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U.S. Department of Agriculture

Forest Service

Agriculture Handbook No. 486

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QUAKING ASPEN:

SILVICS AND MANAGEMENT IN THE LAKE STATES

by

Kenneth A. Brinkman, Principal Silviculturist (Retired), and

Eugene I. Roe, Research Forester (Retired),

North Central Forest Experiment Station

Agriculture Handbook No. 486

December 1975

Forest Service

United States Department of Agriculture

Library of Congress Catalog Card No. 75—600053

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402—Price $1.45

Stock Number 001-000-03462-6

Class Number A 1.76:486

25% discount allowed on orders of 100 or more to one address
Brinkman, Kenneth A., and Roe, Eugene I.

1975. Quaking aspen: silvics and management in the Lake States. U.S. Dep. Agrie,

Agrie. Handb. 486, 52 p., illus.

Summarizes results of 45 years of research in aspen silvics and management in the

Lake States. Discusses regeneration, growth and yield on various sites, effects of thinning, the present and potential markets, and the wildlife and recreation values of

aspen. Provides guidelines to timberland managers for growing continuous crops of

aspen on various sites.

OXFORD: 223:181:176.1.

KEY WORDS: Site requirements, regeneration, protection, growth rates, yield, thinnings, wildlife habitat. Populas tremuloides; P. grandidentata.
PESTICIDE PRECAUTIONARY STATEMENT

Pesticides used improperly can be injurious to man, animals, and plants.

Follow the directions and heed all precautions on the labels.

Store pesticides in original containers under lock and key—out ofthe reach

of children and animals—and away from food and feed.

Apply pesticides so that they do not endanger humans, livestock, crops,

beneficial insects, fish, and wildlife. Do not apply pesticides when there is

danger of drift, when honey bees or other pollinating insects are visiting plants,

or in ways that may contaminate water or leave illegal residues.

Avoid prolonged inhalation of pesticide sprays or dusts; wear protective

clothing and equipment if specified on the container.

If your hands become contaminated with a pesticide, do not eat or drink

until you have washed. In case a pesticide is swallowed or gets in the eyes, follow

the first aid treatment given on the label, and get prompt medical attention. If a

pesticide is spilled on your skin or clothing, remove clothing immediately and

wash skin thoroughly.

Do not clean spray equipment or dump excess spray material near ponds,

streams, or wells. Because it is difficult to remove all traces of herbicides from

equipment, do not use the same equipment for insecticides or fungicides that

you use for herbicides.

Dispose of empty pesticide containers promptly. Have them buried at a

sanitary land-fill dump, or crush and bury them in a level, isolated place.

NOTE: Some States have restrictions on the use of certain pesticides.

Check your State and local regulations. Also, because registrations of pesticides

are under constant review by the U.S. Department of Agriculture, consult your

county agricultural agent or State extension specialist to be sure the intended use

is still registered.

iHijiii

fPRÖTEGü

FOLLOW THC LABKI.

U.S. PErAITMENT OF ACIICUITUIE

111
PREFACE

National timber and wood fiber needs are steadily increasing. At the same

time, greater demands are being made on forest lands for other purposes. Forest

managers thus are faced with a complex problem: how to increase wood production without causing unacceptable adverse effects on scenic, watershed, and

recreation values. Increasing interest is being shown on the possibility of more

intensive management of aspen as one solution to this urgent problem.

In many respects, aspen meets the specifications for the ideal forest tree. Its

vigorous suckers make it easy to regenerate with minimum site disturbance. It

grows rapidly and is so intolerant that natural thinning and pruning occur.

Stands mature in relatively few years. Industry can use aspen wood for pulp,

paper, and fiberboard; larger trees can be used for lumber or veneer. At all

stages in their development, aspen stands furnish food and cover for wildlife.

And the golden aspen leaves provide spectacular fall landscapes.

The silvics and management of aspen have been studied for some 45 years in

the Lake States and Canada. Results of this research and the knowledge and

experience of forest managers were combined to provide this summary of what

is now known about growing the aspen forest for wood and other products.

Some of this information was presented at the Aspen Symposium (August

28-31, 1972, Duluth, Minnesota). Although hundreds of other publications were

reviewed, we included only the most recent or more pertinent papers in the list

of literature cited. This report also contains previously unpublished research

results; a special effort was made to include the latest data on how much

thinnings can increase volume and value yields.

Aspen site requirements, regeneration, protection, growth rates, and yield

are discussed. No attempt was made to prescribe treatments and practices to

maximize volume and value yields for all possible combinations ofsite quality,

stand condition, and anticipated markets. Instead, general aspen management

guidelines are presented. With suitable modifications to fit local situations,

these guidelines can be followed to improve management ofthe aspen resource

in the Lake States.

ACKNOWLEDGMENT

The authors gratefully acknowledge the invaluable assistance of many colleagues in the North Central Forest Experiment Station and Region 9 of the

USDA Forest Service inthe preparation ofthis publication. We are also indebted

to the following individuals for constructive review ofthe manuscript: Dr. J. S.

Maini and Dr. G. A. Steneker, Canadian Forestry Service; Dr. Frank D. Irving

and Z. A. Zasada, University ofMinnesota; R. Schantz-Hansen, Northwest Paper

Company, Cloquet, Minnesota; R. W. Schneider, M. J. Salisbury Company,

Grand Rapids, Minnesota; and Paul O. Rudolf, St. Paul, Minnesota.

IV
CONTENTS

Page Page

INTRODUCTION 1

CURRENT SITUATION 1

Area and Distribution 1

Size and Age Classes 2

Volume 2

Utilization 4

FUTURE OF THE ASPEN FOREST 5

ASPEN'S ROLE IN MAINTAINING OTHER RESOURCES 6

Wildlife 6

Soil and Water 7

Recreation 8

SILVICAL CHARACTERISTICS 8

Seedling Reproduction 8

Seed Production 8

Seedling Establishment 9

Reproduction from Suckers 9

Factors Affecting Suckering 9

Saplings to Maturity 10

Reaction to Competition 10

Growth and Mortality 11

Longevity and Sizes Attained 11

Occurrence in Pure and Mixed Stands 11

Role in Forest Succession 11

Clones and Hybrids 12

SOIL AND SITES 13

Site Classification Based on Height Growth 14

Site Classification by Soil, Topography, and Vegetation 14

DESTRUCTIVE AGENTS 16

Insects 16

Forest Tent Caterpillar 16

Large Aspen Tortrix 17

Poplar Borer 17

Diseases 17

Hypoxylon Canker 18

Decay 18

Shoot Blights 19

Mammals 19

Fire 20

Climatic Factors 20

YIELD TABLES 21

Yield Tables for Unmanaged Stands 21

Yield Tables for Thinned Stands 22

HARVESTING 23

Partial Cuttings 23

Mechanized Harvesting 24

ESTABLISHING VIGOROUS REPRODUCTION 24

Eliminating Residual Trees and Brush 25

Mechanical Equipment 25

Chemical Herbicides 25

Prescribed Burning 26

Increasing the Stocking of Sucker Stands 26

Logging During the Bark-Peeling Season 26

MANAGEMENT ALTERNATIVES 27

Treatments to Increase Growth Rate 27

Thinnings in Sucker Stands 28

Thinnings in Sapling Stands 29

Thinnings in Pole-Sized Stands 31

First Thinning at Age 30 or Later 31

Improving Genetic Quality of Aspen Stands 33

OTHER MANAGEMENT ALTERNATIVES 33

Aspen with Complete Understory 33

Mixtures of Aspen and Other Species 33

Aspen and Balsam Fir as Alternate Crops 34

Converting Aspen Lands to Pine or Spruce 34

GUIDELINES FOR ASPEN MANAGEMENT 35

Good and Excellent Sites (S.I. 70 or Higher) 35

Average Sites (S.I. 50 to 69) 35

Poor Sites (S.I. Less than 50) 36

SUMMARY 36

LITERATURE CITED 37

APPENDIX I.—COMMON AND SCIENTIFIC NAMES

OF PLANT SPECIES MENTIONED 42

Trees 42

Shrubs and Herbs 42

APPENDIX IL—COMMON INSECTS AND DISEASES

DAMAGING QUAKING ASPEN BY SIZE OF TREE

AFFECTED AND SYMPTOMS 43

APPENDIX III.—ASPEN YIELDS BY SITE INDEX,

STAND AGE, AND BASAL AREA (Schlaegel 1971) . 45

QUAKING ASPEN:

SILVies AND MANAGEMENT IN THE LAKE STATES

by Kenneth A. Brinkman and Eugene I. Roe^

INTRODUCTION

The original upland forests ofthe Lake States are

commonly pictured as extensive pure stands of

pine 2 (eastern white pine and red pine), northern

hardwoods, white pine and hardwoods, or farther

to the north, ofwhite pine mixed with white spruce

and balsam fir. However, records indicate that

there were large areas in Minnesota at least that

could best be classed as aspen-birch-conifer and

aspen-birch-hardwoods. ^ We know that aspen

comprised a large proportion ofthe timber volume

in Minnesota in 1899 when Ayres (1900) estimated

the aspen volume in the State as 34.2 million

cords—equivalent to about 17 billion board

feet—compared with the combined volumes of 16

billion board feet for red pine and white pine.

There is evidence from Michigan and Wisconsin

that varying numbers of aspen trees were present in

the pine, spruce-fir, swamp hardwoods, and

northern hardwood types (Roth 1898, Cox 1914,

Frothingham 1915, Truax 1915, Kenety 1917, Morbeck 1922, Stearns 1949, Graham eiaZ. 1963). Thus,

at the time pine logging began, aspen already was a

component ofseveral forest types overmuch ofthe

Lake States; in Minnesota, it formed the dominant

cover on extensive areas.

CURRENT SITUATION

The area of aspen forest has greatly increased

since the time of early settlement. Logging of pine

andother desirable timber was invariably followed

by fire, sometimes accidental but often for land

clearing or to eliminate hazardous slash. Slash

burning was required by law in Minnesota for

many years. These fires were widespread and frequently burned into uncut timber stands as well as

previously burned areas. Aspen invaded some

areas by means of its light, wind-dispersed seed;

more important was the initiation of vigorous

suckers from the roots ofthe fire-killed aspen trees

in the stands. As a result, aspen became the dominant cover type in Lake States forests.

Area and Distribution

Aspen is the largest, most widely distributed forest type in the Lake States region where it occupies

^Respectively, former principal silviculturist and research

forester. North Cent. For. Exp. Sin., USDAFor. Serv., St. Paul,

Minn. Both authors are now retired.

^Common and scientific names of plant species mentioned

are given in Appendix I.

^"Original Forests of Minnesota," compiled from U.S. Land

Office field notes by F. J. Marschner, Office of Agricultural

Economics, for the Forest Service, U.S. Dep. Agrie, 1930.

26 percent ofthe commercial forest land (table 1).

The aspen forest also extends across Canada and

occupies sizable areas in the Northeastern States

and the Rocky Mountains of Colorado and Utah.

According to the latest forest surveys, the three

Lake States contain more than 13 million acres of

commercial forest land in the aspen type. About 6

million acres are in public ownership, and nearly

half of this land is in Minnesota (table 2). Only 6

percent is owned by forest industries. The balance,

nearly 6V2 million acres, is in farm and other private holdings.

The aspen forest is most prevalent in Minnesota,

but Wisconsin and Michigan also have large

acreages (fig. 1). Extensive areas of relatively unbroken aspen land occur in northern Minnesota,

northwestern and north-central Wisconsin, and

the south-central and eastern parts of the Upper

Peninsula of Michigan. Elsewhere in the Lake

States, the aspen type is limited to small areas interspersed with agricultural land and other forest

types. Aspen also is a component of many other

forest types.
QUAKING ASPEN

TABLE 1.—Area of commercialforest land in the Lake States

aspen type by States and stand-size classes

Stand-size class^

State SawtimberPoletimber

Seedlings and

saplings

Totals

Proportion of

commercial

forest land

Minnesota^

Wisconsin^

Michigan^

All Lake States

3284(5)

139(4)

345(8)

768(6)

Thousand acres Percent

3,654(67) 1,513(28) 5,451(100) 32

1,938(53) 1,588(43) 3,665(100) 25

2,145(52) 1,639(40) 4,129(100) 22

7,737(58) 4,740(36) 13,245(100) 26

^Stand-size class is based on d.b.h. of the predominant trees: sawtimber—11 inches and larger; poletimber—5 to 10 inches;

seedlings and saplings—^less than 5 inches.

^Stone 1966. Based on field survey begun in 1962.

^Figures in parentheses show percent of total.

^Spencer and Thome 1972. Based on field survey begun in 1968.

^Chase et aL 1970. Based on field survey begun in 1966.

TABLE 2.—Area of commercial aspen type by ownership

class in the Lake States

Ownership

class

Area Proportion of total

Three Three

Minn.i Mich.2 Wis.3 States Minn. Mich. Wis. States

- - Thousand acres - - Percent

3,004 1,592 1,441 6,037 55 39 39 45

173 307 303 783 3 7 8 6

2,274 2,230 1,921 6,425 42 54 53 49

5,451 4,129 3,665 13,245 100 100 100 100

Public^

Industrial

Other private^

Totals

^Stone 1966. Based on field survey begun in 1962.

^Chase et al. 1970. Based on field survey begun in 1966.

^Spencer and Thorne 1972. Based on field survey begun in 1968.

^Includes Federal (Forest Service, Indian Affairs, Bureau of Land Management, and others). State, county, and municipal

lands.

^Includes farmer-owned and other private lands.

Size and Age Classes

Over half of the area in the aspen type is occupied by poletimber stands, and 36 percent is

stocked with seedlings or saplings (table 1). Only 6

percent of the type is occupied by sawtimber

stands, although some of these are overmature.

With reasonably good management, it should be

possible to maintain a good balance of size classes

over the region.

Most aspen stands in the Lake States are not

mature—28 percent are less than 20 years old and

44 percent are 20 to 39 years old (Stone 1966, Chase

et al. 1970, Spencer and Thorne 1972). About a

fourth ofthe stands are 40 to 60 years old and most

of these could be harvested for pulpwood or sawtimber. Although only 4 percent of the present

stands are distinctly overaged, a large increase in

the older age classes is expected within the next few

decades because many stands probably will not be

harvested for want of markets.

Volume

The aspen type also accounts for the greatest

volume among species growing in the Lake States.

Leuschner (1972) estimated that the volume of

aspen growing stock was 7.5 billion cubic feet in

1968, about 23 percent ofwhich was in forest types

other than aspen.

During the periods between forest surveys, as

shown in table 3, total growing-stock volume in-
LAKE STATES

Figure 1.—Major areas of aspen land in the Lake States.

TABLE 3.—f^et volume of aspen sawtimber and growing stock on commercial

forest land in the Lake States, and increases in volume between periodic

forest surveys; data include both aspen species

State

Year

8urvey

began

Sawtimber Increase Growing

stock

Increase

Minnesota

Michigan

Wisconsin

Million fhm^

19533 1,716

19623 2,388

19554 1,174

1966^ 2,684

1956« 813

1968^ 2,109

672

1,510

1,296

Million ft^^

1,812.0

3,088.2

1,779.0

2,257.1

1,649.9

2,159.5

1,206.2

478.1

509.6

^International Vi-inch rule to a 9-inch top diameter outside bark.

