New Forests20: 213–233, 2000.© 2000Kluwer Academic Publishers. Printed in the Netherlands.

Establishing white spruce in the Boreal White andBlack Spruce ZoneSite preparation trials at Wonowon and Iron Creek, British Columbia

L. BEDFORD1, R.F. SUTTON2,∗, L. STORDEUR3 and M. GRISMER41Forest Practices Branch, British Columbia Ministry of Forests, Victoria, British Columbia,Canada V8W 9C2;2Natural Resources Canada, Canadian Forest Service, Great LakesForestry Centre, Sault Ste. Marie, Ontario, Canada P6A 5M7;35266 Old West SaanichRoad, Victoria, British Columbia, Canada V8X 3X1;4670 Sand Pines Drive, Comox, BritishColumbia, Canada V9M 3V1 (∗author for correspondence)

Received 1 April 1998; accepted 26 March 2000

Key words: blading, disk trenching, fertilization, herbicide, mounding, patch scarification,plantation establishment, plowing

Abstract. Two trials (“Wonowon” and “Iron Creek”) in the Prince George Forest Region ofinterior British Columbia were begun in the mid 1980s to evaluate site preparation treatmentsfor establishing white spruce (Picea glauca[Moench] Voss) in the Boreal White and BlackSpruce biogeoclimatic zone. The 14 treatments (9 or 10 per trial) were: [B.C.] Ministry,Sinkkila, and Bracke mounds; Bracke mounds manually supplemented with 20-, 14-, or 6-cm cappings of mineral soil; fertilized Sinkkila mounds; Bracke patches; fertilized Brackepatches; bladed strips; plowed ground; herbicide; and untreated controls, separately with bothstandard and nominally superior “alternate” planting stock. With minor aberrations, each trialconsists of 5 randomized complete blocks each with one 80-tree plot per treatment; plantingwas in spring, 1984 at Wonowon, 1987 at Iron Creek. All trees in mounding treatments andthe inner 48 trees in other plots were monitored for performance through 1998 at Wonowon,1996 at Iron Creek. The herbicide and plowing treatments, and mounds capped thickly enoughwith mineral soil to inhibit weed regrowth, were clearly superior to others. In the moundingtreatments at Wonowon, survival rate increased with capping thickness, but, while the 14 and20 cm cappings were best, significant differences among them were few after 15 growingseasons. In both trials, patch scarification gave poorer results than did planting without sitepreparation.

Introduction

Problems of regenerating unstocked backlog forest sites in British Columbiawere investigated in a series of trials begun in the 1970s to evaluate sitepreparation techniques and planting stock types. Efforts to reclaim thebacklog intensified in the mid-1980s, stimulated by funding from the first

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Canada/British Columbia Forest Resource Development Agreement (FRDA)and the development and introduction of previously unavailable mechan-ical site preparation equipment. Until then, the bulldozer blade had beenthe only feasible choice, since the use of light equipment was commonlyprecluded by fallen trees, some> 1 m dbh. Blading site preparation oftenachieved early survival of 80% or more in plantings on exposed mineral soil,and, when timed to take advantage of a good seed crop, blading generallysecured acceptable stocking (McMinn and Dobbs 1972).1 But the treatmentwas highly site-specific in effectiveness, and initial promise was fulfilled onlyon a limited range of sites.

Elevated temperatures in mineral soil exposed by site preparation weredocumented by Dobbs and McMinn (1973), who recognized the importanceof this for tree seedling development.

Further attempts to improve outplant performance followed two mainlines of investigation: mixing rather than removing the upper soil layersduring site preparation in order to conserve nutrients within root-reach ofyoung outplants (cf. McMinn 1976); and the use of planting stock betterable than standard stock to overcome competing vegetation (cf. Dobbs 1976).Site preparation treatments included mixing of forest floor with underlyingmineral soil, “inverting” of forest floor organic matter “capped” with mineralsoil, patch scarification, and blade scarification (McMinn and Van Eerden,personal communication, 1977).2

Studies at Wonowon and Iron Creek (Table 1) were among those begunin the 1980s to evaluate the biological effectiveness of a variety of sitepreparation equipment and planting stock options for backlog reforestation inthe Boreal White and Black Spruce (BWBS) biogeoclimatic zone of BritishColumbia (Bedford and McMinn 1990). Performance (survival rates andgrowth) of outplanted spruce after 15 growing seasons at Wonowon and 10growing seasons at Iron Creek, by treatment, is documented here.

Materials and methods

Experimental design

A randomized complete block design, with one 80-tree, 30-× 50-m, plotper treatment in each of five blocks, was adopted at each of two locations,Wonowon and Iron Creek (Figure 1). Aberrations were minor; treatment W6(see below) was replicated only four times, and treatment IC10 was applied inonly two blocks, albeit with double-sized (160-tree) plots. Thus, fewer blockswere available for statistical comparisons between treatment W6 and other

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Table 1. Features of Wonowon and Iron Creek experimentation in the BWBS Biogeoclimatic Zone (DeLong et al. 1990) of British Columbia.

Factor Wonowon Iron Creek

Latitude 56◦37′N. 56◦37′N.

Longitude 121◦49′W. 122◦18′W.

Elevation (m) 900 (mean). 820 (mean).

Biogeoclimatic BWBSmw1 BWBSmw1, bordering wk2 subzone.

(BEC) zone Boreal White & Black Spruce, Peace moist warm Boreal White & Black Spruce, Peace moist warm

variant. Dominant site series 01 (Sw At-Step moss) variant. Dominant site series 06 (Sw-Currant-Bluebells);

and 06 (Sw-Currant-Bluebells); 15–18 site 18 site index for white spruce (m @ 50 yr bh).

index for white spruce (m @ 50 yr bh).

BEC Climate Precipitation mean annual 485 mm, mean May–Sept Same general BEC climate as Wonowon, but moister, and

290 mm. Temperature mean annual 1.1◦C. slightly cooler and may be more variable.

