CURRENT STATUS OF ROADS ON NATIONAL FOREST SYSTEM LANDS

Primary Research and Analysis by Cindy Deacon Williams

January 1999

Based on the current status of roads on National Forest System lands, there are several 

issues that must be addressed in any new roads policy:

 the backlog of road maintenance (i.e., 60% of existing roads are not maintained to 

the safety and environmental standards for which they were designed);

 the backlog of road decommissioning (i.e., funding to retire ecologically harmful 

roads);

 the burgeoning network of “uninventoried” roads (i.e., over 60,000 miles of road 

have been created by repeated usage, but were not built and are not maintained to 

any standard);

 the failure of the size and composition of the National Forest Roads System to 

reflect the shift in public use and demand (i.e., recreation usage has increased over 

40% during the last 10 years and still is rising while timber harvest has declined by 

2/3, yet new road decisions are planned to meet timber harvest needs not 

recreation needs); and

 the lack of policy guidance regarding management of 33 million acres of currently 

roadless areas, including 8 million roadless acres designated as suitable for timber 

production, that are neither designated Wilderness nor proposed for wilderness 

designation nor provided any special classification that highlights their rarity and 

ecological importance. 

 Most importantly the policy must remedy the lack of biological/ecological 

prioritization of all road work – deconstruction, decommissioning 

maintenance, reconstruction.

The National Forest Road System — estimated at 373,000 miles of forest roads — is 

extensive and diverse. Twenty-three percent of the roads are arterial or collector roads that 

serve all users, including passenger cars. Fifty-seven percent are roads that only are 

passable by high-clearance vehicles such as four-wheel drives. Twenty percent are closed 

by gates, but their environmental impacts are not otherwise mitigated. In addition to these 

known roads, the Forest Service has identified an estimated 60,000 miles of "uninventoried 

roads" that were created by repeated use but never built or maintained to any standards. 

The actual number of miles of "uninventoried roads" likely is far greater than this estimate. 

There also are additional public roads on National Forest System lands, such as state and 

county roads that typically are maintained by others. There are more than 7,000 bridges on 

forest roads (three-fourths of these on arterial and collector roads), and untold numbers of 

other stream crossings (e.g., culverts, fords, etc.). 
Current funding levels are inadequate to maintain existing roads to planned standards 

minimally needed to keep ecological impacts at low 

levels. About 60% of National Forest System roads 

are not fully maintained to the planned safety and 

environmental standards for which they were 

designed. The backlog of reconstruction needs on 

National Forest System roads is considerable. For 

example, the backlog on arterial and collector roads 

is estimated to be over $10 billion, due to their age 

(three-fourths are over 50 years old) and their lack of 

adequate regular maintenance. Furthermore, funding 

from 1991 to 1996 for decommissioning roads has 

only financed a reduction of about 0.5% of National Forest System roads per year despite 

the fact that many more roads meet no existing or anticipated future need and their 

continued presence poses grave ecological risk. 

Public use and demands on National Forest System lands have shifted considerably during 

the past 10 years, but the size and composition of the National Forest System road system 

has not been adjusted accordingly. Annual recreation usage has increased from less that 

250 million Recreation Visitor Days to almost 350 million and is projected to continue to 

increase. On the other hand, timber harvest has dropped to below 4 billion board feet from 

a high of about 12 billion board feet annually. Nonetheless, road construction largely still 

is an artifact of timber harvest with roads approved, placed, designed, and constructed 

primarily to meet logging needs.

While a significant portion of the 191 million acres of the National Forest System is 

roaded, approximately 38% (or 73 million acres) remains roadless. Of this, an estimated 

34 million acres currently are designated as wilderness and an estimated 6 million acres are 

designated as proposed wilderness in forest plans. An estimated 33 million acres currently 

are unroaded in blocks of 5,000 acres or more for which the existing forest plans have 

proposed management that could include building new roads. Of the 33 million acres that 

are unroaded and available for management activities that could include roading, an 

estimated 8 million acres are classified as "suitable for timber production," and therefore 

likely to have road decisions guided predominantly by timber harvest priorities. 

