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 Forestry BMPs reduce nutrient losses, minimize overland flow and the dislodgement and
transportation of soil, and stabilize disturbed areas. Site slope and aspect, and the potential for erosion
should be carefully evaluated to estimate the impact of forest. Silvicultural activities that cause
disturbance include building roads and harvesting trails, tree removal, site preparation and reforestation,
revegetating disturbed areas, and wildfire protection.
Very few studies on the impact of road building on sediment loss are available. Impacts are
expected to be very site-specific and the potential for extensive sediment losses is high. Even less is
known about the effect of road building nutrient losses.
Most work on forestry BMPs report that a combination of practices minimized adverse
impacts. Likens et al. (1970) and Pierce et al. (1970) were the first to document an increase in stream
nitrate concentration after clearcutting in the White Mountains of New Hampshire. Continued work in
the White Mountains showed considerable increases in stream nitrate after the first three year of
clearcutting (Martin and Pierce 1980). In other parts of the country, the pattern of increases in stream
nitrate concentration after clearcutting were not as pronounced (Martin et al. 1984).
Stream nitrate concentrations averaged 2 mg/l during the second and third years after
clearcutting in 15 New England watersheds. Typically loggers used streams as a cutting boundary and
left a buffer zone if tracts on both sides of the stream were to be logged. For most of the harvests,
<50% of the watershed area was clearcut. Runoff nitrogen from clearcut watersheds averaged < 2 and
generally < 0.4 mg/l. Reference stream concentrations averaged 0.5 mg/l nitrate nitrogen. The highest
values found were 6.1 mg/l in the White Mountains (Martin et a1. 1984).
In a 15-year study in Pennsylvania, Lynch and Corbett (1990) evaluated the effect of using a
stream side management zone (SMZ) of 100 feet on both sides of a perennial stream. In the SMZ,
trees were harvested that could threaten the stream channel flows if they fell. Equipment movement over
streams was prohibited unless by bridge or culvert. Trails, roads and log landings were planned by a
professional forester and harvesting was prohibited when soils were excessively wet. Lynch and
Corbett (1990) found mean annual nitrate concentrations from 0.28-0.4 mg/l were significantly higher
than the background range of 0.05-0.11 mg/l for the first two years of harvest. Nitrate was also higher
than background for the next 9 years but ranged from 0.8 to 0.14 mg/l.
In a review of harvest and site preparation BMPs used in the South, Reikerk et al. (1989)
found that mountainous region runoff and nutrient losses were substantially elevated after harvest. Total
nitrogen runoff concentrations ranged from 0.5-1.0 mg/l and approached baseline levels of
approximately 0.2 mg/l three years after harvest. Nitrogen export ranged from 0.3-1.4 kg/ha/yr and
returned to baseline levels of around 0.15 kg/ha/yr . Phosphorus losses were not affected appreciably
in the mountains and fluctuated around .01 mg/l (1.3-1.7 kg/ha/yr). Piedmont region nutrient export
was generally unchanged by forest practices. Shearing and windrowing increased nitrogen export to
near 0.2 mg/l (.3 kg/ha/yr) in the first year after harvest from a background near zero in the upper
4.2-7
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