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Acorn Production in Red Oak

by

Daniel C. Dey

1 995

Ontario Ministry of Natural ResourcesOntario Forest Research Institute

P,O. Box 969, 1235 Queen Street EastSault Ste. Marie, Ontario

P6A 5N5

Canadian Cataloguing in Publication Data

Dey, Dan.Acorn oroduction in red oak

(Forest research information paper, ISSN 0319-9118 ; no. 127)lssued by Ontario Forest Research Institute.tsBN 0-7778-4833-3

1. Red oak.2. Acorns.l. Ontario, Ministry of Natural Resources.ll. Ontario Forest Research Institute.l l l . T i t le.lV. Series,

sD397.012D49 1995 634.9'721 C95-964111-4

O 1995, Queen's Printer for OntarioPrinted in Ontario. Canada

Single copies of this publicationare available at no charge fromthe address noted below. Bulkorders may involve charges.

Ministry of Natural ResourcesOntario Forest Research InstituteP.O. Box 9691235 Queen Street EastSault Ste. Marie, OntarioP6A 5N5

Telephone: (705) 946-2981Fax: (705) 946-2030E-mail: ofr i in@epo. gov.on.ca

Cette publication scientifique n'estdisponible qu'en anglais.

Cover art: Carmen Misasi

This paper contains recycled materials.

AbstractDey, Daniel C. 1995. Acorn production in red oak. Ontario Ministry of Natural Resources,

Ontario Forest Research Institute, Sault Ste. Marie, Ontario, Forest Research InformationPaper No.127,22p.

Managers of oak forests are often interested in acom production for oak regeneration andwildlife. Although potential acorn production is genetically controlled, actual productiondepends on weather, site productivity, wildlife and insect activity, and individual treecharacteristics. Crown characteristics such as width, area and dominance, and tree age and dbhare correlated with acorn production.

Manipulation of stand stocking through thinning can increase the amount of oak in the uppercrown classes and enhance individual tree characteristics that promote good acorn production.Identification of good acorn producers before thinning or shelterwood harvests can be used toretain them in a stand. Stocking charts can be used to time thinnings and to estimate acornproduction for individual stands. Maintaining stocking between A- and B{evel ensures completeuse of growing space by trees. As stocking approaches the A-level, thinning back to the B-levelshould maintain oak in the upper crown classes and simultaneously promote maximumdevelopment of individual tree characteristics known to influence acorn production. A methodfor estimating acorn production and preliminary guidelines for acorn management are presented.

Keywords: Red oak, regeneration, acorn production, silviculture, stand stocking, thinning.

AcknowledgmentsI am grateful to Paul ]ohnson for his review of this manuscript.

Table of Gontents

Abstract

Acknowledgments

Introduction .. . .

Importance of Acorns

Overview

Acorn Production

Variability in production . . .

Frequency ofacorn crops .

Factors that affect acorn production

Stocking and Acorn Production

Estimation of Acorn Production

Management Recommendations

Summarv

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L i te ra tu rec i t ed . . . . . 76

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List of Tables

Thble 1. Summary of observed acorn production of oaks throughout the eastern United States. . 2

Table 2. Suggestedguide for rank ingredoakacorncroPs ' . . . . . . . ' . 3

Thble 3. Rankingof acornproductionforindividualtreesinthe redoakgroup .. ' ' . . . . . 6

Thble 4. Maximum crown areas of dominant, forest-grown red oaks and tree densities required

for full utilization of the available growing space by oaks, i.e., B-level stocking. . . . . ' . 7

Table 5. Sumrnary of starrd characteristics for 2 mixed-hardwood stands dominated by red oak,

Bancrof tandFembrokeDist r ic ts . . . . " " " ' 10

Thble 5. Comparison of estimated sound acorn production (per ha) in 2 stands located in the

Bancroft dnd Pembroke Districts and potential acorn yields for hypothetical stands that have

largerd iameteroaksandhigheroakstock ing. . . . " " " ' 12

List of Figures

Figure 1.. Observed (solid circles) and predicted (curved-1ine) production of sound acorns per m2

of crown area of red oak in relation to dbh " " " " 4

Figure 2. Relationship between dbh, density (trees/ha) and sound acorn production per unit

crown area for red oak. " " " " 9

Figure 3. Relationship between dbh, stocking and sound acorn production per unit crown area

fo r redoak . . " " ' 9

Figure 4. Proportion of estimated sound acorns/ha in relation to diameter (dbh) classes in 2

upland o ikstands onthe Bancrof tand PembrokeDist r ic ts . . . . . . . . . . . 11

Introduction

lmportance of AcornsForesters and wildlife biologists are

increasingly becoming interested inmanaging oak forests for acom productionfor both oak regeneration and food forwildlife. Acorns provide food for nearly 200species of wildlife such as chipmunks,squirrels, turkeys, small rodents, deer, bears,foxes, raccoons/ rabbits, waterfowl,woodpeckers, bluejays and other birds(Gysel 1952 Korschgen1962, Goodrum et al.l97'L,Sander 1990, DeGraaf et aI.1992,Auchmoody et al. 1993, Beck 1993, Edwardset al. 1993,Johnson 1994). Many insectspecies (e.g., Curculio spp., Conotrachelusspp.) also use acorns. In years of low tomoderate acorn production, insects maydamage a large portion (50 to 80%) of thecrop (Downs and McQuilken 1944,Christisen 1955, Gysel 1957,Sander 1990,Beck 1993).

Natural regeneration of oak largelydepends on the presence of adequatenumbers of "large" advance reproduction atthe time of final overstory removal. Acornproduction affects the amount of advancereproduction that becomes established inany given year. However, wildlife and insectconsumption of acorns often limits theamount of oak reproduction that becomesestablished.

In the southern Appalachians, acorncrops of less than224 kg/ha are usuallytotally consumed by forest wildlife andinsects (Beck 1993). Production of soundacorns exceeds this level only during yearswith good to bumper acorn crops (BeckP7n. Thus, establishment of oak seedlingsoccurs primarily in years when the nurnberof sound acorns produced exceeds thedemand for acoms by wildlife and insects(Downs and McQuilken 1944, Christisen1955, Gysel195Z Christisen and Kearby1984, Hannah 1988).

