0/3Soil Surface ConditionFollowing Tractor and High-Lead Logging in the Oregon Cascades

C. T. Dyrness

Abstract. Soil surface condition and bulk density were investigated after tractorand high-lead logging. Surface area of four clearcut units was classified intofour disturbance classes. High-lead and tractor areas had about the same pro-portion of the slightly disturbed and deeply disturbed classes (approximately23 percent and 9 percent, respectively). The tractor-logged area had aboutthree times more area within the compacted class than did the high-lead (27vs. 9 percent) and a corresponding decrease in the amount in the undisturbedclass (36 percent of the tractor area vs. 57 percent after high-lead logging).Surface soil bulk densities of samples from undisturbed and slightly disturbedareas were the same as prelogging values. Values for both the deeply disturbedand compacted classes were significantly higher, indicating a decrease in soilporosity. Compaction caused by tractor logging undoubtedly results in someincrease in runoff and erosion. However, these undesirable effects are minimizedif slopes do not exceed 20 to 30 percent and skidroads are located on thecontour.

LOGGING OPERATIONS cause surfacesoil disturbance ranging from re-moval of the protective organiclitter to complete removal of top-soil. Amounts of erosion and streamsedimentation f o 11 o w in g loggingmay vary directly with the degreeof disturbance caused by timberremoval. Therefore, it is impor-tant for forest land managers tohave some knowledge of relativeamounts of disturbance caused bydifferent methods of logging.

Old-growth Douglas-fir in thePacific Northwest is generallylogged in clearcut units by eithertractor or high-lead methods. Inareas of gentle slopes, most loggersprefer tractor yarding, but onslopes greater than 30 to 35 percent,high-lead logging is generally rec-ommended. During the past sev-eral years, considerable controversyhas arisen over the relative amountsof soil disturbance caused by log-ging. Some have maintained thattractor logging should never beallowed in critical watershed areas,even on gentle slopes, because ofexcessive disturbance. Others haveasserted that damage caused bytractor logging is negligible if it isdone during the dry season, whensoils are not easily compacted.

The extent of soil disturbancecaused by logging has been inves-tigated by several workers in thePacific Northwest. Steinbrennerand Gessel (3) studied tractor-

-.'nE AUTHOR is a soil scientist, PacificNorthwest Forest and Range Expt. Sta.,Forest Service, U. S. Dept. Agric., Port-land, Ore.

logged areas in western Washing-ton and found 26 percent of thetotal area occupied by tractor skid-roads. Wooldridge (4) comparedsoil disturbance by skyline-cranelogging with that by conventionaltractor skidding. In the tractor-logged area, 29.4 percent of theground surface was disturbed,while only 11.1 percent was dis-turbed in the skyline area. A com-parison of logging methods in east-ern Oregon and Washington byGarrison and Rummell (2) showedthat exposure of mineral soil aver-aged 20.9 percent in tractor-loggedareas, 15.2 percent of the total areawhere cables were used, and 11.8percent in horse-logged areas.

The Study

This study was designed to assessand compare effects of high-leadand tractor logging on soils withsimilar undisturbed surface condi-tions in the H. J. Andrews Experi-mental Forest, Blue River, Ore.( 1). The study area is located inthe western Cascades about 40miles east of Eugene, Ore.

Three high-lead cutting unitswere chosen having areas of 13, 20,and 28 acres (Fig. 1). Logging wascompleted in January 1963 andwas largely carried out during wetweather. The timber stand was old-growth Douglas-fir with a mixtureof some younger western hemlock.Slopes in the three units weresteep, ranging from 20 to 80 per-cent and averaging about 55 per-cent.

Only one tractor-logged cutting

unit was available—a 10-acre areaon which logging was completed inOctober 1963. Tractor operationswere carried out during the dryseason when soil moisture contentwas at a minimum. The timberstand included 100-year-old Doug-las-fir, western hemlock, and west-ern redcedar interspersed with scat-tered overmature Douglas-fir. Mostof the unit was virtually level ex-cept for a drainageway and twoshort ridges. Slopes along thedrainage range from 10 to 20 per-cent and the short ridge sideslopeswere about 40 percent. No skid-roads were constructed on thesesideslopes.

