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Table 3-Effects of harvesting and fire on peakflows in different habitat types (from Anderson and
<br />others 1976).
<br />Location Treatment Other Information Peakflow Change
<br />Douglas-fir, OR Clearcut
<br /> Clearcut
<br />Douglas-fir, OR Clearcut, 100`y° Bum
<br /> Clearcut, 50% Bum
<br />Douglas-fir, OR Wildfire
<br />Chaparral, CA Wildfire
<br />(%)
<br />Fall Storms +g0
<br />Winter Storms +28
<br />+30
<br />+11
<br />+45
<br />+2282
<br />Chaparral, AZ Wildfire
<br />Wildfire
<br />Wildfire
<br />Chaparral, AZ Wildfire
<br />Ponderosa Pine, AZ Wildfire
<br />Mixed Conifer, AZ Wildfire (Rich 1962)
<br />Wildfire (Rich 1962)
<br />Wildfire (Rich 1962)
<br />Aspen-Conifer, CO Clearcut,
<br />hydrology, some studies have confounded results be-
<br />cause of the combined changes in volume, peak and
<br />timing at different locations in the watershed, and the
<br />severity and size of the disturbance in relation to the
<br />size of watershed (Brooks and others 1997).
<br />Water Quality-Increases in etreamflow after fire
<br />can result in substantial to little effect on the physical
<br />and chemical quality of streams and lakes, depending on
<br />the size and severity of the fire (DeBano and others
<br />1998). Higher atreamflowa and velocities result in addi-
<br />tionaltransport ofsolidand dissolved materialathat can
<br />adversely affect water quality for human use and dam-
<br />age aquatic habitat. The moat obvious effects are pro-
<br />duced by suspended and bedload sediments, but aub-
<br />atantial changes in anion/cation chemistry can occur.
<br />Undisturbed forest, shrub, and range ecosystems
<br />ueually have tight cycles for major cations and anions,
<br />resulting in low concentrations in streams. Diatur-
<br />banceasuch ascutting, fires, and insect outbreaks inter-
<br />rupt ar temporarily terminate uptake by vegetation
<br />andmay affectmineralization,microbial activity, nitri-
<br />fication, and decomposition. These processes result in
<br />the increased concentration of inorganic ions in soil
<br />which can be leached to streams via subsurface flow
<br />(DeBano and others 1998). Nutrients carriedto streams
<br />can increase growth of aquatic plants, reduce the
<br />potability of water supplies, and produce toxic effects.
<br />Most attention relative to water quality after fire
<br />focuses on nitrate nitrogen (N03-N) because it is
<br />highly mobile. High NOs-N levels, in conjunction with
<br />phosphorus, can cause eutrophication of lakes and
<br />Summer Flows +500
<br />Summer Flows +1500
<br />Winter Flows 0
<br />Fall Flows +5800
<br />Summer Flows +g605
<br />Low Summer Flow +1521
<br />Inter. Summer Flow +526
<br />High Summer Flow +g60
<br /> 100%
<br />streams. Moat studies of forest disturbances show
<br />increases in NOs-N, with herbicides causing the larg-
<br />est increases (Newry and Hornbeck 1994, Tiedemann
<br />and others 1978).
<br />Surface Erosion-Surface erosion is the move-
<br />ment of individual soil particles by a force and is
<br />ueually described by three components: (1) detach-
<br />ment, (2) transport, and (3) deposition. Inherent
<br />erosion hazards are defined as Bite properties that
<br />influence the ease which individual soil particles are
<br />detached (soil erodibility), elope gradient and slope
<br />length. Forces than can initiate and sustain the
<br />movement of soil particles include raindrop impact
<br />(Farmer and Van Haveren 1971), overland flow
<br />(Meeuwig 1971), gravity, wind, and anima] activity.
<br />Protection is provided by vegetation, surface litter,
<br />duff, and rocks that reduce the impact of the applied
<br />forces and aid in deposition (Megahan 1986, McNabb
<br />and Swanson 1990).
<br />Erosion is a natural process occurring on land-
<br />scapes at different rates and scales, depending on
<br />geology, topography, vegetation, and climate. Natu-
<br />ral erosion rates increase as annual precipitation
<br />increases (table 4). Landscape disturbing activities
<br />such as mechanical site preparation, agriculture,
<br />and road construction lead to the greatest erosion,
<br />which generally exceeds the upper limit of natural
<br />geologic erosion (Newry and Hornbeck 1994). Fires
<br />and fire management activities (fireline conatrnc-
<br />tion, temporary roads, heli-pad construction, and
<br />poatfire rehabilitation) can also affect erosion.
<br />USDA Forest Service Gen. Tech. Rep. RMRS-GTR-63.2000
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