Timber harvest and intermediatethinnings can have either a positive ornegative effect on the capacity of a stand toproduce acorns. Obviously, the removal ofall oaks from the overstory or thehigh-grading of oak eliminates or severely reducesthe local acorn supply. Shelterwood harvest

frombelow in mature stands or thinningyoung oak stands can be used to maintain orenhance acorn yield. The intent of this Paperis to present a method for estimating acornproduction and preliminary guidelines forthe management of acorn production.Although the emphasis is on red oak(Quercus rubra L.), the concepts presentedare also apptcable to other oaks.

Overview

Acorn Production

Variability in production

Acorn production is highly variableamong oak species, individual trees,locations and years (Downs and McQuilken1944, Christisen L955, Christisen andKorschgen 1955, Gysel 1957,Sharp 7958,Tyron and Carvell 1962,Beckand Olson1968, Goodrum et al. 197L, Beck 1977,Christisen and Kearby 1984,Drake 1991.,Auchmoody et al. 1993, Sork et al. 1993). In agiven area, numbers of acorns produced peryear may range from 0 to 620,000 /ha (Table1) .

Auchmoody et al. (1993) provided aguide for ranking acorn crops (Table 2).They considered any production greaterthan about 309,000 acorns/ha to be a goodor better crop. Others consider 250,000acorns/ha or more to be good crops, andbumper crops may yield up to 620,000aconrs/ha (Beck 1993).

Gysel (195n reported that the A-yearaverage production of red oak acorns was75,600 /ha on good sites in Michigarr. Beckand Olson (1968) stated that acorn

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production levels ranged from 1.6,300 to233,800/ha in mixed oak stands in thesouthern Appalachians. Barni (1980)observed average acorn production levelsthat varied between 27 ,600 and 99,300 /ha nPennsylvania. Average acorn biomassproduction over 12 years was 324kg/ha(about 89,100 acorns/ha) in southernAppalachian oak stands, but this averagewas heavily influenced by a bumper cropthat produced 1,135 kg/ha (about 312,125acoms/ha) (Beck D7n.

Sork et al. (1993) observed that the 8-year average annual acorn production forindividual red oaks varied from 6L to 1,033acorns. The maximum annual crop size fromindividual red oaks ranged from 190 to 3,322acorns. Downs and McQuilken (1944)reported that the 7-year average annualproduction of oaks was 1.,213 acorns per treein the southern Appalachians, althoughthere was much variability between trees. Ina good seed year, oaks produced2,647acorns per tree on average. Christisen (1955)studied the production of acorns in Missourioaks over a 6-year period. He found that inthe best year of production, trees in the redoak group (Erythrobalanus) produced from815 to 1,360 sound acorns per tree.

For all oak species, some trees areconsistently good producers and others areconsistently poor producers (Downs andMcQuilken 1944, Christisen 1955, Christisenand Kearby 1984, Sander 1990, Beck 1993).These tendencies are most often attributed tothe genetic capability of the tree to produceacorns (Downs and McQuiLkenl944, Cypertand Webster 1948, Burns et al'.1954, Sharp1958, Sharp and Sprague 1967, Christisenand Kearby 1984, Sork et al. 1993).

Frequency of acorn crops

Acorn production is sporadic andunpredictable (Sander 1990, Auchmoody etaL.1993, Beck 1993, Cecich 1993, Johnson1994). The inherent periodicity for goodacorn crops of red oak apPears to be 4 yearsbut the actual frequency of good crops mayvary because of environmental factors thatlimit production such as weather, soilfertility, stand density, insects, diseases andwildlife (Christisen and Kearby 1984, Sork etal. 1993). In the red oak group/ some goodacorn producers may yield well in any givenyear while others do not (Sharp 1958).Bumper acorn crops occur when all goodproducers yield a good crop in the samevear.

Thble 2. Suggested guide for ranking red oak acorn crops (from Auchmoody et al. 1993).'

Subjective uop rating No. acorns/ha No. acorns/m2

Bumper

Good

Fair

Poor

Trace

>618,000

31"0,000-61.8,000

1"62,000-309,000

49,000-161.,000

54

33-54

17-32

5-L6

Forest Research lnformation Paper

Good to excellerrt crops of red oak acornsoccur on average every 2 to 5 years (Sander1990). Beck(1977) reported that red oakproduced bumper crops at s-year intervalsover a l2-year period in mixed oak stands inthe southern Appalachians. Durin g a 21.-yearstudy of red oak acorn production innortheastern Wisconsin, Godman andMattson (1976) observed bumper acorncrops every 7 years on average. However,the interval between some bumper cropswas only 2 years. Drake (1991) found thatthere were 3 bumper crops (> 700 kg soundacorns/ha, or >192,500 acoms/ha) during aL3-year period in Pennsylvania. He reportedthat only one other year produced meanacorn yields greater than 150 kg/ha (about41.,250 acorns/ha). Red oak comprised 30 to60% of the basal area in the pole-sized,mixed oak stands he studied.

Factors that affect acorn production

Acorn production is influenced bYweather, insects, wildlife, tree age and size,tree crown position, and the tree's inherentcapacity to produce acorns. In the long-term,tree characteristics and genetics are probablymore important than environmental factors(e.g., weather, wildlife and insects) indetermining actual acorn production (Beck1ee3).

Acorn yields increase with tree age(Downs and McQuilken 1944, Goodrum etaL 1971). Most oak species begin productionwhen trees are about 20 to 25 years old, butsubstantial yields do not occur before age 40or 50 (Reid and Goodrum1957,USDA1974,Sander 1990). Open grown trees may beg*production earlier than trees crowded indense stands (Beck 1993). For many oakspecies, there is a threshold age beyondwhich acorn production levels off for anextended period. Production then declineswith continued increases in age. When treesbecome senescent, they often experiencecrown dieback and become poor acornproducers (Goodrurn et al. 1.971., Huntley1983).

