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Evaluating tillage depth (Morice Forest District, Telkwa River Forestry Road, km 15). The indicated depth of loosenedsoil is approximately 40 cm (total length of probe is 1 m), indicating effective tillage with a winged subsoiler.

rehabilitation in British Columbia are being usedunder a wide variety of soil and site conditions.Field visits during the summer of led to apreliminary conclusion that a careful andknowledgeable operator working with a goodprescription is at least as important for a project’ssuccess as the choice of implement. On many sites,especially those with coarse-textured soils, severalchoices of implement appear to produce good results.Unfortunately, very few projects exist where theinitial conditions and tillage procedure weredocumented well enough to reliably state that thisfirst impression is correct. The effect of treatmentson long-term plots can be evaluated only if initialconditions are recorded.

Long-term studies should address the followingquestions:• Depth of tillage: What tillage strategies work best

on a variety of sites and under varying conditions?Is restoration of a shallow surface layer an effectivetechnique to restore productivity on sites withnaturally shallow rooting depths?

• Resettling and soil structure stability: Under whatsoil/site conditions does resettling cause failure ofthe rehabilitation project? What techniques aresuitable to prevent resettling?

• Minimum treatments: What low-cost rehabilita-tion treatments are effective for a variety of sites,including those with severe disturbance such asmain roads and landings, and those such as ruttedareas, minor trails, and roadside work areas withless severe disturbance?

. Topsoil Conservation and Replacement

In forest soil rehabilitation, topsoil is operationallydefined as the upper layer of the soil where most ofthe roots are located, with or without the forest floor.This definition recognizes that forest floor layers havedistinct characteristics and functions compared tomineral soils, but that separating forest floors frommineral soil horizons is not usually practical usingheavy equipment (Ballard ; Ziemkiewicz et al.[editors] ).

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Replacing topsoil is an effective technique to restoreproductivity in degraded soils (e.g., Heilman ,; Halvorson et al. ). The benefits of topsoilconservation and replacement are related mostly tothe higher soil organic matter levels present in topsoilrelative to subsoils, and the beneficial effect of the soilorganic matter on physical, chemical, and biologicalconditions.

Compared to subsoil materials, topsoils usuallyhave higher aggregate stability (Itami and Kyuma), lower bulk density (Smith and Wass ; Carra), and more favourable pore size distributions,which leads to higher hydraulic conductivity, water-holding capacity, and aeration porosity (Potter et al.; Sharma and Carter ). The loose, openstructure of productive forest soils often depends onthe presence of soil organic matter (Hudson ),but soil texture also plays a role in topsoils derivedfrom medium- and fine-textured parent materials. Inmany parts of British Columbia, soil developmenthas resulted in natural topsoils that contain less claythan subsurface layers (Lavkulich and Valentine[editors] ), and thus have inherently more stablemacropores than their associated clay-rich subsoils.Variation in soil texture within the surface layers ofundisturbed soils may result from translocation ofclays in moist climates, or from additions of volcanicash or wind-derived material to the soil surface.

Nutrient pools and cycling are also enhanced bythe presence of topsoil on rehabilitated sites. For coalspoils in Washington, nutrient content of replacedtopsoils was more than twice as high as for subsoils,even though the levels in topsoil were still well belowthose in undisturbed forests (Heilman ). Foliarnutrient levels in Douglas-fir reflected the soil nitro-gen levels. In this study, - to -year-old Douglas-firgrowing in reclaimed soils with topsoil had a similarsite index to reference plantations on undisturbedsoil. A plantation growing on subsoil material had alower site index.

Topsoil also acts as a seedbank, which is often animportant resource for revegetation with nativespecies (Young ), but which also affects the needfor subsequent treatments to control weeds and vege-tation competing with crop trees (Heilman ).According to Young (), seeds are concentratedin the thin, organic-rich surface layer of soil. Theseedbank layer may represent only a small portion ofa thicker topsoil layer that would be conserved inmany mine reclamation projects, but may closely

reflect the types and amounts of materials commonlyfound near disturbed forest sites in British Columbia.Several factors affect the composition and viability ofseed in soil seedbanks, including the composition ofpre-disturbance vegetation and the ecologicalstrategies (e.g., seed numbers, viability, dormancyperiods, and germination requirements) of the plantspecies present. Removing and stockpiling the topsoildramatically changes the environmental conditionsthat affect the seeds. Some seeds die as stockpiledtopsoil ages, while others have their dormancyrequirements satisfied. For a particular site andrehabilitation objective, changes in seedbankcomposition because of aging may be eitherfavourable or unfavourable.

Farrish () showed that seedling emergencewas similar for loblolly pine grown in topsoil andsubsoil, but that subsequent survival and earlygrowth of roots and shoots was significantly higherfor trees growing in the topsoil. Soil organic matterand nutrient levels were substantially lower for thesubsoil treatments. The growth response wasattributed to soil and plant nutrient status in thiscase, but the effects of low organic matter levels onsoil physical properties affecting aeration and rootpenetration were not evaluated, and may havebeen significant.

When landings and roads are built without theintention to rehabilitate them, topsoil replacementsimply involves retrieving and spreading any materialpiled at the edges of the landing or road (Figure ).When rehabilitation is anticipated, and on steeperground, topsoil is pushed to one side before levelling,or buried at a known location within the fill. If thetopsoil is pushed to the side, full slope recontouringis not needed before the topsoil is respread.

In a study of skid site rehabilitation in New Zealand,Hall () found that ripping and mounding effec-tively reduced soil shear strength, and the cost ofripping alone was modest. However, soil nitrogen onthe ripped soils was well below the critical level forradiata pine, and some amelioration with chemicalfertilizer or legume-derived nitrogen was consideredessential. Respreading topsoil and logging debris wasmore expensive (accounting for % of the costs ofa combined treatment that included ripping andmounding with respreading topsoil and loggingdebris) and nutrient limitations were only partiallyovercome. The equivalent cost of fertilizing to restoresoil nutrients was not discussed, and comparative

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tree performance on sites with and without topsoilwas not available. Lawrie et al. () showed thatspreading topsoil on landings increased the cost ofshallow tillage with an excavator by approximately%. Replacing topsoil during rehabilitation raisespractical problems: the replaced topsoil shouldretain its beneficial physical properties and detri-mental compaction should be avoided. Torbert andBurger () observed that % of trees planted onrestored mine soils in Virginia survived when plantedon areas with minimal traffic, compared to % sur-vival for trees planted on areas repeatedly travelledon during topsoil placement. Height growth after twoyears was also affected by the traffic. The areas ofextensive traffic resulted from a grading operationthat aimed to produce a uniform surface.

