1974 USDA FOREST SERVICE GENERAL TECHNICAL REPORT PNW- 21

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SLOPE STABILITY PROBLEMS ASSOCIATED WITH TIMBER HARVESTING IN MOUNTAINOUS REGIONS OF THE WESTERN UNITED STATES

D. N. SWANSTON

PACIFIC NORTHWEST FOREST AND RANGE EXPERIMENT STATION U.S. DEPARTMENT OF AGRICULTURE FOREST SERVICE PORTLAND, OREGON This paper was presented at the "Symposium on Forest Operations in Mountainous Regions, '' in Krasnodar, U. S. S. R., August 30-September 11, 1971.

SUMMARY

Natural -mass-movements on forested slopes in the Western United States can be divided into two major groups of closely related types. These include, in order of decreasing importance and regional frequency of occurrence: (1)debris slides, debris , debris flows, and debris torrents; and (2) creep, slumps, and flows. Each type requires the presence of steep slopes, frequently in excess of the angle of soil stability. All characteristically occur under high soil moisture conditions and usually develop or are accelerated during periods of abnormally high rainfall. Further, all are encouraged or accelerated by destruction of the natural mechanical support on the slopes.

As forest operations shift to steeper slopes, they play an increas- ing role in initiation and acceleration of soil mass movements. The logging operation itself is a major contributor through (1) destruction of roots, the natural mechanical support of slope , (2) disruption of surface vegetation cover which alters soil water distribution, and (3) obstruction of main drainage channels by logging debris, building stands out at the present time as the most damaging operation with soil failures resulting largely from slope loading (from road fill and sidecasting), oversteepened bank cuts, and inadequate provision for slope and road drainage.

At the present time attempts at prevention and control are limited to identification and avoidance of highly unstable areas and development and implementation of timber harvesting techniques least damaging to natural slope stability.

KEYWORDS: Soil stability, soil . CONTENTS

Page INTRODUCTION...... 1

CLASSIFICATION ...... 1 9 INTERRELATIONSHIP BETWEEN PRINCIPAL FACTORS PRODUCING LANDSLIDE MOVEMENTS ON TIMBERED SLOPES...... 7 EFFECT OF FOREST OPERATIONS ON SOIL STABILITY ...... 9

METHODS OF PREDICTION, PREVENTION, AND CONTROL ...... 10

LITERATURE CITED...... 13 INTRODUCTION depth o€ movement, and character of the failure surface. The classification in shallow soils are terminology is basically that suggested ubiquitous in the western cordillera and by Sharpe (1938) and Eckel (1958). in the circum-Pacific belts where mountain g1 ac iation, tectonic up- The first and most widespread group lift, and strong processes have includes debris slides, debris avalanches, oversteepened slopes creating extremely debris flows, and debris torrents involv- . unstable natural conditions in terms of ing the initial failure of a relatively shallow, the downslope component of gravitational cohesionless soil mass on steep slopes stress. Locally, creep deformation’ and above an impermeable boundary. This landslides, resulting from quasi-viscous group corresponds to Savarenskii’s (1937) flow and progressive failure of pyroclastics consequent landslides and Type A move- and overconsolidated, deep pelitic sedi- ments (slope movements of superficial ments, dominate . deposits) of Zhba and Mencl (1969). These types serve as a dominant erosion In the undisturbed state and under process in such diverse climatic areas normal climatic conditions, these slopes as the maritime coast of Alaska (Bishop maintain a delicate state of balance be- and Stevens 1964; Swanston 1967, 1969, tween major forces tending to create 1970) (fig. 1, area 1) and the drier inter- downslope movement and those tending to mountain areas of Utah, Idaho, and resist it. Natural catastrophic events Montan&/ (Croft and Adams 1950) such as rapid saturation of the soil mass, (fig. 1, areas 2 and 3). Dyrness (1967a) falls, or tree windthrow can quickly also reports them as a common constituent destroy this balance as can any disrupting of recent massive landsliding on the west activities of man. flank of the Cascade Range in Oregon (fig. 1, area 4). With increasing demand for lumber and pulpwood in the United States, more Debris slides are the rapid downward of these steep mountain watersheds are movement of unsaturated, relatively uncon- being directly influenced by forest opera- solidated soils and forest debris by sliding tions. The resulting disruption of natural or rolling and are differentiated from debris slope stability characteristics has accel- avalanches largely by lower soil water erated slope failure in many logged areas, content. Debris flows involve the rapid causing extensive damage to structures downslope movement of water- s aturated and and effectively removing por- soil and debris by true flow processes tions of the watershed from immediate (fig. 2). All three are characterized by reforestation. initial failure of a mass of soil or mixed soil and organic debris above a relatively impermeable boundary. Failure is either by rotational or by translational CLASS IF KAT10 N