About 60% of National 

Forest System roads are 

not fully maintained to the 

planned safety and 

environmental standards 

for which they were 

designed.
Photo credit: J. Sowinski

Road Gully, SW Washington

Wind River

SECTION VI:

ECOLOGICAL EFFECTS OF ROADS 

SUMMARY OF SCIENTIFIC FINDINGS ON ROADS AND AQUATIC 

ECOSYSTEMS

REVIEW OF ECOLOGICAL EFFECTS OF ROADS ON TERRESTRIAL AND 

AQUATIC COMMUNITIES

reprinted with the permission of Conservation Biology

NATION FOREST ROADS POLICY

BRIEFING MATERIALS

PACIFIC RIVERS COUNCIL

MARCH 2000
SUMMARY OF SCIENTIFIC FINDINGS ON ROADS AND AQUATIC ECOSYSTEMS

Primary Research and Analysis by Cindy Deacon Williams

January 1999

This section summarizes findings with respect to the impacts of roads on watershed 

integrity, fish and aquatic habitat, and geomorphic processes, and the ecological value of 

roadless and lightly roaded areas. Additional analyses can be found in a special section 

on the ecological effects of roads in the February 2000 issue of Conservation Biology.

From this summary of scientific findings, there are six issues that must be addressed in 

any new roads policy:

 The physical impacts of roads on watershed integrity (via alteration of 

streamflow, sediment loading, sediment transport and deposition, channel 

morphology, channel stability, substrate composition, stream temperatures, water 

quality, and riparian conditions);

 The effects of the physical impacts of roads on fish and fish habitat (via finesediment effects, changes in streamflow, changes in water temperature, migration 

barriers, and increasing access for disease, exotic fish introductions, and 

increased fishing pressure); 

 The effects of roads on geomorphic processes (including surface erosion and 

mass movement);

 The increased risk of landslide in certain hillslope locations (including the inner 

gorge, swales, and break-in-slope);

 The inevitability, duration, and extent of detrimental impact from roads (via both 

“legacy” problems associated with old roads and new problems associated with 

new roads constructed pursuant to “new and improved” standards); and

 The importance of roadless and lightly roaded areas to ecological integrity.

A. IMPACTS ON WATERSHED INTEGRITY

The physical impacts of roads on watershed integrity are dramatic and have been well 

documented. Roads impact watershed integrity through three mechanisms: they 

intercept, concentrate, and divert water. Roads intercept water falling as rainfall directly 

on road surfaces and cutbanks as well as subsurface water moving underground down the 

hillslope. Roads concentrate flow on the road surface and in adjacent ditches and 

channels. Roads divert both surface and subsurface water from flowpaths that otherwise 

would be taken in the absence of a road. The hydrologic and geomorphic consequences 

resulting from these three processes can be large. Roads directly affect natural sediment 

and hydrologic regimes by altering streamflow, sediment loading, sediment transport and 
Summary of Scientific Findings on Roads

 and Aquatic Ecosystems

Page 2

deposition, channel morphology, channel stability, substrate composition, stream 

temperatures, water quality, and riparian conditions within a watershed (Lee et al. 1997). 

Flow—Roads interrupt hillslope drainage patterns by intercepting surface and subsurface 

flow and concentrating and diverting it into ditches, gullies and channels, thereby 

effectively increasing the density of streams in the landscape and altering the timing and 

magnitude of peak flows and changing base stream discharge (Furniss et al. 1991; Harr et 

al. 1975; King and Tennyson 1984; Wemple et al. 1996) and sub-surface flows (Furniss 

et al. 1991; Megahan 1972). 

Sediment—Roads contribute more sediment to 

streams than any other land management activity 

(Gibbons and Salo 1973; Meehan 1991). Roads 

greatly increase the frequency of landslides, debris 

flows, and other mass movements (Burroughs et 

al. 1976; Clayton 1983; Dunne and Leopold 1978; 

Furniss et al. 1991; Hammond et al. 1988; 

Megahan et al. 1992; Weaver and Hagans 1996). 