.. Information gaps: research needsThree aspects of topsoil replacement in forest soilrehabilitation in British Columbia require furtherstudy. While the effects of topsoil replacement onproductivity could be extrapolated from one disturb-ance type to another, the evaluation of costs and

machine productivity must be investigated for indi-vidual disturbance types.Quantify the benefits of topsoil replacement, incomparison to other methods of restoring soilstructure and nutrient cycles Evidence from manysources indicates that topsoil conservation improvessoil conditions, but the value of such benefits to grow-ing trees is not known for forest soil rehabilitationsituations in British Columbia. Long-term plots areneeded to evaluate tree productivity on areas reha-bilitated with and without topsoil replacement. Oneapproach would include these plots as treatments inrehabilitation research projects that are evaluatingvarious methods of restoring productivity.Investigate biological processes in rehabilitatedsurface soils The biological processes that affectnutrient cycling and their relationship to site produc-tivity are complex. In natural topsoils, populations ofnutrient-cycling organisms are much larger than forassociated subsoils. Studies of nutrient-cyclingprocesses, such as microbial activity, populations ofsoil organisms, and characteristics of soil organicmatter, would provide information about potential

Topsoil piles commonly found adjacent to bladed areas on level ground (Kalum Forest District). Respreading thesepiles should enhance site nutrient conditions and improve productivity.

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indicators of long-term site productivity on a rangeof site types.Determine cost-effective construction methods forconserving and replacing topsoil Conserving andstockpiling topsoil for use in rehabilitation projectswill likely become normal construction practice inforestry operations in the near future because ofForest Practices Code requirements. However, noobligation exists to respread topsoil piles that areadjacent to backlog sites requiring rehabilitation.Conserving, stockpiling, and replacing topsoil addsignificantly to the costs of access construction andrehabilitation. Many rehabilitation specialists inBritish Columbia are either not aware of the potentialbenefits, or do not feel that they justify the addi-tional costs associated with the practice. Research,demonstration, and extension activities are neededto investigate cost-effective ways to manage topsoil.For example, studies of machine productivity (e.g.,Lawrie et al. ) could be carried out to provideinformation for a variety of sites.

. Slope Recontouring

Slope recontouring is a method where contour-builtroads and trails are removed and the slope is restoredto its initial shape. It is also called “road debuilding”on the coast, and in the southeast interior it is animportant technique for skid road rehabilitation.Slope recontouring is carried out to control surfaceerosion, prevent mass wasting, restrict access,improve aesthetics, and restore soil productivity(Beese et al. ). The emphasis placed on restoringproductivity depends partly on administrative issuessuch as the need for future access, and on site factorsthat affect the feasibility of restoring productivity.

Eubanks () described a technique for restoringslopes that focused on hiding the road from view andpreventing traffic from using the road. Although thegoals were different from those of modern watershedrestoration projects in British Columbia, some of therecommendations made by Eubanks were similar andincluded careful location of road takeoffs, topsoilstockpiling, and revegetation using seed. The esti-mated cost for full restoration was about equal tothe initial cost of construction.

In the Nelson Forest Region, logging of steep slopesoften involves construction of contour skid roads.The amount of land affected by skid roads became aconcern in the early s, after researchers drew

attention to degraded soil conditions and reducedproductivity. Soil conditions were especially poor onthe gouged inner portions of skid road surfaces(Smith and Wass ). In response to the concern,and initially with the aim of improving visual qualityof cutblocks on steep slopes, Crestbrook ForestIndustries (Cranbrook) developed a system of skidroad construction and rehabilitation that has evolvedfor over years. Objectives of restoring drainagepatterns, slope stability, and soil productivity weresubsequently incorporated into the rehabilitation work.

Currently, skid road construction, use, andrehabilitation is planned through the entire har-vesting operation by Crestbrook. Features of theoperation’s construction phase include consistentlyplacing topsoil in a small windrow near the outsideof the trail surface, minimizing the cut height, andavoiding calcareous materials, which are unsuitableas a growing medium for trees. Rehabilitationinvolves loosening and out-sloping the runningsurface, replacing the subsoil materials against thecutbank, replacing the topsoil, and scattering theslash across the surface. These techniques wereamong the most advanced viewed in BritishColumbia during site visits in the summer of .

Dykstra and Curran () described an invest-igation that was recently initiated to evaluate forestproductivity on rehabilitated skid roads. Theobjective of the study was to quantify lodgepole pineand Engelmann spruce growth on rehabilitated skidroad disturbance for various site types. A successfullyrehabilitated site shows no differences in growthbetween trees in undisturbed conditions and at allpositions within the profile of the rehabilitated skidroad. On skid roads that have not been rehabilitated,trees growing on the inner gouged portion of the skidroad are commonly smaller than trees growing on theouter portions (Smith and Wass ).

In the Vancouver Forest Region, Hickling et al.() established over measurement sites toevaluate the establishment and early growth of treesgrowing on rehabilitated roads. Most of the sites werein the Coastal Western Hemlock (CWH) biogeoclimaticzone, and trees were planted on roads rehabilitatedwith an excavator as part of operational work carriedout by forest companies. Average survival rates afterone year were over %. Preliminary results indicatedthat, compared to soils with low organic matter content(–.%), high levels of organic matter (>␣ %) inthe surface soils were associated with greater height

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growth of Douglas-fir and western redcedar (over% taller). The use of various forms of tea-bagfertilizer also improved growth, but not to the sameextent that organic matter did. Grass-seeding reducedheight and diameter of Douglas-fir on one site. Deerbrowsing affected % of the plots, and was con-sidered a serious problem where deer used thedebuilt road.