Snowfall mean annual 190 cm. Frost-free period

mean annual 150 days.

Topography 0–5% slope, N to NE. Gently sloping (5%) fan.

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Table 1. Continued.

Factor Wonowon Iron Creek

Soils Brunisolic, Orthic, and Dark Gray Luvisols on Luvisols on lacustrine/lacustro-till, fine

relatively stone-free silt loam lacustro-morainic textured;< 5% coarse fraction; mostly

till; surface soils mostly silty clay loam, some clay loam with some silty clay loam.

clay loam; B horizons, compact clay loam to

silty clay loam, at 15–30 cm.

Drainage Predominantly mesic to subhygric in convex Mostly subhygric, with some

areas, hygric in depressions. hygric and mesic areas.

Organic layer Moders, mostly 4–6 cm thick,< 15 cm in wettest areas. Moders, mostly 7–18 thick,< 50 cm in wet spots.

Rooting depth 15–30 cm. 9–25 cm.

History 120-year-old stands, partly lodgepole pine/white spruce Stand of white spruce, lodgepole pine,

c. 280 m3/ha, partly white spruce/aspen with trembling aspen, and balsam poplar

some lodgepole pine c. 140 m3/ha conifers, clearcut selectively logged for large spruce in 1966,

1977 leaving some aspen; NSR regen survey clearcut 1977, sheared and windrowed with

1982 (Menzies1 personal communication, 1984). little exposure of soil, winter 1985/6.

1 Menzies, D, 1984. Letter dated 22 June to R.G. McMinn. Canadian Forest Products Ltd., Fort St. John Division, R.R.#1, Site 13, Comp. 2,Fort St. John, B.C. V1J 4M6.

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Figure 1. Layout of trials at Wonowon and Iron Creek, British Columbia.

treatments at Wonowon and between treatment IC10 and other treatments atIron Creek. Treatments were allocated at random within blocks.

Both trials included mounding investigations. At Wonowon, the focus wason the thickness of the mineral soil cap on overturned forest floor overlyinginsitu forest floor. At Iron Creek, machines of three different designs producedmounds that differed in various ways including the thickness of mineralsoil cap. The proportion of mounds capped by 10 cm or more of mineralsoil varied between 6 and 62%, with Bracke mounds having significantlythinner, and Ministry mounds having significantly thicker, caps comparedwith Sinkkila mounds (Hedin 1987a).

Ancillary investigations on root system development, microclimate, andthe residual effect of herbicide, amplify the results reported here. AtWonowon, Heineman et al. (1999) examined root system development of

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12-year-old white spruce in two of the site preparation treatments. Gold-stein (personal communication, 1998)3 determined soil growing degree days(GDD, base 5◦C) at 10 cm and at the interface between the forest floor andunderlying predominantly mineral horizon at Iron Creek in 1988, 1989, and1990.4 In July 1996, Boateng et al. (2000) assessed the residual effect ofVisionr herbicide treatment on plant species diversity both at Wonowon andIron Creek.

The treatments and planting stock

Information distilled from Parolin et al. (1981), Hedin (1987a,b), Hesse(personal communication, 1986),5 Coates and Haeussler (1987), Gibbard andSutherland (1987), Bedford and McMinn (1990), and McMinn et al. (personalcommunication, 1990)6 characterises the sites (Table 1).

Wonowon (Treatments W1 through W9)The treatments here were applied to a site occupied by dense, well establishedvegetation; unlike the Iron Creek trial, no preliminary shearing was carriedout at Wonowon. Logistical difficulties delayed completion of some sitepreparation until shortly before planting, a factor, neither formally included,nor amenable to statistical evaluation, in the trial.

W1. Untreated control. Bareroot white spruce of the then standard BritishColumbia 2 + 1 stock type, seedlot 4345, were planted without site prepara-tion. Excepting treatment W2, all treatments at Wonowon were planted withthe standard stock.

W2. Alternate stock. White spruce 1P + 2, larger than the standard stock, butof the same seedlot, were planted without site preparation.

W3. Herbicide. After spruce budset and hardening, Visionr was appliedpost-planting in early September 1984 at the high experimental rate of 5 kga.i./ha by backpack sprayer to patches about 1 m in radius centered on each ofthe 48 monitored outplants per plot, i.e., about one-third of the surface areaof the plot occupied by the monitored trees received herbicide. The sprucewere not protected from the overspray other than by incidental shielding bywell developed competition already present. Any damage to the spruce fromthe herbicide would have been indistinguishable from winter kill, but onlymonitoring common to all treatments was undertaken. By the second growingseason, however, virtual elimination of competition was reported.

W4. Bracke patcheswere produced in August 1983 by a Bracke Mounderused as a Bracke Scarifier, i.e., with the mounding shovels disconnected.

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W5. Bracke moundswere produced in August 1983 by the 4-tined mattockwheels of an early version of the Bracke Mounder, the shovels of whichcould not be raised enough to avoid spreading the newly made mounds. TheMounder was towed by a D7 tractor fitted with a front-mounted Beals V-bladeto part moderately heavy slash and relatively large stumps, but otherwise theforest floor was disturbed as little as possible. Made in a single pass, themounds were quite variable, with mineral soil cappings estimated to averageonly about 2 cm thick.

W6–W8.Supplemented Bracke mounds. Mounds made as in W5 were manu-ally supplemented with mineral soil to increase cap thickness by 6- (W6), 14-(W7), and 20-cm (W8).

W9. Blade scarificationof strips was carried out in August 1983 with a BealsV-blade mounted on a D7 prime mover; removal of the forest floor and Ah

layer exposed silty clay mineral soil. Scarification was intermittently discon-tinuous, where, for instance, the centrally-mounted “stinger” had ridden overstumps and debris.

Iron Creek (Treatments IC1 through IC10)The Iron Creek site was sheared and windrowed just over a year prior toplanting, and, although vegetation quickly reestablished itself, the plantedstock here faced much less competition than did the outplants at Wonowon.