Other factors being equal, trees of largediameter produce more acorns than trees ofsmall diameter (Moody 1953, Downs andMcQuilken 1944, Goodrum et al. 197 1,johnson t994). For some oak species,including red oak, acorn productionincreases with increasing diameter to athreshold beyond which production declines(Frgure 1) (Downs 1944). Gysel (195nobserved that acorn production of red oakincreases rapidly as dbh increased up to 36cm. In the southern Appalachians, maximumacorn production for red oak occurs in treeswith diameters between 41 and 56 cm(Downs 1944).

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N0.127

Production declines rapidly as tree diameterfurther increases. This may be due to loss oflive crown and overall vigor as older treesbecome senescent.

Crown size, health and class are majorfactors that influence acom production(Toumey and Korstian1937, Downs andMcQuilken L944, Burns et aL 1954, Christisen1955, Christisen and Korschgen 1955, Reidand Goodrum1957, Matthews 1963,Christisen and Kearby 1984, Sander 1990,Drake 1991). Acorn yields were larger foroaks with wide crowns and large crownsurface areas than for trees with smallnarrow crowns (Christisen 1955, Goodrumet al. 1971). Sork et al. (1993) reported thatthe mean mature acorn crop per tree wassignificantly correlated with crown area.Downs and McQuilken (1944) stated thattotal acorn production was related directlyto crown size and indirectly to bolediameter. Dominant and codominant oaks,whose crowns receive fulIsunlight,produced more acorns than the more heavilyshaded intermediate or suppressed trees(Sharp 1958, Sharp and Sprague 1967).Drake (1991) found that 96"h of dominantoaks and 76% of codominant trees producedacorns, whereas only a small proportion ofoaks in the suppressed (e.g., 9%) andintermediate (e.g., 38%) crown classesproduced any acorns during al3-year studyperiod.

Free-to-grow crowns that receive fullsunlight have a higher density of live,healthy branches than small, shaded crowns.Acorn production increases as the number oflive, healthy branches increases (Verme1953). Oaks with unhealthy, low-vigorcrowns/ as evidenced by dead limbs in theupper crown, do not produce acorns inquantity (Shaqp 1958). Larger diameter redoaks usually have more foliage and livebranchwood biomass than smaller-diametertrees (Loomis and Blank 1981), which maybe one reason why acorn productionincreases with increasing tree diameter.

Bole diameter is a useful indicator of theaverage acorn production potential of oaks(Downs 1944,Downs and McQuilken 1944).Tree diameter also is correlated with crownwidth and crown area (Krajicek et al. L961,Minckler and Gingrich1970, Sampson L983,Lamson 1,987). This relationship betweentree diameter and crown size has been usedto develop stocking charts and equations foroak-dominated ecosystems (Gingrich 1'9 67,Sampson 1983, McGill et al. 1991). Loomisand Blank (1981) found that both dbh andthe live crown ratio of red oak weresignificantly related to foliage and livebranchwood biomass, which influence theproduction of acorns. Therefore, treediameter, an easy-to-measure treecharacteristic, is directly related to many ofthe factors known to influence acomproduction including crown size, tree ageand crown density.

Stocking and Acorn Production

Maintaininghigh red oak stocking levelsmay not ensure acom production becauseonly a minority of oaks are inherently goodacorn producers (Beck 1993). For example,there may be only 50 oaks/ha that are goodproducers (Johnson 1994). The best approachto maximizing acorn production would be toidentify the good acorn producers andprovide them with adequate growing spacethroughout their development. However,doing that would require investments inacorn surveys and periodic thinnings.

It is difficult to identify the inherentlygood producers without long-term fieldobservations of acorn production. Ideally,observations of acorn production for 5 ormore years could be used to identify thegood producers. Alternatively, the acom-producing capacity of individual trees can beassessed in a single year of good to excellentproduction in a given stand. Longer termobservations are preferrable because trees inthe red oak group that are good producerson average do not always produce acornsabundantly in the same year (Shary 1958).

Forest Research Informalion Paper

Shary (1958) outlined procedures forsampling and rating acorn production. Touse his method, oaks must be observed fromeady to mid-August because acoffIs arelarge enough at that time to view themthrough binoculars and acorn predatorshave not had time to destroy the crop.Acorns of red oak are located beneath theleaves of the current year's growth and,hence, are visible from below. They areattached by short stalks to the previousyear's stem growth. A bright skybackground makes it easier to view acornsas the observer looks up through thebranches. Acoms should be counted on theterminal60 cm (excluding the current year'sgrowth) of healthy branches in the upperthird of the crown. Acorn production ofindividual oaks can be ranked using theguidelines presented in Table 3. Good acomproducers can be identified using thismethod over several acorn crops and thesetrees can then be reserved from harvest.

Christisen and Kearby (1984) providedan alternative method for ranking acorrLcrops. They used acorn cluster size and thepercentage of the crown that contains acornsto assign L of 9 acorn productivity ratings toa tree. The uniformity of acorn productionon a tree is also an important considerationin their ranking system. The relative size ofacorn clusters varies among oak species, asdoes the spatial distribution of acorns in thecrown. For red oak, a large acorn cluster

may contain 5 to7 acorns. Trees in the redoak group seldom have acorns on limbs inthe lower half of the crown. Thus, indetermining the uniformity of acornsthroughout the crown, only the upper half ofthe crown should be considered.

Even without knowingwhich oaks arethe good acorn producers, oak stockingguides could be used to schedule thinningsthat might increase the potential of a stand toproduce acorns. Growing spacerequirements of red oak in mixed-speciesstands have been developed in Wisconsin(McGill et al. 1991) and New England(Sampson L983), and in oak-hickory standsin the central United States (Gingrich P6n.

As defined by these guides, B-levelstocking represents the lowest level ofstocking for fulIsite utilization. It alsosignifies the point where inter-treecompetition for growing space begins whentrees are uniformly distributed throughoutthe stand. At this level of stocking, maincanopy trees have the maximum amount ofgrowing space that they can use for crowndevelopment. For example, the crown areasof red oaks at B-level stocking range fuom44rn-r for trees 30 cm in dbh to 105 m2 for trees50 cm in dbh (Table 4). Thus, 227 oaks thataverage 30 cm in dbh would completely usethe growing space on 1. ha, or 95 oaks/hathat average 50 cm in dbh.