Based on their preliminary results, Hickling et al.() provided a description of what a successfulrehabilitation project might aim for, including:• a road that takes its place in the natural landscape

(recontoured to natural state);• organic material that is mixed into the surface,

along with the transplanting of young trees orbrush; and

• stockpiled materials and other available resourcesthat are used appropriately.

.. Information gaps: research needsEvaluate conifer growth on recontoured roads andskid trails We lack reliable information on the pro-ductivity of rehabilitated roads and contour-builtskid trails. The work initiated in the Nelson ForestRegion (Dykstra and Curran ) and by Hicklinget al. () illustrates the types of studies that willgain such information.

. Reforestation and Revegetation Techniques

Numerous strategies can re-establish productiveforests on degraded sites; each approach includes arange of options for plant species, establishmentmethods, and subsequent vegetation managementtechniques. On sites with low potential for erosion,and where soil properties are suitable, a simple andlow-cost strategy involves establishing suitableconifer or hardwood crop trees and allowing shrub,herb, and other understory species from nearby areasto subsequently invade the site. This strategy cansucceed on flat sites (low erosion hazard) withmedium- to coarse-textured soils (rapid infiltration,limited potential for resettling following tillage), andwhere topsoil is respread (seedbank of native speciesavailable). The trees can establish by either naturalregeneration from seed, or by planting suitable con-tainer or bareroot stock types. Simple approachessuch as these are likely suitable on many sites, butadditional revegetation techniques are often required,including those that provide visual cover, control

erosion, restore and maintain soil physical properties,or enhance site nutrient pools and nutrient cycling.

.. Coniferous and hardwood crop treesThe goal of establishing trees on rehabilitated soils isthe same as that for general silvicultural planting onundisturbed sites—that is, to achieve high survivalrates and rapid early growth. Early successionalspecies such as Douglas-fir on the coast and lodge-pole pine in the interior have been favoured forrehabilitation, partly because they are adapted tothe harsh conditions on disturbed areas. As moreexperience is gained, however, other species mayprove equally successful, depending on the site condi-tions. Recently on the coast, plots were established toevaluate the performance of western redcedar, west-ern hemlock, amabilis fir, yellow-cedar, and red alder(Hickling et al. ). In the interior, white birch,white spruce, and western larch were also establishedon rehabilitated sites. The unique characteristics ofeach of these species, and others including subalpinefir, aspen poplar, and black cottonwood, will likelyensure that they are used in rehabilitation work onsome sites.

Successful establishment and early growth ofplanted trees requires that a healthy individual of asuitable seedling stock type is planted in a suitablemicrosite. On undisturbed portions of recentlyharvested cutovers in British Columbia, this usuallyoccurs, and plantation failures are rare. For rehabil-itated sites, however, seedling mortality rates areoften much higher, and early growth is usually slowerthan for undisturbed soils. Each element in this seriesof events (i.e., plant, stock type, site) needs evaluationwhen developing techniques to establish fast-growingplantations on rehabilitated sites. Armson ()described how poor root development, which mayresult from low-quality stock or poor soil conditions,can lead to seedling establishment problems. Armsonalso described how root systems, that fail to expandduring periods of rapid growth, can lead to poorperformance and mortality at the sapling, or pole,stage of stand development. Therefore, along with theneed to restore soil properties to suitable conditions,the quality of biological material used in rehabil-itation is also an important factor affecting success.

Arnott et al. () showed that + barerootlodgepole pine outperformed + container seedlingson landings near Fort St. James. The bareroot stocktype was larger when planted, and maintained

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consistently larger annual height increments through-out the five-year study. Hickling et al. () alsoshowed that larger stock types (PSB ) of Douglas-fir grew faster on rehabilitated roads in coastalBritish Columbia.

Williston and Ursic () recognized the need formicrosite planting, but found that nursery practicessuch as fertilization and top pruning had little effecton success of loblolly pine planted for erosion controlin the United States. Shallow planting was the mostcommon cause of failure, while auger planting in asix-inch posthole and carefully selecting the plantingspot improved survival. Some ineffective techniquesincluded very deep planting, kaolin root dip, waxcoatings to reduce transpiration, fertilizing at lbs/acre, and interplanting with legumes.

The range of cultural techniques available in amodern nursery is much wider than that available in. In addition, the awareness that mycorrhizae andother biological partners play an important role inwater and nutrient uptake has led to the developmentof various biological inoculants with the potential toimprove seedling performance. Mycorrhizalinoculation was tested as a means of improvingplanted seedling performance, but the results forundisturbed sites with adequate moisture supplieswere mixed.

Walker et al. () compared the performanceof one-year-old bareroot loblolly pine seedlingsinoculated with the mycorrhizal fungi, Pisolithustinctorius, to that of control seedlings colonizedprimarily by Telephora terrestris. The seedlings wereoutplanted with or without fertilizer on a recon-toured coal mine site that was also revegetated with aherbaceous ground cover. The loam soils had .%organic matter, a pH of ., and .% total nitrogen.Survival and growth of loblolly pine after seven yearswas improved by the presence of P. tinctorius. Theeffect of the P. tinctorius was attributed to improvedwater and nutrient uptake evaluated throughmeasurements of xylem pressure potential and foliarnutrient analysis. Fertilization with kg/ha each ofnitrogen, phosphorus, and potassium reducedsurvival and had no effect on growth. The effect ofthe fertilizer was primarily to enhance the growth ofherbaceous cover, which often overtopped the pine inthe fertilized plots.

Amaranthus and Perry () showed that soiltransfer increased survival and mycorrhizal coloni-zation of Douglas-fir seedlings planted on old

clearcuts by up to %. These authors found that thesource of transferred soil was an important factoraffecting success, and believed that the resultsdemonstrated that ectomycorrhizal fungal inoculumhad been transferred with the soil. Subsequent workby Colinas et al. (), however, showed that thesituation was more complex—soil that was treatedwith fungicide also enhanced the formation ofmycorrhizae on planted seedlings. They suggestedthat some aspect of the rhizosphere biology wasaltered by the transferred soil, which led to enhancedectomycorrhizal colonization of the roots by inocu-lum already present in the clearcut.

