A FOREST FIRE SWEEPING UP A SEOPE IN THE ROCKY MOUNTAINS 



without serious damage to the largest 

 trees. 



The ancient .fires were started by hght- 

 ning and by Indians. Traces of injuries 

 to the big trees in California are found 

 dating back over 1,000 years. 



It is a common belief that the virgin 

 forest represents the maximum product of 

 the soil. This is because there are present 

 many large and old trees. Most virgin 

 forests, however, in this country have 

 been thinned by repeated fires, and the 

 present product does not by any means 

 represent what might be standing on the 

 ground if there had not been any such 

 injury. 



A'lany illustrations of this are found in 

 the mountains of the West, where past 

 fires have left the forests open and 

 broken and with a greatly depleted yield 

 of timber (see photo, page 664). As 

 soon as these forests were put under 

 protection by the national government 

 an immense amount of young growth 

 began to spring up in the open stands, 

 indicating possibilities for production of 

 timber entirely beyond anything repre- 

 sented by the virgin stands. 



With the opening up of the forest re- 

 gions by settlement, railroad construc- 

 tion, lumbering, and other development, 

 forest fires began to increase at an enor- 

 mous rate. Lumbering was almost in- 

 variably followed by fire, and many of 

 the most disastrous conflagrations have 

 resulted from fires which gained their 

 first headway in the dry tops left after 

 logging. 



In every forest there is a certain 

 amount of inflammable material, consist- 

 ing of dry leaves, decayed vegetable mold, 

 branches, twigs, cones, dry grass, and 

 other litter. The most common type of 

 fire is that which runs over the surface 

 of the ground, consuming this material. 

 This is called a surface fire. Sometimes 

 a fire may start when only the upper 

 layer of leaves is dry, and may run 

 slowly through the woods without seri- 

 ous injury. More commonly they occur 

 in very dry weather and burn all the 

 ground cover, destroying all small trees 

 and either killing or injuring the larger 

 trees. 



Repeated fires of this character rapidly 

 reduce the density of a forest, for some 



663 