Table 3. Ranking of acorn production for individual trees in the red oak group (adapted fromSharp 1958).

Ranking of production Average number of acorns/branchr

Excellent

Good

Fair

Poor

>24

L6-23

9-1.5

N0.127

A-level stocking represents themaximum density where each tree has theminimum growing space it needs to survive.Competition is greater at the A-level ofstocking than at the B-level. Thus, oakswould have smaller crowns at the A-level ofstocking than if grown under less densestand conditions. Full site utilization occursbetween A- (100%) and B-level (55%)stocking.

At B-level of stocking, the crown areas ofindividual oaks are potentially at theirmaximum. Acorn pioduction of individualtrees is optimalbut the density of oak isrelatively low. As stocking increases abovethe B-level for a given diameter, the number

of potential acorn producers increases,which may lead to an increase in total standacorn production. However, as stand densityincreases, inter-tree competition causes oakcrowns to become smaller and to have lessfoliage and fewer fine branches, therebypotentially reducing the acorn production ofindividual trees. At some threshold stocking,increasing the number of oaks in the standmay cause a net decline in total acornproduction because the additional trees maynot add enough to total stand production tooffset reductions in individual treeproduction that result from decreases incrown s2e. There may be an ideal range ofstand stocking that maximizes stand-levelacorn production but this is not now known.

Table 4. Maximum crown areas of dominant, forest-grown red oaks and tree densities requiredfor fullutilization of the available growing space by oaks, i.e., B-level stocking.

Maximum crown area' Trees/ha2Dbh

(cm) (m')

227

175

105

124

1.46

1 Calculated using the following equation (adapted from Sampson 1983):

CA = 1..477 + 0.4396D8H + 0.0327D8H2,

where CA = crown area of dominant, forest-grown red oak (mz) and

DBH = diameter breast height (cm).

2 Calculated by dividing the area in t ha (10,000 m') by the crown area (m2) of an individual red oak.

141,

115

95

81

68

44

57

71

6 /

30

35

40

45

50

55

60

]

Forest Research Information Paper

Estimation of Acorn Production

Downs (1944) observed red oak acornproduction in relation to dbh over a 7-yearperiod in the southern Appalachians. If weassurne that his study stands were fullystocked (i.e., A-level stocking), we can usethe main canopy tree area equationdeveloped by McGill et al. (1991) to calculatethe crown area of Downs' red oaks.

l1l CA = 0.55 + 0.148*DBH + 0.02*DBH2,where:cA = crown area per tree (m'?) andDBH = diameter breast height (cm).

The number of sound acorns per m2 ofcrown area is determined by dividing theactual production for a tree of given dbh(Downs 19 Qby its crown area (Figure L).

The relationship between acornproduction per unit crown area and tree dbhis defined by the following nonlinear model(r*=0.9964) (Figure 1):

[2] AP = 3,463,971*EXP(-0.125*DBH -

277 .434* (1 / DBH)), where:AP = ?corn production per m2 of crown areafor a red oak of grven dbh,EXP = the exponential function, andDBH = diameter breast height (cm).

Equation [2] was used to estimate total acomproduction over a range of density andstocking of red oak (Figures 2 and 3).

The size and nurnber of oaks in a standinfluences acom production as shown inFigure 2. Maximum acorn production occursbetween 50 and 60 cm dbh for any givendensity of oak. When 140 oaks in thisdiameter range occur per ha, approximately212,000 to 215,000 sound acoms/ha will beproduced on average. Figure 2 can be usedas a guide to approximate averageproduction of sound acorns from aninventory of the red oak in a stand and tocomparatively evaluate the effects ofsilvicultural alternatives on acorn supply.

Either stand averages or individual treedata may be used with Figure 2. Moreprecise acom estimates can be calculated byfollowing the procedures outlined inAppendix I. Acorn production calculatedusing stand-level average dbh and density ofoaks results in conservative estimatesbecause the relatively few, but largediameter (40 to 60 cm) oaks, which arecapable of producing large quantities ofacorns, are not considered directly.However, estimates based on stand averageoak characteristics may be appropriate forregional or landscape-level plannnhg,especially when detailed stand data are notavailable. Individual tree characteristicsobtained by sampling a stand can be used tomore accurately estimate sound acornproduction and should be used indeveloping stand-level prescriptions.

Inventories of 2 upland oak stands, onenear Papineau Lake, Bancroft District andthe other near Foymount, Pembroke District,were used to estimate sound acornproduction. Both stands have a closedcanopy of mature (80+ years old), mixed-hardwoods including red oak, sugar maple(Acer saccharum Marsh.), beech (F agusgrandifolia Ehrh.), red maple (Acer rubrumL.),white ash (Fraxinus americana L.) andbasswood (Tilia americanaL.). Red oakcomprises 30% or more of the basal area inboth stands. In either stand, there is littleevidence of recent disturbances from eitherlogging or catastrophic events such as fire orwind. Table 5 summarizes average standcharacteristics for both stands based on 23(Bancroft) and 31 (Pembroke) 0.08 hacircular plots in which all trees >2.54 cm dbhwere measured.

The estimated sound acorns/ha is 31155at Bancroft and6'1.,664 at Pembroke based onstand average oak dbh and density(Appendix I). If, however, individual oakdata are used to estimate sound acornproduction, then the Bancroft stand can

N0.127

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Figure 2. Relationship between dbh, density (trees/ha) and sound acorn production per unitcrou)n area for red oak. The solid star represents aaerage stand conditions and estimated soundacorn production for 2 oak-dominated stands in tlrc Bancroft and Pembroke Districts.

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Figure 3. Relationship between dbh, stocking and sound acorn production per unit croam area forred oak. The solid star rEresents average stand conditions and estimated sound acorn przductionfor 2 oak-dominated stands in the Bancroft and Pembroke Districts.

Forest Research Information Paper

produce 62,444/ha and the Pembroke stand71.,200/ha. These values compare favorablywith observed red oak acorn crops inMichigan (Gysel 1957), Pennsylvania (Barni1980) and North Carolina (Beck1,977).

