Soil Disturbance Effects of Hoe-Forwarding on Tree Growth and Site

Extension NoteForest Research

Coast Forest Region2100 Labieux Road, Nanaimo, BC, Canada, V9T 6E9, 250-751-7001

Soil Disturbance Effects of Hoe-Forwardingon Tree Growth and Site Productivity:15-Year Results at the Woss Study Site

by Mary-Jane Douglas and Kevin R. Brown

KEYWORDS:Hoe-forwarding,soildisturbance, siteproductivity, forestmanagement.

CITATION:Douglas, M.J. and K.R.Brown. 2009. SoilDisturbance Effects ofHoe-Forwarding onTreeGrowth and SiteProductivity: 15-YearResults atthe WossStudySite.ResearchSection,Coast ForestRegion,MFR,Nanaimo,BC. Extension NoteEN-027.

CONTACTS:•Mary-Jane Douglas,

MSc, PAg, RPFForesol ConsultingLtd., 2037 KellandRd.,BlackCreek, BC,V9J [email protected]

•Kevin R. Brown,PhD, PAg, RPBioKR Brown andAssociates, 4043ZinniaRd., Victoria,BC, V8Z 4W2

EN-027 Pedology March 2009

BRITISH COLUMBIA

Coast Forest Region

1.0 INTRODUCTION

For more than a decade, it has been recognizedthat ground-based harvesting systems disturbforest soils. Compaction and rutting of soils mayultimately affect tree survival and growththrough increased soil density, decreased rootingvolume, and reduced soil aeration and waterpermeability (Heilman 1981; Minore et. al 1969).These effects on tree growth, which may persistfor several decades (Hatchell et al. 1970, Butt1987, Miller et al. 1996), may lead to short- andlong-term reductions in tree growth and forestproductivity. The level of soil disturbance willvary with soil texture, forest floor thickness, andsoil water content at time of harvest (Miller andSirois 1986, Corns 1988). In addition, machinetype, size and operating practices will directlyinfluence the level of disturbance. Concernsabout soil disturbance levels from ground-basedharvesting systems led to the development ofthe “Site Degradation Guidel ines for theVancouver Forest Region” (BC Ministry ofForests 1991).

Long-term data from properly designedexperiments, which could be used to validate soildisturbance guidelines, were lacking at that time.Early attempts had been made to assess longer-term effects on tree productivity throughretrospective studies on previously logged sites(Thompson 1989, 1990; Douglas and Schwab1991). Data from such studies were difficult tointerpret, due to lack of proper experimental

design, limited knowledge of site conditions at thetime of harvest, and, typically, insufficientnumbers of sample trees (Douglas and Schwab1991). Proper assessment of site conditions andtreatments at the time of harvesting, and insubsequent years, is essential.

Hoe-forwarding was introduced to coastal BC inthe late 1980s for use on gently sloping terrain.The system was expected to reduce soil disturbancein comparison to ground-based skidders andbulldozer logging systems by reducing groundpressure, particularly when puncheon (logs anddebris placed under the tracks of the machine)was used. However, the level of soil disturbanceand the actual effects of the hoe-forwardingharvesting system on site productivity wereunknown at the time.

Two benchmark studies were therefore establishedon Vancouver Island in the early 1990s to recordlevels of soil disturbance created by this machine,and to measure tree growth over the longer termas an indication of site productivity. The first trialwas establ ished near Holberg on northernVancouver Island to examine responses of westernhemlock in the CWHvh1 biogeoclimatic variant.The second trial was established near Woss in theCWHmm1 variant to examine responses ofcoastal Douglas-fir. Periodic results from these twotrials have provided site-specific growth responsedata in relation to varying levels of soi ldisturbance. Fifteen-year results from the secondtrial, established near Woss, are reported here.

Research Disciplines: Ecology ~ Geology ~ Geomorphology ~ Hydrology ~ Pedology ~ Silviculture ~ Wildlife


Extension Note EN-027 March 2009 ForestResearch, CoastForestRegion, MFR-2-

2.0 METHODS

2.1 STUDY SITE

The Woss site lies within the CWHmm1 biogeoclimatic variantat an elevation of 370 m. It is representative of the 03: HwCw– salal site series, with minor proportions of 01: HwBa –pipecleaner moss (Green and Klinka 1994). Site topography isrelatively uniform with flat to gently sloping terrain. Soils aresandy loam to loamy sand Orthic Humo-Ferric Podzols,developed from ice-contact, morainal parent materials that aremoderately wel l drained. Coarse fragment content isapproximately 55%, ranging from gravel to large boulders.Thickness of the forest floor at the time of logging averaged 29cm. Under the Forest Practices Code (BC Ministry of Forests1999), this site would have been rated as “moderate to low hazard”for soil compaction and puddling.