Based on a review of literature and J’ Walter F. Megahan. Summary of research current research (fig. l), soil mass move- on mass stability by the Intermountain Forest and ments in timbered areas can be broken Range Experiment Station, Soil Stabilization Project, down into two major groups differentiated Boise, Idaho. Unpublished proceedings, USDA Forest roughly on the basis of type material, Service, Berkely Mass Erosion Cod., Oct. 17-20, 1967. 0 Scale of Kilometers 0 0 81 1 1 F 1/27033600

principal cities --- - international boundaries & major mountain ranger 0 slope stability study areas

Son Francisco

Figure 1. Relief map of western North Amer-ica showing the distribution of mountainous and 1oca.tion of Xmportant slope stability study areas. Numbers shown are referred to in the text.

2 Figure 2-a. Debris , combination on a recently logged, till-covered slope. Fail- ure occurred daring a period of high intensity rainfall in a zone of concentrated subsurface drainage. The sliding material was weathered till less than 1.0 meter thick overlying compacted unweathered till. The slope angle is about 34° (75 percent grade). Note scouring of the avalanche path below spoon-shaped zone of initial failure and flow development at slope base.

Figure 2-b. Debris avalanches along the South Fork of the Salmon River, Idaho. These failures occurred in a shallow granitic soil follow- ing saturation during a high intensity rainstorm. The soil is a lithosol less than 0.3 meter thick. The slope is in excess of 31° (70 percent grade).

3 sliding followed by a rapid downslope move- slopes covered with deep, cohesive soils. ment. Rotational sliding defines initial The movement is quasi-viscous, occur- failure of a soil mass by outward rotation ring under shear stresses sufficient to along a curved surface. Translational produce permanent deformation but too sliding defines initial failure of a soil small to produce discrete shear failure. mass along a relatively flat, inclined Kojan (1967) has described soil creep surface. The main slide scarp is bare as a major erosion process in the nor- in both cases and may be spoon- or wedge- thern California Coast Ranges (fig. 1, shaped. The soil mass disaggregates area 5). He points out that creep is not almost immediately after initial failure only a direct contributor of sediment to producing a debris slide or avalanche, streams but also is a critical factor in the depending on initial . The progressive failure of overconsolidated slide or avalanche frequently assumes materials ultimately resulting in the the characteristics of .a flow as the soil and -type movements. mass moves downslope and increases in water content. Debris torrents are a Slumps and begin special type of debris flow occurring in initially as rotational failures usually main drainage channels (fig. 3). These triggered by soil saturation and may be caused when soil material, mainly rapid increases in from short debris avalanches in steep- in the immediate area of failure. walled tributary gullies, accumulates Slumping involves the downward and behind temporary obstructions such as backward rotation of a soil block or logs and forest debris. This accumulated group of blocks with small, lateral mass is then released as a large-volume displacement. The main scarp has a debris flow by failure of the debris dam steep headwall and is generally bare during high flow. They may also and concave toward the toe. The toe occur as the result of failure at the heads is hummocky or broken by individual of narrow drainages. slump blocks and, if an earthflow is involved, may be lobate in shape. The second group includes deep Earthflows frequently incorporate much seated soil creep, slumps, and earthflows. larger masses of soil which move These three entities are closely related downslope through a combination of in terms of their occurrence and genetic flowage and slumping. The main scarp process (fig. 4). is usually circular or spoon-shaped with a steep headwall and narrow lower This group corresponds most closely orifice through which the soil flow to Savarenskii's (1937)insequent landslides issued. The toe is characteristically and to Zkba and Mencl's (1969)Type B hummocky and lobate in form. Earth- slope movements (slides in pelitic uncon- flows in pyroclastic materials are solidated or partly consolidated rocks). common on the west flank of the Cascade Range in Oregon. In the Creep is the slow, continuous down- northern California Coast Ranges, slope movement of mantle material as discrete slumping combined with deep- the result of long-term application of seated creep frequently results in gravitational stress. It occurs in varying transitional slides and earthflows degrees in association with most other which supply substantial amounts of types of soil mass movement but domi- sediment to streams. nates as a major process in itself on

4 Figure 3-a. Three debris torrents in the Maybeso Creek valley. Prince of Wales Island, Alaska. All three developed during a high-intensity storm in the fall of 1961. Initial failure occurred at debris dams near the upper limit of logging in all three ravines.