In these Ontario stands, half of theestimated acorn production comes froml3'/'of the overstory oaks, whose diameters are>40 cm (Figure 4). While only 3% of the oaksoccur in the 50 cm and larger dbh classes,they producel.4% of the estimated soundacom crop. A rather small proportion of theestimated acorn crop (9%) is contributed byoaks with diameters

30 cm class(40.7%)

N0.127

Bancroft

Pembroke

20 cm class(1O.7yo)

60 cm class(6 .1%)

50 cm class(6.8%)

20 cm class(7.0o/o)

60 cm class(4.o%)

40 cm class(37.0%)

30 cm class(4o.0%)

Figure 4. Proportion of estimated sound acorns/lxa in relation to diameter (dbb classes in 2upland oak stands on the Bancroft and Pembroke Districts.

Forest Research Information Paper

Figure 3 can be used to evaluatesilvicultural treatrnent effects on acornproduction. Two oak stands on the Bancroftand Pembroke Districts averaged 94%stocking based on trees of all species thatwere >5 cm dbh and in the intermediate orlarger crown classes. Oak stocking in thesestands is52% and the oak averages 30 cm indbh. These stands can produce about 40,000sound acorns/ha (Ftgure 3). Thinning torelease crop trees in young oak stands cansubstantially increase acoflr production.Increasing mean stand dbh of oaks from 30to 40 cm would increase acom production at50% oak stocking from 39,235 /ha to113A67 /ha (Table 6). When oak stocking is70% andmean dbh for oak is 40 cm,158,854acorns/ha may be produced on average.

Our ability to maximize mean oak dbh islimited by site productivity. Linking siteproductivity to FEC ecotypes in the future

will help define diameter growth potentialfor specific site conditions. Also,management concems may influence thedesired level of oak stocking. For instance,pure oak stands may experience greaterreductions in growth and survival thanmixed-species stands following catastrophicevents such as gypsy moth outbreaks or oakdecline. Therefore, a reasonable goal may beto maintain oak stocking at 30 to75"/o onsites of average to fair productivity. Onhigher quality sites, 10 to 30% oak stockingmay be all we can expect without substantialsilvicultural inputs. Although we lackdetailed guidelines for setting size andstocking thresholds for oak on specificecotypes, prescriptions for stands with anoak component should define standcharacteristics in relation to acornproduction targets.

Thble 5. Comparison of estimated sound acorn production (per ha) in 2 stands located in theBancroft and Pembroke Districts and potential acom yields for hypothetical stands that havelarger diameter oaks and higher oak stocking. The shaded area is estimated acorn productionbased on current average conditions for the Bancroft and Pembroke stands.

I Stocking of red oak in a stand, which is computed using the main canopy equation of McGill et al. (1991).

Stockingl

(%)

Mean stand dbh

30 cm

Mean stand dbh

40 cm

Mean stand dbh

50 cm

50 113467 1"30,L50

60 47,082 1.36,161 156,180

70 54,929 L58,854 182,209

80 62,776 L81,548 208,239

12

No,127

ManagementRecommendations

It is not usually possible to control theexogenous factors that affect acornproduction such as the weather, or wildlifeand insect populatons. However, we cancontrol the amount of overstory oak, itsphysical characteristics and the inherentcapacity of oak in a stand to produce acorns.

When oaks are about 40 or 50 years old,good producers should be identified andmaintained in a codominant or betterposition in the stand. Dominant andcodominant oaks willbe the best acornproducers. Good acorn producers should bereleased from competition by thinning sothat their crowns are exposed to full sunlighton all sides. This practice will promotecrown expansion and increase live branchdensity, which should increase acornproduction. Area-wide thinning is notnecessary because the release of goodproducers is all that is needed to maximizeacorn production.

Crop-tree thinning oaks in young stands(7 to 22 years old) increases diameter growthand should increase oak stocking in theupper crown classes as the stand develops(Ward 1995). An additional thinning may beneeded to promote the continued growth ofintennediate and suppressed oak saplingsinto the upper crown classes. Discriminatingagainst non-oaks and non-acorn producingoaks in thinning should increase the amountof acorn bearing crown area in the uppercrown classes, especially when trees arereleased at an early age. However, acornproduction in young oak stands does notalways increase following thinning. Drake(1991) found that acorn production was notsignificantly increased 10 years afterthinning young (e.g.,42 to 58 years old),even-aged oak stands. His results wereconfounded by 5 years of defoliation by thegypsy moth that occured after thinning.

Acorn production is reduced in oaksdefoliated by gypsy moths (Gottschalk19BB).

The stocking chart (McGill et aL.1,997)can be used to time thinnings. As a youngoak forest develops, thinning shouldmaintain stand stockingbetween the B- andA-level. This will ensure that the availablegrowing space is fully used by trees.Thinning back to the B-level, as needed, willpromote maximum crown development onthe residual oak. Oaks maintained at highstocking levels for long periods will havesmaller crowns with less dense foliage andfewer live branches than oaks that arereleased when stand stocking approachesthe A-level.

Acorn production is maxim?ed inmature stands when oaks average 40 to 60cm in dbh and comprise 55"/' or more ofstand stocking on sites with average orbetter productivity. When initial stocking ofoak is less than 55o/o,practically all uPPer-canopy oaks should be retained to maximizeacorn production. To achieve 55% stockingof red oak when dbh ranges from 40 to 60cm, there would be approximately 141 to 68oaks/ha, respectively (Table a).

Thinning may be less beneficial whenmanaging older stands. Increases in acornproduction are limitedby the decliningbiological potential of older oaks, whicheventually become senescent. The crowns ofolder oak are less able to increase in size,mass and area after thinning than arecrowns of younger trees. Also, as standsreach maturity and some oaks begindropping into the lower crown classes, thereis less opportunity to increase their growthpotential than when they are alwaysmaintained in the upper crown classesthrough periodic thinning (Ward andStephens 1994).

In older stands, thinning is less likely toresult in increases in the absolute amount ofoak in the overstory because these trees aremore susceptible to decline (Wetteroff 1993).

13

Forest Research Information Paper

Oak decline causes reductions in the acornproduction of individual trees and decreasesin stand production as overstory oaks die.Many oak forests in Ontario are 90 to 110years old, and oak decline symptoms areoften present, especially on sites withshallow soils (Evans et al. 1994,Sajan et al.1994,Guyette and Dey 1995).