The original stand consisted of 40% Douglas-fir (Pseudotsugamenziesii ), 38% western hemlock (Tsuga heter ophyl la), 19%western redcedar (Thuja plicata), and 3% amabilis fir (Abiesamabilis). The understory vegetation consisted of a moderatelydeveloped shrub layer including salal (Gaultheria shallon), dullOregon grape (Mahonia ner vosa), red huckleberry (Vacciniumpar vifolium ) and Alaskan blueberry (V. alaskaense), a poorlydeveloped herb layer with sporadic vanilla leaf (Achlys triphylla ),and a well developed moss layer (Hylo comium spl endens,Eurhynchium oreganum , Rhytidiadelphus loreus, and Rhytidiopsisrobusta).

2.2 EXPERIMENTAL DESIGN

The study area was logged by hoe-forwarding between December1991 and mid-February 1992 at a time when soil water contentwas high. The hoe-forwarding machine used was a KomatsuPC400-5 log loader, weighing approximately 120,000 lb with anominal ground pressure of 11.2 psi. Puncheon was rarelyused on this site. It was originally planned that the site be loggedwith one-pass hoe-forwarding during the summer with the useof puncheon prescribed only “where necessary”. Due tooperational constraints, this site was instead logged in winterunder rather unfavourable, very moist to wet soil conditions.

Study locations were sections of trails established by the hoe-forwarder during operational logging. Fifteen 20-metre stripswere established along the tracked trails (Figure 1). An additional15 control l ines were establ ished in untrafficked areasimmediately adjacent to the trafficked lines.

Soil properties for each treatment line were assessed post-harvest including a determination of mineral soil texture, forestfloor depth, and soil moisture content immediately after logging.No determination of mineral soil bulk density was made onthis site. Soil disturbance was assessed using a similarmethodolog y to Curran and Thompson (1991), withmodifications for puncheon impressions and deposits. Resultsof the disturbance assessment are reported in Douglas andCourtin (2002).

Ten Douglas-fir (Pseudotsuga menziesii) seedlings were to beplanted down the centre of each track (“track”), in betweenthe tracks (“between-track”), and beside the track (“flank”) at2m spacing. A single row of 10 Douglas-fir seedlings was to be

planted along the control. During planting, a mixture of bothDouglas-fir and western redcedar (Thuja plicata) seedlings wasestablished along the treatment lines. However, at least 10Douglas-fir seedlings were identified for each treatment, for atotal of 611 measurement trees across the trial.

2.3 TREE MEASUREMENTSTree height and root collar diameter were assessed at the timeof planting and after the first, third, fifth, and ninth growingseasons (Figures 2, 3 and 4). In Year 15 (Figures 5 and 6),diameters were measured at breast height (DBH; 1.3m) forthe larger trees; root collar diameter was measured for treesless than 1.3 m tall. Tree survival was assessed at eachmeasurement date.

Cumulative growth increments were calculated as the differencebetween height or diameter at planting and later measurementdates. By Year 15, differences in diameter increment were nolonger comparable due to a number of trees less than 1.3 macross the treatments. Therefore, treatment differences involume increment were also assessed. A volume equationdeveloped by Kovats (1977) for coastal Douglas-fir was used.This equation includes a correction factor to account fordifferences in diameter measurement position as shown below:

V=a*Db*Hc*e ((h/H)*d)

Where V = volume in cm3

D = diameter at measurement height h in cmH = total height in cmh = distance from point of germination to point of diametermeasurement in cma = 0.03548b = 1.70435c = 1.38551d = 2.30499e = base of natural logarithms

2.4 FOLIAR ANALYSIS

Foliage was sampled and analyzed to determine treatmentdifferences in foliar contents of N, P, K, Ca, Mg, Al, S, Cu, Zn,Fe, Mn, and B. In each block, one shoot per each of five treeswas collected from each treatment, using the same trees sampledin Year 5, and composited. Severely stressed and dying treeswere not sampled. Samples were confined to current-year first-order (terminal) shoots and were collected from the upper thirdof the crown. On the largest trees, samples were collected atapproximately 4.8 m (maximum height of the pruning pole).