A principal objective of the studywas to determine the extent of soilsurface disturbance after yarding.The following four soil surface dis-turbance classes were set up anddescribed.

Undisturbed.—Litter still inplace and no evidence of compac-tion.

Slightly disturbed (Fig. 2).Three conditions fit this class :

Litter removed and undis-turbed mineral soil exposed ;Mineral soil and litter inti-mately mixed, with about 50percent of each ; and

(e) Pure mineral soil depositedon top of litter and slash toa depth of 2 inches.

Deeply disturbed. — Surfacesoil removed and the subsoil ex-posed. The soil surface is veryseldom covered by litter or slash(Fig. 3).

Compacted. — Obvious corn-

Reprinted from the JOURNAL OF FORESTRY, Vol. 63, No. 4, April 1965Purchased by the U. S. Forest Service for official use.

APRIL 1965 273

1404,"

-t`•FIG. 1.—General view of two of the high-lead cutting units FIG. 2.—Slightly disturbed soil surface condition after high-

used in this study. lead logging.

paction due to passage of a log ormobile equipment. The soil sur-face under large cull logs is as-sumed to be in this condition.

The percentage of the total clear-eut area in each disturbance classwas determined by means of pointsampling along transects. Pointobservations were made at 10-footintervals along six randomly lo-cated transects crossing each cut-ting unit.

Slash density classes were alsorecorded at 10-foot intervals. Sam-ple observations were made onsquare-foot areas, located by usingthe soil disturbance observationpoints as centers. Slash classes areas follows :

Heavy — Entire square footcovered with slash at least 1 footdeep.

Light—Ten percent or moreof the area covered with slash lessthan 1 foot deep.

Absent — Total slash coverless than 10 percent.

Cull log—Log over 12 inchesin diameter.

Another objective of the studywas to determine to what extentphysical properties of the surfacesoil were changed in the four dis-turbance classes. Bulk density waschosen as a criterion because itoffered a convenient measurementof the extent of alteration of phys-ical soil properties caused by log-ging. Bulk density samples werecollected with a core sampler fromthe surface 2 inches of soil beforelogging and from areas represent-ing each soil surface disturbanceclass after logging. Twenty sam-

ples were collected from each soilcondition, a total of 100 per log-ain o. method.

To insure maximum uniformityof surface soil conditions, only onesoil type was sampled for each log-ging method. In the high-lead area,the soil sampled was the Andrews'series, a fine-textured, moderatelydeep, reddish-brown soil derivedlargely from residual red breccia.In the tractor area, the soil is clas-sified as the Carpenter 2 series, amoderately deep, medium-texturedsoil derived from glacial till. BothAndrews and Carpenter soil haveshotty and porous, reddish-brownsu rface horizons.

'Provisional series, not yet correlated."Ibid.

Results

A total of 1,800 individual ob-servations of soil disturbance andslash density were made on fourcutting units. The three high-leadcutting units were remarkably uni-form with respect to soil distur-bance (Table 1). The most exten-sive disturbance occurred in unitL141, with a total of 38 percentof the area deeply or slightly dis-turbed. The difference among high-lead units, however, is not great,since comparable figures for theother two are 31 and 25 percent.

Largest differences between trac-tor and high-lead logging are inthe proportion of the logged areawithin the undisturbed and com-pacted classes (Fig. 4). The per-

FIG. 3.—Deeply disturbed soil surface condition after high-lead logging.