These results might have relevance for rehabil-itated sites, where soils would probably have lowamounts of inocula for mycorrhizae and other soilorganisms, and where soil aeration and moistureconditions are altered compared to undisturbed soils.

.. Grasses, legumes, and native shrubs for soilameliorationVarious revegetation strategies are available to en-hance productivity on degraded soils. Revegetation isnecessary to control surface erosion. Vegetation alsohelps to restore the soil by increasing soil organicmatter levels. Techniques for controlling erosion withgrass and legume plantings were the subject of sev-eral research projects carried out by the B.C. Ministryof Forests in the early s. Results were presented inseveral reports and the techniques are well developedto address erosion concerns in forestry (Carr ,; Homoky , ; Beese et al. ). Althoughmuch was learned, some revegetation issues remainunresolved and others were raised more recently, in-cluding:• the ecological benefits and hazards associated with

establishing grasses and legumes on rehabilitatedforest soils;

• the potential for improving soil structure throughbiological tillage; and

• the enhancement of site nutrient pools throughnitrogen fixation.

Grasses and legumes Agronomic seed mixes arewidely used in soil rehabilitation, and sometimesthe purpose of this work was unclear. For example,several forest districts developed rehabilitationpolicies in the s that required landings on allcutovers to be loosened and seeded to grass andlegume mixes. In many cases, seeding grasses andlegumes took precedence over planting trees, even on

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sites where no erosion hazard existed. While many ofthese landings provide valuable forage for cattle, andsoil conditions may have been improved, they are notyet developing into productive forests.

In , several landings near Williams Lake wereloosened and seeded with combinations of lodgepolepine and grass seed as part of a trial on the effective-ness of landing rehabilitation techniques (Vyse andMitchell ). Although the experiment wasabandoned shortly after it was installed, recentobservations indicate that lodgepole pine wassuccessfully established from seed on landings notseeded to grass (Figures and ). Grass may hampergermination and subsequent establishment of pineon sites in this area. Poor germination of pine seedon the study sites was documented in the first yearof the trial, but in subsequent years more of the seedgerminated. Competition between trees and grass,and cattle damage to seedlings, may also causereforestation problems (Figure ). More recentevidence from throughout British Columbiaillustrates that, where delayed seeding or other

factors have resulted in poor development of grassand legume cover crops, growth of pine trees issatisfactory (Figure ), suggesting that grasses andlegumes are not an essential part of soil rehabilitationon all sites.

Amaranthus et al. () observed that seedingannual ryegrass (Lolium multiflorum) in an areacharacterized by extended summer drought causedlow soil moisture levels and increased mortality ofsugar pine seedlings planted the following spring. Inthe following year, the grass died and the thatch coveracted as a mulch, which resulted in increased soilmoisture content and improved survival for treesplanted into the thatch. On unseeded plots, baremineral soil covered –% of the area, but nativespecies re-established to cover % of the area aftertwo growing seasons. Grass covered % of theseeded areas after one year. Differences in mycor-rhizae between seeded and unseeded plots were notconsistent. The authors did not encourage grassseeding because other studies indicate that grassesrestrict mycorrhizal formation. This can occur

Landing rehabilitated as part of EP 777 in the Williams Lake Forest District. The entire landing was tilled andlodgepole pine established from seed. The left-hand portion was not seeded to grasses, and reasonable stockingand growth of lodgepole pine was observed 20 years after rehabilitation.

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directly by inhibiting ectomycorrhizae, or indirectlyby slowing the invasion of native shrubs that haveectomycorrhizae.

In another study of the effects of grass seeding ontree establishment, Carpenter and Albers ()showed that moisture stress and mortality werehighest in June for alder seedlings planted into adense stand of fescue (Festuca arundinacea Schreb.)on surface mine soil in Kentucky. Leaf water potentialand soil moisture content were generally lower fortrees planted in plots with fescue and where fescuewas mowed, compared to plots where grass cover wasscalped away or where it was temporarily set back byherbicide.

Although grass seeding can result in moisturestress to trees in dry climates, the negative effects ofgrass are not well documented in moist climates in

The right-hand portion of the landing fromFigure 12 (Williams Lake Forest District), whichwas seeded to grasses and legumes. Very fewpine survived.

Seedling damaged by cattle trampling in arehabilitated roadside work area (Moffat Road,Williams Lake Forest District).

Rehabilitated landing with good pine growth,but poor germination of birdsfoot trefoilbecause of delayed seeding (Kispiox ForestDistrict). Favourable seedbed conditions persistfor only a short time after tillage.

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British Columbia. Several examples from variousareas of the province show healthy forests growing onrehabilitated sites that also support vigorous standsof grass and legume (Figure ). Grasses and legumesmay provide a cost-effective means of enhancing soilorganic matter and nutrient levels on these sites(Figure ). In the Interior Cedar–Hemlock (ICH)and Engelmann Spruce–Subalpine Fir (ESSF)biogeoclimatic zones of interior British Columbia,seeding with grasses and legumes is employed toreduce competition between crop trees and nativevegetation (Steen and Smith ). Early resultssuggested that the shorter agronomic grasses andlegumes displaced taller native species, which was theobjective, but had little effect on conifer crop trees.Hickling et al. () suggested that the growth oftree seedlings planted in grass-seeded areas wasslightly reduced in coastal British Columbia.

Biological tillage Information in Table indicatesthat the roots of some tree species can penetratecompacted soils better than others; the same is truefor agricultural crops. This observation has led someresearchers to suggest that such plants could be usedas “biological plows” to penetrate compacted soillayers, and create channels for the roots of cropspecies. Henderson () estimated that this effectwas true of lupine, which improved wheat yields by kg/ha, on a sandy soil in Australia that wascompacted by agricultural machinery.

