TABLE 3-2 Magnitude and Duration of Direct Effects on Watershed Outputs of Three Sets of Processes That Modify Hydrology in Forests: Fire, Forest Harvest and Silviculture, and Roads and Trails

 

Processes That Modify Hydrology in Forests

Watershed Output

Fire

Forest Harvest and Silviculture

Roads and Trails

Water yield

High-severity fire increases annual water yields; little effect of low-severity fire

Increase water yield; magnitude and duration of response varies (see text)

Little or no effect

Peak flows

High-severity fire increases peak flows; effect is short-lived

Increase peak flows; magnitude and duration of response varies (see text)

Increase peak flows; effects may be long-lived and affect extreme events

Low flows

High-severity fire increases low flows; little effect of low-severity fire

Increase low flows in short term; deficits may develop as forests regrow

Little or no effect

Erosion, landslides, sedimentation

High-severity fire increases erosion and sedimentation in streams; less effect from low-severity and prescribed fire

Increase surface erosion, landslides, and sedimentation; effects may be long-lived

Increase surface erosion (road surfaces and gullies below culverts) and landslides; increase sedimentation in streams

Water temperature and chemistry

Increases water temperature due to riparian forest removal; fire retardants and ash affect chemistry; effects are short-lived

Increase water temperature due to riparian forest removal; effects of fertilizer mostly small and short-lived; short-lived post-harvest increases in nitrate

Deliver road chemicals (e.g. salt, oil) to streams

Research gaps

Uncertainty about effects beyond a few years; magnitude and persistence of downstream effects; effects of salvage logging

Uncertainty about effects beyond one or two decades; magnitude and persistence of downstream effects; effects on habitat and aquatic ecosystems

Uncertainty about road effects on extreme floods and in watersheds >1 km2

NOTE: These are general effects, not predictions, so qualifying adjectives such as “may,” “usually,” etc., are omitted. See text for factors that influence when, where, and to what extent these effects apply.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement