SOIL COMPACTION: CONCERNS, CLAIMS, AND EVIDENCE Dick Miller nd Hrry Anderson ABSTRACT Soil resistnce to penetrtion ws mesured in ten 7 to 27-cre opertionl units in overstocked mixed-conifer stnds t the Fritz Timber Sle in Northest Wshington. Different combintions of felling nd yrding equipment were used to thin eight of these units; no combintion ws replicted. Two other units remined nonhrvested controls. Using recording penetrometer, resistnce ws mesured to the 33-cm depth (13 inches) t ten sttions on 5 17 100-foot long, rndomly oriented trnsects in ech unit. Ground-bsed hrvesting equipment operted on nd off designted trils. Although trils occupied 6 57% of the hrvested units, totl re of strong compction on these trils vried gretly (0 42%). Consequences of soil compction for tree performnce t this sle re re unknown. In fct, consequences of soil disturbnce for trees hve seldom been mesured in the Northwest. At the reltively few plces where trees were mesured, response to compction rnged from mostly negtive through none to positive. Therefore, current clims bout dire consequences of compction for long-term site productivity must be bsed lrgely on limited smpling, ssumptions bout the consequences of compction for tree performnce, nd specultion. We ssert tht uncertinty bout the consequences of compction nd other forms of soil disturbnce will remin until long-term tree performnce is correctly mesured over wide rnge of regionl soils nd climtic. Keywords: commercil thinning, hrvesting equipment, soil bulk density, penetrtion resistnce, penetrometer, Northest Wshington Point 2. But, the consequences of soil disturbnce for subsequent tree performnce hve been mesured only t limited number of loctions, nd usully for short periods. Point 3. Yes, uncertinty bout the ctul consequences of compction (nd other forms of soil disturbnce) will continue until tree performnce is relibly mesured over wide rnge of regionl soils nd climtic conditions nd for long period of time. Tht is our concern nd we will suggest wys to collect such direct evidence. POINT 1. HARVESTING EQUIPMENT DISTURBS THE SOIL (FRITZ TIMBER SALE) Methods Sle lyout. The eight hrvested units nd the two nonthinned control units were 7 27 cres in size (Figs. 1 nd 2). The dots represent strting points for rndomly oriented trnsects used to smple soil compction. Figure 1. Units on flt terrin. Dots re strting points for trnsects. INTRODUCTION We suspect tht mny of you hve observed soil disturbnce by hevy equipment used to hrvest trees. You nd others re probbly concerned tht soil compction, rutting, or displcement of topsoil could reduce future tree survivl or growth. The scientific literture shres your concern (Grecen nd Snds 1980; Froehlich nd McNbb 1984; Geist et l. 1989; Pge - Dumroese et l. 1993; Wronski nd Murphy 1994). In this presenttion, we ddress concern bout longterm soil cpcity by supporting the following points: Point 1. Yes, ground-bsed hrvesting equipment used to thin overstocked forests disturbs the soil over much of the hrvested re to vrying severity. To support this point, we will report results from soil investigtion in the recent Fritz Timber Sle on the Colville Ntionl Forest. Figure 2. Units on steep terrin. Cots re strting points for trnsects. Published in Smll Dimeter Timber: Resource Mngement, Mnufcturing, nd Mrkets proceedings from conference held Februry 25-27, 2002 in Spokne, Wshington. Compiled nd edited by D.M. Bumgrtner, L.R. Johnson, nd E.J. DePuit. Wshington Stte University Coopertive Extension. (Bulletin Office, WSU, PO Box 645912, Pullmn, WA 99164-5912. MISC0509. 268 pp.
98 Miller nd Anderson Stnd description. All units on flt terrin were in the sublpine-fir type with bout 900 1100 stems per cre tht verged 5.0 5.9 inches d.b.h (Tble 1). Of these trees, 24 57% were cut. Units on steep terrin generlly exceeded 30% slopes; the timber type ws either Dougls-fir or lodgepole pine. Before-thinning density in steep units ws bout 440 800 trees per cre, less thn in the flt units, but men d.b.h. verged bout 1 inch lrger. About 53 69% of these trees were cut. Soils. Units on flt terrin included severl soil series, which rnged from low to high in their susceptibility to compression when subjected to lod (Tble 2). High compressibility ws relted to finer soil textures (silt loms); conversely low compressibility ws ssocited with sndy lom textures. Sndy lom textures were more prevlent in the steep units. Hrvesting methods. Different combintions of felling or yrding equipment were used in ech of the eight commercilly thinned units; no combintion ws replicted (Tble 3). Trees were felled by chin sw in only one unit; trees in the remining units were felled by mchines. Ground-bsed yrding equipment ws used on flt units nd on one of the four steep units. Designted trils were spced t either 40 or 130 feet (centerto-center distnce). Corridors for skyline cbles re-used some of the trils used erlier by either feller-buncher (tht bunched whole trees) or trcked hrvester tht felled nd processed cut-to-length logs for retrievl by cble. Both the hrvester nd the feller-buncher hd extendble booms tht enbled the opertor to cut trees within 30-foot rdius. Theoreticl coverge of tril/corridors. Designted trils were bout 14 feet wide. Therefore, with centerto-center spcing of 40 feet, designted trils would cover bout 35% of the hrvested re (Tble 4). At this tril spcing, both the feller-buncher nd hrvester could fell nerby trees, yet remin on the tril. With designted tril spcing of 130 feet, however, the edgeto-edge distnce between trils ws 116 feet (130 minus 14 feet). This would require equipment opertors either to move off designted trils or leve bout 60 foot wide portion nonthinned. Note tht fewest trees were cut on Unit 2, where chinsws were used to fell trees. Mesurement of soil strength (resistnce to cone penetrtion). Resistnce to penetrtion ws mesured to the 33-cm depth (13 inches) t ten systemticlly locted sttions on 100-foot long, rndomly oriented trnsects (Fig. 3). There were 5 17 trnsects in ech unit. At nerly ll sttions, three profiles of soil resistnce were registered by Rimik CP-20 cone penetrometer. Dt from these subsmples were verged to obtin sttion men for ech 1.5 cm depth. Post-hrvest mesurements were mde tht sme summer or fll shortly fter ech unit ws hrvested in 1998 on steep terrin nd in 1999 on flt terrin. The two control units were smpled concurrently. The loction of ech sttion reltive to skid trils ws documented: Code 2 = skid tril rut, Code 6 = beside or between ruts, nd Code 0 = nontril loction. Some Code 6 smpling points could hve been on displced soil. Mesurement of soil bulk density. Fine-soil bulk density ner the midpoint of the 0- to 7.5-cm depth ws mesured before (summer 1997) nd fter hrvest (fll 1999). Soil cores (68.7 cm 3, 5.4 cm dimeter) were collected t systemtic loctions long trnsects but only within units on flt terrin. Tble 1. Site nd stnd chrcteristics Before Unit Men thinning Cut No. Are slope Forest type Trees Dq b Trees BA Ac. % c -1 in. % Flt terrin: 2 27 15 Sublpine fir 1101 5.2 24 34 3 24 7 Sublpine fir 1080 5.9 49 56 4 20 13 Sublpine fir 879 5.0 33 46 19 17 10 Sublpine fir 1025 5.9 57 54 Control 7 12 Steep terrin: 8 8 31 Dougls-fir 802 6.1 53 56 9 12 36 Dougls-fir 438 7.1 69 54 16 16 33 Lodgepole pine 701 6.4 64 56 17 18 25 Lodgepole pine 537 6.4 66 55 Control 17 40 Lodgepole pine Trees 1.0-in. d.b.h. nd lrger. Source: Cmp, A. Nonpublished dt, Pcific Northwest Reserch Sttion. Wentchee Forestry Sciences Lb. b Dq = qudrtic men dimeter = dimeter of tree of verge bsl re; BA = bsl re
Tble 2. Soil series in flt nd steep terrin, by unit; bsed on soil survey by Zuluf nd Strr (1979). Unit Prent mteril No. Are Series nme Cp Bse Compressibility Flt terrin: % 2 60 Neuske silt lom silty till silty till H 40 Scr sndy lom till till L 3 45 Nevine lom sh compct till M 30 Scr sndy lom till till L 20 Ghee lom sh outwsh L 5 Neuske silt lom silty till silty till H 4 75 Neuske silt lom silty till silty till H 25 Scr sndy lom till till L 19 100 Scr sndy lom till till L Control 50 Nevine lom sh compct till M 50 Ghee lom sh outwsh L Steep terrin: 8 100 Merkel sndy lom sh grnitic till L 9 50 Merkel sndy lom sh grnitic till L 50 Rock lnd L 16 50 Merkel sndy lom sh grnitic till L 50 Rock lnd L 17 80 Merkel sndy lom sh grnitic till L 20 Nevine lom sh grnitic till M Control 100 Merkel sndy lom sh grnitic till L H=high, M=moderte, L=low Miller nd Anderson 99 Tble 3. Hrvesting equipment; designted trils corridors were 14-feet wide with center-to-center spcings of 40 or 130 feet. Terrin nd Forwrding-yrding unit Ground-bsed Cble system No. Are Tree felling Processing to logs Equipment Spcing Skyline Corridor spcing c ft ft Flt (7-15 % men slopes): 2 27 Chin sw Hrvester b Forwrder c 130 - - - 3 24 Hrvester Hrvester Forwrder 40-4 20 Feller-buncher c Whole tree Skidder c 130 - - - 19 17 Feller-buncher Hrvester Forwrder 130 - - - Steep (25-36 % men slopes): 8 8 Hrvester f Hrvester - - 40 Uphill 80 9 12 Hrvester Hrvester Forwrder c 40-16 16 Feller-buncher d Whole tree - - 40 Downhill 40 17 18 Hrvester Hrvester - - 40 Downhill 80 Skgit model 333 yrder, dpted with third drum; Christy hul-bck crrige b Trcked Kbelco model 200 single-grip hrvester with Kto 500 sw hed; cut logs to length (CTL) c Rubber-tired Vlmet model 892 forwrder (14-ton cpcity) d Trcked Timbco model 445 B feller-buncher with Qudco Hot-Sw felling hed on n extendble boom e Rubber-tired Ct model 518 skidder with swinging grpples f Trcked Vlmet model 500T single-grip hrvester (with tilting cb); cut logs to length (CTL)
100 Miller nd Anderson Tble 4. Designted trils: theoreticl coverge Spcing between Width Centerline Edges Needed Percentge of hrvest re rech (width CL distnce) - - - - - - - - - - - - - - - Feet - - - - - - - - - - - - - - 14 % 40 26 13 35 130 116 58 11 Figure 3. Designted tril with slsh plce by trckedhrvester. Figure 3b. Soil strength ws mesured by cone penetrometer. Figure 3c. The generl terrin of the Fritz Timber Sle.