Management of older stands can be doneso that acorn production capacity ismaintained by either retention of knownacorn producers or by leaving oaks in theupper crown classes. When conductingshelterwood harvesting or intermediatethinnings, reserve oaks that: (1) aredominant and codominant, (2) have large,healthy crowns/ (3) have abundant foliageand live branches, (4) are between 40 and 60cm in dbh (in mature stands), or (5) arebetween the ages of 50 and 100 years. Oaksfailing to meet these criteria may beremoved in thinnings or harvests. However,non-oaks in the overstory should beremoved fust. Oaks can be removed withoutsignificantly reducing acorn production ifthe harvested trees: (1) are mature and haveintermediate or suppressed crowns, (2) havelarge, dead branches in the upper crown, (3)have small and narrow crowns/ (4) havebroken crowns/ (5) have partially developedcrowns due to competition with neighboringtrees, or (6) seldom produce acorns.

In the southem United States,reconunendations are to retain from 12 to 25well-formed oaks (2 25 cm in diameter)/hato provide acorns for wildlife species(Murray and Frye 1957, Strode1957,Baternan 1959). Downs and McQuilken(1944) suggested leaving 25 good acornproducers (>42 cm in dbh)/ha toaccomodate acorn predators and stillprovide enough acorns for adequate oakregeneration. When reserve trees are smaller(e.g.,30 to 40 cm in dbh),50 oaks/ha shouldbe left.

l,eaving 25 oaks/ha that are 42 cm indbh would result in a maximum crown

cover of 78% (according to Sampson 1983) or3.5 m'?lha residual basal area. Retention of50 oaks/ha that are 30 cm in dbh wouldresult in a maximum overstory canopy coverof 22% or 3.5 n4 /ha residual basal area. Thisamount of residual overstory should notsignificantly affect the development ofreproduction provided that shade tolerantsaplings >2.5 cm in dbh have been removedduring harvest. Miller and Schuler (1995)reported that from 30 to 37 codominantresidual trees/ha (4.0 to 5.9 rfi /ha) had nonoticeable effect on the development ofcentral Appalachian hardwood reproductionL0 years after a harvest, in which all trees>2.5 cm in dbh were felled. This low level ofresidual overstory density and crown coverwill not negatively effect long-termdevelopment of reproduction. If thisrelatively sparse residual overstory consistsof codominant or better oaks, then acornproduction can be sustained for long periodswhile the new stand is regenerating anddeveloping seed bearing oaks.

SummaryOptimum production of acorns is critical

for successful oak regeneration and isimportant for many wildlife speciesdependant on acoms as a food source.Production is highly variable amongindividual trees; some trees are consistentlygood producers while others are not. Thefrequency of good acorn crops can besporadic and unpredicatable, but theinherent periodicity for good crops is 4years. Biotic and abiotic factors determinethe actual level of production in any givenyear.

Tree age, diameter and crowncharacteristics influence acom production.Production increases with increasing ageand diameter to a point, beyond which itdeclines as trees become senescent.Maximum production occurs in oaks that are40 to 60 cm in dbh and 50 to 100 years old.Oaks with wide, dominant crowns that have

14

N0.127

large surface areas exposed to direct sunlightcan produce large crops.

A method has been presented here forestimating acorn production of stands orindividual oaks based on tree dbh anddensity. The method was developed usingempirical acorn production data andstocking relations for red oak. Theseestimates can be used to evaluatesilvicultural alternatives and to assesstreatment effects on acofn production.

Estimates of average sound acornproduction are 62,444/ha and 71200 lha for2 upland oak stands on the Bancroft andPembroke Districts, respectively. Thesevalues compare favorably with observed redoak acorn production in Michigan,Pennsylvania and North Carolina. A largeproportion (50%) of acorns are produced bythe relatively few,large oaks (>40 cm dbh) inmature upland oak forests in Ontario. Oakswith dbhs 30%

15

Forest Research Information Paper

oak by basal area). A method is given forestimating acorn production, which is an

Literature GitedAuchmoody, L.R., H.C. Smith, and R.S.

Walters. 1993. Acorn production innorthern red oak stands in northwesternPennsylvania. USDA For. Serv. Res. Pap.NE-680.5 p.

Barnl R.T. 1980. Production and utilizationof acorns on the Quehanna Wild Area.Thesis. Penn. St. Univ. Sch. For. Res.48 p.

Bateman, B.A. 1959. Timber and game adesirable combination. Louisiana St.Univ. Agric. Exp. Sta. Res. Rep. 32.2p.

Beck, D.E. 1977.Twe|ve-year acorn yield insouthern Appalachian oaks. USDA For.Serv. Res. Note SE-244.8p.

Beck, D.E. 1993. Acorns and oakregeneration. P. 96-104 lz Proc., OakRegeneration: Serious Problems,Practical Recommendations. USDA For.Serv. Gen. Tech. Rep. SE-84.

Beck, D.E., and D.F. Olson, Jr. 1968. Seedproduction in southem Appalachian oakstands. USDA For. Serv. Res. Note SE-91.7p .

Burns, P.Y., D.M. Christisen, and J.M.Nichols. 1954. Acorn production in theMissouri Ozarks. Univ. Missouri Agric.Exp. Sta. Bull.611.

Cecich, R.A. 1993. Flowering and oakregeneration. P. 79-95 ln Proc., Oakregeneration: serious problems practicalrecofiunendations. USDA For. Serv. Gen.Tech. Rep. SE-84.

Christisen, D.M. 1955. Yield of seed by oaksin the Missouri Ozarks. I. For. 53:439-44'l'.

important consideration when developingprescriptions for oak stands.

Christisen, D.M., and W.H. Kearby. 1984.Mast measurement and production hMissouri (with special reference toacoms). Missouri Dept. Conserv.Terrestrial Ser. #13. 34 p.

Christisen, D.M., and L.J. Korschgen. 1955.Acorn yields and wildlife usage inMissouri. Trans. North Am. Wildl. Conf.2Q:337-357.