Road and stream crossings are a major source of sediment to streams (Eaglin and Hubert 

1993; Furniss et al. 1991). Plugged culverts and fill slope failures are frequent and often 

lead to catastrophic increases in stream channel sediment (Donald et al. 1997; Furniss et 

al. 1997; Weaver et al. 1987). 

Channel morphology—Unnatural channel widths and slope and stream bed form occur 

upstream and downstream of stream crossings, and these alterations in channel 

morphology may persist for long periods of time (Heede 1980).

Roads contribute more 

sediment to streams than 

any other land 

management activity.
Summary of Scientific Findings on Roads

 and Aquatic Ecosystems

Page 3

Channelization—Concentration and diversion of flow by roads into headwater areas can 

cause incision of previously unchanneled portions of the landscape (Montgomery 1994).

Water Quality—Roads contribute to water quality 

degradation through increased sedimentation (as 

noted above), applied road chemicals (Furniss et al. 

1991; Norris et al. 1991; Rhodes et al. 1994), and 

toxic spills (Furniss et al. 1991; Idaho Department 

of Transportation 1996). Further, because roads 

provide easy access for both people and livestock, 

they concentrate impacts from other public land use 

activities and provide avenues for both legal and 

illegal stocking of non-native fishes (Lee et al. 

1997) and the introduction and spread of noxious weeds (FICMNEW 1998).

B. IMPACTS ON FISH AND AQUATIC HABITAT

The physical impacts of roads have detrimental effects on fish and fish habitat. The 

physical impacts of roads discussed above have a widespread and profound effect on fish 

habitat and fish communities and populations across a range of environments and 

conditions (Lee et al. 1997). Serious degradation of fish habitat affecting all life-stages 

of fishes (including migration, spawning, incubation, emergence, and rearing) can result 

from poorly planned, designed, located, constructed, or maintained roads (Furniss et al. 

1991; Henjum et al. 1994; MacDonald et al. 1991; Rhodes et al. 1994). Mechanisms 

through which roads have these deleterious impacts include fine-sediment effects, 

changes in streamflow, changes in water temperature caused by loss of riparian cover or 

conversion of groundwater to surface water, migration barriers, and access for disease, 

exotic fish introductions, and increased fishing pressure.

Sediment—The increased sediment flux into streams that is associated with roads causes 

aggradation, filling of pools, and increased channel widths and width-to-depth ratios 

(Jackson and Beschta 1984; Lisle 1982; Madej 1982). With increasing road density there 

is a clear decline in the frequency of pools and the frequency of large pools —

fundamental components of high-quality fish 

habitat (Lee et al. 1997). As pools are filled by 

sediment they support fewer fish and the 

individuals that reside in them suffer higher 

mortality (Alexander and Hansen 1986; Bjornn et 

al. 1977). Furthermore, elevated levels of fine 

sediment adversely affect salmonid embryo 

survival (Bjornn and Reiser 1991; Chapman 1988; 

Everest et al. 1987) and have been linked to 

decreased fry emergence, decreased juvenile 

densities, loss of winter carrying capacity via loss 

of concealment cover, and increasing predation 

(Bjornn et al. 1977; Chapman 1988; Chapman and McLeod 1987; Everest et al. 1987; 

Scrivener and Brownlee 1989; Thurow 1997; Weaver and Fraley 1993; Young et al. 

With increasing road 

density there is a clear 

decline in the frequency of 

pools and the frequency of 

large pools — fundamental 

components of high-quality 

fish habitat.

Roads contribute to water 

quality degradation 

through increased 

sedimentation, applied 

road chemicals, and toxic 

spills. 
Summary of Scientific Findings on Roads

 and Aquatic Ecosystems

Page 4

1991). Increased fine sediment in stream gravel reduces intragravel water exchange, 

thereby decreasing oxygen concentrations, increasing metabolic waste concentrations, 

and restricting movements of alevins (Bjornn and Reiser 1991; Chapman 1988; Coble 

1961; Cordone and Kelly 1961; Everest et al. 1987). This loss of unembedded interstitial 

areas in stream substrates also is correlated with a severe reduction or elimination of 

tailed frogs (Corn and Bury 1989; Welsh 1990) and benthic organism populations 

(Chutter 1969; Hynes 1970). Increased fine sediments in rearing areas are correlated 

with reduced juvenile salmonid densities (Alexander and Hansen 1986; Bjornn et al. 