*Ciibic-foot volume to a 4rinch top outside bark ofsawtimber and poletimber trees. Divide values by 79 to convert to solid wood

cords.

^Stone 1966.

^Findell et al, 1960.

«Chase et al, 1970.

«Stone and Thome 1961.

''Spencer and Thorne 1972.
QUAKING ASPEN

creased 40 percent. In Minnesota, the increase was

66 percent in 9 years, about 7 percent per year.

Better markets for aspen reduced net volume

growth in Wisconsin and Michigan, and local

shortages have been reported. For the Region as a

whole, however, the data indicate a net growingstock increase of over 2 million cubic feet in the

intervals between forest surveys.

In the Lake States, aspen sawtimber volume

nearly doubled in a decade, faster in Wisconsin

than elsewhere. Most of the aspen growing stock

consists oftrees in the 5- to 9-inch diameter classes,

so the trend toward larger trees is expected to continue for some time.

Although quaking aspen predominates in the

aspen types, bigtooth aspen may be locally abundant. It is the dominant species on 9 percent ofthe

aspen land on State forests in the eastern part ofthe

Upper Peninsula (Mich. Conserv. Dep., unpublished data) and equal volumes of the two species

were found in lower Michigan (Chase et al. 1970).

Bigtooth aspen grows on a somewhat narrower

range ofsites than quaking aspen, and it seldom is

found on the driest sites or on wet sites, such as

swamp margins. When the two aspens grow side by

side, most bigtooth trees outgrow quaking aspen

trees (Graham et al. 1963).

Utilization

Aspens are relatively fast-growing, short-lived

trees. On dry or excessively wet sites, they barely

attain pulpwood size at maturity, butthey can produce high-quality saw logs on the best sites. Aspen

trees reach physiological maturity on most sites

before they reach saw log size (fig. 2). Thus, the

major use of aspen is for pulp or chipboard.

Because ofthe relative scarcity ofthe more valuable softwoods, the use of aspen for these products

has greatly increased, and this trend is continuing.

Aspen provided more than half of the total reported pulpwood cut of the Region in 1969; the

paper industry used 2 million cords, more than

three times as much as pine (Blyth 1970). In spite of

this increasing demand, however, volume growth

of aspen continues to exceed consumption. The

present volume is about 40 percent greater than it

was 10 years ago, and probably is adequate to supply anticipated industry needs for about two decades.

F-522789

Figure 2,—A typical quaking aspen stand nearing maturity.

The current harvest or removal of aspen falls

short ofthat necessary to offset its rapid growth—

the annual desirable or allowable cut (table 4).

Although no recent data are available, this seems

especially true in Minnesota. Growth and removal

are more nearly in balance in Wisconsin and

Michigan because the supply is closer to the

pulpmills and papermills.
LAKE STATES

TABLE 4.—Relation ofactual removal^ ofaspen growing stock on commercial

forest land to the annual desirable cut in the Lake states

Actual removals

State

Annual

desirable

cut

Amount Proportion of

desirable cut

Minnesota^

Michigan^

Wisconsin*

Total

Thousand

cords

1,632

1,050

816

3,498

Thousand

cords

527

864

1,109

2,500

Percent

32

82

136

72

^Removals in Michigan and Wisconsin include volumes ^^ost" to land clearing, cultural operations, and changes in land use.

*Stone 1966. Based on field survey begun in 1962.

^Chase et al, 1970. Based on field survey begun in 1966.

^North Central Forest Experiment Station unpublished data.

FUTURE OF THE ASPEN FOREST

During the next 20 years, the area in aspen forest

is expected to decrease. Some aspen land is being

cleared for pasture or cropland. Other areas will be

used for new roads and utility lines, and a limited

acreage will be planted with conifers. The greatest

reduction in the aspen type will result from aspen

stands being allowed to convert naturally to the

more tolerant hardwoods and conifers.

Because the understories of most aspen stands

are dominated by other species, Heinselman (1954)

predicted widespread conversion of aspen to other

forest types unless the natural succession is interrupted by cuttings, fire, or other disturbance. A

third of the aspen type could be completely replaced by more permanent forest types, and partial

conversion could occur on another 14 percent of

the aspen area. Successional trends are toward

northern hardwoods, spruce-fir, ash-elm, oak,

swamp conifers, and pine types in decreasing order

of importance.

Despite this expected loss, aspen volume may be

even greater 20 years hence than at present. The

imbalance of actual versus desirable cut is expected to continue for some time; in part because

additional ingrowth will occur on the large area of

seedling and sapling-sized stands, which now total

about 4.7 million acres in the three States.

Improved markets for aspen wood and increasing awareness of the other values of aspen stands

are expected to result in better management ofthe

resource. Opportunities for profitable aspen management will be enhanced where both saw logs and

pulpwood can be sold. Meeting other objectives

such as improving wildlife habitat or esthetic values also may be important.

Because of its abundance and relatively shortfibered pulp, aspen pulpwood has brought a lower

price than that ofsome other species. This situation

is changing because better markets are developing

for aspen, not only because of lower raw material

costs but also because the kraft process used in

pulping hardwoods creates fewer pollution problems. Several sulphite mills have closed while

kraft-mill capacity is expanding inthe Lake States.

Use of aspen by the housing industry will undoubtedly increase if an adequate supply of large,

sound logs becomes available. The recent decision

to grade aspen lumber under softwood rules has

already created increased demands for aspen saw

logs. A number of new mills have been built to use

aspen, and the capacity of others is being increased.

Although the better grades of aspen lumber are

easily sold, most logs are too small to produce much

ofthis material (Zasada 1948). An aspengrade yield

study made at Red Lake, Minnesota, showed that

saw logs with scaling diameters of 8 to 12 inches

yielded lumber grading about 85 percent No. 2 or

No. 3 Common.'* In contrast, 45 percent of the

*USDA Forest Service. Unpublished results are on file at the

Northeast. For. Exp. Stn., Upper Darby, Pa.
QUAKING ASPEN

lumber sawn from larger (13- to 18-inch) logs was in

No. 1 Common or better grades. Their study included logs of both bigtooth and quaking aspens,

but large logs of both species produced similar

percentage yields of the higher grade lumber (or

veneer).

The choice logs come from large trees that now

are found in appreciable numbers only in overmature stands where cull is high. Thus, high-quality

logs form only a small proportion ofthose cut from

present stands. If larger, high-quality trees could

be grown in shorter rotations, decay and other defects would be minimal. The results of management studies (described later) indicate that this can

be achieved, at least on the better aspen sites.

ASPEN'S ROLE IN MAINTAINING OTHER RESOURCES

The aspen forests of the Lake States also are

valuable because they contribute to other important resources. The aspen type and its associated

vegetation furnish food and cover for many forms

of wildlife. In the Central Rocky Mountain Region, aspen suckers provide valuable browse for

sheep, but aspen areas are seldom used for this

purpose in the Lake States. Because they regenerate promptly after logging or fire, the aspens help

stabilize the water regime of streams and lakes.

Furthermore, aspen forests have considerable

esthetic and recreation values.

Wildlife

In the aspen type, the objectives of producing

both timber and wildlife are fully compatible because the clearcutting necessary to perpetuate

aspen results in highly desirable habitat for deer,

moose, and grouse. To meet timber, wildlife, and

esthetic objectives, aspen management should

provide for clearcutting numerous small, welldispersed areas each year. This will produce vigorous aspen stands with the wide range in age classes

needed for maximum production ofgrouse. Young

sprout stands are utilized by deer and moose

throughout most of the year.

Deer and Moose

Aspen suckers are a favored winter food of

moose Ç4lces americana) (Aldous and Krefting

1946), and are heavily browsed by white-tailed deer

{Odecoileus virginiana). Aspen once was considered relatively unimportant as deer food in the

Lake States because of an abundance of more

palatable browse (Aldous and Smith 1939). It is

now recognized that numerous, well-distributed

small clearcuttings in aspen stands will provide the

browse and the forbs essential for maintaining

good deer populations (Rutske 1969).