Following collection, samples were stored under refrigeration,then oven-dried at 70oC for a minimum of 48 hours. Needleswere removed, and needle mass and mass of 100 needles weredetermined. Samples were analyzed for elementalconcentrations at the Ministry of Forests and Range analyticallaboratory. Total N and S were determined by micro-Dumascombustion using an automated NCS analyzer. For otherelements, samples were digested in a microwave digestor witha mixture of 30% H2O2 and concentrated HCl and HNO3

(Kalra and Maynard 1991), then analyzed by inductively-coupledargon plasma emission spectrometry (ICAP).



Figure 4. Treatment line H-4 at nine years. Note between-tracktrees (left) track trees (centre) and flank trees (right).

Figure 6. Trees on control line C-5 at 15 years.Figure 5. Treatment line H-4 at 15 years. Note between-tracktrees (left) track trees (centre) and flank trees (right).

Figure 3. Treatment line H-4 at five years. Note between-tracktrees (left) track trees (centre) and flank trees (right).

Figure 2. Treatment line H-4 at three years. Note trees plantedbetween the track (left), on the track (centre) and on the flank (right).

Figure 1. Treatment line H-4soonafterlogging. Note track impressionindicated by dotted lines. (Photo courtesy Alex Inselberg.)

Flank tree

Track tree

Between-track tree

Between-track tree

Between-track tree

Track tree

Track tree

Flank tree

Flank tree

Between-track tree

Track tree

Flank tree

Track



2.5 DATA ANALYSIS

The four treatments (control, track, between track, and flank)were randomly allocated within each of the 15 blocks. Arandomized complete block design was used to test for meandifferences in height and volume growth after 15 growingseasons between treatments levels. The analysis of variancewas carried out using the proc mixed procedure with SAS®statistical software.

To test for significant differences in treatment means, multiplecomparison tests were carried out using a Tukey adjustment toensure the overall Type I error for all treatment comparisonswas less than or equal to 0.05. If the overall treatment p-valuewas not significant (p-value > 0.05), no comparison of treatmentmeans was tested.

Treatment mean needle masses and elemental concentrationswere analyzed by analysis of variance using JMP statisticalsoftware (SAS Institute). Relationships between needle massand elemental concentration were further analyzed bycorrelation (Pearson correlation coefficient) analysis.

3.0 RESULTS AND DISCUSSION

3.1 FIFTEEN-YEAR DOUGLAS-FIR SURVIVAL

Survival of Douglas-fir may have been consistently better onthe control plots over the first 15 years (Table 1). Ninety-twoper cent of the control trees were remaining at Year 15compared with 86 to 88 per cent survival for the other threetreatments. A total of 540 test trees remained in 2007.

Damage by Roosevelt elk (Cervus canadensis r oosevelti) hascontributed to tree mortality during the trial, and was a keyfactor for mortality from 9 to 15 years. These animalsfrequented the trails created by the hoe-forwarder and causeddamage to measurement trees growing along the tracks, alongwith some damage to control trees. Damage consisted of barkstripping, sometimes girdling the tree, or breakage of the crown,leading to re-growth of multiple leaders and poor stem form.However, damage by these animals did not appear to affectoverall treatment differences.

Root disease (Armillaria ostoyae) also contributed to mortalityon this site. Identifying signs were resinosis on the lower stemof measurement trees beginning in Year 5 and the presence ofcharacteristic mycelial fans under the bark (Stefan Zeglan, pers.comm., February 1997). Mortalities due to root rot appearedlimited to one area of the trial, and were more common on thebetween-track treatment. However, the disease may also bepresent on other areas of the trial.

3.2 FIFTEEN-YEARHEIGHT INCREMENT OFDOUGLAS-FIR

Douglas-fir trees growing on the control had significantly betterheight growth in Year 15 (p=0.0432) than those growing onthe tracks (Figure 7). Height growth on the controls was greaterby 31% (0.31 m) relative to the track at Year 5, and by 12%through Years 9 and 15 (0.33, 0.71 m). By Year 9, trees growingon the tracks had become well established, with possible rootexpansion beyond the compacted tracks. Height growth in thebetween-track and flank treatments generally appeared to beslightly less than in controls (Figure 7), but differences werenot statistically significant.

It appears that height growth of the track trees may beimproving in relation to the other treatments over time. AtYear 5, height increment on the track trees was significantlyless than the other three treatments (p<0.001; Figure 7). ByYear 9 only the control and between-track trees had significantlybetter height growth than the track trees (p=0.0141), and after15 years, only the control trees were significantly taller thanthose on the tracks (p=0.0432).

3.3 FIFTEEN-YEAR VOLUME INCREMENTSimilar to height growth, volume increment of Douglas-fir at15 years was significantly better on the control treatment thanon the tracks (p=0.0222; Figure 8). As with height, volumeincrements in the flank and between-track treatments did not

Table 1. Tree survival by year.

a

a

a

b

b

b

ab

a

a

ab

ab

a

0

200

400

600

800

Year 5 Year 9 Year 15

Heigh

tInc

reme

nt(c

m)

Control Track Between Track Flank

Figure 7. Cumulative height increment of Douglas-fir throughfive, nine, and 15 years. Error bars represent standard errorand letters represent differences between treatments withineach consecutive year. Treatments with the same letter arenot significantly different.

Heigh

tInc

rem

ent(

cm)

Year Control Track Between Track FlankTree % of Tree % of Tree % of Tree % of

numbers original numbers original numbers original numbers original1993 172 100 143 100 142 100 154 1001995 165 96 133 93 134 94 146 951997 164 95 130 91 133 94 146 952001 163 95 130 91 132 93 143 932007 158 92 125 87 125 88 132 86

differ from the control or track treatments at 15 years.

Volume increment on the control appears to be increasing overtime in relation to the other three treatments (Figure 8). For thefirst nine years, volume growth of the control trees was slightlylower than those growing between the tracks, and slightly greater(but not significantly so) than those on the track. By Year 15,volume increment of the control trees was 53% larger (7.5 dm3

tree-1, P = 0.022) than those on the track, and slightly larger (butnot significantly so) than the between-track and flank trees.

3.4 FOLIAR ANALYSIS OF DOUGLAS-FIR

After 15 years, needle mass per shoot varied with treatmentand was significantly greater in controls than in the tracks,between tracks, or flanks (Table 2). This was consistent withtreatment rankings for stem height and volume increments over15 years. Needle mass per shoot was positively correlated (P <0.05) with 100-needle mass (r=0.51, n=60) and foliar N (r=0.27) and S (r=0.34) concentrations and negatively correlatedwith foliar P (r=-0.27).

One-hundred-needle masses and foliar elemental concentrationswere generally not affected by treatments after 15 years,although Zn concentrations were slightly higher in the control,and concentrations of N, P, K and B may have been lower onthe between-track treatment than in other treatments. A lackof difference between treatments is not particularly surprising,as roots of trees in adjacent treatments are likely intermingledand now competing for nutrients from the same soil volumes.In contrast, after five years, S was lowest in controls and otherelements were unaffected (Douglas 1998). Fol iar Nconcentrations at Year 15 appear to be deficient (Ballard andCarter 1986), as may be foliar K (Mika and Moore 1990).

Concentrations of N, P, S, Mn, Zn and, especially, K appearedto be lower after 15 years than after five (Douglas 1998). Theapparent changes over time may not be meaningful, given thatdifferent analytical laboratories and procedures were used inthe two sets of analyses. Sampling relatively lower in the crownin larger trees in Year 15 might a lso have affectedconcentrations of some elements.

4.0 SUMMARY AND CONCLUSIONS

Although the soils on this site were rated as moderate to lowhazard for soil compaction and puddling using the “Hazard

ab

a

ab

b

b

b ab

a

a

ab

ab

ab

0

5

10

15

20

25

30

Year 5 Year 9 Year 15

Vol

ume

Incr

emen

t(dm

3tre

e-1

)

Control Track Between Track Flank

Figure 8. Cumulative volume increment of Douglas-firthrough five, nine, and 15 years. Error bars representstandard error and letters represent differences betweentreatments within each consecutive year. Treatments with thesame letter are not signif icantly different.

Table 2. Needle mass and foliar elemental concentrations and elemental ratios after 15 years in relation to treatment. P valuesfor contrasts are not shown if P > 0.05. Abbreviations: C = control, T = track, B = between track, F = flank, NM/S = needle massper shoot, 100NM = mass of 100 needles.