Materachera et al. () evaluated plant speciesfor their ability to penetrate a soil mediumcompacted to a strength of kPa (penetrometerresistance), and found that all species had their rootelongation reduced by over %. The roots of dicotyle-donous plants generally had larger diameters andpenetrated the medium better than graminaceous

Surface soil conditions on the landing illus-trated in Figure 16 (Quesnel Forest District).Grasses and legumes contribute soil organicmatter and nutrients to develop a productivesoil.

Landing rehabilitated in 1987 in the QuesnelForest District. Excellent pine growth on sandysoil with organic-rich surface horizon. Excellentgrowth of grass and legume. Steel probepenetrated to 20 cm.

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monoctyledons with smaller-diameter roots. The bestspecies included lupine, medic, and fava bean. In sub-sequent field tests (Materachera et al. ), lupineand safflower produced the greatest effect on watersorptivity of the compacted layers, but sorptivitieswere still well below levels for a tilled subsoil. The soilstrength values used in the study by Materachera etal. () are near the upper limits of valuespresented in Table .

The use of biological plows to rehabilitatecompacted forest soils has not been investigated.However, studies that would be of obvious interestinclude evaluating root thickness of forest trees andshrub species in British Columbia compared to rootthicknesses for species already tested, and usingbiological plows to restore severely disturbed sites,and as additional treatments to stabilize andmaintain soil structure after conventional tillage.Native shrubs A native shrub program was initiatedin by the B.C. Ministry of Forests under ProjectE.P. . Over native British Columbia tree andshrub species were propagated, a propagation manualwas written, and field trials were established between and before funding for the program wasdiscontinued. The results of this work appear inseveral publications including Marchant and Sher-lock (), Homoky (, ), and Carr ().

Native woody species are useful in rehabilitationbecause they provide deep rooting and long-termerosion control, although it takes longer for the sur-face cover to develop than with grasses and legumes.However, on sites where immediate erosion control isnot a major concern, or where other measures havebeen taken to control surface erosion in the shortterm, they may provide a method for re-establishingecosystem characteristics similar to those ofundisturbed areas. Marchant and Sherlock ()recommended that the selection criteria for speciesbe based on the biogeoclimatic subzones. Theypresented criteria that affected rehabilitationsuccess, which were subsequently grouped intothree major criteria:. known biological and ecological characteristics of

each candidate species;. performance in field trials; and. performance in propagation trials.Nitrogen-fixing species The potential benefits ofestablishing nitrogen-fixing species to restorenutrients on rehabilitated sites has been known forsome time, but few studies have quantified the

nitrogen inputs to rehabilitated soils from seededlegumes or nitrogen-fixing shrubs. For coastal sites,considerable information is available about the ef-fects of red alder on soil properties and the potentialrates of nitrogen fixation (e.g., Tarrant et al. ).For interior sites, use of legumes was investigated inthe Prince Rupert Forest Region on rehabilitatedlandings (Marsland ), on blade scarified areas(Coates et al. ), and on cutovers subject tovarious forms of site preparation (Trowbridge andHoll ). This work has successfully establishedspecies such as birdsfoot trefoil on landings, andalsike clover on blade-scarified areas. Establishinglegumes to enhance site nitrogen levels resulted inincreased foliar nitrogen levels for lodgepole pine,but height growth after four years was not affected.

The establishment, growth, and development ofgrey alder (Alnus incana) and lupine (Lupinus spp.)on low-productivity sites in northern Sweden werestudied by Huss-Dannell and Lindmark (). Thesandy soils had been subjected to repeated severefires, harvesting, or windthrow, and had thin morhumus layers, low soil organic matter, pH values near., and low soil nitrogen. Survival of alder after sixyears ranged from very good (–%) to poor (–%), with better performance indicated for warmersites. Survival and growth of alder was similar fornursery-raised and locally transplanted seedlings, andfor fenced and unfenced plots. Lupinus nootkatensiswas the most successful lupine, either establishedfrom seed or by planting nursery-grown stock.Liming and scarifying the site improved the successof sown lupines. A companion experiment, in which kg/ha per year of alder leaves were added to thesoil (which represents approximately the amountexpected from established stands of alder or lupine)showed that the forest floor achieved the propertiesof more productive sites after only six years.

For restoration purposes, the authors concludedthat lupin seemed hardier than alder. Lupines areeasier and cheaper to establish because they are sownfrom seed, and their high reproductive potential isuseful when complete site occupancy after about fouryears is desired. The authors noted, however, thatlupines are toxic to cattle, and that they requiredinoculation with Rhizobium. Huss-Dannell andLindmark () considered alder as an effectivespecies for soil restoration.

One strategy for using nitrogen-fixing speciesinvolves planting conifers before lupines are sown.

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This is so that the trees do not face severe compe-tition in the first three years after planting; after thatthey are likely well established, and begin to shade thelupine out. When alder is chosen to restore soils,conifers may be planted at the same time because thealder does not shade the ground as much as lupine.

Other potential sites of nitrogen fixation in forestecosystems is the subject of recent studies. Nitrogenfixation associated with coarse woody debris(Graham et al. ) and in the rhizosphere of pinetrees (Bormann et al. ) are of interest as potentialnitrogen sources on degraded soils.

.. Information gaps: research needsEstablishing a productive second-growth forest is theultimate test of success for rehabilitation projects.The renewed focus on rehabilitating soils for coniferproductivity suggests that investment is necessaryin revegetation research. As described previously(Figure ), the amount of ongoing operational reha-bilitation work in British Columbia is increasingrapidly and the need for information is acute.The following knowledge gaps were identified.Testing conifer and hardwood species and stocktypes for rehabilitated sites and evaluatingbeneficial micro-organisms The range of speciesand stock types suitable for use on rehabilitated sitesneeds expanding. Large conifer stock types have beenrecommended for coastal areas (Hickling et al. )and in the interior different stock types have shownvarying rates of early growth on degraded sites(Arnott et al. ). In addition, the potential benefitsof using biological inoculants to enhance rhizospherepopulations of beneficial organisms should beinvestigated. Initially, a program of operationalmonitoring for survival and early growth of a rangeof stock types and species seems a practical approach.The efforts should expand if an unacceptable rate ofplantation success on rehabilitated sites is observed.Native plants Native plants can provide manybenefits, but their potential is only starting tobe realized. For example, native species that areunpalatable to cattle could be used in areas wherecattle damage to crop trees is a problem. The lossof the B.C. Ministry of Forests native shrub programin the s has resulted in a significant informationgap at a time when the demand is great. Native spe-cies could be used as biological plows, or otherwisedeveloped as low-cost alternatives for rehabilitatingdegraded sites. One research approach would involve