The most important deer-producing areas in

Michigan are those where the aspen types predominate (Byelich et al, 1972). In Wisconsin,

McCaffery and Creed (1969) found consistently

higher deer activity during the summer months in

aspen than in northern hardwood forests. Their

studies showed that numerous small, permanent

openings in stands growing on loamy soils provided

highly preferred summer deer habitat, but they

concluded that such openings were difficult to establish and maintain because these better soils

usually are invaded by northern hardwoods. In

contrast, natural openings are relatively abundant

and stable on the sandy soils where aspen, oaks,

and pines predominate. These forest types commonly provide substantial levels of high quality

deer food during their entire rotations.

The management practices necessary for growing

repeated crops of aspen also create conditions that

benefit deer and moose—an abundance of aspen

suckers is available for the first 5 years after clearcutting (Rutske 1969). In contrast, overmature

stands provide little usable browse and forbs for

these animals. If such stands are not harvested,

they often are succeeded by more shade-tolerant

forest types that are less valuable for deer and

moose habitat.

Even where there is a poor market for aspen,

existing needs for wildlife habitat and expected

future needs for wood and fiber often justify a

cooperative program of planned clearcuttings by

wildlife and timber managers. Because the species

remaining after commercial logging in the aspen

type may hinder sucker development, wildlife

funds are being used to maintain and renew potentially productive deer range. Byelich et al. (1972)

reported that 12,000 acres in the aspen-birch type

were treated in Minnesota in 1969 and 1970; Wisconsin cut about 22,000 acres in 1969. Between 1958

and 1969, about 69 square miles of aspen, aspenbirch, and other aspen types in Michigan were cut

or sheared with bulldozers to improve deer range.

These cuttings usually were located near deer yards

and were designed to stimulate sprout growth of

aspens and associated species. However, wildlife
LAKE STATES

managers generally agree that the area cut specifically for deer habitat is far less than that needed to

improve deer populations enough to meet demands of the public.

In 1971, Michigan increased charges for deer

licenses to fund an intensified program of deer

habitat management. The objectives are to reverse

the downward trend of deer populations and to

increase the herd to 25 or 30 deer per square mile.

The program will emphasize preservation, improvement, and expansion of the aspen type. A

combination of commercial harvest cuttings and

prescribed treatments will be used to provide an

equitable distribution of tree size classes. Present

plans are to treat about 400,000 acres within the

next 10 years.

Beaver

The bark, leaves, twigs, and branches of aspen

are preferred by beaver (Castor canadensis) to

those of all other tree species in the Lake States.

Beavers will "cut" aspens as far as 400 feet away

from water, and will take trees of any size if necessary. A study in Michigan showed that an average

beaver colony requires from 0.4 to 1.0 acre ofaspen

timber a year (Bradt 1947).

Ruffed Grouse

No other species oftree or shrub seem to fill the

food and shelter need of ruffed grouse (Bonasa

umbellus) as well as quaking and bigtooth aspens

(GuUion and Svoboda 1972). In North America,

distributions of these aspens and of grouse generally coincide. Although grouse can persist in

warmer climates in the absence of aspen, the birds

seldom are as abundant as in the northern areas

where aspens are or have been an important component of the forest cover.

GuUion and Svoboda (1972) summarized results

of long-term studies of aspen-birch relationships

in Minnesota. Aspen leaves and staminate flower

buds provided the most important year-long food

resource. During the winter, grouse fed on the

staminate flower buds of aspen six times as much as

on buds of all other hardwood species combined.

The nutrient-rich male flower buds of aspen are

available when snow covers the ground. During the

coldest part of winter, grouse usually stay buried

under the snow almost continuously, emerging

only for a brief evening feeding period. In 15 to 20

minutes, the birds can consume enough of the

easily-detached aspen buds to satisfy their daily

food needs. This short feeding period minimizes

exposure to predators such as owls and thus reduces winter losses of grouse. However, heavy use

of staminate flower buds actually begins many

weeks before snow covers the ground, and at least

the male grouse continue to prefer the developing

staminate catkins of aspen well into spring, long

after snow melt.

Aspen leaves are a primary source of summer

food, and a variety ofaspen age classes providesthe

kind of habitat needed by grouse throughout their

life cycle (Bump et al. 1947; Ediminster 1947; Gullion 1967, 1969). Newly regenerated aspen stands

provide high quality brood habitat for hens and

their chicks for perhaps a decade. Sapling and

small pole stands provide good winter cover for

birds of all ages, and may support a breeding

grouse per 3 or 4 acres. Older stands provide a

winter-long food resource and are often used by

nesting hens, especially where the hens can fly

directly to male aspen trees where they feed on

new-grown leaves.

Where producing ruffed grouse for recreational

hunting is a major objective, GuUion and Svoboda

(1972) suggest that aspen management should provide stands of at least three age classes near each

10-acre breeding activity center. This could be

achieved by growing aspen on 40 to 50 year rotations, harvesting the trees by clearcutting no more

than 10 out of any 40 acres at one time and spacing

the logging at about 10-year intervals.

Soil and Water

The aspens are unique in their ability to stabilize

soil and watershed conditions. Fire-killed stands

are promptly replaced by abundant root sprouts.

The trees produce abundant leaf litter that contains more nitrogen, phosphorus, potash, and calcium than leaf litter from most other hardwoods.

The litter decays rapidly, forming nutrient-rich

humus that may amount to 25 tons per acre (ovendry weight basis) (Stoeckeler 1961).

Because it readily absorbs moisture from rainfall and snowmelt, the humus layer reduces runoff

and aids percolation and recharge of the ground

water. This humus and leaf litter serve as a mulch

to reduce evaporation from the surface ofthe mineral soil.

More snow accumulates under aspen stands, so

the soil does not freeze as deeply as under pine or

spruce forests (Weitzman and Bay 1963). Snowmelt

begins earlier in the spring under the leafless aspens (Weitzman and Bay 1959) (fig. 3), and the
QUAKING ASPEN

F-487809

Figure 3.—Snow begins to melt by mid-April in aspen

stands.

frozen ground thaws sooner, permitting more

rapid infiltration of the mehed snow.

In northern Minnesota, Verry (1972) found that

clearcutting aspen stands temporarily increased

total water yields and hastened snowmelt in the

spring. Peak water yields occurred a few days earlier in clearcut areas but water quality was not

adversely affected.

Recreation

Although aspen stands have only limited scenic

appeal during most ofthe year, they are a primary

attraction for visitors to the north country during

autumn. The varying blends of aspen's golden foliage and whitish bark with the dark greens of conifers and the vivid colors of other hardwoods provide spectacular vistas that are enjoyed by thousands each year.

Aspen sites may make poor campgrounds, however, because they seem to be a favorable habitat

for mosquitoes and black flies. Trampling and disturbance by campers may lead to early mortality of

an aspen stand, so areas stocked with other species

are apt to make more durable campgrounds.

The most important recreational value of aspen

stands results from the desirable wildlife habitat

they provide. There are many opportunities for the

visitor to hunt deer, moose, and grouse and to see

these and other wildlife where vigorous aspen

stands are maintained in a variety of age classes.

SILVICAL CHARACTERISTICS

The aspens are unique in that almost all stands

originate as suckers that arise from existing root

systems. Seedlings seldom are numerous enough to

form a stand, but seedling reproduction has enabled aspen to invade many new areas after fire or

logging. Because aspen seedlings grow faster than

any associated species except pin cherry, a few

seedlings can persist to form the nucleus of a new

stand that is expanded by root sucker production

after fires occur.