Volu

me

Incre

men

t(dm

3tre

e-1)

g g g kg-1

Trt NM/S 100NM N P K Ca Mg SC 4.6 0.56 11.6 1.6 4.6 2.6 1.0 1.0T 3.6 0.54 11.3 1.5 4.4 2.6 1.0 1.0B 3.7 0.51 11.0 1.4 4.1 2.7 1.0 1.0F 3.8 0.53 11.4 1.6 4.4 2.6 1.0 1.0

P valueTrt 0.003 0.379 0.180 0.116 0.142 0.665 0.216 0.943

C vs TBF <0.001B vs CTF 0.045 0.021 0.036

mg kg-1

Fe B Cu Mn Zn N/P N/S K/NC 42 12 3 337 15 7.7 11.9 0.40T 32 12 3 317 13 7.5 11.7 0.39B 33 11 3 331 13 7.9 11.8 0.37F 34 12 3 309 13 7.4 11.9 0.39

P valueTrt 0.395 0.167 0.592 0.472 0.213 0.597 0.994 0.392

C vs TBF 0.037B vs CTF 0.043

Assessment Keys” (BC Ministry of Forests 1999), it is clearthat trafficking these soils under wet soil conditions has led tosome longer-term consequences for site productivity. To Year15, height growth of Douglas-fir trees growing on theuntrafficked control plots was consistently better than thosegrowing on the tracks. Volume increment of the control trees,initially similar to the track trees to Year 9, was significantlygreater than the track trees by Year 15 (7 dm3 tree-1), when thecontrol had gained a competitive advantage over theunderbrush. Height and volume growth in the between-trackand flank trees were not significantly different to either thecontrol or track trees at Year 15. Therefore, it is apparent thateven medium- to coarse-textured (sandy loam to loamy sand)soils require some protection from the effects of trafficking ifthey are to be logged under wet, winter conditions.

Foliar elemental concentrations indicated nutrient deficienciesin Douglas-fir across the study site after both five and 15 years,suggesting nutrient supply is an inherent limiting factor on thissite. The medium- to coarse-textured soils, in combination withhigh coarse fragment and low soil organic matter contents, areresponsible for this relatively poor inherent nutrient supply.

This research also suggests that tracks created by ground-basedharvesting systems and compacted with increasing levels oftrafficking may be poor planting positions for new seedlings.A recommendation for similar sites where the tracks arecompacted is to utilize undisturbed, between-track or flankpositions to establish future crop trees. Soil compaction alongthese tracks can be identified through difficulty in penetratingthe soil with an ordinary planting shovel.

Soil disturbance results for this site were obtained only for thetracked areas of the treatment, since the intent was to determinethe effects of specific disturbances. This approach does notconsider the allowable limits for soil disturbance across a specificarea or cutblock defined by the previous Forest Practices Code,or now allowable under the Forest Range and Practices Act.Results of a survey by Thompson (1997) showed that eighthoe-forwarding sites surveyed using Forest Practices Codeprocedures were all compliant and within the allowable fiveper cent detrimental disturbance limit set out by the Ministryof Forests at that time.

5.0 MANAGEMENT IMPLICATIONS

Seasonal or weather operating restrictions should also apply tosites rated as having moderate to low compaction and puddlinghazard, i.e., mesic and drier sites with sandy loam to loamysand soils. Hoe-forwarding during wet soil conditions withoutthe use of protective puncheon may result in detrimentaldisturbance, leading to reduced growth and performance ofDouglas-fir or other species over the longer term. The extentof such detrimental effects can be controlled with the use ofprotective puncheon or mats, and by the pattern used duringlogging. In addition, rehabilitation of localized, heavily disturbedareas will also reduce the overall level of detrimental soildisturbance across the cutblock.

6.0 REFERENCES

Ballard, T.M. and R.E. Carter. 1986. Evaluating forest standnutrient status. BC Ministry of Forests, Land ManagementReport No. 20. 60 pp.

BC Ministry of Forests. 1991. Site Degradation Guidelinesfor the Vancouver Forest Region. Vancouver Forest Region.Draft document.

BC Ministry of Forests. 1999. Hazard Assessment Keys forEvaluating Site Sensitivity to Soil Degrading ProcessesGuidebook, 2nd ed, Version 2.1. For. Prac. Br., BC Min.For., Victoria, BC. Forest Practices Code of BritishColumbia Guidebook. 24 pp.

Butt, G. 1987. Effects of skidder compaction on treeproductivity. MacMillan Bloedel Limited, Nanaimo, BC.Unpublished Report. 62 pp.

Corns, I.G.W. 1988. Compaction by forestry equipment andeffects on coniferous seedling growth on four soils in theAlberta foothills. Can. J. For. Res. 18: 75-84.

Curran, M. and S. Thompson, in association with the ForestSite Degradation and Rehabilitation Committee. 1991.Measuring soil disturbance following timber harvesting. BCMinistry of Forests, Land Management Handbook FieldGuide Insert 3.

