A NATIONAL PLAN FOR AMERICAN FORESTRY 321 



LOGGING 



Logging in the United States, which includes the removal of other 

 products besides logs, is very variable in the proportion of the trees 

 which it removes and its effects on run-off and erosion. Although a 

 few small areas mostly farm woodlands are only culled of a few of 

 the larger or choicer trees at any one time, the common commercial 

 practice on the 10 million acres of forest annually cut over is a very 

 close approach to clear cutting. Through a combination of cutting 

 and fire about 850,000 acres of this are devastated each year that is, 

 left in such condition that they are incapable of producing another 

 commercial crop of timber within a tree generation. The greater 

 part of this area is almost devoid of standing trees, particularly in 

 the softwood forest regions of the South and West, but some of the 

 eastern hardwood land may have a considerable stand worthless as 

 a source of wood but very satisfactory as a watershed protection. 



Logging alone, if neither preceded nor followed by fire, destroys a 

 smaller proportion of the understory of young trees and shrubby 

 species than of the main stand. However, important areas are still 

 logged by high-powered machinery that drags logs over the ground 

 and wipes out the lesser vegetation. It may even so churn the soil 

 as nearly to obliterate the litter. 



On a clear-cut area there is no longer appreciable interception of 

 precipitation by tree crowns, and little high shade to retard snow melt 

 or prevent evaporation from the soil. Temporarily, at least, there is 

 small transpiration. There is, however, a very considerable shading 

 of the ground by slash. This, in a good stand of southern pine, may 

 cover 25 to 40 percent of the ground, and, in such conifer types as 

 Douglas fir, western white pine, southern white cedar, or red spruce, 

 may cover practically 100 percent. After a year or two, this slash 

 itself may become powder dry, but it continues to exert some bene- 

 ficial effect on evaporation from the soil. It may persist for as many 

 as 10 to 20 years. 



In many forest types, clear-cut areas are very abundantly invaded 

 within a season or two by herbaceous plants. These at least serve to 

 check erosion and start to rebuild the extremely important litter. 



During a few years after logging, a sloping clear cut or severely cut 

 area will unquestionably erode somewhat. The skid trails produced 

 by power handling of logs in the California pine region, and logging 

 elsewhere, have been found to start erosion. 



It is impossible to generalize concerning the time which must elapse 

 before reforestation restores conditions in cut-over land to the point 

 where total run-off and seasonal run-off are essentially the same as in 

 the preceding tree generation. Clear cutting has converted some 

 forest types from all-aged to even-aged ones of probably permanently 

 different character. An even-aged stand, for example, must permit 

 of much less wind movement than an all-aged, once it has raised its 

 canopy well above the ground. A sprout forest will, of course, restore 

 the conditions more promptly than most seedling forests, because of 

 the early vigorous growth. 



This is borne out by the results of a watershed study at the Wagon 

 Wheel Gap in the high mountains of Colorado, 24 in which the Forest 



Bates, C. G., and Henry, A. J. Forest and Stream Flow Experiments at Wagon Wheel Gap, Colo. 

 Final report. Mo. Weather Rev. Suppl. 30. 1928. 