Seedling Reproduction

Although abundant seed is produced, both

quaking aspen and bigtooth aspen reproduce from

seed only under favorable conditions. The scarcity

of seedling reproduction has been attributed to

various factors: the short duration ofseed viability;

presence of a germination and growth inhibitor in

the "seed hair"; unsuitable seedbeds during the

crucial establishment period; or seedling losses to

disease, insects, or drought (Maini 1960).

Seed Production

Aspen trees start flowering when they are about

10 years old and produce some seed nearly every

year thereafter. Both flowers and trees are normally unisexual, but a few perfect flowers are produced on some trees. Because most aspens originate as root suckers, the stands usually are a mixture of male and female clones consisting of a few

to several hundred trees. Clonal differences are

most evident in the spring, when trees of some

clones can be seen leafing out while adjacent trees

are still dormant.

In the Lake States, aspen seed is shed over a

3-week period during early May to mid-June, beginning earliest on protected sites and in the southern portion ofthe region. The tiny aspen seeds (2.5

million per pound) are carried long distances by

the wind (Maini 1972). Good seed crops are borne

about every 5 years.

8
LAKE STATES

Seedling Establishment

Viability offreshly fallen seed normally exceeds

90 percent (USDA Forest Service 1974) and is retained up to 3 weeks (Kittredge and Gevorkiantz

1929). On moist seedbeds, germination begins

within 12 hours afterseed fall and is completed in a

day or two.

Establishment of seedlings requires an exact

combination of environmental conditions. Bare

mineral soil, particularly recently burned land,

forms the best seedbed. Seedling survival and initial development require the maintenance of a

moist soil forseveral days—ifthe surface dries out,

the seedling will die. During this critical stage and

for some time thereafter the seedlings can also be

killed by heat, fungi, competing vegetation, and

heavy rains.

Seedlings may reach 6 to 24 inches in height by

the end oftheir first year and have roots extending

6 to 10 inches in depth and up to 16 inches laterally

(Shirley 1941, Day 1944). Although their root systems develop rapidly, seedlings make little height

growth untilthey are about 3 years old. Such established seedlings are capable of producing a few

suckers after fire or other disturbance (Day 1944,

Steneker 1972).

Reproduction from Suckers

Aspen stands continually produce weak, inconspicuous suckers, most of which live only a few

years. After a stand is logged or killed-back by fire,

however, so many suckers arise that a new aspen

stand is virtually inevitable. In the Lake States,

from 3,500 to 22,850 suckers per acre have been

reported 1 year after logging (Kittredge and Gevorkiantz 1929, Zehngraff 1946, Strothmann and

Heinselman 1957, Graham et al. 1963). Most

sprouts arise from small lateral roots located

within 3 inches of the soil surface, predominantly

in the humus layer and the upper part of the mineral soil (Farmer 1962b, Sandberg and Schneider

1953). This continuous reserve of suckers plus the

ability to produce many vigorous new suckers help

explain aspen's rapid dominance of cutover and

burned lands in the Lake States.

Another factor favoring abundant sucker development is the wide distribution of aspen's shallow

root system. Although most suckers arise within 25

feet of cut trees, suckers have been found over 100

feet from the parent tree (Buell and Buell 1959).

Suckers soon develop many feeding roots which

supplement the parent root system and facilitate

rapid growth. Some of the suckers may remain

attached to the parent roots for years; others

gradually become separated as the old roots decay.

There is no evidence that decay ofthe parent roots

of quaking aspen has any adverse effect on individual trees.

Interconnected root systems may persist as long

as 90 years (Quaite 1953). Thus, most stands of

quaking aspen, like bigtooth aspen (DeByle 1964,

Barnes 1966), contain groups of trees having a

common root system.

Because they develop on established root systems, quaking aspen suckers grow faster than

seedlings. Under full light, suckers will reach a

height of 3 to 4 feet or more by the end ofthe first

full growing season (Zehngraff 1947) and 10 to 15

feet after 5 years.

Factors Affecting Suekering

Aspen root suekering is largely controlled by

apical dominance; cutting or killing the overstory

tree interrupts the flow of growth regulators from

the stem to the roots (Farmer 1962a, Steneker

1972). Thus, dormant buds on all root systems are

free to develop in clearcut areas. The exposed soils

in such areas often reach 75 to 80° F which further

stimulates sucker production (Maini and Horton

1966).

The most important of several factors affecting

the production and development ofquaking aspen

suckers is the proportion of the stand left after

logging or fire. Where only part of the stand is cut

or killed, sucker production will be stimulated on

fewer root systems. Suckers arising after such partial cuttings often grow slowly and some are killed

because ofthe competition and shade provided by

the remaining trees and the brush characteristic of

many aspen stands (Zehngraff 1949). Occasionally,

underbrush is so dense that no suckers develop

(Ghent 1958). The best sucker production and development follows either complete clearcutting or

a burn that kills all of the parent trees and brush

(fig. 4).

The density of the parent stand before cutting

also appears to affect sucker production. In Michigan, 1 year after clearcutting there were 5,200 suckers per acre in quaking aspen stands where basal

areas had been less than 50 square feet, 7,000 suckers per acre in stands where the basal area had

ranged from 51 to 100 square feet, and 9,900 suckers per acre in stands where the basal area had been

over 100 square feet (Graham et al. 1963). In Minnesota, suckering was found to be most abundant
QUAKING ASPEN

F-439548

Figure 4.—This 10-year-oId stand of aspen suckers developed after a complete clearcutting. There are

about 4,800 stems per acre.

following removal of stands having a basal area of

80 or more square feel per acre (Sandberg and

Schneider 1953).

Sucker production also is related to clonal differences. In lower Michigan, Utah, and Manitoba,

some quaking aspen clones were found to sucker

more abundantly than others (Farmer 1962a,

Maini 1967, Steneker 1972, Tew 1970).

Evidence on the effect of parent stand age on

sucker production is conflicting. Stoeckeler and

Macon (1956) found that sucker production increased to age 50, although Graham et al. (1963)

concluded that peak production occurred at age

35. However, age appears to have little practical

significance; where stands are clearcut, quaking

aspen will produce an abundance of suckers over

its whole lifespan.

Season ofcutting affects the number and vigor of

aspen suckers (Steneker 1972). Zehngraff (1946)

found that winter logging resulted in at least four

times as many suckers as did summer or spring

logging; differences in sucker production were less

where stands were logged in late summer (Stoeckeler and Macon 1956).

Winter logging results in more vigorous suckers

because they appear the following summer, get an

equal start with the released brush, and soon outgrow it. Sprouts arising after spring cuttings still

may be growing in the fall and are often killedback by freezing. Sprouts following summer cuttings do not appear until the second season after

competing brush has had a year to develop. For

practical purposes, however, stands can be harvested in any season if a complete clearcut is

achieved because adequate sprouts will arise to

ensure a new aspen stand.

Sucker production is also influenced by fire intensity. A moderate burn that kills the aspen tops

and undergrowth and destroys the litter and part of

the duff will produce more suckers than either a

light or severe fire (Horton and Hopkins 1965). A

succession of infrequent fires will increase the

density of sucker stands (Kittredge 1938, Shirley

1941), but annual fires may eliminate the suckers

because the depleted food reserves in the roots

have little opportunity to be replaced (Gates 1930,

Buckman and Blankenship 1965).

Saplings to Maturity

Reaction to Competition

Quaking aspen is more intolerent of shade than

any other important coniferous or deciduous tree

species found in the Lake States (Baker 1949,

Graham 1954). Because it is intolerant, aspen

prunes well in closed stands, and has pronounced

ability to express dominance even in overstocked

stands (Kittredge and Gevorkiantz 1929). Aspens

require nearly full light for satisfactory survival

and growth; overstory trees left after logging or fire

restrict development of the young aspen.