Miller nd Anderson 101 Results (from Fritz) Percentge of re in trils, by equipment combintions. We hve two independent estimtes of the combined re in designted nd supplementl trils (Tble 5). The first is bsed on the percentge of ll smpling sttions (10 per trnsects) tht fell in or ner tril ruts (Codes 2 nd 6). By this estimte, 6 57% of the unit res were in trils. The second estimte ws bsed on similr number, but different 100-foot long trnsects in ech unit. Where these trnsects crossed mchine trils, the intercepted distnce ws expressed s percentge of totl trnsect length (Tepp, in review). Trils occupied 12 38% of the hrvested re bsed on this second estimte. Bulk density in surfce soil of flt terrin (tril vs. non-tril portions). Among the four hrvested units on flt terrin, fine-soil bulk density on trils verged 3 14% greter thn tht in non-tril portions (Tble 6). Note tht the USFS. Northwest Region s stndrd for judging compction s detrimentl is 20% or more increse in BD of soils derived from volcnic sh or pumice (USFS 1998). By this stndrd, verge compction on the trils in flt units ws not detrimentl. Becuse some of the non-tril portions lso could hve been compcted, we clculted 20% increse in the men before-hrvest BD s our threshold stndrd. Bsed on this stndrd, 15% of unit 19 hd detrimentl compction. Tble 5. Percentge of thinned re in trils, by unit. Terrin Hrvesting equipment Tril Penetrometer Monitoring trnsects nd unit spcing trnsects Trils Difference No. % of sttions No. % of totl length Flt: 2 Chin sw, hrvester, forwrder 130 13 21 13 12-10 3 Hrvester, forwrder 40 14 57 14 29-13 4 Feller-buncher, whole-tree skidder 130 10 17 10 28 3 19 Feller-buncher, hrvester, forwrder 130 8 39 8 38-1 Steep: 8 Hrvester, uphill skyline 40 10 6 14 19 13 9 Hrvester, forwrder 40 15 18 16 28 10 16 Feller-buncher, whole-tree, downhill 40 14 27 14 25-1 17 Hrvester, downhill skyline 40 18 13 17 30 17 Totl trnsect lengths per unit rnge from 800 to 1700 feet. Adpted from Tepp (in review). Tble 6. Fine-soil bulk density fter hrvest in the 0- to 7.5-cm minerl soil depth in trils (ruts nd djcent soil) vs. other portions, in flt terrin. Visul strt Trils Non-tril Difference Unit No. Equipment St. No. Men SE Mg m -3 % St. No. Men SE Mg m -3 % Absol Mg m -3 Rel % 2 Chin sw, hrvester, forwrder 25 0.851 0.000 0.0 100 0.782 0.024 3.1 0.069 8 3 Hrvester, forwrder 74 0.695 0.015 2.2 57 0.676 0.020 3.0 0.019 3 4 Feller-buncher, whole-tree skidder 29 0.816 0.044 5.4 65 0.701 0.025 3.6 0.115 14 19 Feller-buncher, hrvester, forwrder 30 0.823 0.046 5.6 48 0.763 0.029 3.8 0.060 7 SE = stndrd error of men; derived from nested ANOVA (2-stge smpling)
102 Miller nd Anderson A few 70-yer-old trils of former fire-slvge sle were redily identifible in some units on steep terrin by pucity of vegettion nd shllow ruts. Lterl berms were bsent or indistinct, so topsoil displcement ws less evident. Soil in trils remined compcted, especilly below the 5-cm depth (Fig. 4); however, mximum resistnce ws less thn 1500 kp. Note tht 2000 3000 kp is generlly considered detrimentl to root growth (Powers et l. 1998). kp. Our smple size ws lrge, 32 58 smpling sttions per coded condition. * Figure 6. Trils in unit 4 were designted t 130-foot intervls. Therefore, the feller-buncher hd to leve designted trils to fell intervening trees, which were then yrded s whole trees with rubber-tired skidder. About 75% of the unit ws Neuske silt lom, highly compressible soil. Note the lrge difference in soil resistnce t sttions ssocited with trils (ruts nd djcent soil) compred with off-tril sttions. Note lso tht resistnce generlly exceeded 2000 kp t lower depths, but this root-restricting resistnce ws close to the surfce in the trils. Figure 4. Averge soil resistnce in steep unit 17, by loction of smpling sttion (3 subsmples per sttion). Note the residul men compction in 70-yer-old trils of former slvge sle. Soil resistnce incresed fter recent thinning in the Fritz Sle (Figs. 5 nd 6). The increse ws greter in the finer textured soils of the