316 A NATIONAL PLAN FOR AMERICAN FORESTRY 



Water erosion, however, is not the only form of erosion. Wind 

 erosion, resulting in the formation of sand dunes, occurs in areas 

 where trees or other vegetation are not able to hold light soils from 

 transportation by high winds. Destructive dunes exist west of the 

 Adirondack Mountains in New York, along the eastern shore of 

 Lake Michigan and other Great Lakes, and in places along the Pacific, 

 Atlantic, and Gulf coasts. Forests offer a possibility for the control 

 of sand dunes in localities where climatic conditions are sufficiently 

 humid to permit the establishment of a forest cover. In Europe 

 many dune areas have been transformed by planting to good timber- 

 producing forests, some of which served admirably for wood products 

 in the World War. The establishment of trees or similar vegetation 

 on dune areas breaks the force of the wind, and the litter cover, once 

 complete, protects the soil from wind transportation. 



CONSEQUENCES OF DISTURBING THE FOREST COVER 



FIRE 



Fire is the most wide-spread and one of the most destructive 

 disturbances of the forest cover. Even the lightest fire consumes 

 some of the inflammable materials on the ground the litter in all 

 its forms. The extent of destruction of these materials depends in 

 the main upon their moisture content, and the humidity and other 

 climatic factors at the time of the fire. In many forest types it is a 

 common occurrence for the litter to be entirely consumed by a fire 

 which does not do any spectacular damage to the standing trees. 

 Thus is destroyed the enormously important protective soil covering, 

 a chief factor in the forest's favorable influence on run-off and erosion. 

 A fire which is hot enough to consume most of the litter ordinarily 

 also destroys part of the humus in the top soil, thus damaging its 

 loose, porous, granular structure, and making it less receptive to 

 penetration of rain. 



Bennett 20 in reporting on an unpublished finding of S. W. Phillips 

 and I. T. Goddard at the Red Plains Erosion Experiment Station 

 near Guthrie, Okla., in the spring of 1930, states that on two plots 

 in post-oak timber one on which the forest litter was burned, and 

 the other, immediately alongside, on which the natural ground cover 

 of leaves and twigs was left undisturbed the run-off was measured 

 during a period of almost continuous rainfall in May. Run-off from 

 the unburned plot was clear and amounted to 250 gallons per acre, 

 but that from the burned plot, having the same soil and slope, was 

 muddy and attained a volume of 27,600 gallons per acre. The 

 excess of run-off from the burned area over that from the unburned 

 area plus the 16.7 tons per acre absorbed by the leaf -litter itself was 

 approximately 90 tons per acre. The absorbed w r ater w r ent to replen- 

 ish the underground soil water supply while that held by the litter 

 was largely evaporated. From the burned plot an average of 0.15 

 ton of soil per acre per year was eroded, and from the unburned plot 

 0.01 ton. 



In spruce forests of the East, particularly at high altitudes, fires 

 have been very destructive. Here the mineral soil is shallow, and in 



20 Bennett, H. H., Relation of Erosion to Vegetative Changes, pp. 385-415. Scientific Monthly, No- 

 vember 1932. 