IC1. Untreated controls. White spruce of the then standard British Columbia1 + 0 PSB 313 planting stock, seedlot 2665, were planted without sitepreparation.7

IC2. Alternate planting stock. Here 1 + 0 PSB 211 lodgepole pine wereplanted without site preparation. This stock was heavily browsed and is notfurther considered here.

IC3. Herbicide. Visionr was applied in ideal conditions on 21 August 1986as a pre-planting treatment with 2.5 kg a.i./ha broadcast spray over the wholeof each plot.

IC4. Bracke patcheswere produced in July 1986 by a Bracke Scarifier fittedwith 3-tined mattock wheels.

IC5. Bracke patches + fertilizer. Patches were prepared as in treatment IC4,then fertilized with 30 g of 26-week 18-6-10 Osmocoter sprinkled over a15-cm radius around each seedling immediately after planting.

IC6. Sinkkila moundswere prepared in July 1986 in a single-pass operationby a Sinkkila HMF Scarifier mounted on a John Deere 740A line-skidder;24% of the mounds were capped by 3–5 cm, 26% by 6–9 cm, and 18% by 10–

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13 cm of mineral soil, and 14% by 5 cm or more of well-decomposed organicmatter; the other mounds were more thinly capped, but all were planted.

IC7. Sinkkila mounds + fertilizer. Mounds prepared as in treatment IC6 werefertilized with 30 g of 26-week 18-6-10 Osmocoter as in treatment IC5.

IC8. Bracke mounds(c. 6 cm mineral soil capping) were produced in July1986 by a Bracke Mounder, better able than the early version (see W5, above)to lift its mounding shovels clear of newly made mounds, equipped with a 3-tined mattock wheel and towed by a Clark 668 skidder. By the same criteriaapplied in treatment IC6, 29% of the mounds in IC8 had cappings thinnerthan 3 cm of mineral soil or 5 cm of well decomposed organic matter. Allmounds were planted.

IC9.Ministry moundswere made by the [B.C.] Ministry [of Forests] Mounderin July 1986 in a single-pass operation. The digging buckets mounted onthe ripper parallelogram of the prototype mounder were hydraulically driveninto the ground during forward motion of the D7 prime mover then raisedand flipped to deposit the overturned mineral mound. Development of theMinistry Mounder was subsequently discontinued, but similar mounds aremade by excavators, the current equipment of choice for mounding in BritishColumbia. By the IC6 criteria, 21% of mounds were thinly capped (< 3 cmmineral,< 5 cm decomposed organic matter). Averaging 36 cm high, theyremained “tombstone-like” for at least 3 years if undisturbed by planting.

IC10. Breaking plow bermswere prepared in July 1986 by a land-breakingplow pulled by a D8 tractor; each of the three mouldboards was 66 cm wideand set at a maximum depth of 36 cm. The furrow slices, upside-down side-by-side, buried inverted forest floor beneath mineral soil. One block was toowet to plow. In two other blocks a poorly drained central strip was not treated,but plowing on either side provided sufficient area for planting.

Planting

Spring planting at 3-× 3-m spacing at Wonowon in 1984 and Iron Creekin 1987 followed mechanical site preparation. On mounds at Wonowon, theattempt was made to plant deeply enough into the center of the mound tojuxtapose seedling roots and inverted organic matter at the base of the mound;at least 5 cm, and in some cases “much more”, of the stem was buried. SomeJ-rooting occurred. At Iron Creek, planting was typically into the sloped sideof the mound (Hedin 1989). In the patches, stock was planted just below thehinge. Other planting was in boot-screefed spots after minimal preparationof the immediate planting spot by the removal of loose surficial forest floormaterial by scuffing with the planter’s boot.

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Assessment of planted stock performance

The inner 48 trees in treatments W3 and IC6-9, and otherwise all trees, ineach plot were monitored almost every year for total height, annual heightincrement, stem diameter measured at the lowest point on the stem two fingersabove the forest floor, and a rating of condition that included assessmentsof the viability of buds on the leading shoot and uppermost whorl, identi-fication of agents of damage, and a gross descriptor of overall tree quality(“good”, “moderate”, “poor”, “almost dead”, and “dead”). Stem volumeswere calculated using the right-cone formula.

Data analysis and methodology

The latest data available (15th-year for Wonowon, and 10th-year for IronCreek) for each dependent variable were subjected to classical anova (SASInstitute 1994) and Duncan’s Multiple Range Test. Possible confounding ofblock and treatment effects by the minor aberrations in experimental designwas assessed by analyzing with and without portions of the data. Wonowondata were analyzed both with and without Block B, in which treatment W6is not replicated. Iron Creek data were analyzed with and without breakingplow data, which lack full replication.

Results

Survival

Rates of white spruce survival (Table 2) after 15 growing seasons at Wonowonwere highest in the three supplemented mounding treatments, (74–64%), andleast in the blading (27%) and patch scarification (38%) treatments, whichaccentuated difficulties faced by root system development. Few spruce diedat Wonowon after 10 growing seasons. Higher survival rates were obtainedat Iron Creek, where 10th-year survival reached 95% in the breaking plowtreatment and 93% on Ministry mounds. Both of these treatments providedloosened, easily penetrable soil in the rooting zone, but survival was also 93%in the herbicide treatment, which did not involve soil cultivation. Favoringhigher rates of survival at Iron Creek compared with Wonowon were thepreliminary shearing prior to the application of treatments and the use of abetter-performing stock type.

In both trials, survival rate and total height at the end of the observa-tion period show modest positive correlation (Figure 2), with r2s of 0.57at Wonowon and 0.54 at Iron Creek. In each trial, the treatment having thehighest survival also had greatest mean height growth.

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Table 2. Performance of white spruce at Wonowon after 10 and 15 growing seasons: survival,mean total height, mean annual height increment, and mean stem volume, by treatment.

