The Impact of Forest Management on Water Supply and Quality Essay

The Impact of Forest Management on Water Supply and Quality Forest management can have either detrimental or positive effects on watershed supply and quality. The type of effect depends on the type of operation(eg. harvesting vs. reforestation), the way it is conducted, and the view point of the land manager(eg. more or less water yield). Timber harvesting activities tend to increase the water yields of a watershed. Evapotranspiration is decreased by the removal of vegetation. This decrease in ET causes the amount of soil water that is moving into the channel system to increase. Lower ET rates also increase the amount of water available for deep percolation that provides baseflow (Satterlund and Adams, 1992). The decrease in ET may be short lived. For example, when a stand is thinned, the remaining trees quickly capture the increase of resources that is made available through the thinning. Understory vegetation also increases growth after removal of the overstory. Therefore, timber harvesting should be viewed as a temporary reduction in ET rates. Another way harvesting increases the water yield of a watershed is by increasing runoff. When an area is totally or partially harvested, temporary or permanent logging roads are usually constructed. These logging roads can capture subsurface flow and divert it to ditches associated with the road. These roads can divert surface flow that would ordinarily by dispersed and infiltrate (Satterlund and Adams, 1992). Because of the surface characteristics of roads, precipitation that falls on them has a reduced capacity to infiltrate. The effects of logging roads can be temporary or permanent. Temporary logging roads eventually revegetate, and may even be planted with herbaceous pla... ... encourage sediment deposition. Some forest management practices include fertilization. This can degrade water quality if nutrients are allowed to enter the stream system. Fertilization normally takes place at stand establishment as a site preparation technique. Because this is a time in the forest's life where ET is reduced and runoff is increased, the greatest risk of contamination is then. Fertilization is also accasionally applied in mid-rotation. Fertilizer applied during this time period is not likely to affect water quality. Reforestation of a highly disturbed watershed will improve water quality. The amount of erosion will be lessened, and nutrient inputs from agricultural land can also be intercepted and taken up by the forest. Reference Satterlund, D.R. and Adams, P.W. 1992. Wildland Watershed Management. John Wiley and Sons, Inc. New York.