320 A NATIONAL PLAN FOR AMERICAN FORESTRY 



only 4 cubic feet from plots with woodland coyer undisturbed. About 

 4 cubic yards per acre of soil were lost by erosion from the burned 

 plots and only the barest trace from the unburned. Serious erosion is 

 occurring over much of the foothill belt. 



In 1929 a fire burned over a considerable portion of the Camas 

 Creek watershed on the Challis National Forest in Idaho. It was 

 evident in the next year that the fire had materially increased erosion. 

 Extensive dry erosion (i. e., trickling of dry soil down steep slopes) 

 and heavy sheet erosion had occurred. This process, begun immedi- 

 ately after the fire, was still going on in 1932. 



Serious erosion was also evident on many of the older fire-swept 

 areas. Such examples may be found around Lookout Mountain on 

 the Idaho National Forest which was burned in 1919 or before, and 

 on Sabe Mountain on the Bitterroot National Forest in Idaho, 

 burned in 1910. The exposed roots of the snags and the elevated 

 clumps of bear grass indicate that some 5 inches of soil has been 

 eroded from the burned-over slopes since the 1910 fire. 



A torrential rain on the Challis National Forest in 1932, for example, 

 caused excessive run-off to originate on a 1931 burn, resulting in a 

 heavy deposit of sand and debris in tributaries of Loon Creek, suffi- 

 cient to destroy all possibility of fishing in the stream at least for a 

 number of years. Run-off, the result of a heavy rain in 1932 on a 

 1931 burn in Richardson and Mann Creeks on the Idaho National 

 Forest, caused deep gully erosion on the slopes and erosion of the 

 stream channel to bedrock. The debris that was swept down these 

 creeks into the Salmon River was sufficient to dam the swift-flowing 

 Salmon River to a depth of 20 to 25 feet and a length of 450 feet, and 

 to cause a new rapids to be formed in the river. 



A marked effect of fire on stream flow has been evident under some- 

 what more humid conditions in the northern Rocky Mountains. In 

 1919 about 18 percent of the Clearwater River drainage, largely tim- 

 bered, above Kamiah, Idaho, was burned over, but reclothed rapidly 

 with brush and herbaceous vegetation. The Clearwater River gage 

 records of the United States Geological Survey and data of the 

 Weather Bureau for 10 years, 5 before and 5 after the fire, were 

 analyzed by L. F. Watts, of the Northern Rocky Mountain Forest 

 Experiment Station. These indicated a somewhat higher flow, in 

 relation to precipitation, following the fire, but one much less equable. 

 The average date of peak flow of the Clearwater was advanced by 14 

 days, in contrast with that of the Salmon River, the drainage of 

 which had suffered much less from fire, which was only 2 days earlier. 

 The average flow of the Clearwater on the peak days was 9.5 percent 

 greater after 1919, in spite of the fact that the highest peak of the 

 period occurred in 1917, as a result of exceptional rainfall in April 

 and May. Furthermore, the April to June run-off increased from 66 

 percent of the total annual flow to 73.5 percent, and the July to 

 September run-off decreased from 13 percent of the yearly flow to 9 

 percent. In other words, after the fire the spring flood was 1 1 percent 

 greater than before the fire, and the summer run-off was 32 percent 

 less. April to June flow is, of course, chiefly the result of surface 

 run-off from melting snow, while July to September run-off results 

 almost entirely from the slow drainage of ground water. The fires 

 appeared to have increased the spring flood flow, but largely at the 

 expense of summer flow. 