1977; Chapman and McLeon 1987; Everest et al. 1987; Shepard et al. 1984).

Flows—Road-related alterations in the timing and 

magnitude of peak flows and changes in base 

stream discharge and sub-surface flows affect the 

predictability and stability of streamflow, factors 

found to strongly influence salmonid densities by 

influencing overwintering survival and 

reproductive success (McFadden 1969; Seegrist 

and Gard 1972). For example, post-spawning high 

flows can wash out eggs, displace fry, and 

otherwise increase mortality (Latta 1962; Shetter 

1961). 

Temperature—Increases in temperature are correlated with construction of roads along 

valley bottoms next to stream channels and the resultant removal of riparian vegetation 

and reduction in riparian canopy cover. Such temperature increases can elevate stream 

temperatures beyond the range for rearing, increase susceptibility of fishes to disease, 

reduce metabolic efficiency, shift species assemblages, and inhibit upstream migrations 

(Beschta et al. 1987; Hicks et al. 1991). 

Migration Barrier—In addition, road/stream crossings are a common migration barrier to 

fish (Clancy and Reichmuth 1990; Evans and Johnston 1980; Furniss et al. 1991); 

increasing numbers of culverts are correlated with decreasing fish densities (Eaglin and 

Hubert 1993). Improper culvert placement can reduce or eliminate fish passage (Belford 

and Gould 1989; Beechie et al. 1994). 

C. Impacts on Geomorphic Processes

The detrimental impacts of roads on geomorphic processes (including sedimentation and 

landslides) are large in magnitude and long in duration. Roads produce geomorphic 

responses ranging from the chronic, long-term contributions to streams of relatively small 

amounts of fine sediment to the catastrophic contributions of large amounts of sediment 

during mass failures. In addition, roads may alter stream channel morphology directly by 

encroaching in the floodplain or indirectly by modifying channel flowpaths and 

extending the drainage network into previously unchannelized portions of the hillslope. 

Further, the results of these geomorphic changes produce cumulative consequences that 

can be felt considerably downstream.

Road-related alterations in 

the timing and magnitude 

of peak flows and changes 

in base stream discharge 

and sub-surface flows 

affect the predictability and 

stability of streamflow.
Summary of Scientific Findings on Roads

 and Aquatic Ecosystems

Page 5

Surface Erosion—Chronic surface erosion from road surfaces, cutbanks, and ditches is

well documented (Bilby et al. 1989; Megahan and Kidd 1972a; Reid and Dunne 1984; 

Sullivan and Duncan 1981), and often is the dominant source of road-related sediment 

input to streams. Roads were identified as the major source of sediment in the Chattooga

River Basin in Georgia (Van Lear et al. 1995). In the initial years after construction, 

rates of surface erosion appear highest (Megahan and Kidd 1972a) and, on unpaved 

roads, are closely correlated to traffic volume (Reid and Dunne 1984; Sullivan and 

Duncan 1981). However, because of maintenance problems, roadbeds and road-related 

ditches and channels are continuing sources of sediment long after construction is 

complete (Miller et al. 1985; Swift 1984, 1988).

Mass movement—The most dramatic and visible effect of a road often is its effect on the 

flow of water through the watershed. In some 

instances, road-induced changes in watershed 

hydrology can have serious consequences. Weaver 

and Hagans (1996) found that roads were associated 

in an apparently causal manner with 15% to 61% of 

the new landslides following the February 1996 

storm in the Oregon and Washington Cascades and 

Oregon Coast Range Mountains. That same storm 

resulted in a flood event in the Fish Creek watershed 

on Oregon’s Mt. Hood National Forest that caused 236 landslides, of which 34% were 

attributed directly to the road system (Reeves et al. 1997). Similarly, very high 

associations between the road system and landslides were found in Idaho following 1997 

spring storms, with 65% of landslides observed in the North Fork Clearwater Basin and 

72% in the Lochsa River Basin associated with roads (Weaver et al. 1998). In addition to 

the detrimental effects on vulnerable fish species and their habitat through increased 

sedimentation, these landslides resulted in serious personal injury and downstream 

property damage. 