flt terrin thn in sndier textures on slopes. * Figure 5. Unit 3 hd designted trils t 40-foot spcing; therefore, the hrvester could redily cut trees in the intervening portions nd pile logs long the tril. A rubber-tired forwrder trnsported these logs to the lnding. Note the much greter resistnce in the ruts (trcks) especilly t 5-cm nd lower depths. Note lso tht below 20 cm, verge resistnce exceeded 2000 Figure 5. Averge soil resistnce in flt unit 3 fter hrvester-forwrder combintion nd 40-foot tril spcing (center-to-center). Note greter resistnce in the trcks thn in djcent soil, some of which could be displced berm. Figure 6. Averge soil resistnce in flt unit 4 fter combintion of felling by feller-buncher nd whole-tree skidding; 130 foot tril spcing. Note resistnce t sttions in trils (ruts nd nerby soil) exceeded 2000 kp close to surfce. * Note tht different combintions of equipment were ssigned to ech unit. This lck of true repliction precludes sttisticl testing to indicte which equipment provides the lest impct on soil. Although we used different methods to ssess soil compction fter hrvesting (Lndsberg et. l., pending review), we provide only the post-hrvest comprisons in this presenttion. * Tril vs. nontril. This method of comprison equls the usul, retrospective (fter-hrvest) monitoring in which one smples soil on trils nd compres these estimtes of soil resistnce or bulk density to corresponding estimtes from non-tril portions. When interpreting retrospective results, one must verify or ssume (1) tht trils were plced on soils representtive of the remining portions (soils were similr), (2) tht soil moisture conditions on nd off trils were similr when smpled, hence (3) tht differences cn be explined by equipment impct ( typicl monitoring question). Bsed on this fter-hrvest monitoring, we note tht verge resistnce in trils of only one of eight units exceeded the proposed stndrd defining detrimentl resistnce (Tble 7). Of the sttions locted on trils, 0 70% hd penetrtion resistnce equl to or exceeding 2000 kp on the 15- to 25-cm depth. This equted to s much s 40% of Unit 3 being detrimentlly compcted (Fig. 7).
Miller nd Anderson 103 Tble 7. Averge difference in fter-hrvest soil resistnce on trils (ruts nd djcent soil) versus non-tril portions, by unit nd depth in minerl soil. Terrin Surfce soil (0-10 cm) Stndrd zone (15-25 cm) nd Equipment Tril Non-tril Difference Tril Non-tril Difference Unit Flt: kp % kp % 2 Chin sw, hrvester, forwrder 1682 852 830 97 1926 1720 206 12 3 Hrvester, forwrder 1257 1092 165 15 2258 2192 66 3 4 Feller-buncher, whole-tree skidder 1890 890 1000 112 2976 1803 1173 65 19 Feller-buncher, hrvester, forwrder 1514 1058 456 43 2198 1714 484 28 All Men 1586 973 613 63 2340 1857 483 26 Steep: 8 Hrvester, uphill skyline 627 717-90 -13 794 888-94 -11 9 Hrvester, forwrder 887 816 71 9 1416 989 427 43 16 Feller-buncher, whole-tree, 790 754 36 5 1058 850 208 24 downhill skyline 17 Hrvester, downhill skyline 1046 757 289 38 1396 986 383 35 All Men 838 761 77 10 1166 928 238 26 Dr. Robert Powers (PSW Reserch Sttion, USFS) hs proposed to the U.S. Forest Service (Pcific Southwest Region, Region 5) tht detrimentl soil dmge be defined s 500 kp or more increse in soil strength (15- to 25-cm depth in minerl soil). Figure 7. Percentge of hrvested re in trils (ruts nd nerby soil) nd with penetrtion resistnce of 2000kP or more in the 15- to 25-cm depth of trils, by unit number. Additionl non-tril re could hve compcted soil. Conclusions from the Fritz Timber Sle 1. Among the eight thinned units tht we investigted, 6 57% of the hrvested re ws in designted nd supplementl trils. Supplementl trils were mde where equipment hd to leve widely spced (130 ft) designted trils to fell intervening trees. 2. Extent nd severity of compction ws greter on flt units, where ll yrding ws by forwrders or skidders nd where three of four units hd soils of silt lom or lom textures. 3. Consequence of this disturbnce to tree performnce is unknown. Will this be ssessed in the future?