Figure 3-b. Channel scour event in undisturbed timber on the H. J. Andrews Experimental Forest, Oregon. This event occurred as a result of failure near the head of the drainage.

Figure 3-c. Debris torrent developed in an intermittent stream channel along the South Fork of the Salmon River in Idaho. Initial failure occurred in road fill near the ridgetop.

5 Figure 4. Examples of natural slumps and Figure 4-b. Massive earthflow in a earth flows. recently logged area on the west a) Massive slump and earthflow in a flank of the Cascades. Depth of weathered till bank near Hollis, Prince soil not available, but failure of Wales Island, Alaska. Depth of occurred in relatively deeply weathering approximately 4 feet. weathered pyroclastic materials. Slope approximately 15° (34 percent grade).

Figure 4-c. Massive slope failure in the northern California Coast Ranges. The failure has resulted from creep and progressive failure in a deeply weathered series of greywackes, shales, bedded cherts, and limestone lenses of Cretaceous Age.

6 INTERRELATIONSHIP BETWEEN PRINCIPAL FACTORS PRODUCING LANDSLIDE MOVEMENTS ON TIMBERED SLOPES Direct application of Figure 5 shows the geometrical theory to analysis of mass movement relationship of these various factors. Any processes is difficult because of the hetero- increases in the tangential component of geneous nature of soil materials, the ex- gravitational stress will increase the treme variability of soil water conditions, tendency for the soil to move downslope. and the related variations in stress-strain Increases in shear stress result from relationships with time. It does, however, increasing slope of the failure surface ( a ) provide a convenient framework in which or increases in the effective weight of the to discuss the general mechanism and soil mass (W). Increases in slope may complex interrelationships of the various result from land rejuvenation by mountain factors active in development of soil mass building, sea level change, or local glacial movements on timbered slopes. and stream modification. Increases in weight of the soil result from increased In simplest terms, failure in a mate- water content or surface loading. Shear rial results if the shear stress acting on the stress can also be augmented temporarily material (force producing nonelastic defor- by application of wind stresses transferred mation) equals the or internal to the soil through the root systems of resistance to shear stress of the material. trees, by local buildup of internal stresses in the soil by creep deformation, by fric- Soil mass movements result from tional "drag" produced by seepage pressures, changes in the soil shear strength-shear and by removal of downslope support by stress relationship in the vicinity of fail- undercutting or progressive failure. ure. This may involve a mechanical read- justment among individual particles or a Shear strength is governed,by a more more complex interaction among both inter- complex interrelationship of soil and slope nal and external factors acting on the slope. characteristics. These factors include: (a) , the capacity of soil particles Shear stress (r ), or the tangential to adhere or stick together. This is a component of gravitational stress along a distinct soil property independent of gravi- basal zone of sliding, can be expressed tational stresses , produced by cementation, by the formula capillary tension, or weak electrical bond- ing of organic colloids and particles; = W sin a (b) the angle of internal ( 4 ), which where W = effective weight of the soil is an expression of the degree of interlock- a = slope of failure surface. ing of individual grains; and (c) the effective weight or normal component of gravitational Shear strength (S) or resistance to stress (W cos a), which includes both downslope gravitational stress is expressed weight of the soil mass and any additional by the formula surface loading plus the effect of slope gradient ( a ). The tangent of the angle of S=C+Wcosatan($ internal friction ( 4 ) times the effective where C = cohesion weight (W cos a) constitute a mathematical W = effective weight of the soil expression of frictional resistance (s = W a = slope of failure surface cos a tan ($ ). Moisture content and active ($ = angle of internal friction. pore water pressure (pressure produced by

7 1

/ \ / \ \ \ V \

\ L

d4‘ ‘

E.E+I= Equal and opposite normal forces acting on the soil mass

p,F+l = Equal and opposite shear forces acting on the soil mass w = Weight of the soil mass = Inclination of the sliding surface

= Shear stress = w sin cy c = Cohesion, a soil property

d= Normal stress on the sliding surface = wcosar += Angle of internal friction, a soil property

= Frictional resistance = w COS^ tan q5

Figure 5. Diagram of forces acting on a mass of soil on a slope. For simplicity, the lateral and shear forces acting on the mass are assumed equal and opposite and therefore cancel. The driving forces tending to cause downslope movement then consist of the weight of the soil mass (W) and its tangential component (T) or shear stress. Resisting forces consist of cohesion (C) which is inde- pendent of the, frictional forces and frictional resistance (s) which is proportionally related to the normal component of the soil weight (a) through the angle of internal friction (4).

