years, at which point vegetation may cover the site sufficiently to prevent 

 further losses. 



After cutting, the nutrients removed from the forest in the harvestable stems 

 must be replaced. To prevent nutrient deficiencies following future cuttings 

 (Bormann and Likens 1979) harvest rotations must be based on the time it takes 

 for these nutrients to be replenished from atmospheric, geologic, or 

 meteorologic sources (see "Biogeochemicals" above). The northern hardwood 

 stands studied in New Hampshire would require approximately 65 years to 

 replenish nutrients removed by stem-only harvesting. Other forms of logging 

 that are becoming popular, such as whole-tree (all above-ground portions) or 

 complete tree (includes roots) logging, have been found to remove two to four 

 times as much nitrogen as stem-only harvesting (Hornbeck 1977). The other 

 nutrients would be expected to be decreased comparably. More time must be 

 allowed between rotations to replenish nutrients, following these more 

 intensive harvesting practices. In addition, these practices result in 

 greater disturbance to the forest floor, increasing decomposition and 

 erodability of the forest floor and delaying revegetation. 



An estimated nutrient budget based on sustained yield practices in Maine's 

 forests indicated that levels of nitrogen, sulfur, phosphorus, and potassium 

 could become deficient after a few rotations of complete-tree harvesting. In 

 order for this type of harvesting practice to continue profitably nutrients 

 and organic matter must be replenished; otherwise, high productivity is a 

 short-term benefit only. 



The extent to which forest systems are affected by tree removal depends on the 

 care with which logging is carried out. Excessive disturbance of the forest 

 floor and residual understory vegetation from heavy machinery may expose the 

 soil to erosion and delay regeneration. For example, improperly placed roads 

 can cause excessive erosion and result in soil compaction. Cutting too close 

 to streams may cause bank erosion and higher water temperature (because of 

 increased sunlight). Large clearcut areas may not have an adequate seed 

 source nearby if adequate seed sources are not present in the duff, which they 

 usually are not in Maine's spruce-fir stands (Frank and Safford 1974). 

 Cutting on steep slopes with shallow soils also may lead to erosion and 

 delayed regeneration. Since peak runoff is increased by clearcutting, a 

 watershed approach to cutting patterns (selective cutting or block cutting) is 

 most desirable; that is, only a certain portion of a watershed is harvested at 

 any one time to prevent serious soil, nutrient, and runoff problems. 



Other practices that may affect the forest system are spraying herbicides and 

 pesticides and piling and burning slash. Herbicides are used to kill woody 

 deciduous trees and shrubs and herbaceous plants (such as raspberry, cherry, 

 birch, and aspen) that often dominate clearcut sites for many years after 

 cutting. These species outgrow the commercially desirable species in much of 

 Maine's forest land, which delays the rotation time of merchantable species. 

 Selective herbicides are used to kill these "weed" species when adequate 

 regeneration is present or prior to planting seedlings. The long term effect 

 of removing this stage of succession from a regenerating forest system is not 

 known (Bormann and Likens 1979). These species are adapted to rapid growth 

 and their presence is important to the prevention of long-term degradation 

 following human disturbance. Deciduous species have lower acidity in their 

 litter, which promotes greater soil fertility. Their loss would affect many 



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