screening of appropriate species and varieties fordesirable characteristics.Effect of agronomic species on forestecosystems Some concern exists that agronomicgrasses and legumes used for rehabilitation coulddisplace native species. Trials show that grass andlegume seed mixes can control competing vegetationon cutovers (Steen and Smith ). However, othersfeel that native plants quickly invade seeded areas andrestore the natural ecosystem. Once crown closureoccurs, agronomic species can lose their competitiveadvantage because of shading. Also, the chances ofagronomic plants displacing native species increase indry environments, especially in the southern interior,and dry sites in other areas where the native vegetationis dominated by grasses and shrubs. A retrospectiveapproach could provide useful information on thesetopics for select ecosystems in diverse regions ofBritish Columbia. These studies could, for example,evaluate vegetation succession on historic sites wherehydroseeding was used to control erosion along roadrights-of-way.Role of grasses in forest soil rehabilitation Tra-ditionally, grasses have played a dominant role inroad and landing rehabilitation. That role may needre-examining in light of the information nowavailable about moisture competition, potentialallelopathic effects on tree seedlings (Amaranthuset al. ), and cattle trampling damage to seedlings.Other studies (Walker et al. ) show that seedlingsand herbaceous cover can co-exist on surface-minedland. The range of site types where competitionbetween trees and seeded ground cover hindersrehabilitation success should be determined.Research could initially focus on evaluating methodsfor establishing trees on sites previously tilled andseeded to grass. In addition, techniques to preventcattle trampling damage to seedlings on rehabilitatedsites should be developed further.

. Soil Amelioration: Fertilizers, Amendments,and Mulches

On many degraded sites, soils are deficient in organicmatter and nutrients, and even after tillage may haveunstable pore structure, low available water retention,and poor nutrient-retention characteristics. Variousstrategies can address limitations on individual sites,including fertilizer application, application of organicresidues, and mulching.

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.. FertilizersFertilizer is used in rehabilitation work to enhanceplant establishment, accelerate plant growth, andmaintain productivity (U.S. Department of Agricul-ture ). Fertilizer use is recommended for erosioncontrol work and the fertilizer is frequently blendedwith the seed mixture in hydroseeding operations(Beese et al. ). The purpose of initial applicationsis to enhance plant establishment and promote earlygrowth. Subsequent applications are recommendedto maintain the cover of seeded grasses and legumes(Carr ).

Fertilizing to meet the nutritional demands of treeseedlings on rehabilitated sites may involve applica-tion at time of planting to enhance early growth ofseedlings located on rehabilitated roads (Hickling etal. ). Broadcast, or single-tree, fertilization afterestablishment is an approach used if vegetationcompetition is not a problem. For subsequentfertilizer applications, foliar testing can reliablyindicate tree nutrient status, and should occur beforefertilizing to improve the growth of established trees(Ballard and Carter ).

While some fertilizer is often required to establisha productive forest on rehabilitated sites, the possibilityof applying too much fertilizer should be considered.Fertilizer should not be used alone as a means to re-establish site nutrient pools. Unless vegetation or anutrient-demanding organic amendment such aswood waste is present to utilize the nutrients, muchof the added fertilizer (especially in the form of NO

–

and K+) will be lost either to the atmosphere or indrainage water. Over-fertilization does not affect localareas alone; the global consequences of profligatefertilizer use were described by Vitousek ().

.. Nutrient-poor residuesOrganic amendments with low nutrient content areavailable in all areas of British Columbia, and are per-haps the only practical material to amend soil organicmatter on rehabilitation projects in remote areas.Depending on the source of the material, C:N ratioscan range from : or higher for wood chips orfresh sawdust (Arends and Donkersloot-Shouq ),to : for primary paper mill sludge (Zhang et al.). Some residues have relatively low values suchas : and : for brown and green needles, respec-tively (Pluth et al. ). Various organic materialshave been used as soil conditioners (Saini andHughes ; Graves and Carpenter ; Schuman

and Sedbrook ; Olayinka and Adebayo ).Various methods are used to process, spread, andincorporate materials into soil. Woody materials withhigh C:N ratios can immobilize soil nitrogen as theadded residue decomposes. Nitrogen fertilizer, sewagesludge, manure, or other nutrient-rich materials areusually added with woody residues to prevent nitro-gen deficiency in plants.

Saini and Hughes () added t/ha of shreddedtree bark (C:N = :) to clay loam potato soils inNew Brunswick, along with kg/ha N. The shreddedmaterial was spread with a manure spreader anddisced into the surface. The bulk density declined to kg/m from , and increases were observed foraggregate stability (.% compared to .), oxygendiffusion rate (. g /cm compared to .), waterpercolation rate (– times faster), and potatoyields (. t/ha compared to .). Assuming a bulkdensity of approximately kg/m for the shreddedbark, the application rate represented a -cm layer.

Ground or chipped woody residues can potentiallyimprove soil structure and prevent resettling infine-textured soils. Schuman and Sedbrook ()investigated the application of sawmill residues,which consisted of fresh wood chips, sawdust, andbark, to abandoned bentonite spoils at rates of , ,and t/ha (dry weight basis). Fertilizer was alsoadded at a rate of , , and kg N/ha for thethree treatments. This reduced the C:N to :.Wheatgrasses and other forage species wereestablished from seed. Over four years, forageproduction averaged , , and kg/ha for thethree treatments. Average soil moisture content wastwice as high in the plots receiving wood waste as inthe controls. Wood waste improved productivity ofthese clay soils, and the medium application rate of t/ha (a .-cm layer, assuming a bulk density of kg/m) achieved a large part of the gain.