Treatment Survival Height Increment Volume

Yr 10 Yr 15 Yr 10 Yr 15 Yr 10 Yr 15 Yr 10 Yr 15

(%) (%) (cm) (cm) (cm) (cm) (cm3) (cm3)

Untreated 55 bc1 52 c 108 c 249 b 15 c 38 bc 106 d 1313 d

Large stock 60 ab 58 bc 115 c 264 b 16 bc 39 abc 150 cd 1700 d

Herbicide 61 abc 61abc 157 ab 344 a 25 a 47 ab 386 a 4071 ab

Bracke patch 41 c 38 d 92 c 217 b 11 c 31 c 83 d 1202 d

Bracke mound2 56 bc 56 bc 138 b 344 a 21 ab 50 a 241 bc 3287 ab

Bracke mound +6cm 64 ab 64 abc 148 ab 337 a 22 ab 50a 264 b 2991 bc

Bracke mound +14cm 70 ab 69 ab 165 a 362 a 25 a 47 ab 383 a 3990 ab

Bracke mound +20cm 74 a 74 a 163 a 363 a 25 a 49 ab 392 a 4528 a

Blading 28 d 27 e 115 c 267 b 16 bc 38 bc 137 d 1830 cd

1 Within columns, values followed by the same letter do not differ significantly (P 0.05)by Duncan’s Multiple Range Test, determined on transformed values; actual survival ratesshown.2 Note the differences between the Bracke mound treatments, W5 here and IC8 at Iron Creek.

Figure 2. Relationship between mean total height and survival after 15 growing seasons atWonowon and 10 growing seasons at Iron Creek; within sites, letters indicate the significance(P 0.05) of differences in survival among treatments, determined by Duncan’s Multiple Rangetest.

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Table 3. Performance of white spruce at Iron Creek after 10 growing seasons:survival, mean total height, mean annual height increment, and mean stemvolume, by treatment.

Treatment Survival Height Increment Volume

(%) (cm) (cm) (cm3)

Untreated 83 abc1 149 cd 22 cd 307 cd

Herbicide 93 ab 201 ab 32 ab 840 ab

Bracke patch 81 bc 123 d 19 de 194 d

Bracke patch + fertilizer 91 ab 160 bcd 26 bcd 351 cd

Sinkkila mound 84 abc 181 bc 28 bf 579 bc

Sinkkila mound + fertilizer 84 abc 186 bf 30 abc 621 bc

Bracke mound2 89 ab 190 abc 29 abc 577 bc

Ministry mound 92 ab 200 ab 32 ab 778 ab

Breaking plow 95 a 230 a 38 a 1050 a

1 Within columns, values followed by the same letter do not differ significantly(P 0.05) by Duncan’s Multiple Range Test.2 Note the differences between the Bracke mound treatments, IC8 here and W5at Wonowon.

Growth

Mean total heights of white spruce after 10 growing seasons were 34 and 38%greater at Iron Creek than at Wonowon in the two treatments that are mostclosely comparable between the two trials, Bracke patch and untreated control(Table 3). In those same two treatments, current 10th-year height increments,too, were greater at Iron Creek than at Wonowon, by 73% in the Bracke patchand 47% in the untreated control. Growth at Iron Creek can be presumed tohave responded to the same factors that benefited survival. Each of the quitedifferent herbicide treatments in the two trials are giving excellent results.As well, the successs of mounding is obvious. Mounds with supplementarycappings of 14 or 20 cm have given best and virtually identical results, butquite good results are being obtained even from thinner cappings. The greatest15th-year annual height increment in any (not just mounding) treatment atWonowon, for instance, occurs in Bracke mounds capped with 6 cm or lessmineral soil. The best all-round performance, including survival, however,has been secured by the breaking plow treatment at Iron Creek.

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Discussion

Beginning with the least disruptive treatment, we discuss treatments ofincreasing site impact.

Performance with no site preparation (other than preliminary shearing)

Low first-year survival (78%) among standard (bareroot) white spruce atWonowon presaged further losses that reduced survival to 61% within fourgrowing seasons. More so than containerized stock, bareroot stock is subjectto reduced water conductance on transplanting (Grossnickle and Blake 1987),especially at low soil temperature (Sutton 1991), which would tend toincrease the danger of winterkill of shoots, especially before newly intro-duced root systems have adjusted to their new situations. A 6% differential insurvival in favor of larger alternate stock at Wonowon compared with standardstock at the end of the first growing season, was still in evidence, but not signi-ficant, after 15 growing seasons. These results from single stock lots cannotsupport firm conclusions, but the somewhat higher survival rate of some-what larger planting stock planted directly into dense herbaceous vegetationaccords with expectation. While these indications suggest some potential forusing larger planting stock to improve early seedling performance, substan-tial mortality is probably unavoidable among stock planted directly into wellestablished competing vegetation. After 15 growing seasons, annual heightincrements in the two treatments were virtually identical, and the 15 cmdifferential in mean total height was not significant.

Survival rates at Iron Creek similarly reflect difficulties experienced byyoung outplants on backlog sites in the absence of sufficient ameliorative sitepreparation or tending. Tenth-year survival rates for standard (plug) stock atIron Creek, for instance, show an upward trend with increasing ameliorationadditional to the preliminary shearing and windrowing common to all treat-ments. This resembles the pattern of survival in Brand’s (1991) 2-year studyof survival among white spruce planted into undisturbed forest floor amongseveral other treatments that reduced the layer of organic insulation.

At Wonowon, substantial differentials in annual height increment betweenthe untreated control and the best treatments narrowed somewhat in thelast half decade. All in all, the superior performance of white spruce insome of the other treatments compared with the untreated control is perhapsless remarkable than the fact that the modest performance of the latter wasachieved without site preparation.