Mass movement can occur as shallow debris slides, deep-seated slumps, and rapid debris 

flows. In areas ranging from the Pacific Northwest to New Zealand, mass movements 

were 30 to 300 times greater in roaded than in unroaded watersheds (Sidle et al. 1985). 

Erosion rates on roads and landings in the Klamath mountains of southwest Oregon were 

100 times greater than those on the undisturbed area (Amaranthus et al. 1985). Eightyeight percent of landslides within Idaho were associated with roads (Megahan et al. 

1992). Total sediment production from logging roads in the Idaho batholith was 770 

times higher than in undisturbed areas; approximately 71% of the increased sediment 

production was due to mass erosion and 27% to surface erosion (Megahan and Kidd 

1972b). Ninety-one percent of the annual sediment production by land use activities in 

the South Fork of the Salmon River has been attributed to roads and skid trails (Arnold 

and Lundeen 1968). Roaded and logged watersheds in the South Fork Salmon River 

drainage have significantly higher channel bed substrate embeddedness ratings than 

undeveloped watersheds (Burns 1984). Increased rates of landsliding in roaded areas as 

compared to unroaded forested areas also have been documented in Washington (Reid 

1981) and northern California (Hagans et al. 1984). The majority of sediment from 

timber harvest activities is related to roads and road construction and associated increased 

The most dramatic and 

visible effect of a road 

often is its effect on the 

flow of water through the 

watershed.
Summary of Scientific Findings on Roads

 and Aquatic Ecosystems

Page 6

erosion rates (Beschta 1978; Chamberlain et al. 1991; Dunne and Leopold 1978; Furniss 

et al. 1991; Gardner 1979; MacDonald and Ritland 1989; Meehan 1991; Megahan et al. 

1978; Reid 1993; Reid and Dunne 1984; Rhodes et 

al. 1994; Swanson and Dyrness 1975; Swanston and 

Swanson 1976). Although roads typically are 

associated with shallow debris slides and rapid 

debris flows, road construction also has accelerated 

deep-seated earthflows either through destabilizing 

the toe area or diverting water onto the earthflow 

complex (Hicks 1982). Road-related mass soil 

movements can continue for decades after the roads have been constructed (Furniss et al. 

1991). 

Locational predisposition—In addition to the reported correlation between mass 

movement and roads, a number of geomorphic locations within a watershed are more 

susceptible to landsliding than are others. Most landslides observed in Idaho by Weaver 

et al. (1998) were observed to be most likely to occur in the inner gorge, swale, or breakin-slope (93%, 86%, and 68% respectively for the North Fork Clearwater, Lochsa River, 

and Boise River basins). These three locations also have been identified as being at 

higher risk of landslide during infrequent, high intensity, or long duration storm events in 

northwestern California by LaHusen (1984) and in Oregon and southern Washington by 

Weaver and Hagan (1996). The risk of landslide in these areas is even greater when 

these hillslope locations are roaded (Weaver et al. 1998).

D. LIKELIHOOD OF OCCURRENCE

Detrimental impacts from roads are inevitable and the extent of such impacts is large. 

The legacy of past road building is large. Within the range of the northern spotted owl, 

there are about 180,000 km (or 111,800 mi) of roads, including 250,000 stream crossings 

(about 1.25 per km or 2 per mi) and a significant 

number of culverts are unlikely to be able to 

withstand a 25 year storm event (FEMAT 1993). 

Within the Interior Columbia Basin Ecosystem 

Management Project (ICBEMP) area, there are at 

least 204,333 km (or 126,900 mi) of inventoried 

roads and an additional 61,300 to 102,166 km (or 

38,100 to 63,500 mi) of uninventoried roads (Lee et 

al. 1997). In the Chattooga River Basin, 80% of the 

roads contributing sediment to the river are 

unpaved, multipurpose roads paralleling or crossing 

tributary streams (Van Lear et al. 1995).