Cypert, E., and B.S. Webster.1948. Yield anduse by wildlife of acoms of water andwillow oaks. J. Wildl. Manage. 12(3):227-231..

DeGraaf, R.M., M. Yamasaki, W.B. Leak, andJ.W. Lanier. 1992. New England wildlife:management of forested habitats. USDAFor. Serv. Gen. Tech. Rep. NE-144.271' p.

Downs, 4.4.1,944. Estimating acorn cropsfor wildlife in the southernAppalachians. J. Wildl. Manage. 8(a):339-340.

Downs, A.A., and W.E. McQuilken. L944.Seed production of southemAppalachian oaks. J. For. 42:913-920.

Drake, W.E. 1991. Evaluation of an approachto improve acorn production duringthinning. P. 429-441, in Proc., 8th centralhardwood for. conf. USDA For. Serv.Gen. Tech. Rep. NE-148.

Edwards,J.W, D.C. Guynn,Jr., and S.C.Loeb. 1993. Seasonal mast availability forwildlife in the Piedmont Region ofGeorgia. USDA For. Serv. Res. Pap. SE-287.1.3p.

Evans, H.J., C.G. Jones, T. Bouwmeester, S.G.Payne, and W.A. Ingram. 1994. Results offorest insect and disease surveys in thecentral region of Ontario, 1993. Nat.

16

N0,127

Resour. Can., Can. For. Serv. Inf. Rep. O-X438.47p.

Gingrich, S.F. 1,967 . Measuring andevaluating stocking and stand density inupland hardwood forests in the CentralStates. For. Sci. 13(1):38-53.

Godman, R.M., and G.A. Mattson. 1976. Seedcrops and regeneration problems of L9species in northeastern Wisconsin.USDA For. Serv. Res. Pap. NC-123.5 p.

Goodrum, P.H., V.H. Reid, and C.E. Boyd.7977. Acom yields, characteristics, andmanagement criteria of oaks for wildlife.J. Wildl. Manage. 35:520-532.

Gottschalk, K.W. 1988. Gypsy moth andregenerating Appalachian hardwoodstands. P.241:254 ir Proc., Guidelines forRegenerating Appalachian HardwoodStands. Soc. Amer. For. Publ.88-03.

Guyette, & and D. Dey. 1995. Ahistory offire, disturbance, and growth in a redoak stand in the Bancroft District,Ontario. Ont. Min. Nat. Resour., Ont.For. Res.Inst. For. Res.Inf. Pap. 119. 16p'

Gysel, L.W.1957. Acorn production on good,medium, and poor oak sites in southernMichigan. J. For. 55:570-574.

Hannah, P.R. 1988. The shelterwood methodin northeastern forest types: a literaturereview North. l. Appl. For.5:70-77.

Huntley, J.C, 1983. Squirrel den treemanagement: reducing incompatibilitywittr timber production in uplandhardwoods. P. 488-495 in Proc.,SecondBiennial South. Silv. Res. Conf. USDAFor. Serv. Gen. Tech. Rep. SE-24.

Johnson, P.S. 1994. How to manage oakforests for acorn production. USDA For.Serv. Tech. Brief TB-NC-l.3 p.

Korschgen, L.I. 1962. Foods of Missouri deer,with some management implications. J.Wildl. Manage. 26 (2) :1,64-17 2.

Krajicek,I.E., K.A. Brinkman, and S.FGingrich. 196L. Crown competition--ameasure of density. For. Sci. 7(1):35-42.

Lamson, N.I' 1987. D.b.h./crown diameterrelationships in mixed Appalachianhardwood stands. USDA For. Serv. Res.Pap. NE-610.3 P.

Loomis, R.M., and R.W. Blank. 1981.Estimating northem red oak crowncomponent weights in the northeasternUnited States. USDA For. Serv. Res. Pap.NC-194.9 P.

Matthews, 1.D.1963. Factors affecting theproduction of seed by forest trees. For.Abstr. 24:1.-1'3.

McGill, D,, J. Martin, R. Rogers, and P.S'

Johnson. 1991.. New stocking charts fornorthem red oak. Univ. Wisconsin Dept.For. For. Res. Notes No.277.8 P.

Miller, G.W., and T.M. Schuler.1995.Development and quality in two-agecentral Appalachian hardwoods - 10-year results .P.364-374in Proc. 10thCentral Hardwood For. Conf. USDA For.Serv. Gen. Tech. ReP. NE-197.

Minckler, L.S., and S.F. Gingrich.1270.Relation of crown width to tree diameterin some upland hardwood stands ofsouthern Illinois. USDA For. Serv. Res.Note NC-99.4P'

Moody, R.D. 1953. Mast production ofcertain oak species in Louisiana.Louisiana Wildl. & Fish. Comm. P-R Rep.24-R.25p.

Murray, R.W, and O.E. Frye,Jr. 1957. Thebobwhite quail and its management inFlorida. Florida Game & Fresh WaterFish Comm. Game Publ.2. 56 p.

Reid, V.H., and P.D. Goodrum. 1957. Factorsinfluencing the yield and wildlife use ofacorns. P.46-79 inProc.6th Annual For.Sy-p. Louisiana St. Univ.

Sajan, R.1., E.J.Czerwinski, and S.Melbourne.1994. Results of forest insect

17

Forest Research Information Paper

and disease surveys in the southernregion of Ontario, 1993. Nat. Resour.Can., Can. For. Serv. Inf. Rep. O-X-437.4o p.

Sampson, T.L. 1983. A stocking guide fornorthern red oak in New England.Thesis. Univ. New Hampshire.98 p.

Sander, LL. 1990. Quercus rubraL. northernred oak. P.727-7331n Silvics of NorthAmerica. Volume 2 hardwoods. USDAFor. Serv. Agric. Handb. 654.

Sharp, W.M., and V.G. Sprague. 1967.Flowering and fruiting in the white oaks:pistillate flowering, acorn development,weather, and yields. Ecol. 48(2):243-257.

Sork, V.L., J. Bramble, and O. Sexton. 1993.Ecology of mast-fruiting in three speciesof North American deciduous oaks. Ecol.74(2):528-541..