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Herbicidal site preparation

The glyphosate treatments in the Wonowon and Iron Creek site prepara-tion trials are among the earliest and best replicated in interior BritishColumbia. Boateng et al. (2000), surveying the vegetation in the herbi-cide and untreated control treatments at Wonowon and Iron Creek in July1996, determined that the Shannon-Wiener and Simpson indexes indicatedno adverse effect of glyphosate treatments on the diversity of vascular plantspecies and community structure 10 and 12 years after application. Similarresults were reported earlier from Ontario (Sutton 1993). Both the post-planting (Wonowon) and pre-planting (Iron Creek) treatments gave resultsnot differing significantly from the best of the mechanical site preparationtreatments.

At Wonowon, initial mortality was high after planting directly into densecompetition. Also, subsequent exposure of the spruces in bared patchescreated by application of the rather high rate of herbicide probably resulted infurther loss among weakened trees. Certainly, the benefits to the planted stockwhen relieved of competing vegetation were not immediately forthcoming inthese circumstances. But, while the bared patches persisted for several years,the strength of the positive response of white spruce to the treatment becameapparent, and by July 1996 the significantly larger spruce in the treatedpatches than in the untreated control provided the only visual distinctionbetween the two treatments (Boateng et al. 2000). After 15 growing seasons,survival (61%), mean stem volume, and current annual height increment,were not significantly inferior to the best of the other treatments. Similarresponses to preplant herbicide treatment were obtained by Harper et al.(1997) in a nearby trial, in which white spruce, 12 years after planting inthe glyphosate and hexazinone treatments, were 3.5 and 3.4 times larger inmean stem volume, respectively, than were the controls. At Iron Creek after10 growing seasons, white spruce in the herbicide treatment applied as sitepreparation prior to planting had more than twice the mean stem volume and11% higher survival than control trees. Letchford and Hawkins (1996), too,reported 10-year results from a study in the Prince George area of BritishColumbia in which white spruce were 84% larger in the herbicide treat-ment than the untreated control and had 13% higher survival; herbicide sitepreparation was the most cost-effective of the treatments investigated. Theeffectiveness of the technique, and its minimal environmental impact, shouldencourage the forest manager to consider such options.

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Patch scarification

At Wonowon, survival in this treatment declined from 58% at the end of thefirst growing season to 38% after 15 growing seasons, and mean growth wasless than in any of the other treatments. The poor performance is attributableat least in part to the inhospitability to seedling root systems of micrositessubject to flooding. At Iron Creek, too, spruce growth after Bracke patch sitepreparation was less than in any other treatment. Soil GDD, base 5◦C at10 cm depth, averaged 96% of the untreated control during the 1988/90 periodof observation, and soil moisture tension (measured only in 1990) neverexceeded –100 J kg−1 (Goldstein 1998, idem). After 10 growing seasons,height, diameter, and volume were significantly lower than in any of themounding, herbicide, and breaking plow treatments, and survival was nohigher than in the untreated control.

Fertilization

Response of outplants to an application of fertilizer sprinkled around themonto the surface of Bracke and Sinkkila mounds at Iron Creek was muted.But, in the Bracke patch treatment, the 10th-year differentials in favor offertilization (survival rate 10%, and total height 37 cm) suggest rectificationof a nutritional disadvantage caused by the treatment in the absence of fertil-ization. Similarly, in the Sub-Boreal Spruce Zone of British Columbia, Brand(1991) found after two growing seasons that the response of interior spruceto fertilization was greatest in scarified plots from which organic matter,containing much of the nutrient capital, had been displaced.

Except in remediation of severe single-nutrient deficiencies, fertilizationof crop trees in young plantations must overcome two major difficultiesbefore it can produce a positive growth response. First, anylimiting constraintmust be relieved directly or indirectly. Secondly, the crop must benefit fromfertilization more than does the competing vegetation. Also, too much fertil-izer causes direct injury, and, commonly, a nutrient deficiency is created oraggravated by the application of nutrients other than those that are limiting(Sutton 1968). Brand (1991) found that second-year biomass, but not height,of interior spruce was significantly increased by slow-release fertilizationcomparable with fertilization in the present study, but results from operationaltrials of establishment fertilization have generally been mixed (Brockley1988). Negative responses to fertilization are probably under-reported in theliterature. Positive responses are commonly unspectacular, as in the presenttrial.

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Mounding

The generally positive response to mounding site preparation is in part predi-cated on increased rooting-zone temperatures. Mound type is one of manyfactors influencing soil temperature relations (von der Gönna 1989). At IronCreek, temperatures and diurnal fluctuations were greater in Ministry moundsthan in Sinkkila and Bracke mounds. Goldstein (1998, idem) found higherlevels of growing-degree days (base 5◦C, 10 cm depth) in the Ministry moundtreatment in each of the 3 years measured than in the Bracke mound, Sinkkilamound, and breaking plow treatments, which were next warmest and similarto one another. The Bracke patch and control treatments had fewest GDD.Through the 1988/1990 period of observation, soil GDD averaged 155% and128% of the untreated control in the Ministry mound and Bracke moundtreatments, respectively. Spruce performance roughly paralleled this GDDdistribution, but the relationship is tenuous.

To capitalize on warming in the rooting-zone, a seedling must access suffi-cient available moisture. The warmest mounds at Iron Creek were also thedriest, at least at 10 cm depth; in 1990, for instance, the moisture stress (–2700J kg−1) developed by August 8 at 10 cm depth in Ministry mounds would havejeopardized survival had deep planting not been used in anticipation. Planting5–10 cm deeper than normal greatly reduced water stress among outplantsplanted on inverted humus mounds in Sweden (Örlander et al. 1990). Cellenlargement and cell division are generally considered to begin to slow downat –600 J kg−1 and to cease at about –1500 J kg−1 (Hsaio 1973), the latterlevel just exceeded in the Bracke mound treatment during the 1990 growingseason. Neither the control nor the Bracke patch treatments approached theselimiting soil moisture deficits in 1990.

An obvious but no less important benefit of mounding is the reducedsusceptibility of outplantings to seasonal flooding on poorly drained fine-textured soils.