Douglas, M.J. 1998. Impacts of the hoe-forwarding harvestingsystem on site productivity, five year report, Woss studysite. Unpublished report submitted to FRBC.

Douglas, M.J. and P.J. Courtin. 2002. Impacts of hoe-forwarding on site productivity: nine-year results from theWoss study. Forest Research Extension Note, EN-015Pedology. 7 pp.

Douglas, M.J. and J.W. Schwab. 1991. Retrospective studypertaining to conifer growth on skidroads in the Prince RupertForest Region. Contract report to Ministry of Forests. 25 pp.

Green, R.N. and K. Klinka. 1994. A field guide for siteidentification and interpretation for the Vancouver ForestRegion. Land Management Handbook No. 28. Min. ofForests, Victoria, BC. 285 pp.

Hatchell, G.E., C.W. Ralston, and R.R. Foil. 1970. Soildisturbances in logging: effects of soil characteristics andgrowth of loblolly pine in the Atlantic Coastal Plain. J. For.68: 772- 775.

Heilman, P. 1981. Root penetration of Douglas-fir seedlingsinto compacted soil. Forest Science 47: 660-666.

Kalra, Y.P. and D.G Maynard. 1991. Methods manual forforest soil and plant analysis. For. Can. Inf. Rep. NOR-X-319.

Kovats, M. 1977. Estimating juvenile tree volumes forprovenance and progeny testing. Can. J. For. Res. 7:335-342.

Mika, P.G. and J.A. Moore. 1990. Foliar potassium statusexplains Douglas-fir response to nitrogen fertilization in theinland Northwest, USA. Water, Air, and Soil Poll. 54:477-491.





Miller, J.H. and D.L. Sirois. 1986. Soil disturbance by skylineyarding vs. skidding in a loamy hill forest. Soil Sci. Soc. Am.J. 50: 1579-1583.

Miller, R.E., W. Scott, and J.W. Hazard. 1996. Soil compactionand conifer growth after tractor yarding at three coastalWashington locations. Can. J. For. Res. 26: 225-236.

Minore, D., C.E. Smith, and R.F. Woollard. 1969. Effects ofhigh soil density on seedling root growth of sevennorthwestern tree species. USDA Forest Service, PacificNorthwest Forest and Range Experiment Station, ResearchNote: PNW-112. 6 pp.

Thompson, S.R. 1989. Growth of juvenile lodgepole pine onskidroads and calcareous soils in the MSa and ESSFabiogeoclimatic subzones of southeastern BC. Working plan.BC Ministry of Forests, Research Section, Nelson, BC.

Thompson, S.R. 1990. Growth of juvenile lodgepole pine onskidroads in the MSa and ESSFa biogeoclimatic subzonesof southeastern BC. Preliminary results. Prepared forCrestbrook Forest Industries in co-operation with the BCMinistry of Forests, Research Section, Nelson, BC.

Thompson, S. 1997. Benchmark soil disturbance survey resultsfor the Vancouver Forest Region. Contract Report. 19 pp.

ACKNOWLEDGEMENTSSeveral individuals and organizations have been involved withthis project over the years. Initial funding for this project camefrom the Forest Soil Conservation Research Fund of the BCMinistry of Forests and Range. Bob Green, Terry Rollerson,and Wendy Bergerud provided suggestions for installation ofthe trial. Canadian Forest Products Ltd. (now Western ForestProducts Inc.) cooperated in the trial by providing a suitablesite, and providing assistance during the installation and re-measurement years. Individuals included John Chittick, PatBryant and Rob Woodside, and Holbrook and Dyson Logging.Dr. Terence Lewis carried out the original design and installationof this trial, and has since provided invaluable advice to thestudy. Various other individuals have also contributed assistanceand technical advice including: Roy Vidler, Ian Bercovitz, ChrisBrown, Bill and Bev Herman of Pacific Soil Analysis Inc.,Alex Inselberg, Wendy Kotilla, and Polly Wilson. Paul Courtinwith the Ministry of Forests and Range provided in-kind supportfor field measurements and maintenance as well as report writingand publication over the past 14 years. The 15-yearmeasurements were funded by the Forest Science Programadministered by PricewaterhouseCoopers. The assistance andinput of each of these individuals and organizations is gratefullyacknowledged.

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Soil Disturbance Effects of Hoe-Forwarding on Tree Growth and Site