-glacial silts and sands 

 form an excellent soil, and upon them whatever future agriculture 

 there may be in Alaska will chiefly be developed. 



CLIMATE. 



The climate of the southern and southeastern coast region of 

 Alaska is mild and wet. The annual precipitation at Juneau and 

 Sitka is from 80 to 90 inches. At these points the precipitation is 

 chiefly in the form of rain, and only during a short time in the 

 middle of the summer are there likely to be days when rain does not 

 fall. In the mountains immediately above tide water, however, the 

 snowfall is very great. This increases to the northward, and at 

 Vaidez a winter's snowfall of nearly 60 feet has been recorded. The 

 lowest temperature on record at Sitka is 4° F. below zero, and the 

 highest 87°. At Juneau the lowest record is 10° below zero, and the 

 highest 88°. The Sitka temperature is but little cooler than that of 

 the northern part of Puget Sound or of Scotland. 



Sharply contrasted with the climate of southeastern and southern 

 Alaska is that of the central plateau region of the interior. The 

 Pacific Mountain system cuts off the warm, moisture-laden ocean 

 winds so that the interior has a semiarid continental climate subject 

 to sudden changes and great extremes. Satisfactory records are 

 lacking, but such as are available indicate an annual precipitation in 

 the Yukon Valley of about 15 inches, including melted snow. As low 

 as 80° F. below zero has been registered in winter, and in the summer 

 as high as 93°. The summers are short and comparatively hot; the 

 winters long and intensely cold. The snowfall is light, but there is 

 no thawing from the " freezeup " in the fall, generally in October, 

 until the " breakup " in the latter part of April or early in May. 

 Under these conditions, which have existed for ages, the ground has 

 become permanently frozen to great depths. On the other hand, 

 there are occasional areas on the hillsides and in the river valleys 

 where the ground does not freeze more each winter than is thawed 

 out during the summer. When the normal covering of moss is 

 cleared from the deeply frozen ground, and the sun given a chance 

 to get at it, a few years' cultivation results in its thawing out for 

 several feet below the surface. 



Despite the low temperatures and long winters of the Yukon 

 Valley, there is ordinarily a good growing season of at least three 

 months. During much of this time daylight is almost continual, and 

 growth is rapid. This compensates in a marked degree for the short- 

 ness of the season; and since the evaporation is not great the vegeta- 

 tion is by no means of an arid character, notwithstanding the small 