8 the head of water in a saturated soil and mechanical support by windthrow, , transferred to the base of the soil through or timber harvesting can produce substan- the pore water) act to modify the component tial decreases in mechanical soil strength. of frictional resistance by reducing the value of the normal component of gravita- EFFECT OF FOREST OPERATIONS tional stress. This is frequently expressed ON SOIL STABILITY by the modified equation for effective weight (W cos a - P ) where p is pore Timber harvesting as a direct factor water pressure. in accelerating soil mass movements was first identified (Croft and Adams 1950) in Decreases in the cohesive properties shallow soils on steep, recently logged of soils may be produced by certain proc- slopes along the North Fork of the Ogden esses of soil formation such as leaching River in Utah (fig. 1, area,3). Here, and eluviation, or by destruction of capillary debris avalanches were initiated by com- tens ion through increasing water content . bined heavy spring rains and snomelt, As slope angles of potential failure surfaces but the authors felt that a contributing approach or exceed the soil's angle of factor was a lessening of the mechanical internal friction, shear strength may also support of the slope, chiefly by timber be reduced due to a reduction in the com- cutting and burning. ponent of frictional resistance. Increased weight of the soil mass caused by surface Reconnaissance investigations in loading increases the normal component southeast Alaska by Bishop and Stevens of gravitational stress. (1964) have also shown a direct correla- tion between timber harvesting and accel- Rising pore water pressures reduce erated soil mass movements following shear strength as a result of decreased heavy rains in the fall of 1961. More effective weight of the soil mass. At the detailed work in this area (Swanston 1967, same time, seepage pressures resulting 1969, 1970) has shown that sections of from frictional rrdragrtof water flowing almost every logged slope exceed the downslope through the soil may add sig- natural angle of stability of the soils nificantly to the tangential component of ( - 34"). This condition is aggravated shear stress. In highly cohesive soils, by high intensity in the spring and increasing water content may also help fall (occasionally in excess of 25 mm in to mobilize the clay particles through 24 hours). Shear strength tests on roots saturation and further add to increased taken from clearcut units of various ages creep rates and even ultimate failure. in southeast Alaska showed a marked decrease in strength 3 to 5 years after Root systems of trees and other cutting.2/ This 3- to 5-year time period vegetation can serve as cohesive binders roughly corresponds to the lag between or, if theypenetrate entirely through the time of logging and massive debris ava- soil zone, can anchor the soil mantle to lanching in southeast Alaska (Bishop and the substrate and thus provide an effective Stevens 1964). stabilizing influence. In some extremely steep areas in the Western United States, ' this may be a dominant factor in shear g/ D. N. Swanston and W. J. Walkotten. Tree rooting and soil stability in coastal forests of south- strength of the slope soil (Swanston 1967, east Alaska. Study No. FS-NOR-1604:26, on file at 1969, 1970). Under natural conditions, the Pacific Northwest Forest and Range Experiment the destruction of such effective Station, Juneau, Alaska.