1

TABLE 1.-PERCENT OF TOTAL CUTTING UNIT AREA IN FOUR SOIL SURFACEDISTURBANCE CLASSES AND FOUR SLASH CLASSES

High-lead TractorClasses Unit L222 Unit L141 Unit L221 Unit L522Soil surface disturbance:

Undisturbed 58.1 50.7 62.7 35.6Slightly disturbed 21.0 24.5 18.9 26.4Deeply disturbed 9.6 13.6 5.8 8.9Compacted 9.6 7.1 10.7 26.8

Totals 98.3 95.9 98.1 97.7Slash :

Heavy 32.3 25.5 23.0 25.4Light 34.7 37.0 41.3 42.6Absent 23.6 29.6 24.5 26.4Cull log 10.0 7.9 11.9 6.3

Total2 100.6 100.0 100.7 100.71 The areas represented by the difference between the totals and 100 percent are

nonsoil areas, i.e., stumps, rocks outcrops, and stream bottoms.2May total more than 100 percent because "cull log" plus one of the other three

classes were sometimes recorded at a single point.

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centage of the area in the slightlyand deeply disturbed classes is ap-proximately the same for both log-ging methods. Tractor loggingcaused appreciable increase in theproportion of area described ascompacted (26.9 percent vs. 9.1percent for high-lead) and a cor-responding decrease in the propor-tion of undisturbed area (35.6 vs.57.2 percent for high-lead). Mostcompaction in the tractor-loggedunit was on skidroads where sur-face soil had been stripped of andbare subsoil compacted by passageof the tractor.

Compaction in the high-leadunits was generally quite different.There it was caused by skiddedlogs ; disturbance other than com-paction (e.g., surface soil removal)was, in many cases, not very ex-tensive. The compacted areas wereusually in shallow troughs of sur-face soil, at least partially coveredby scattered litter and slash.

In the tractor-logged area, skid-roads occupied approximately 28percent of the total area. This com-pares very closely with the 26 per-cent reported by Steinbrenner andGessel (3) .

Distribution of slash left on theground following logging wasabout equal for the two methods(Table 1). Data indicate that slash

•

was fairly well distributed in allunits, with only about 25 percent ofthe area free of slash.

Bulk density in the surface 2inches of soil was seriously alteredin only two disturbance classes--deeply disturbed and compacted(Table 2). Bulk density values forundisturbed and slightly disturbedclasses are similar to preloggingvalues for both methods of yarding.Apparently, slight disturbance haslittle effect on physical characteris-tics of the surface soil and largelyinvolves removal of protectivelitter. Greater bulk densities foundin deeply disturbed areas are usu-ally due to exposure of the densersubsoil. In addition to this typeof disturbance, tractor logging re-sults in the deposition of largeamounts of loose soil, such asskidroad berms. These deposits,although classed as deeply dis-turbed, have a much lower bulkdensity than is characteristic forthis disturbance class after high-lead logging. As a consequence,bulk density values in the deeplydisturbed class averaged lower fortractor logging than for high-lead.

Discussion and Conclusions

Tractor logging caused more sur-face soil disturbance Than didhigh-lead logging. Almost all in-

creased disturbance was in the formof compaction-the tractor-loggedunit had about three times morearea in the compacted disturbanceclass than did the high-lead units.Bulk density sampling indicatedthat compaction significantly de-creases porosity of the surface soil.In the tractor-logged area, undis-turbed soil had approximately 77percent pore space, while com-pacted soil averaged only about 63percent.

Extensive compaction may, insome cases, result in serious ero-sion and site deterioration. Thedecrease in pore space 1 ikely causesa substantially lower infiltrationrate and larger amounts of surfacerunoff. In addition, most com-pacted soil in tractor-logged areasoccurs in bare skidroads whichserve to channel runoff water. Al-though skid trails in high-leadareas are also trough shaped, theyare frequently protected by somelitter and scattered slash. Stein-brenner and Gessel (3) found thata 15-percent increase in the bulkdensity of skidroad soils resultedin 93-percent loss in permeability.

