tigated the effect of thinning on black spruce growth (Steneker. 1969, Weetman ... Minnesota DNR, Division of Forestry, for providing the study sites, arranging the ..... Stemwood production during the first five years after thinning. Can. For. Serv.
Strip Thinning and SpacingIncreases Tree Growth of Young Black Spruce Joanie Burns and Klaus J. Puettmann, Departmentof Forest Resources,Universityof Minnesota, St. Paul MN 55108; and Don Perala, USDA Forest Service, North Central Forest Experiment Station, 831 HW 169 E, Grand Rapids MN 55744.
ABSTRACT. Two differentthinningmethodswere appliedto three6- or 7-yr-oldblacksprucestandsin northernMinnesotawhichweremeasuredafter20 yr. Overall,thinningimprovedthegrowingconditions for croptrees.Stripthinningwitha 0.6 m leavestripandthreewidthsof clearedstrips(1.5 m, 2.1 m, and2.7 m), and •Toacing to 1.5 m, 2.1 m, and 2.7 m resultedin reducednumbersof crop trees,but with larger diameters and, in the spacingthinnedplots, greater heights.Becauseof thesecontradictingtrends,standvolumewas unaffectedby thinning.Crop tree growthwasnot affectedby the width of the clearedstrip, but thedistances betweentheleavetreesin thesquarespacingwerepositivelyrelatedto theincreasedgrowthresponse after thinning.Thestudyisstilltooyoungtoevaluatetheeconomic feasibilityofboththinningtreatments, butshorter rotationsor substantiallyincreasedvolumeseempossibleby early thinningsof black spruce.North. J. Appl. For. 13(2):68-72.
Blackspruce isanimportant species innorthern North America,occupying800,000haof commercialtimberlandin the Lake States alone. Two-thirds
of this land is found in
virtuallypurestandsin thelowlandorganicsoilsof northeast-
mine what rangeof youngstanddensitieswill resultin both goodtreeandstandgrowth.This informationwill helpland managersmake effective decisionsfor sustainableblack spruce management.
ern Minnesota(Perala 1971).
Dense,even-agedstandsof blacksprucearecommonly initiated after fire (Johnston1990). Current management practicesdo not include precommercialor commercial
thinnings(Johnston 1977).While severalstudies haveinvestigatedtheeffectof thinningonblacksprucegrowth(Steneker 1969, Weetman et al. 1980, Lavigne et al. 1987, Newton 1988,ShepardandShottafer1990),few studieshaveinvestigatedhow early densitymanagementaffectsfuture stand development. Becauseblacksprucegrowsslowly,thinning treatmentswill only be implementedif they providesufficientgrowthresponseandif implementation is inexpensive. Strip thinningis fairly inexpensiveandhas thereforebeen suggested asanalternative toolfor species or sitesfor which management potentialis marginal. This studywas initiated to comparethe effectsof strip thinning,squarespacingthinning,andno-thinningto deterNOTE:
We aregratefultothelateDr. William F. Johnston for thedesignand installationof thisstudy.We alsoappreciatethe cooperation of the Minnesota DNR, Divisionof Forestry,for providingthestudysites,
arranging theloggingandsitepreparation forregeneration, andother assistance throughoutthe courseof the study.We acknowledge Professor SanfordWeisbergof theUniversityof Minnesota,School of Statistics, forhishelpin thestatistical analysis ofdatacollected for the study.KlausPuettmannis the corresponding author.
68
NJAF13(2)1996
Objectives The objectiveof this studywas to investigategrowthof youngblacksprucestandsgrowingat variousdensitieson organicsoilof varyingfertility andlocation.Specificobjectives include(1) to examinethe effectsof squarespacing, stripthinning,andno-thinningon growthanddevelopment of individualtreesandstands,and(2) to examinethe effects of differentthinningintensitieson growthanddevelopment of trees and stands.
Methods
This studywas establishedin 1971 and 1972 in organic soilsin KootchichingCounty in northcentralMinnesota Three studyareaswhere black spruceforestwas clearcut and broadcastburned 7 to 9 yr earlier were chosen.The first site is the 1964 Block V Burn; a black spruce-alderherb forest in the Big Falls Experimental Forest. Natural seedingfrom surroundingtimber producedblack spruce seedlingsaveraging21,300 trees/ha 2 yr after burning The 50 yr site index was estimatedto be 12.5 m. The site is extremely brushy and is highly variable with dense patchesandopeningsthroughout.