Sawdust (initial C:N of :), supplemented witheither inorganic nitrogen (final C:N of :), or dairymanure (final C:N of :) was evaluated as anamendment to improve the organic matter contentof a sandy loam soil (Olayinka and Adebayo ).Two application methods were used: incorporationand mulching. For maize grown in a greenhouse,incorporating unamended sawdust reduced drymatter yield (. g per pot) compared to the control(. g per pot), but amended sawdust improvedgrowth (.–. g per pot). In the field experiment,the amount of amendment added was substantially

35

lower ( t/ha versus equivalent of t/ha estimatedfor the greenhouse experiment). Untreated sawdust,whether incorporated to surface soil or applied as amulch, reduced dry matter yield (. t/ha) relative tothe control (. t/ha). Amended sawdust improvedgrowth in the field (.–. t/ha).

These results illustrate the potential for improvingplant growth when woody amendments are used inrehabilitation work. The use of harvesting residuesand sawmill wastes will likely be encouraged in thenear future, particularly as sawmills adjust to theloss of burning permits, and seek alternative meansfor disposal.

Although a considerable body of knowledge fromother areas is available, applying woody residues todegraded forest soils is still experimental. Theprinciples in British Columbia are similar to thoseelsewhere, but more experience is needed with specificmaterials in local situations so that potential benefitscan be realized (e.g., increased soil productivity,appropriate use of a waste material), while mini-mizing environmental consequences (e.g., reducedsite productivity because of over-application orinappropriate fertilizer regime, toxic leachateproduction because of over-application, or fertilizerleaching because of inappropriate fertilizer regime).Operational experimentation with these residues invarious situations should be encouraged.

.. Nutrient-rich amendmentsUsing nutrient-rich byproducts, such as sewage sludge(McNab and Berry ; Simpson ), urban refuse(Roldan and Albaladejo ), paper mill biologicalwaste (Zhang et al. ), and manure (Aoyama andNozawa ; Robertson and Morgan ), to im-prove soil physical properties and nutrient status iswell documented. For many of these materials,composting before applying helps to control detri-mental side effects, such as the introduction of plantpathogens, weeds, phytotoxic substances, or odors.A wealth of recent literature exists on the processesinvolved in composting and the potential uses ofcomposts and other nitrogen-rich wastes (e.g.,Kayhanian and Tchobanoglous ), but local expe-rience still needs developing in British Columbia.

McNab and Berry () described experimentalresults in which three species of pine were planted ona site denuded by air pollution, and subsequentlyameliorated with t/ha of dried sewage sludge. Allthree species of pine grew faster in the presence of

sewage sludge than when inorganic nitrogen wasapplied at kg/ha, a rate intended to match theone-year release from the sludge. Additional releaseof nitrogen (i.e., higher than kg/ha) from thesludge might be responsible for the improvedresponse.

A trial in the Prince George Forest Region(Kranabetter and Bulmer ) showed that theparticle size of wood waste had a significant effect onthe composting process. Sawdust helped to maintainan open structure in a well-aerated compost pile thatmaintain high temperatures over an eight-weekperiod. Rapid decomposition occurred initially in acompost pile with pulp fibre waste and sewage sludge,but decomposition slowed after three weeks becauseof poor aeration. In the sawdust compost after sixweeks, nitrate was the dominant form of mineralnitrogen, while ammonium was the dominant formin the pulp fibre compost. Some unexpected resultscan occur when using composts and other materials.Applying high rates of ( t/ha) of urban refuse(C:N = ) to degraded soils in Spain resulted inreduced formation of mycorrhizae on pine (Roldanand Albaladejo ). The major species of fungicolonizing seedling roots was also affected by chang-ing application rates. A moderate rate ( t/ha)provided the best results for inoculated seedlings.

The Greater Vancouver Regional District andother communities in British Columbia have gainedexperience in recent years in using sewage sludge, fishwastes, and other materials to improve forest sitesand to reclaim surface mine sites. Although nutrient-rich residues will probably improve soil conditionsand tree growth, many of the field sites that needrehabilitating are far removed from the urbancentres where these materials are usually produced.Transport costs are often so high that their use isjustified only on sites in close proximity to the sourceof the material.

.. MulchesMulches applied to the soil surface control erosion,preserve water, and moderate soil temperatures. Inhydroseeding for erosion control, thin mulches areused to stabilize soil surfaces and enhance the estab-lishment of grasses and legumes. Thicker mulches(approximating the thickness of forest floors on simi-lar sites in the area) derived from logging residues orother materials may have a unique application tocertain forest soil rehabilitation projects.

36

Graves and Carpenter () showed that as mulchthickness varied through -, .-, -, and -cm incre-ments, soil moisture content changed significantlywith each increment, while soil temperature changeswere not significant for mulch thickness greater than. cm. Applying a .-cm layer of bark mulchimproved the stocking levels obtained for threedeciduous tree species established from seed,compared to control treatments with no bark mulch.Survival of planted bareroot seedlings was also higherfor plots with either a . or cm bark mulch layer.Average leaf water potential for European alderduring the growing season was reduced by applyingthe bark mulch, compared to plots with no mulch orwith grasses and herbs.

Although some results show that mulch alone isineffective for rapidly improving mineral soil physicalproperties (Donnelly and Shane ), mulches areeffective in combination with tillage treatments toprotect soil structure (Luce ). Mulches derivedfrom woody materials (branches, needles, bark),which resist decomposition, will probably providelonger-term effects than material such as straw,which decomposes rapidly.

