FORESTS 



Impacts of Forest Management 

 on Water Quality 



Other than changes brought about 

 by the (usually rare, except for forest 

 fires) catastrophic natural disturb- 

 ances over which we have little or no 

 control, the major changes wrought 

 in water quality from forested water- 

 sheds are those resulting from man's 

 activities. Major disturbances and 

 and activities due to forest manage- 

 ment and man's activities include: 

 fire, forest clearing or removal, timber 

 harvest, road and right-of-way con- 

 struction, cultural operations, insect 

 and disease control, solid waste dis- 

 posal, and recreational activities and 

 developments. 



Forest Fires — Whether natural, 

 deliberate, accidental, or incendiary, 

 forest fires are generally conceded to 

 have a deleterious effect on water 

 quality. The degree of influence de- 

 pends on the type and intensity of 

 the fire, the time of year, and topo- 

 graphic and soil conditions. Ground 

 fires occurring on stable soils may 

 produce only minimal deterioration 

 in water quality, while intense fires 

 on sensitive soils and on steep slopes 

 may occasion serious damage. Effects 

 on water quality may be due to in- 

 creased water temperatures, increased 

 ash, mineral, and organic content, as 

 well as higher sediment and turbidity 

 loads due to increased runoff and ero- 

 sion. The effects may be restricted to 

 a single season or year or they may 

 last up to several decades. 



Fire used as a management tool — 

 e.g., to effect deliberate ecological 

 change, to control insects and disease, 

 or for slash disposal — is ordinarily 

 planned in areas and at seasons when 

 damage to water quality would be 

 minimal. 



Forest Clearing — Removal of for- 

 est for agricultural land use, for urban 

 or industrial development, or for vege- 

 tative-type conversion (e.g., forest to 

 grass) may completely alter the 

 water-quality regime. Changes will be 

 greatest during the period of maxi- 



mum disturbance. Following recov- 

 ery, the water-quality regime will take 

 on the characteristics of the new 

 land-use pattern. In some cases — 

 e.g., the conversion of pinyon juniper 

 or chapparal forest types to grass — 

 there may be an improvement in 

 water quality from the sediment- 

 turbidity standpoint. 



Timber Harvest — The effects of 

 timber harvesting on water quality 

 will depend on the intensity and type 

 of harvest operation and on the man- 

 ner of product removal. Light selec- 

 tion cuts will normally have minimal 

 or no effect, while clear cuts that open 

 up large areas will tend to increase 

 water temperatures and increase the 

 potential for subsequent erosion and 

 sedimentation. Contrary to popular 

 belief, the removal of the forest crop 

 itself ordinarily does not occasion 

 serious damage except on very steep 

 slopes or on unusually sensitive soils. 

 The major damage is usually due to 

 harvesting and removal methods — 

 i.e., skid trails, log landings, heavy- 

 equipment disturbance, and, espe- 

 cially, road construction and inade- 

 quate maintenance. On occasion, 

 yarding areas or equipment servicing 

 areas may provide a source of con- 

 tamination as a result of oil, gasoline, 

 or chemical spills. 



Road Construction — Road and 

 right-of-way construction in forests is 

 a major problem insofar as water 

 quality is concerned. During and fol- 

 lowing clearing and construction, 

 substantial areas of raw roadbed and 

 cut-and-fill slopes are exposed to ero- 

 sion; frequently, large amounts of 

 erosional materials are washed into 

 stream channels. Damage can be sub- 

 stantially reduced through road loca- 

 tion, carefully supervised construc- 

 tion methods, immediate rehabili- 

 tation of exposed areas, and good 

 maintenance practices. The same 

 holds true for the construction of 

 rights-of-way for power lines, pipe- 

 lines, and waterways (surface or un- 

 derground). 



Cultural Operations — In addition 

 to the harvesting process, intensive 



forest management may i; 

 or more cultural operations such as 

 forest thinnings and cleanings. When 

 such operations are done mechani- 

 cally, little or no impairment of water 

 quality should result. However, when 

 chemicals such as sodium arsenate 

 or 2,4,5-T are applied, caution must 

 be exercised to keep such materials 

 away from streams. 



Insect and Disease Control — To 

 protect commercial and noncommer- 

 cial forests, wilderness, and recrea- 

 tion areas as well as forest parks from 

 periodic disease and insect epidemics, 

 control operations are essential. The 

 most effective and most economic 

 control methods have involved chemi- 

 cals such as DDT. The environmental 

 dangers inherent in chemical control 

 methods, including water-quality de- 

 terioration, have become increasingly 

 apparent and controls have recently 

 been imposed. In some cases, con- 

 trolled light ground fires in forest 

 areas have been applied to destroy 

 vectors. Such operations have little 

 influence on water quality if applied 

 carefully under controlled conditions. 

 Ecologic controls also have little or 

 no impact upon water quality. 



Solid Waste Disposal — In har- 

 vesting timber crops as well as in 

 the primary conversion (sawmilling), 

 relatively large volumes of solid 

 waste in the form of slash, slabs, and 

 sawdust need disposal. To accelerate 

 new forest development, to destroy 

 breeding areas and food for forest 

 insects and disease pests, and to en- 

 hance the forest environment it has 

 been a common practice to burn the 

 forest slash. While such practices 

 have only minimal effect on water 

 quality, they are being halted in many 

 forest areas due to air-pollution con- 

 siderations. Similarly, at primary 

 conversion plants there are major 

 problems in the disposal of sawdust, 

 slabs, and edgings. Again, fire has 

 been used as a primary method of 

 disposal but is now being drastically 

 reduced due to air pollution. Some 

 of this waste material is being used 



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