Because they most often invade land once occupied by other forest types, quaking aspen stands

have no characteristic underbrush or ground cover

10
(Roe 1935). Instead, such vegetation is mostly composed of the species whose underground parts are

able to survive fire and therefore persist for many

years. In the Lake States, the following shrub

species are most common in aspen stands: beaked

hazel, dwarf bush honeysuckle, mountain maple,

common chokecherry, alder, raspberry, and

blackberry. Herbaceous vegetation may include

bigleaf aster, wild sarsaparilla, Canada beadruby,

dwarf red blackberry, bunchberry dogwood, yellow beadlily, roughleaf ricegrass, sweetscented

bedstraw, strawberry, spreading dogbane,

fireweed, rosy twistedstalk, early meadowrue,

sedges, goldenrods, sweet-fern, and lady fern.

The composition and development ofbrush and

ground cover varies with site quality. The richer

sites typically have a tall, dense undergrowth that

offers serious competition to the intolerant aspen

suckers. On the poorer sites, the undergrowth is

relatively sparse and short.

Growth and Mortality

Height growth ofroot suckers is especially rapid

after the first few years. On the better sites, dominant trees attain heights of 25 feet in 13 years, 37

feet in 20 years (Shirley 1941), and 70 to 80 feet in 50

years (Kittredge and Cevorkiantz 1929). Subsequent growth is slower, and the stands ultimately

deteriorate because of decay and attendant breakage. By the time most Lake States stands are 80 to

100 years old, only a few decadenttrees remain. On

the poorer sites, however, the stands may begin to

show decadence at about 25 years of age (SchantzHansen 1945). Overmature aspen stands tend to be

succeeded by brush or other tree species because

vigorous suckers do not develop unless the aspens

are cut.

Longevity and Sizes Attained

Although quaking aspen is considered a shortlived species, individual trees may persist for a

long time. Heinselman (1973) suggested that some

aspen trees in northern Minnesota probably survive for 150 to 200 years. Trees 130 to 140 years old

were found in northern Michigan (Graham et al.

1963), and trees 170 to 180 years old were reported

in Canada (Kirby et al. 1957, Basham 1960).

Aspens up to 45 inches d.b.h. and 100 feet in

height have been found in Saskatchewan.^ In the

Lake States, the largest known diameter is 38

^Personal report from J. B. Prince, Saskatchewan Office of

Industrial Development, Regina.

LAKE STATES

inches and the tallest tree is 110 feetin height; both

trees were found in northern Minnesota. Trees in

mature stands range from 65 to 80 feet in height;

maximum diameters of 15 to 16 inches are attained but average stand diameter seldom exceeds

about 12 inches.

Farther east and near the southern edge of the

range of aspen in the Lake States, the trees do not

grow as large or live as long as in Minnesota and

northward. The heart rots that eventually result in

cull trees apparently develop more rapidly in

southern than in northern latitudes (Graham et al.

1963). Thus, the recommended maximum rotation

age is 65 to 80 years in eastern Canada and the

Prairie Provinces (Kirby et al. 1957, Jarvis 1968)

compared with 35 to 60 years in the northern Lake

States (Zehngraff 1947, 1949) and 35 to 45 years in

lower Michigan (Graham et al. 1963).

Occurrence in Pure and Mixed Stands

Quaking aspen may occur in essentially pure

stands but aspen also grows with many other tree

species. Common associates in northern Minnesota and Canada are paper birch, jack pine,

balsam fir, white spruce, black spruce, northern

white-cedar, black ash, and balsam poplar.

Farther south and east, aspen may grow with sugar

maple, red maple, basswood, white ash, northern

red oak, bur oak, paper birch, yellow birch, bigtooth aspen, pin cherry, red pine, and eastern

white pine.

The associated species may occur in the upper

crown canopy or form a definite understory that is

released to become the dominant forest type after

death or harvest of the aspen. In most areas, this

established understory is dominated by the more

tolerant species—sugar and red maples, northern

red oak, bur oak, balsam fir, white spruce, eastern

white pine, northern white-cedar, and black

spruce. The presence of these species as an unI derstory is responsible for the large amount of natural conversion taking place in the aspen forest of

the Lake States.

Role in Forest Succession

Under favorable conditions, quaking aspen

seedlings will gain a foothold on sites where they

did not grow before, particularly after fires, logging, or windstorms. Even where aspen was only a

minor component of disturbed stands, its suckers

often dominate the site after a succession of fires.

And where aspen was already dominant, logging or

natural catastrophe can perpetuate it.

11
QUAKING ASPEN

Because of its abundant windblown seed and

aggressive suckers, aspen can become the dominant species on sites formerly occupied by other

hardwoods or conifers. In northwestern Minnesota, north-central North Dakota, and the

Prairie Provinces of Canada, grasslands often are

invaded by aspen suckers. If not held in check by

mowing or burning, these suckers form semipermanent groves (Ewing 1924, Buell and Buell 1959,

Maini 1960).

Aspen cannot reproduce successfully under its

own shade, so it forms a relatively short-lived temporary forest type that can readily be invaded and

eventually dominated by more shade-tolerant

species (fig. 5). Soil moisture and fertility strongly

influence the ecological succession. On dry sites,

aspen may be replaced by red pine, red maple, or

oaks; on sites with intermediate moisture, by white

pine; and on moist fertile sites, by northern

hardwoods, white spruce, and balsam fir. Succession on the wettest sites is toward balsam fir, black

spruce, black ash, and northern white-cedar, but

brushy species often form a semipermanent type

on these wetter sites.

The rate of natural conversion is most rapid on

the better sites and varies with the aggressiveness

and growth rate of the invading species. On some

sites, conversion is a slow process and aspen persists for several generations even in the absence of

fire.

Sugar maple and balsam fir grow more rapidly

under a full aspen cover than do pines, partly because oftheir greater tolerance and partly because

they tend to invade better sites. Hence, the succession to hardwood or spruce-fir types normally occurs at a more rapid rate than that from aspen to

pines. In northern lower Michigan, conversion of

aspen to sugar maple-beech may require 20 to 35

years as compared to 30 or 40 years for pine (Gates

1930).

Clones and Hybrids

Although limited, there is evidence that quaking

aspen, like other species ofwide geographic range,

has probably developed clones that are adapted to

local climates. In Saskatchewan, seedlings of local

origin have heavier root systems and stop growing

earlier in the fall than seedlings from Wisconsin

(Vaartaja 1960). Two distinct forms exist in Utah

and Colorado; one attains full leaf development 2

to 3 weeks earlier than the other and is dominant at

higher elevations (Baker 1921, Cottam 1954). These

may be clones that are extensive in range because

F-385067

Figure 5.—Stand of 50-year-old aspen converting naturally to balsam fir and black spruce.

they also differ in time ofleaffall, bark color, and

abundance of staminate flowers.

In the Lake States, most aspen stands are composed of intermingled clones; each may consist of

from one to hundreds ofstems. Single clones may

occupy as much as 3.8 acres (Steneker 1972) but the

typical range is from 0.05 to 0.2 acre (Barnes 1966).

Millions of clones probably exist within an area the

size ofthe Lake States. For example, Barnes (1959)

found 31 different quaking aspen clones in stands

on two relatively uniform sites in northern lower

Michigan. These clones showed distinct differences in leafshape, time ofleafing, fall coloration.

12
LAKE STATES

bark, stem form, suckering ability, or growth capacity. Studies of clones from northern Wisconsin

and the Upper Peninsula revealed similar inte relouai variations as well as differences in woodfiber length, in specific gravity, and in the characteristics ofthe paper made from the fibers (Buijtenen et al. 1959, 1962).

As in other species of the genus Populas, most

cells of quaking aspen clones are diploid; they

contain two sets of 19 chromosomes each (Joranson

1953). However, three small clones containing

three sets of chromosomes have been found in the

Lake States. These triploid clones grow faster and

produce better fiber than do the usual diploid

clones, so they seem to offer considerable promise

in aspen breeding (Buijtenen et al. 1958).