Strode, D.1957. T.S.I. and wildlife habitat: apreliminary report. Florida Wildl. L0:10-1.3,4't-42.

Toumey, J.W, and C.F. Korstian. 1937.Foundations of silviculture upon an

ecological basis. P.263-366 inlohn Wiley& Sons, New York.

Tyron, E.H., and K.L. Carvell.1962. Acornproduction and damage. West VirginiaAgric. Exp. Sta. Bull. No.466T.

USDA. 1974. Seeds of woody plants in theUnited States. USDA For. Serv. Agric.Handb.466T.883 p.

Verme, L.J. 1953. Production and utilizationof acoms in Clinton County, Michigan.Thesis. Mich. St. Univ. 77 p.

Ward, J.S. 1995. Intensity of precommercialcrop-tree release increases diameter andcrown growth in upland hardwoods. P.388-398 in Proc. 10th Central HardwoodFor. Conf. USDA For. Serv. Gen. Tech.Rep. NE-197.

Ward,J.S., and G.R. Stephens. 1994. Crownclass transition rates of maturingnorthern red oak (Quercus rubraL.).For.Sci.40(2):221.-237.

Wetteroff, J.1., lr. 1993. Management andprediction of red oak decline in theMissouri Ozarks. Thesis. Univ. Missouri.220 p.

18

Appendix I

Forest Research Information Paper

Oak dbh and density are required to estimate sound acorns/ha. Sampling individual oakstands is the most reliable method of data collection and produces accurate estimates of acornproduction. Either variable radius plots (prism cruising,2 m BAF) or fixed area plots (e.g.,0.08ha circular plot) can be used to sample the overstory. Although only information on oak in theoverstory is used in predicting acorn production, other stand data may be collected at the sametime for use in prescription development, timber sale preparation or ecosystem classification.The number of plots per stand will vary dependhg on budget, time, desired precision, standvariabitty and intended use of the data.

Two methods for estimating acom production are presented here. First, production isestimated using stand average dbh (cm) and density (trees/ha) of overstory oaks. The secondexample estimates sound acorn production based on 23 fixed area plots that were systematicallylocated along transects in an oak stand on the Bancroft District.

Example 1: Stand averages

In the Bancroft stand, the average dbh of red oak is 28.8 cm and there are 237 oaks/ha (TPH).

Calculate the crown area for an oak of giaen dbh:

t1l CA = 0.55 + 0.148*DBH + 0.02*DBH2, whereCA = crown area per tree (m'?) and DBH = diameter breast height (cm).Therefore:

CA = 0.55 + 0.148*28.8 + 0.02*(28.8)2 =21.401, r*

Determine sound acorn production per square meter of croum:

I2l APSQM = 3 A63,97 L 6 1 3*EXP(-0. 125*DBH - 277 .434* (1 / DBH)), whereAPSQM= sound acorns per square meter of crown and EXP = the exponential functionThus,APSQM = 3,463,97'1..6L3*exp(-0 .125*28.8-277.434*(1, /28.8)) = 6.201.6 sound acorns/ha

Finally, sound acornproduction/ha (APROD) is foundby:

t31 APROD = APSQM*CA*TPHHence,

APROD = 6.20]6*21,.401*237 = 314547 - 3'1.,455 sound acoms/ha

20

N0.127

Example 2: Individual tree data

Sound acorn production/ha (APROD) is estimated for each oak measured using the procedure inExample 1. The TPH factor is a constant for fixed area plots and varies with plot size. One treeon a 0.08 ha circular plot represents 12.4 trees/ha. However, the TPH factor varies withindividual tree dbh in variable plot sampling. lndividual tree estimates are totaled for each plot.Stand production is obtained by averaging plot totals.

For the 23 fixed area (0.08 ha circular) plots in Bancroft, the intermediate products and acornestirnates are presented for a single plot, followed by the plot totals and stand average.

PLOT DBH APSQM APROD

14.3

15.4

17.4

18.0

1.9.3

z5.J

24.2

28.0

28.0

29.6

30.7

33.9

39.6

44.2

46.6

61..6

63.3

6.7562

7.5724

9.1804

9.6940

1.0.8562

15.0730

1,5.8444

20.3740

20.3740

22.4540

23.9434

28.5514

37.7740

46.1.644

50.8780

85.5580

90.0562

12.4

12.4

1.2.4

12.4

12.4

12.4

12.4

12.4

12.4

12.4

12.4

12.4

12.4

12.4

12.4

't2.4

12.4

0.0022

0.0076

0.0468

0.0739

0.1774

1.3699

1..7660

5.2047

5.2047

7.2802

8.8772

13.9647

22.2428

25.9492

26.s604

17.3593

1,5.8407

0.18

0.71.

5.33

8.88

23.88

256.04

346,97

1,314.9't

1.,31.4.91.

2,027.02

2,635.63

4,944.02

10,41.8.46

1.4,854.30

16,756.38

1841,6.80

17,689.26

Total 91,013.68

Forest Research lnformation Paper

APROD APROD

1,

2

J

4

5

6

7

8

9

10

11

12

9'L,0L4

51,556

32,593

58,608

50,297

92,618

89,732

52,582

45,580

2'1,,064

56,692

67,377

13't4

15

16

17

18

19

20

21.

22

23

45,045

1.02,354

64,373

1.5,026

73,794

54264

69,333

59,584

84,685

11,4,923

43,11.6

Stand Average 62A44+25,060

22

50818(1 .0k P.R. , 95 12 31)lssN 0319-9118lsBN 0-7778-4833-3

FRIP #1270001FRIP #1270002FRIP #1270003FRIP #1270004FRIP #1270005FRIP #1270006FRIP #1270007FRIP #1270008FRIP #1270009FRIP #1270010FRIP #1270011FRIP #1270012FRIP #1270013FRIP #1270014FRIP #1270015FRIP #1270016FRIP #1270017FRIP #1270018FRIP #1270019FRIP #1270020FRIP #1270021FRIP #1270022FRIP #1270023FRIP #1270024FRIP #1270025FRIP #1270026FRIP #1270027FRIP #1270028FRIP #1270029FRIP #1270030FRIP #1270031FRIP #1270032