Contrary to earlier unpublished reports that few roots of 10-year-old treesoccurred in the mineral caps of mounds, with prolific rooting confined tothe underlying inverted organic matter, Heineman et al. (1999) at Wonowonfound the structural (main) lateral roots of 12-year-old spruce occurred3 to 5 cm below the surface, independently of substrate, in both treat-ments examined, i.e., Bracke + 14 cm mounds and the untreated control.More than twice as many roots exited mounds than extended beyond 50-cm from control trees, and their total cross-sectional area was five timesgreater. Mean depths were similar, and the main lateral roots occurredmainlyin the mineral cap of mounds until exiting the perimeter. Root systemsymmetry was similar in both treatments. Depth of rooting in mounds mightbe a function of mound maturation and the development of increasingly

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hospitable conditions for root growth in the surface layer of revegetatingmounds.

At Wonowon white spruce has responded well to mounding site prepara-tion. Thick cappings of mineral soil gave early indications of superiority overtreatments with thinner cappings, and a strong (r2 = 0.95) positive linear rela-tionship between survival and thickness of mineral soil capping on Brackemounds was still evident after 15 growing seasons. Mounds supplementedwith either 20 or 14 cm of mineral soil gave very similar excellent growthof spruce, but performance on Bracke mounds capped with 6 cm or less ofmineral soil improved relative to that on the more thickly capped moundsbetween the 10th and 15th growing seasons, as differences between the thickvs. thin capping treatments became largely insignificant, notwithstanding stillsizable differentials.

In another study with PSB 313 white spruce planted at standard depth(“to the level of the root collar”) in the Sub-Boreal Spruce Zone of west-central British Columbia (Macadam and Bedford 1998), a mound cappingdepth of 20 cm gave significantly greater seedling height (17%) and diameter(22%) after 8 growing seasons than did similar mounds with thinner (12 cm)cappings; trees planted 6 cm deeper (burying the lowermost branches) did notbenefit from the thicker capping, for in addition to increasing survival rates,deep planting gave consistent, albeit not statistically significant, increasesin height growth, particularly in mounds with 12-cm cappings where theincrease averaged 15% compared with standard planting. Also in the Sub-Boreal Spruce Zone of British Columbia, Hawkins et al. (1995) found that10th-year height, ground-level stem diameter, and stem volume were alllarger in spruce planted on mounds capped with 24 cm of mineral soil thanon mounds with cappings of 12 and 6 cm. Differences were non-significant,and the 12 and 6 cm mounds gave virtually identical performance; survivalafter 10 years was 93–97% in the capped mounds compared with 34% in thecontrol.

Compared with the blading, patch scarification, and no site preparationtreatments, small, thinly capped mounds, such as the unsupplemented Brackemound and the +6 cm supplemented cap treatments at Wonowon, promoted asignificant growth response in spruce over 15 growing seasons.

At Iron Creek after 10 years, white spruce in the Bracke mound treatmenthad a mean stem volume little more than half that in the best (plow) treatment;the 6 cm average capping thickness in the Bracke mound treatment was lesseffective than the Ministry mounds here, but the differences between thosetreatments are less than might be expected; widespread winterkill occurred onexposed outplants, which were particularly vulnerable to such injury duringtheir first winter after planting before root systems had fully adjusted. Few

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trees on mounds escaped damage. Certainly, the superiority of the Ministrymound treatment compared with the Bracke mound after 10 years (e.g., 10 cmin total height, 3% in survival) is modest and not significant.

Bracke mounds at Iron Creek might have been even more effective hadcapping thickness been greater or less variable. However, while a cappingthickness of at least 12 to 14 cm is probably optimum in most cases, the depthand character of the forest floor, and soil factors, such as texture, structure,coarse fragment content, and hydrology, will influence the results (Macadamand Bedford 1998).

Plowing

Breaking plow site preparation clearly gave better growth and survival thanany other treatment at Iron Creek. Plowing ameliorates two important factorscommonly constraining the growth of young outplants in boreal regions:low temperature in the rooting zone, and competition from other vegetation.Modest increases in soil temperature, less than those in the mounding treat-ments, occurred through the 1988/1990 period of observation; soil GDD (base5 ◦C at 10 cm depth) averaged 116% of the untreated control. During the1990 growing season, soil moisture tension levels, very similar to those inthe Bracke mound treatment, marginally exceeded levels thought to inhibitgrowth (Hsaio 1973), but were much lower than levels in the Ministrymounds.

Complete plowing, as in this trial, buries the pre-existing vegetation anddetrital organic matter, and increases pore space. Vegetation control hereoutlasted excellent intial control by mounding, where competition was over-topping and side-shading mound-planted spruce within 10 years. Tillagemarkedly reduced the frostiness of a weedy site at Eberswalde, Germany,(Geiger and Fritzsche 1940), and, while up to 35% of the spruce in sometreatments at Iron Creek were damaged by frost during the first growingseason, only 1% of the outplants in the breaking plow treatment were sodamaged (Bedford and McMinn 1990), presumably saved by re-radiationfrom the exposed mineral soil.