104 Miller nd Anderson POINT 2. THE CONSEQUENCES OF SOIL DISTURBANCE FOR SUBSEQUENT TREE PERFORMANCE ARE SELDOM MEASURED Est of the Cscdes. All est-side studies re bsed on dt collected 8 64 yers fter overstory removl or clercutting (Tble 8). Effects of trils in estside commercil thinnings on residul tree growth hve not been reported. Note tht ll investigtions re retrospective rther thn controlled-tretment. The linkge between soil disturbnce nd tree performnce (the vrible needed for economic nlysis) must be quntified to know the prcticl consequences of soil compction. Tble 8. Estside: Investigtions of tree growth on skid trils vs. off skid trils, by type of hrvest. Are nd species Loctions Soil texture Tree ge Results Source No. yers Thinning: no reports 0 None Overstory removl: b WA, ponderos pine 3 lomy (sh) 9-18 -20 % stem volume Froehlich et l. (1986) -5 % tree height WA, lodgepole pine 1 shy 11 0 % volume, tree height Froehlich et l. (1986) OR, ponderos pine 1 sndy lom 64-6 % to -12 % tree BA growth Froehlich (1979) Cler cutting: OR, ponderos pine 1 lomy 8-38 % tree height Cochrn nd Brock (1985) (t + 20 % increse in BD) N. ID, ponderos pine 1 silt lom (sh) 20-25 -20 % d.b.h. (displcement) Clyton et l. (1987) -10 % d.b.h. (compction) N. ID, lodgepole pine 2 silt lom (sh) 15-19 -22 to-25 % d.b.h. (compction) Clyton et l. (1987) 15 to -25 d.b.h. (displcement) BC, conifers 4 lom to silt lom 16-18 -14 to +4 % tree height Smith nd Wss (1980) BC, conifers 5 lomy (clcreous) 9-22 -12 to-15 % height Smith nd Wss (1979) BC, conifers 3 sndy (cid) 9-22 +18 to 22 % height Smith nd Wss (1979) BC, Englemn spruce 3 sndy lom 9-10 tree volume lest on trck, Senyk (2001) most on berm BC, lodgepole pine 3 sndy lom 9-10 tree volume lest on trck Senyk (2001) t two loctions nd most t one loction Skidrods, not trils, were investigted in BC. These rods re blded into steep slopes. Growth usully differs with position on running surfce nd sidecost (cut, trck, fill). b The influence of residul overstory trees on growth of younger, mesured trees complictes inferences bout skid-tril effects.