.. Information gaps: research needsUse of woody residues in soil rehabilitation Despitethe potential benefits of using woody residues torehabilitate soils, their use is not widespread inBritish Columbia. This partly reflects the logisticalproblems associated with preparing and deliveringamendments to field sites, but also reflects:• a poor understanding of their potential benefits;

and• concern about the risk of degrading site

productivity through inappropriate use.However, some rehabilitation practitioners are

gaining local experience with their use, and a researcheffort is justified to determine the effects of thesematerials on productivity. Also, more informationis needed on the specific aspects of using theseamendments, such as identifying potential sources,developing methods for transport, and monitoring todocument their effects in various ecosystems. Becausethese materials alter the soil physical properties aswell as nutrient cycling, their effects should beevaluated in field trials.Use of nutrient-rich residues in soil rehabilitationA large body of knowledge is available concerningprocesses of composting and the detailed

transformation of organic matter within compostpiles. Sufficient information probably exists (e.g.,Kayhanian and Tchobanoglous ) for thesuccessful composting of most materials likelyused to rehabilitate forest soils.

The results of Olayinka and Adebayo ()illustrate the hazards of relying on greenhouseexperiments to predict field performance. Fieldperformance of nutrient-poor amendments wasbetter than would have been predicted from the pottrial, likely reflecting the effect of residues on soilorganic matter and soil water retention capacity.

Research on the use of nutrient-rich amendmentsfor soil rehabilitation should focus on high-valuelands close to the source of the waste. Many potentialamendments derived from wastes represent aproblem for the owner of the waste, so research canalso address waste management concerns as well asenvironmental restoration.Use of mulches Evaluating the benefits associatedwith the use of mulches should be considered whendeveloping treatments for field studies ofrehabilitation.

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6 CONCLUSION

The primary goal of soil rehabilitation efforts is toimprove soil conditions and establish productive for-ests on degraded lands. Research is needed to enhancethose efforts by improving our knowledge of how soilproperties and processes affect productivity on reha-bilitated soils, and how rehabilitation techniques canimprove soil conditions and tree growth.

Soil rehabilitation research should be focused atthe incremental and strategic research levels (Binkleyand Watts ). Incremental research is required toprovide land managers and rehabilitation practitionerswith information about problems that affect thesuccess of rehabilitation projects. Strategic researchis required to provide higher levels of managementwith information about the benefits associated withsoil rehabilitation investments made in response tothe Forest Practices Code, and the role of soil rehabil-itation in maintaining the productivity of our forests.The following information gaps should be addressedto meet the information needs of operationalrehabilitation projects that are currently beingimplemented by Forest Renewal BC, which aretherefore considered incremental research (Binkleyand Watts ).• Developing and calibrating short-term tillage

evaluation techniques.

• Determining cost-effective construction methodsto conserve and replace topsoil.

• Testing conifer and hardwood species and stocktypes for rehabilitated sites, and evaluating benefi-cial micro-organisms.

• Using woody residues in soil rehabilitation.• Using nutrient-rich residues in soil rehabilitation.• Using mulches in soil rehabilitation.

The following information gaps should be ad-dressed to meet the information needs of forestmanagement. Results of these projects, which fallunder the category of strategic research (Binkleyand Watts ), could be expected within three tofive years.• Evaluating the long-term success of various tillage

strategies for various site types.• Quantifying the benefits of topsoil replacement,

compared to other methods of restoring soil struc-ture and nutrient cycles.

• Investigating biological processes in rehabilitatedsurface soils, and evaluating soil quality.

• Evaluating conifer growth on recontoured roadsand skid trails.

• Using native plants in rehabilitation.• Using agronomic species in forest ecosystems.• Using grasses in forest site rehabilitation.

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41

Jones, C.A. . Effect of soil texture on critical bulkdensities for root growth. Soil Sci. Soc. Am. J.:–.

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Munson, A.D., H.A. Margolis, and D.G. Brand. .Intensive silvicultural treatments: impacts on soilfertility and planted conifer response. Soil Sci.Soc. Am. J. :–.

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APPENDIX 1 PEOPLE CONSULTED WHEN PREPARING THIS REPORT

Name Agency/Company Address

Bill Chapman B.C. Min. For., Cariboo Region Williams Lake

Lorne Walker B.C. Min. For., Quesnel District Quesnel

Rita Cassavant B.C. Min. For., Quesnel District Quesnel

Jeff Alexander Lignum Ltd. Williams Lake

Derek Hodgkins Inland Timber Management Williams Lake

Graeme Hope B.C. Min. For., Kamloops Region Kamloops

Geoff Ellen Consultant Clearwater

Ed Collen Weyerhauser Ltd. Armstrong

Don Brimacombe Weyerhauser Ltd. Kamloops

Kelly Fay Riverside Forest Products Kelowna

Shayne Brown-Clayton Riverside Forest Products Kelowna

Stephen Homoky Consultant Logan Lake

Mike Curran B.C. Min. For., Nelson Region Nelson

Lawrence Redfern Crestbrook Forest Industries Cranbrook

George Delisle Pope and Talbot Midway

Doug Lang Pope and Talbot Nakusp

Sue Harris Pope and Talbot Nakusp

Paul Sanborn B.C. Min. For., Prince George Region Prince George

Richard Kabzems B.C. Min. For., Prince George Region Fort St. John

Eric Ravnaas B.C. Min. For., Dawson Creek District Dawson Creek

Graeme Anderson B.C. Min. For., Prince George Region Fort St. John

Dan Lousier University of Northern B.C. Prince George

Marty Kranabetter B.C. Min. For., Prince Rupert Region Smithers

Margaret Marsland B.C. Min. For., Kispiox District Hazelton

Rod Meredith B.C. Min. For., Kalum District Kispiox

Lance Loggin Skeena Sawmills Terrace

Phil Burton Consultant Smithers

Jim Dunkley B.C. Min. For., Port McNeill Port McNeill

Terry Rollerson B.C. Min. For., Nanaimo Nanaimo

Milt Holter B.C. Min. For., Mid-Coast District Hagensborg

Neil Oborne Interfor Ltd. Hagensborg

Al Barber Canadian Forest Products Woss

John Senyk Canadian Forest Service Victoria

Bill Carr Carr Environmental Consulting Cloverdale

Dave McNabb Alberta Environmental Centre Vegreville, Alberta

Ed Fields Tilth, Inc. Monroe, Oregon

Lisa Lewis U.S. Dep. Agric. Forest Service Olympia, Washington

Richard Miller U.S. Dep. Agric. Forest Service Olympia, Washington