Blading

Blade site preparation at Wonowon gave poor results. Heavy soil, impededdrainage, blading, and spruce are ill suited companions. Mortality was high(70% within 6 years), a product of severe frost heaving, overtopping byalder (AlnusL. sp.), and smothering of seedlings by vegetation encroachingfrom the edges of the bladed strips. Growth differed insignificantly fromthe untreated control. Many seedlings, although planted close to the edge

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of the bladed strip, where fertility may be unimpaired or even augmented,were chlorotic for some years, possibly as much a reflection of root damagefrom heaving as a response to ponding and the loss of the upper, relativelyfertile and better-structured soil layers. In this instance, site preparationwas counter-productive, especially as only half as many trees survived inthe bladed treatment as in the untreated control. In another study, in theSub-Boreal Spruce Zone of B.C., survival after two growing seasons wassignificantly higher after blading than without site preparation (Brand 1991);removal of the forest floor increased the soil GDD (base 0◦C averaged at2 and10 cm depths) by about 50% in each of the first two growing seasons.Also in the Sub-Boreal Spruce Zone of central B.C., Bulmer et al. (1998)found significantly (P 0.001) greater mean internode length for the 5 yearsabove breast height among white spruce on coarse-textured glaciofluvial sitesafter bladed than burn site preparation. Without site preparation, too fewtrees survived for evaluation. Bulmer et al., while noting that, even on soilsof coarse texture, blading had not reduced growth relative to burning afterapproximately 15 years, also cautioned that the cumulative effects of nutrientremovals on productivity might yet appear in the longer term. Even 20 yearsafter severe blading site preparation on a mesic clay loam in the Riding Moun-tain of Manitoba, the growth of white spruce was still strongly depressed(Ball 1990). In the short term, flooding and heaving on fine-textured soils,and, in the medium term, competition from untended vegetation, wouldseem to be more immediate if not more pressing problems for white spruceestablishment.

Conclusions

Treatments to which outplanted white spruce responded well whereverapplied were: plowing, herbicide, and mounding, with inverted organic mattercapped thickly enough with mineral soil to inhibit weed regrowth. Moundssupplemented with 14 cm of mineral soil gave results as good as those with20 cm supplements. Thinner cappings of mineral soil also gave quite goodresults, though with lower survival, especially when less than 6 cm. Bladingand patch scarification gave results no better, or even worse, than obtainedwithout site preparation. Thus, exposure of mineral soilper sedoes notguarantee benefit to young outplants, for the determining influence on theseedling will be the integrated effect of all microsite factors. Soil temperatureis important but not omnipotent. Especially for spruce, the development ofroot systems able to access adequate fertility and moisture would seem to bethe key to vigorous establishment. For outplants to benefit from site prepara-tion, they must be relieved of limiting constraint. Whether it be increased soil

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temperature, decreased competition for a period, or freedom from floodingduring the growing season, etc., the silvicultural plan ideally should identifythe limiting constraint(s) and specify appropriate amelioration for each site.

Acknowledgements

Experimentation at Wonowon was established by Dr. R.G. McMinn ofForestry Canada with assistance from Canadian Forest Products, Ltd., andRobur Maskin, A.B., manufacturers of Bracke equipment. Partial fundingunder the Canada/British Columbia Economic and Regional DevelopmentAgreement and Forest Renewal British Columbia is acknowledged. Fundingassistance does not constitute or imply endorsement of any statement orinformation contained herein. Helpful comments by Jean Heineman, RichardKabzems, Anne Macadam, and Amanda Linell Nemec are appreciated.

Notes

1. McMinn, R.G. and Dobbs, R.C. 1972. Some effects of site preparation in spruce/fir typesin the north central interior of British Columbia. Paper presented at Annual Meeting, Can.Bot. Assoc., Halifax, N.S., 19 June, 1972, 7 pp. (mimeo).

2. McMinn, R.G. and Van Eerden 1977. Response of white spruce and lodgepole pine seed-lings to various site treatment options. Can. Dep. Environ., Can. For. Serv., Victoria, B.C.,File Rep. PC-21-111, Experiment 74-F1, 9 pp. mimeo. Report on file with senior author.

3. M. Goldstein, Soilcon Laboratories, Ltd., Richmond, B.C. Report on file with seniorauthor.

4. A summation of the degrees by which the daily temperature at a specified point exceedsa specified baseline level.

5. G.W. Hesse, Herbicide spraying at the Iron Creek, Mackenzie and Stewart Lake sites;field record of calibration, spraying, weather, and equipment. Report on file with seniorauthor.

6. McMinn, R.G., Bedford, L., and Mackinnon, A. 1990. Testing the biological effectivenessof mechanical site preparation equipment, Iron Creek site. B.C. Min. For., Victoria, B.C.,Estab. Rep., FRDA 1.10, 10 pp. mimeo. Report on file with senior author.

7. “PSB” denotes plug planting stock raised under the StyroblockTM container growingsystem (Beaver Plastics Ltd., Edmonton, Alberta); the first digit indicates the top diameter(cm), the next two digits the depth (cm), of the container cavity.

References

Ball, W.J. 1990. Site preparation affects white spruce seedling performance after 20 years.For. Can., Edmonton, Alberta, For. Manage. Note 47, 7 pp.

232

Bedford, L. and McMinn, R.G. 1990. Trials to appraise the biological effectiveness of mech-anical site preparation equipment in British Columbia: FRDA Project 1.10. pp. 3–12. In:Titus, B.D., Lavigne, M.B., Newton, P.F. and Meades, W.J. (Eds.) The silvics and ecologyof boreal spruces. 1989 IUFRO Working Party S1.05-12 Symposium Proc. For. Can., St.John’s, Newfoundland, Inf. Rep. N-X-271.

Boateng, J.O., Haeussler, S. and Bedford, L. 2000. Boreal plant community diversity ten yearsafter glyphosate. Western J. Appl. For. 15: 15–26.

Brand, D. 1991. The establishment of boreal and sub-boreal conifer plantations: an integratedanalysis of environmental conditions and seedling growth. For. Sci. 37: 68–100.

Brockley, R.P. 1988. The effects of fertilization on the early growth of planted seedlings: aproblem analysis. Can. For. Serv./B.C. Min. For., Victoria, B.C., FRDA Rep. 011, 16 pp.

Bulmer, C., Schmidt, M.G., Kishchuk, B. and Preston, C. 1998. Impacts of blading andburning site preparation on soil properties and site productivity in the sub-boreal sprucezone of central British Columbia. Nat. Resour. Can., Can. For. Serv., Victoria, B.C., Inf.Rep. BC-X-377, 33 pp.