Miller nd Anderson 105 POINT 3. WHAT EVIDENCE IS RELIABLE FOR JUDGING RISK TO LONG-TERM SITE PRODUCTIVITY? Conventionl soil monitoring ( effectiveness monitoring of USFS) hs n re nd severity stndrd. Severl types of soil disturbnce re recognized in ddition to compction. Compction severity tht exceeds specified threshold (e.g., 20% increse in bulk density) is considered detrimentl compction; this counts s risk to soil cpcity or qulity (Fig. 8). The combined, estimted re of detrimentl disturbnces should not exceed 20% of the totl (gross) hrvested re, including the permnent rods which obviously remove lnd from production (USFS 1998). * Tree monitoring (termed vlidtion monitoring by the USFS) would test this ssumed linkge between tree performnce nd chnged soil properties. * For exmple, one would mesure: Seedling survivl nd erly growth; this is simplest to do nd indictive of short-term effects Growth of residul trees fter thinning or prtil cutting; this is more difficult to ccomplish Cubic volume yields per cre in mture stnds; the most difficult to estimte, but the definitive mesure * We ssert tht monitoring tree growth Provides the necessry direct evidence for judging risk to long-term site productivity Cn indicte which type, severity, nd pttern of soil disturbnce relly ffects tree performnce SUMMARY Point 1. Incresed soil resistnce fter hrvesting t the Fritz Timber Sle re consistent with results from other investigtions. Ground-bsed hrvesting equipment used to thin these overstocked forests disturbed soil over much of the hrvested re. Estimted combined re of severe compction (> 2000 kp) vried gretly mong the eight units (0 42%). Point 2. Reltive to the millions of cres of commercil forest in the Inlnd West, the consequences of soil disturbnce for subsequent tree performnce hve seldom been mesured. Without locl experience nd longer periods of observtion, current clims bout dire consequences of soil compction to long-term site productivity must be bsed lrgely on ssumptions, circumstntil evidence, nd specultion. Figure 8. Percentge of hrvested re in trils nd with 20% or more increse over verge prehrvest bulk density (0 to 7.5 cm depth) in specified hrvest unit. * At Fritz (8 units) 6 to 42 % of the thinned re ws in trils nd corridors We detected compction (incresed soil resistnce) on these trils, but ws it relly detrimentl to soil cpcity to grow trees? * Soil monitoring: Provides numbers indicting the types, severity, nd coverge of soil disturbnce Provides indirect evidence: soil properties re chnged. From this circumstntil evidence, mny ssume tht tree performnce will be reduced; But performnce cn lso be incresed on compcted soil in some situtions (Powers nd Fiddler 1997) Point 3. Uncertinty bout the consequences of soil compction nd other forms of soil disturbnce will remin until tree performnce is relibly mesured over wide rnge of regionl soils nd climtic conditions, nd over long period of time. Tke-wy Messge: If you re concerned bout tree performnce, then collect direct evidence mesure trees. ACKNOWLEDGMENTS We becme involved with the Creting Opportunities project (CROP) fter Dr. Jon Lndsberg retired from USFS. We summrized dt (collected by Forest Service crews from Wentchee Lb) nd re prepring reports for publiction. We thnk the CROP nd Dr. Lndsberg for the opportunity to complete this work. We re lso grteful to Jeffery Tepp for the orderly trnsfer of dt files nd ssorted records, to John Senyk nd Andrew Youngblood for technicl review, nd to Sherry Den for helping prepre our visul presenttion.