Erosion danger posed by com-paction was considerably modifiedby slope and orientation of skidtrails. For example, tractor skid-ding in this study was carried outon slopes of less than 20 percentand skidroads followed the contourwherever possible. As a result,runoff velocity tended to be re-duced and sediment transportedonly short distances. Where trac-tor skidroads are placed up anddown steeper slopes, erosiondamage is much greater.

Some workers have noted a re-lationship between poor survivaland growth of tree seedlings andsoil compaction. Youngberg (5)found a highly significant decreasein the growth of planted Dougla Q

-fir seedlings on compacted tractorroads as compared with seedlingsin other cutover locations.

Areas in the slightly disturbed

TABLE 2.-MEAN SOIL BULK DENSITY VALUES BEFORE AND AFTER LOGGING ON THE H. J. ANDREWS EXPERIMENTAL FOREST, 1963

Method Prelogging Undisturbed Slightly disturbedgm./cc.

0.712 ( ±-0.070)1 0.753 (±0.084) 0.785 (±0.138)High-lead Tractor 0.657(±0.077) 0.603 (±0.126) 0.584(±0.118)

'Standard deviation.

Deeply disturbed Compacted

0.990(±0.114) 0.952(±0.179)0.772(±0.114) 0.975(±0.182)

SOIL SURFACE DISTURBANCEPERCENT OF TOTAL AREA

60

MEASURES OF DISTURBANCE

UNDISTURBED

SLIGHT DISTURBANCE

DEEP DISTURBANCE

III COMPACTED

LOGGING: HIGH-LEAD TRACTORFIG. 4.—Surface soil disturbance following high-lead and tractor logging.

50

40

30

20

10

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class may be more susceptible tosoil movement than is indicated bytheir bulk density measurements.It is possible that soil disturbancemay affect structural properties ofthe soil which are not measured bybulk density. Furthermore, sus-ceptibility to soil movement may beincreased simply by removal of theprotective covering of organicmatter although bulk density re-mains unchanged.

It was interesting to note that ahigh proportion of the cutting unitarea was completely undisturbed oronly slightly disturbed. On high-lead units, the undisturbed classoccupied at least 50 percent of thearea, while the combined undis-turbed and slightly disturbed class-es averaged 79 percent. In thetractor unit, these two classestotaled 62 percent of the area.Thus, over much of these typicalcutting units, physical conditions ofthe surface soil were affected verylittle, no matter which loggingmethod was used. It does notnecessarily follow, however, thatbecause of the relatively small areaof seriously disturbed soil, water-shed damage will be negligible.Fortunately, "sore spots" which re-sult in serious stream siltation gen-erally occupy only a small fractionof a total watershed area, especiallyif they are located near streamchannels.

The results of this study indicatethat although tractor loggingcauses more soil disturbance thanhigh-lead, the difference is notvery great when tractors are usedduring the dry season on gentleslopes. Under these conditions,damage to the site would probablynot be considered excessive exceptin cases where special problems ofsoil instability or reforestationexist.

Literature CitedBERNTSEN, CARL M., and JACKROTHACHER. 1959. A guide to theR. J. Andrews Experimental Forest.U. S. Forest Service, Pacific North- 4.west Forest and Range Expt. Sta. 21pp. Illus.GARRISON, GEORGE A., and ROBERT S.RUMMELL. 1951. First-year effects of 5.logging on ponderosa pine forestrange lands of Oregon and Washing-ton. Jour. Forestry 49:708-713. Illus.

3. STEINBRENNER, E. C., and S. P.

GESSEL. 1955. The effect of tractorlogging on physical properties ofsome forest soils in southwesternWashington. Soil Sci. Soc. Amer.Proc. 19 : 372-376.WOOLDRIDGE, DAVID D. 1960. Water-shed disturbance from tractor andskyline crane logging. Jour. Forestry58:369-372. Illus.YOUNGBERG. C. T. 1959. The influenceof soil conditions, following tractorlogging, on the growth of plantedDouglas-fir seedlings. Soil Sci. Soc.Amer. Proc. 23:76-78.