9 Dyrness (1967a) investigated acceler- hole extending as deep as ated soil mass movements on the west 18.3 meters into , have shown flank of the Cascade Range following heavy measurable and persistent patterns of rains in the winter of 1964-65. He reported creep. Rates vary greatly from place to that out of 47 recorded debris avalanches, place and are apparently related to the debris flows, earthflows and slumps, 78 fundamental variables of mineralogy, percent were directly associated with logging fabric, and compressional and weathering and roadbuilding. Slumps and earthflows history of the rock. Kojan believes that caused by road fill failures, road back- weathering history and the rate of release slope failures, and failures due to road of locked-in stress from preconsolidation drainage waters were the most frequently of the Pliocene sediments is a'critical occurring events. Road fill failures con- factor in the creep rate. Discrete slump- stituted the greatest single event, but ing combined with deep-seated creep together all three types of failure made up combine to form transitional slides which more than 65 percent of all the mass move- account for as much as 70 percent of the ments that occurred (fig. 6). The majority natural sediment reaching some streams. occurred in shallow soils on slopes with a No work has been done directly on the gradient of over 50 percent (23"). Bedrock effects of timber harvesting in this area, geology was closely related to the soil but Kojan (personal communication) be- mass movements, with the largest numbers lieves that such activities have a "profound occurring on soils derived from pyroclastic and extensive effect" on this type of land- rocks, especially greenish tuffs and slide .occurrence. . Recent work (Paeth 1970) sug- gests that the instability of the greenish METHODS OF PREDICTION, tuff and soils is due to a high PREVENTION, AND CONTROL montmorillonitic clay content. During periods of high rainfall, the soils exper- Current research on the effect of ience substantial reductions in shear resis- forest operations on soil stability is di- tance as the result of osmotic swelling. rected toward: (a) anticipation of hazard- ous sites, (b) avoidance of disturbances In Idaho, Megahan (see footnote 1) systematically damaging to slope stability, reports about 90 percent of the soil mass and (c) reduction of landslide incidence movements which occurred along the South after disturbance. Fork of the Salmon River during a storm in April 1965 (a total of 89 events) result- The ability to identify hazardous ing from soil failures along the logging sites is probably the most useful and road right-of-way. Most open-slope fail- economical management tool available. ures occurred in shallow granitic soils on Many of the techniques presently being slopes in excess of 50 percent. Again, used effectively in southeast Alaska and the greatest number of these resulted from northern California are applicable else- road fill failures followed by failures re- where in the Western United States with sulting from obstructed road drainage adequate Imowledge of site conditions and (fig. 6). failure mechanisms. In the northern California Coast Ranges aerial photos In the northern California Coast are being used extensively to identify, Ranges, Kojan (1967) has identified deep- delineate, measure, and interpret topo- seated soil creep as a major erosion proc- graphic features related to deep-seated ess. Creep measurements, using bore creep and sliding. The interpretations

10 Figure 6. Examples of mass soil movements resulting from failure along a road right-of-way, a) Road fill failure in the Cascade Range of Oregon. Fail- ure resulted from plugged side drainages and resultant satura- tion of the road prism.

Figure 6b. Backslope failure along a logging road in the Salmon River of Idaho. Fail- ure resulted from undercutting of the slope toe.

Figure 6c. Failure due to inadequate road drainage in the Cascade Range of Oregon.

11 are supplemented by geologic maps com- Avoiding activities that are system- piled from surface outcrops and drill atically damaging to slope stability will cuttings which aid in the interpretation keep slope distur6ance to a minimum dur- and extrapolation of observed creep pat- ing forest operations. These include re- terns. Maps of seismic refraction sur- stricting forest road construction on poten- faces have also been prepared with the tially unstable slopes and preventing damage object of correlating velocity data and to the slopes by timber harvesting equip- strength parameters with observed creep ment and methods. A number of promising rates. Vertical color-infrared photographs new timber harvesting methods are also are being used to identify slope areas of being investigated or are undergoing limited high soil moisture content. practical trials. These include balloon logging and helicopter transport, both of Air photo interpretation has also been which have a tremendous potential for re- used extensively in southeast Alaska to ducing ground damage to a minimum. identify, measure, and delineate current or recent debris avalanche activity. Isoline Most direct methods of stabilization maps of slope angle have .also been pre- and control of disturbed areas are expensive pared for many individual watersheds from and difficult. At present, these methods are air photo and topographic map meamre- not being applied extensively to unstable areas ments. The area above a critical isoline in the Western United States but may be in corresponding to the measured or esti- the near future as timber and esthetic values mated internal friction angle of the local increase. There have been some limited soil defines areas of "imminent slide attempts to stabilize disturbed areas by vege- hazard. It In a region where slope gradient tation planting. This has been done with some alone constitutes a major factor of slope success in the Western States with grass hd stability, these maps clearly indicate legumes on road and sidecast slopes to areas of probable landsliding or where reduce surface (Wollum 1962, additional engineering-geological inves ti- Bethlahmy and Kidd 1966, Dyrness 1967b). gations are necessary. A map has also At least one attempt to stabilize a debris been prepared of southeast Alaska show- avalanche track using a mixture of reed can- ing landslide distribution as it relates to ary grass and alder wildlings has also been regional rainfall patterns. This map has tried in southeast Alaska. This shows prom- shown a direct correlation between areas ise although more careful and extensive inves- of high rainfall and debris avalanche tigations are needed to make a final judgment concentration. Currently, maps are being of its effectiveness. The United States Forest compiled showing the relationship between Service is currently experimenting with the commercial timber distribution and high hand seeding of debris avalanche tracks with hazard areas. alder in southeast Alaska.