106 Miller nd Anderson LITERATURE CITED Cochrn, P.H. nd T. Brock. 1985. Soil compction nd initil height growth of plnted ponderos pine. Res. Note PNW-434. U.S. Deprtment of Agriculture Forest Service, Pcific Northwest Forest nd Rnge Experiment Sttion, Portlnd, OR. 4 p. Clyton, J.L., G. Kellogg, nd N. Forrester. 1987. Soil disturbnce-tree growth reltions in centrl Idho clercuts. Res. Note INT-372. U.S. Deprtment of Agriculture Forest Service, Intermountin Reserch Sttion, Ogden, UT. 6 pp. Froehlich, H.A. 1979. Soil compction from logging equipment: Effect on growth of young ponderos pine. Journl of Soil Wter Conservtion 34: 276-278. Froehlich, H.A. nd D.H. McNbb. 1984. Minimizing soil compction in Pcific Northwest forests. In: Stone, E. L. (ed.). Forest soils nd tretment impcts. Proceedings of the 6th North Americn Forest Soils Conference, Deprtment of Forestry, Wildlife, nd Fisheries, University of Tennessee, Knoxville, TN. Pp. 159-192 Froehlich, H.A., D.W.R. Miles, nd R.W. Robbins. 1986. Growth of young Pinus ponderos nd Pinus contort on compcted soils in centrl Wshington. Forest Ecology nd Mngement 15: 285-294. Geist, J.M., J.W. Hzrd, nd K.W. Seidel. 1989. Assessing physicl conditions of some Pcific Northwest volcnic sh soils fter forest hrvest. Soil Science Society of Americ Journl 53: 946-950. Grecen, E.L. nd R. Snds. 1980. Compction of forest soils: A review. Austrlin Journl of Soil Reserch 18: 163-189. Lndsberg, J.D., R.E. Miller, H.W. Anderson, nd J.S. Tepp. (Pending review). Soil resistnce nd bulk density s ffected by commercil thinning on flt nd steep terrin in northestern Wshington. U. S. Deprtment of Agriculture Forest Service, Pcific Northwest Reserch Sttion. Pge-Dumroese, D., A. Hrvey, M. Jurgensen, nd R. Grhm. 1991. Orgnic mtter function in the westernmontne forest soil system. In: Hrvey, A.E. nd Neuenschwnder, L. F. (comps.). Proceedings-mngement nd productivity of western-montne forest soils; 1990 April 10-12; Boise, ID. Gen. Tech. Rep. INT-280. U.S. Deprtment of Agriculture Forest Service, Intermountin Reserch Sttion, Ogden, UT. Pp. 95-100. Powers, R.F. nd G.O. Fiddler. 1997. The North Americn Long-Term Soil Productivity Study: progress through the first 5 yers. In: Proceedings, Eighteenth Annul Forest Vegettion Mngement Conf., Jn 14-16, 1997, Scrmento, CA. Published by the Forest Vegettion Mngement Conference, Redding, CA. Smith, R.B. nd E.F. Wss. 1979. Tree growth on nd djcent to contour skidrods in the sublpine zone, southestern British Columbi. Rep. BC-R-2. Cndin Forest Service, Pcific Forestry Reserch Centre, Victori, BC. 26 pp. Smith, R.B. nd E.F. Wss. 1980. Tree growth on skidrods on steep slopes logged fter wildfires in centrl nd southestern British Columbi. Inf. Rep. BC-R-6. Cndin Forest Service, Pcific Forestry Reserch Centre, Victori, BC. 28 pp. Senyk, J.P. 2001. Tree growth on displced nd compcted soils. Tech. Trnsfer Note No. 26. Cndin Forest Service, Pcific Forestry Reserch Centre, Victori, BC. Tepp, J.S. In review. Assessing visul soil disturbnce on eight commercilly thinned sites in northestern Wshington. U.S. Deprtment of Agriculture Forest Service, Pcific Northwest Reserch Sttion. USFS. 1998. USDA Forest Service Mnul, FSM 2520 (Wtershed Protection nd Mngement) R-6 Supplement No. 2500-98-1, Effective Aug 24, 1998. Wronski, E.B. nd G. Murphy. 1994. Responses of forest crops to soil compction. In: Slone, B.D., nd vn Ouwerkerk, C. (eds.). Soil compction in crop production. Elsevier Science. Pp. 317-342. Zuluf, A. nd W.A. Strr. 1979. Soil survey of North Ferry re, Wshington, prts of Ferry nd Steven counties. U.S. Deprtment of Agriculture Soil Conservtion Service nd Forest Service nd Wshington Agriculturl Experiment Sttion. 121 p. nd 73 mps. Authors Dick Miller, Retired USDA Forest Service-PNW Reserch Sttion Forestry Sciences Lbortory 3625 93rd Ave. SW Olympi, WA 98512-9193 360-956-2345 ext 669 millersoils@ol.com Hrry Anderson USDA Forest Service-PNW Reserch Sttion Forestry Sciences Lbortory 3625 93rd Ave. SW Olympi, WA 98512-9193 The use of trde or firm nmes in this publiction is for reder informtion nd does not imply endorsement by the US Deprtment of Agriculture of ny product or service.