Some clones are distinctly above average in

form, quality, and growth rate (fig. 6). However,

the poor suckering ability of some of these clones

can result in inadequate regeneration following

cutting (Garrett and Zahner 1964, Tew 1970). As

aspen management becomes more intensive, more

efforts probably will be made to favor outstanding

clones that can be readily identified.

Although the species usually do not flower at the

same time, hybrids of bigtooth and quaking aspen

have been found in lower Michigan (Barnes 1961),

in Minnesota (Pauley 1956), and in eastern Canada

(Marie-Victorin 1930). Both aspens hybridize naturally with white poplar (Peto 1938, Little et al.

1957). Artificial crosses have been made ofquaking

aspen with white poplar, bigtooth aspen, and

European aspen (Heimburger 1936, 1940). Some

hybrids with European aspen have shown excellent quality and growth rate (Church 1963, Pauley

et al. 1963, Einspahr and Benson 1964).

F-506157

Figure 6.—Superior clone of aspen showing good form

and growth rate. The trees are about 60 years old.

SOIL AND SITES

In the Lake States, quaking aspen grows on a

wide range ofsoils—on infertile dry sands (as scattered trees), on rich loams, on heavy clays, and on

waterlogged mineral soils and peats. Aspen also

forms stands in the ledge rock area (Laurentian

Shield) of northeastern Minnesota.

Growth rate varies with soil fertility and available moisture. Moist fertile loams can produce

large saw log- and veneer-quality aspens, but deep

dry sands and some rocky areas will produce only

limited yields of pulpwood.

Because most Lake States soils are of glacial origin, site quality of aspen may vary considerably

within short distances. However, there are large

areas where the sites are relatively uniform. Some

ofthe best sites are on the heavy-textured high-lime

soils of glacial Lake Agassiz and the surrounding

territory in northwestern Minnesota. Poor sites

predominate in the gravelly moraines found in

north-central Wisconsin and in east-central Minnesota, and the lacustrine red clay belt of northwestern Wisconsin and western upper Michigan

(Kittredge and Gevorkiantz 1929, Stoeckeler 1960).

Aspen grows slowly on sandy soils because oflow

moisture and nutrient levels. The slow internal

drainage and insufficient aeration of clay soils also

restrict growth rates (Stoeckeler 1960). Growth on

sandy soils is somewhat better where the water

13
QUAKING ASPEN

table is between 18 and 60 inches deep, but a higher

water table appears to be detrimental (Wilde and

Zicker 1948, Wilde and Pronin 1950).

The availability ofsoil nutrients also influences

growth rate. Average annual growth of quaking

aspen on soils containing high levels of Ca, Mg, K,

and N was more than four times that on soils in

which the levels of these elements were low (Voigt

et al, 1957). Stands growing on soils containing an

abundance of calcium carbonate had a site index

10 feet higher than that of stands on the more acid

soils (Stoeckeler 1961).

Site Classification Based on Height

Growth

To facilitate the estimation of aspen site quality,

particularly where this is not readily apparent as in

young stands, Kittredge and Gevorkiantz (1929)

prepared a set ofsite indexcurves that were revised

by Gevorkiantz in 1956 (fig. 7). These curves are

based on the height ofthe average dominant trees at

or projected to 50 years and segregate aspen sites

into five classes ranging from very poor (S. I. 40) to

excellent (S.I. 80). The revised curves are generally

adequate for use in the Lake States except on the

sandy soils of the eastern Upper Peninsula and

00

/

^

80 /

^

//

^

^

BO /

^

^

/

/. ^

40 /Y//^

y ^^'—

^

^/

20 k

/ .

/y

20 40 60

AGE - YEARS

Figure 7.—Site index curves for quaking aspen. (Adapted from

Kittredge and Gevorkiantz 1929 by Gevorkiantz 1956.)

northern lower Michigan, which were not sampled.® Graham et al. (1963) prepared site index

curves and yield tables for quaking aspen in northern lower Michigan based on height attained at 30

instead of 50 years.

Site Classification by Soil,

Topography, and Vegetation

Many attempts have been made to classify quaking aspen sites on the basis oftheir soil characteristics and understory vegetation. Heinselman and

Zasada (1955) concluded that aspen site quality was

determined by the interaction of many environmental factors. The most important of these were

soil texture and fertility, ground water, and topography.

The site prediction scheme for aspen shown in

table 5 was developed by Strothmann (1960). It is

based on soil characteristics (texture of the upper

36 inches of the profile, acidity, and water table

depth) and on topographic characteristics (aspect,

slope, and position on slope) (tables 6 and 7).

Strothmann omitted fire history in this scheme because he found it had no measurable effect on site

quality. He also found that site quality tended to

improve as subsoil pH increased on fine-textured

soils having deep water tables.

Plant indicators appear to have limitedvalue for

estimating aspen site quality (Kittredge 1938, Roe

1935, Sisam 1938). Ingeneral, site quality was excellent where understory vegetation associated with

the northern or bottomland hardwood types was

found under aspen stands, but where an understory typical of red pine or jack pine types occurred, the aspen was slow growing. Understories

usually found in oak, spruce-fir, and white pine

stands indicated sites ofintermediate quality. Thus

understory vegetation might be used in conjunction with soil characteristics in a regional classification of aspen sites.

Soil-site relationships in aspen may be confounded by clonal variations. Steneker (1972)

found significant differences in the total heights of

quaking aspen clones that grew together. In lower

Michigan, trees ofsome bigtooth aspen clones were

as much as 24 feet taller than those of other clones

on the same site (Zahner and Crawford 1965).

Clonal variations of this magnitude would seriously affect the accuracy of site index determinations.

®Similar site index curves have been prepared for aspen in

northern Ontario (Plonski 1956) and Saskatchewan (Kirby ei al,

1957).

14
LAKE STATES

TABLE 5.—Aspen site prediction scheme combining soil and topography ratings

(based on 235 plots)

Topography

rating^

Site index

Soil

rating^

Plots

Average Highest Lowest

On sloping land:

Favorable

Average

Unfavorable

On flat land: 3

Excellent

Good

Fair

Poor

Excellent

Good

Fair

Poor

Excellent

Good

Fair

Poor

Excellent

Good

Fair

Poor

86

78

74

76

69

66

72

68

59

44

74

70

66

57

90

97

74

85

77

87

79

76

72

45

90

91

82

70

^See table 7 for descriptions of topography ratings.

^See table 6 for descriptions of soil ratings.

^Having slope of less than 5 percent.

TABLE 6.—Rating ofsoilfactors^

Soil

rating

Stone

content^

Silt plus

clay content^

Poor

Fair

Fair

Good

Good

Good 3

Excellent^

Poor

Fair

Fair

Fair

Good

Percent

0-30

31 or more

Percent

0-9

0-9

10-20

21-30

31 +

31 +

31 +

0-9

0-9

10-20

21-30

31 +

^Strothmann 1960.

^Percent of total cubic volume in upper 36 inches of soil

3Subsoil pH 6.9 or less.

^Subsoil pH 7.0 or higher.

No.

83 2

59 13

74 1

— 0

60 7

57 12

52 10

— 0

68 3

61 10

50 4

43 2

57 63

57 46

53 52

50 10

Depth to

water table

Inches

60+

0-60

0-60

0-60

0-24

24+

24+

60+

0-60

0-60

0-60

0-60+

15
QUAKING ASPEN

TABLE 7.—Rating oftopographic factors

Topography

rating Slope ' Aspect' Topographic position

Average

Unfavorable

Unfavorable

Unfavorable

Average

Unfavorable

Percent

5-20 S and SW Lower slope

Upper and middle slope

W, NW, N, NE, E, SE Lower slope

Upper and middle slope

21 or S and SW Lower slope

more Upper and middle slope

W, NW, N, NE, E, SE Lower slope

Upper and middle slope

— — Depression

— — Ridgetop

'Slope and aspect were assumed to have no influence on site quality on land having a slope of less than 5 percent (Strothmann

1960).