In recent years, road maintenance has been sharply reduced because funds for 

maintenance as well as timber purchaser conducted maintenance have declined. This has 

resulted in chronically poor road maintenance. In the southern Appalachians, forest roads 

often are not maintained at all, are subjected to maintenance that is inadequate for the 

level of road use, or are scheduled for maintenance in such a way that the work is poorly 

Road-related mass soil 

movements can continue 

for decades after the roads 

have been constructed.

In the Chattooga River 

Basin, 80% of the roads 

contributing sediment to 

the river are unpaved, 

multipurpose roads 

paralleling or crossing 

tributary streams.
Summary of Scientific Findings on Roads

 and Aquatic Ecosystems

Page 7

timed relative to storm patterns (Swift 1984, 1988). This pattern is not unique to the 

East. There has been a progressive degradation of road drainage structures and function 

in the Columbia River Basin (Lee et al. 1997) and about 60% of all National Forest 

System roads are not fully maintained to the planned safety and environmental standards 

for which they were designed (USDA Forest Service 1998). 

In addition, however, it is important to note that increases in sedimentation from new 

roads and landings are unavoidable even using the most cautious logging and roading 

methods. Few studies have systematically and quantitatively evaluated the extent to 

which new road design, siting, construction and engineering practices have reduced the 

ecological impacts of roads (McCashion and Rice 1983). An analysis of the effects of 

new road construction and siting practices in the Oregon Coast Range suggested some 

reduction in slide frequencies over those resulting from the old roading practices 

(Sessions et al. 1987), however, the new practices were not “put to the test” as no large 

storms occurred during the study period. Examination of the improved road design 

practiced by the Boise National Forest indicated that while the new practices were an 

improvement over the old roading practices, total accelerated sediment yields still were 

51% over natural sediment yields (Megahan et al. 1992).
Summary of Scientific Findings on Roads

 and Aquatic Ecosystems

Page 8

E. Ecological Value of Roadless and Lightly-Roaded Areas

Roadless and low road density areas are important refuges for many at-risk fishes. The 

ecological importance of unroaded areas has been highlighted in a number of assessments 

and reports (FEMAT 1993; Henjum et al. 1994; Lee et al. 1997). Unroaded areas have 

the potential to maintain natural processes unaltered by land management activities and 

may be important refugia for strongholds of salmonids and other native fishes (Lee et al. 

1997). Sedell and Everest (1991) and McIntosh et al. (1994) documented substantial 

decreases in the quality and quantity of large, deep pools — a primary indicator of high 

quality, in-channel habitat condition — throughout managed areas of Oregon, 

Washington, and Idaho between 1935 and 1945, while during the same period they 

documented an increase in large, deep pools (i.e., an improvement in aquatic habitat) in 

unmanaged portions of the landscape. The areas identified as “key watersheds” within 

the range of the northern spotted owl were 48% to 70% unroaded (FEMAT 1993). 

Similarly, the population status review in the Interior Columbia River Basin conducted as 

part of the ICBEMP process generally found strong fish populations to be most likely in 

less disturbed subwatersheds, with nearly 60% of 

the salmonid strongholds predicted to occur in 

unroaded watersheds (Lee et al. 1997), despite the 

fact that the historically most productive 

watersheds typically lay elsewhere. For some 

species of fish, the correlation with road density is 

extremely high. For example, one of the 

watershed characteristics most useful in predicting 

the presence of bull trout is road density, with the 

trout less likely to be present as road density increases and more likely to be present as 

road density declines (Lee et al. 1997). Furthermore, the ICBEMP aquatic report found 

that greater short-term and long-term watershed and ecological risks are associated with 

conducting management activities (e.g., timber harvest, road construction, etc.) in an 

unroaded area than with proceeding cautiously with management activities in areas 

already impacted by roads. That is, because unroaded areas provide ecological services 

crucial to watershed integrity, the potential short- and long-term harm from entering an 

unroaded area exceeds that of continued management activity in already roaded areas. 

One of the watershed 

characteristics most useful 

in predicting the presence 

of bull trout is road 

density.
Summary of Scientific Findings on Roads

 and Aquatic Ecosystems

Page 9

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