Coates, D. and Haeussler, S. 1987. A guide to the use of mechanical site preparation equipmentin north central British Columbia, 2nd ed. Revision by MacKinnon, A., Bedford, L., andMaxwell, J. [B.C.] Northern Silviculture Committee in cooperation with For. Can./B.C.Min. For., Victoria, B.C., FRDA Handb. 002, 64 pp.

DeLong, C., MacKinnon, A. and Jang, L. 1990. A field guide for identification and interpreta-tion of ecosystems of the northeast portion of the Prince George Forest Region. B.C. Min.For., Victoria, B.C., Land Manage. Handb. 22, 108.

Dobbs, R.C. and McMinn, R.G. 1973. The effects of site preparation on soil temperature inspruce-fir cutovers in the British Columbia interior. Can. Dep. Environ., Can. For. Serv.,Ottawa, Ontario, Bi-mo. Res. Notes 29(1): 6–7.

Dobbs, R.C. 1976. Effect of initial mass of white spruce and lodgepole pine planting stock onfield performance in the British Columbia interior. Can. Dep. Environ., Can. For. Serv.,Victoria, B.C., Inf. Rep. BC-X-149, 14 pp.

Geiger, R. and Fritzsche, G. 1940. Spätfrost und Vollumbruch. Forstarchiv 16: 141–156. Citedby Geiger, G. 1950. The Climate Near the Ground. Harvard Univ. Press, Cambridge, MA,482 pp.

Gibbard, D.A. and Sutherland, B.J. 1987. 1986 site preparation equipment trials in Alberta:Donaren 180D powered disk trencher, Sinkkila HMF scarifier. Can./Alberta For. Res.Devel. Agree., Edmonton, Alberta/Ottawa, Ontario, Can. Dep. Supply Services Cat. No.FO 42-91/16-1987E, 37 pp.

Grossnickle, S.C. and Blake, T.J. 1987. Water relations patterns of bare-root and container jackpine and black spruce seedlings planted on boreal cutover sites. New For. 1: 101–116.

Harper, G.J., Herring, L.J. and Hays-Byl, W.J. 1997. Conifer and vegetation response in theBWBSmw1 12 years after mechanical and herbicide site preparation. B.C. Min. For., Res.Branch, Victoria, B.C., Work. Pap. 29, 32 pp.

Hawkins, C., Letchford, T. and Krasowski, M. 1995. Artificial regeneration of spruce on cold,wet soil: 10 years along. Water, Air and Soil Pollution 82: 115–124.

Hedin, I.B. 1987a. Field assessment of inverted humus mounds produced by three site prepara-tion implements in north central British Columbia. For. Can./B.C. Min. For., Victoria,B.C., FRDA Rep. 008 (FERIC Spec. Rep. SR-44), 38 pp.

Hedin, I.B. 1987b. Trials of the Sinkkila HMF scarifier in north central British Columbia. B.C.Min. For., Res. Branch, Victoria, B.C., FRDA Rep. 006 (FERIC Special Rep. SR-40),21 pp.

233

Hedin, I.B. 1989. Inverted humus mounds: follow-up assessments. For. Can./B.C. Min. For.,Victoria, B.C., FRDA Rep. 072 (FERIC Spec. Rep. SR-58), 12 pp.

Heineman, J.L., Bedford, L. and Sword, D. 1999. Root system development of 12-year-old white spruce (Picea glauca[Moench] Voss) on a mounded subhygric-mesic site innorthern interior British Columbia. For. Ecol. Manage. 123: 167–177.

Hsaio, T.C. 1973. Plant response to water stress. Ann. Rev. Plant Physiol. 24: 519–570.Letchford, T. and Hawkins, C.D.B. 1996. White spruce response to mounding and herbicide.

pp. 115–116. In: Comeau, P.G., Harper, G.J., Blache, M.E., Boateng, J.O. and Gilkeson,L.A. (Eds.) Integrated Forest Vegetation Management: Options and Applications. Can.For. Serv./B.C. Min. For., Victoria, B.C., FRDA Rep. 251.

Macadam, A. and Bedford, L. 1998. Mounding in the Sub-boreal Spruce Zone of West-centralBritish Columbia: 8-year results. For. Chron. 74: 421–427.

McMinn, R.G. 1976. Is there a better method of mechanical site preparation for spruce-balsamsites? B.C. Min. For., Victoria, B.C., Refor. Notes 3(1): 6–7.

Örlander, G., Gemmel, P. and Hunt, J. 1990. Site preparation: a Swedish overview. For.Can./B.C. Min. For., Victoria, B.C., FRDA Rep. 105, 61 pp.

Parolin, R.W., Read, A. and McMinn, R.G. 1981. Operational trial of a spot scarifier. pp.240–247. Forest Regeneration: Proc. Symposium on Engineering Systems for ForestRegeneration, Amer. Soc. Agric. Engineering, St. Joseph, Michigan, Publ. 10–81.

SAS Institute 1994. SAS/STAT User’s Guide. Release 6.10 edition. SAS Institute Inc., Cary,North Carolina, USA.

Sutton, R.F. 1968. Ecology of young white spruce (Picea glauca[Moench] Voss). Ph.D. thesis,Cornell Univ., Ithaca, New York, 500 pp.

Sutton, R.F. 1991. Soil properties and root development in forest trees; a review. For. Can.,Ontario Region, Sault Ste. Marie, Ontario, Inf. Rep. O-X-413, 42 pp.

Sutton, R.F. 1993. Species composition in two boreal mixedwoods before and 10 years afterhexazinone treatment for establishing underplantedPicea glauca(Moench) Voss. For.Ecol. Manage. 57: 201–212.

von der Gönna, M.A. 1989. First year performance and root egress of white spruce (Piceaglauca[Moench] Voss) and lodgepole pine (Pinus contortaDougl.) seedlings in mechan-ically prepared and untreated planting spots in north central British Columbia. M.F. thesis,Univ. B.C., Vancouver, B.C., 130 pp.