12

, LITERATURE CITED

Bethlahmy, N., and W. J. Kidd 1966. Controlling soil movement from steep road fills. USDA For. Serv. Res. Note INT-45, 4 p., illus. Intermt. For. & Range Exp. Stn. , Ogden, Utah.

Bishop, D. M. , and M. E. Stevens 1964. Landslides on logged areas in southeast Alaska. Northern For. Exp. Stn. USDA For. Serv. Res. Pap. NOR-1, 18 p. , illus.

Croft, A. R. , and J. A. Adams 1950. Landslides and sedimentation on the North Fork of @den River, May 1949. USDA For. Serv. Intermt. For. & Range Exp. Stn. Res. Pap. INT-21, 4 p. , illus.

Dyrness, C. T. 1967a. Mass soil movements in the H. J. Andrews Experimental Forest. USDA For. Serv. Res. Pap. PNW-42, 12 p., illus. Pac. Northwest For. & Range Exp. Stn., Portland, Oreg.

1967b. Grass-legume mktures for roadside stabilization. USDA For. Serv. Res. Note PNW-71, 19 p., illus.’ Pac. Northwest For. & Range Exp. Stn. , Portland, Oreg.

Eckel, Edwin B. 1958. Landslides and engineering practice. Highway Res. Board Spec. Rep. 29, NAS-NRC Publ. 544, 232 p., illus. , Wash. , D. C.

Kojan, Eugene 1967. Mechanics and rates of natural soil creep. Fifth Annu. Eng. Geol. & Soils Eng. SGp., Idaho Dep. Highways, Univ. Idaho, Idaho State Univ. ,

! Pocatello, Proc. 1967, p. 233-253.

Paeth, Robert Carl 1970. Genetic and stability relationships of four Western Cascade soils. 126 p., illus. Ph. D. thesis, Oregon State Univ., Corvallis.

Savarenskii, P. F. 1937. Inzhenernaya geologiya. Moskva.

Sharpe, C. F. S. 1938. Landslides and related phenomena. 137 p. , illus. New York: Columbia Univ. Press.

Swanston, D. N. 1967. Debris avalanching in thin soils derived from bedrock. USDA For. Serv. Res. Note PNW-64, 7 p., illus. Pac. Northwest For. & Range Exp. Stn. , Portland, Oreg.

13 1969. Mass wasting in coastal Alaska. USDA For. Serv. Res. Pap. PNW-83, 15 p., illus. Pac. Northwest For. & Range Exp. Stn., Portland, Oreg.

1970. Mechanics of debris avalanching in shallow till soils of southeast Alaska. USDA For. Serv. Res. Pap. PNW-103, 17 p., illus. Pac. Northwest For. & Range Exp. Stn., Portland, Oreg.

Wollum, A. G. 1962. Grass seeding as a control for roadbank erosion. USDA For. Serv. Pac. Northwest For. & Range Exp. Stn., Res. Note PNW-218, 5 p., illus. Portland, Oreg.

Zgruba, Q., and V. Mencl 1969. Landslides and their control. 205 p., illus. New York: Am. Elsevier Publ. Co., Inc. (Prague: Acad., Publ. House Czech. Acad. Sci.).

14 The mission of the PACIFIC NORTHWEST FOREST AND RANGE EXPERIMENT STATlON is to provide the knowledge, technology, and alternatives for present and future protection, management, and use of forest, range, and related environments. Within this overall mission, the Station conducts and stimulates research to facilitate and to accelerate progress toward the following goals: 1. Providing safe and efficient technology for inventory, protection, and use of resources. 2. Development and evaluation of alternative methods and levels of resource management. 3. Achievement of optimum sustained resource produc- tivity consistent with maintaining a high quality forest environment. The area of research encompasses Oregon, Washington, Alaska, and, in some cases, California, Hawaii, the Western States, and the Nation. Results of the research will be made available promptly. Project headquarters are at: Fairbanks, Alaska Portland, Oregon Juneau, Alaska Olympia, Washington Bend, Oregon Seattle, Washington Corwallis, Oregon Wenatchee, Washington La Grande, Oregon

Mailing Address: Pacific Northwest Forest and Range Experiment Station P.O. Box 3141 Portland, Oregon 97208

GPO 990-683 The FOREST SERVICE of the U. S. Department of Agriculture is dedicated to the principle of multiple use management of the Nations forest resources for sustained yields of wood, water, forage, wildlife, and recreation. Through forestry research, co- operation with the States and private forest owners, and man- agement of the National Forests and National Grasslands, it strives as directed by Congress -- to provide increasingly greater service to a growing Nation.