The other sites are the 1965 Williams
Burn in Pine Island
StateForestand the 1965 Block II Burn in the Big Falls ExperimentalForest.Both areasare very wet and densely carpetedwith sphagnum mossandlabradortea. The WilliamsBurnwasseededandaveraged32,000trees/ha2 yr after burning.Naturalseedingoccurredfrom surrounding timber on the Block II Burn,andblackspruceseedlingsaveraged 50,000 trees/ha2 yr after burning.Fifty-year siteindex for BlockII wasestimatedin an adjacentstandto be 9.8 m and for the Williams
Burn to be "intermediate"
between that of
Block II and Block V (Johnston1978).
Occurrence of additionalvegetation onthesitesvariedconsiderably. Generally, thetwowettersiteshadgreater amounts of lowlyingvegetation, whilethegreatest amount oftallshrubs and woodyvegetation wason theBlockV site.Contraryto earlier reports thatunderstory vegetation wasgenerally notprevalent in BlockII (Johnston 1978),understory vegetation, suchassphagnummoss,labrador tea,canada mayflower,berries,andgrasses, wasmuchmoreprevalentontheWilliamssitethanonBlockII. All threesiteshadoccasional openings andpatches wherelittle additionalvegetationwas growing.Accordingto the forest ecosystem classification of Simset al. (1989), the vegetation typeof BlockV isV35-blackspruce/speckled alder/sphagnum, andthatof theothertwo sitesis V36-blackspruce/bunchberry/ sphagnum/feathermoss. ThesoilsofallthreesitesaretypeS125wet/organic(sphagnum). The occurrence of a varietyof smallerplantsandshrubsis notonlyimportantto standdiversity,butalsoto wildlife. All threesitesexhibitedsignsof useby deer,bears,anda number of bird species.
Experimental Designand Treatments The study usesa randomized,complete-blockdesign. Each of the three studyareashas two blocks,with seven treatmentsper block and threetreatmentgroups: 1 Spacing--Thinned to 1.5 m, 2.1 m, and 2.7 m square spacing.
2 Stripthinning--Leavestrip0.6 m wide,clearedstrips1.5 m, 2.1 m, and 2.7 m wide.
3 Unthinnedcontrols--Twoplotsper block. Leavetreesin thespacedplotswereselectedprimarilyto achievedesiredspacing,andlargertreeswereselectedover smallertreesonly when spacingwas not affected(Wilson 1952).The initial treatmenttookplacein 1971or 1972.Due to invasionof hardwoods andblackspruce,thethinnedplots in Block II were rethinned in 1973, and thosein Block V were
sprayedat a rateof two anda quarterkilograms/hawith 2,4D in waterduringthefall of 1972.Little damagewasevident in residualblack spruce(Johnston1978). Cuttingof hardwoodsandtall shrubsthatsubstantially overtoppedresidual blacksprucewasagainnecessary in 1976or 1977on Block II and the Williams
Burn.
Thestudyplotswereremeasured duringJune1993.Analysis was basedon the methodof nonoverlapping triangles
(Kher 1969,FraserandvandenDnessche1972).Nine points wererandomlyselected in eachtreatmentplot.Thethreecrop treesclosestto andencompassing thepointswereidentified and the distancesbetweenthem measured,henceallowing croptreedensityto be calculated.Croptreesweredefinedas treeslikely to surviveuntilmaturity(age100).Treesize(dbh > 1 cm), vigorandpositionin thecanopy,aswell asspacing to neighboring croptreeswereconsidered. Croptreespacing wasbasedon densityinformationfrom naturalstands(Fox andKruse1939)thatindicatedan averagespacingof treesat age100of 1.7m. Heightanddiameterat breastheight(dbh) of thethreecroptreesweremeasured, andnumberof noncrop treesinsidethe trianglewas counted.The presenceof any other herbaceousplantswas recorded.Standvolume was calculatedbasedon basalarea and averageheightof crop trees(GevorkiantzandOlson1955). Statisticalanalysisused the analysis of variance and contrast functions of
MACANOVA ¸ (Bigham andOehlert 1993)totestfordiffer~ encesbetweentreatmentgroups.In additionthe data were testedfor significant(P_