DESTRUCTIVE AGENTS

Quaking aspen stands may be damaged or destroyed by any ofseveral agents. Insect infestations

often reduce both volume growth and the value of

timber. The average annual losses to Hypoxylon'

in the Lake States are estimated to be 300 million

cubic feet; this has a value of about $2 million on

today's market (Marty 1972). Although fire is a useful tool in aspen management, it can also have

adverse effects.

Insects

Of the many insects known to attack aspen, leaf

feeders cause the most conspicuous damage.

Stands may be completely denuded by the forest

tent caterpillar and widespread injury sometimes

is caused by the large aspen tortrix.

Forest Tent Caterpillar

The foresttent caterpillar is the most spectacular

defoliator of aspen and of many other deciduous

trees over large areas in the Lake States and adjacent Canada. Epidemic populations can develop

in the same areas at 10- to 15-year intervals (fig. 8).

Although they appear when the aspen leaves are

beginning to unfold, the caterpillars are relatively

inconspicuous until they are nearly full grown

(Batzer and Morris 1971).

Enormous areas may be affected by the caterpillars. During the 1950's, one outbreak covered

'Common and scientific names of these and other aspen

insects and diseases are listed in Appendix II,

Figure 8.—Aspen trees completely defoliated

tent caterpillars.

F-307419

by forest

16
LAKE STATES

about 80 million acres in Ontario (Sippell 1962).

Most outbreaks last from 3 to 5 years; during this

period, stands may be completely defoliated several times. High caterpillar populations may be

abruptly reduced by low temperatures that kill

both the newly hatched caterpillars and the leaves

(Rose 1958, Hildahl and Reeks 1960). Populations

eventually decline because of parasitism or ofstarvation in areas where the insects have exhausted

the food supply (Christensen et al, 1951).

Although defoliated aspen stands commonly

produce another crop of leaves 3 to 4 weeks after

the caterpillar quits feeding, loss of the foliage

reduces current growth (Dils and Day 1950, Batzer

et al. 1954, Barter and Cameron 1955, Pollard

1972). Duncan and Hodson (1958) found that a typical outbreak (one light defoliation followed by 2

years of heavy defoliation) caused a volume loss of

0.6 cord per acre in average aspen stands, but as

much as 2.25 cords per acre were lost in fully

stocked stands growing on good sites.

Normally, few quaking aspen trees die following

a typical infestation. The infestations in the 1930's

coincided with a period of severe drought, however, and this resulted in heavy mortality, particularly of trees in the lower crown classes.

An outbreak can have beneficial effects. Where

there are understory conifers, such as balsam fir,

heavy defoliation of overtopping aspen results in a

marked increase in radial growth of the conifers

(Froelich et al. 1955, Duncan and Hodson 1958).

And where the outbreak is accompanied by

drought that kills part ofthe aspen overstory, many

understory conifers are permanently released.

Thus, an infestation can hasten natural conversion

of aspen to conifers.

Widespread infestations ofthis insect cannot be

economically controlled at the present time. However, defoliation of valuable aspen stands can be

prevented by aerial applications of registered insecticides when the caterpillars are about V2-inch

long.

Large Aspen Tortrix

The only other important aspen defoliator in the

liáke States is the large aspen tortrix. This leaf

roller periodically causes extensive defoliation of

quaking aspen throughout much of its range

(Adams and Moore 1963, Beckwith 1973). Prentice

(1955) reported serious defoliation on 10,000

square miles in northern Manitoba and infestations have covered other large areas in the Lake

States, Canada and Alaska. Outbreaks are characterized by the buildup of large populations that

persist for 2 or 3 years and then suddenly collapse.

Feeding by the tortrix larvae is first noticeable in

the spring. Where populations are high, aspen

buds may be destroyed before they expand, but

healthy trees usually produce more leaves by midsummer. Defoliation usually occurs in May or

June when the larvae feed on leaves tied together

by webbing (Beckwith 1973). Despite the loss in

current volume growth caused by defoliation, most

aspens survive. Although the larvae also will feed

on a number of broadleafed species, the tortrix

becomes a problem only where quaking aspen is a

major component ofthe forest stand. Natural controls include feeding by birds and attacks by many

species of parasites. Starvation stress apparently is

a major factor responsible for population collapse

of this species.

Poplar Borer

During their 3-year life cycle, larvae ofthe poplar borer make large tunnels in aspen trees. These

tunnels ruin the wood for veneer and greatly reduce its value for lumber. Infested trees also are

more susceptible to wind breakage.

Graham et al. (1963) reported that 64 percent of

the quaking aspen trees growing in lower Michigan

during the early 1960's showed evidence of being

infested and that infested trees were equally abundant on all sites. However, Christensenet al. (1951)

reported finding many more infested trees on poor

sites than on good sites.

Most successful borer attacks are concentrated

in individual trees or in small groups of trees scattered throughout stands. Among trees 2 to 7 inches

d.b.h., Ewan (1960) found that "brood trees" were

typically the larger and faster growing individuals

and that the more open the stand the higher the

amout ofborer infestation. Although his data were

inconclusive, trees larger than 7 inches are believed to be less susceptible to borer attack because

their thicker bark interferes with egg laying.

No adequate control measures for the poplar

borer are known. In Saskatchewan, the periodic

removal of infested aspens proved worse than no

control because opening ofthe stand was followed

by an increase in new infestations (Peterson 1948).

Diseases

Quaking aspen in the Lake States is subject to a

number ofdiseases. The more common ones attack

17
QUAKING ASPEN

the leaves and shoots, others cause cankers on the

main trunk or larger branches, one causes a prominant roughening of the bark, and several initiate

decay ofthe heartwood of the trunk or of the butt

section and roots. However, Hypoxylon canker,

shoot blights, and wood rots cause most ofthe economic damage.

Hypoxylon Canker

Hypoxylon canker, which is known to have been

present since about 1920 (Povah 1924), is currently

recognized as the most serious disease of quaking

aspen in the Lake States. Bigtooth aspen is less

frequently attacked (Graham et al. 1963), but many

young quaking aspen stands are so heavily infected

that their future productivity is questionable

(Christensen et al. 1951, Anderson 1956). Graham

et al. (1963) reported that 22 percent of all polesized and larger quaking aspen trees examined in

lower Michigan had Hypoxylon cankers; they estimated that annuallosses to the disease in this area

alone amounted to 250,000 cords.

Cankers usually form only on young bark (Bier

1940), so older trees are attacked higher above the

ground than young trees (Day and Strong 1959) (fig.

9). Trees seldom are killed by cankers on branches

or on the trunk nearthe top ofthe crown (Christensen et al. 1951). However, most trees with bole

cankers die because of girdling or stem weakening

and subsequent wind breakage (fig. 10).

The amount of Hypoxylon canker present in an

aspen stand is not directly related to site quality,

vigor, or sex of the tree. The probability of infection is much greater on poor sites, however, because the slow-growing trees require so many years

to reach merchantable size (Anderson 1953, Anderson 1958). Mortality in low-density stands is

about twice that in well-stocked stands (Anderson

1956). There is some evidence that the disease is

associated with wounds inflicted by the poplar and

other wood borers (Graham and Harrison 1954);

apparently the galleries of these insects provide

infection courts.

No direct control measures are known for

Hypoxylon disease. The soundest approach is to

maintain well-stocked stands of aspen throughout

the rotation (Anderson and Anderson 1968).

Decay

Decay-causing organisms are responsible for the

greatest volume losses in aspen, and most of this

damage is attributed to white heart rot. This fungus

F-516562

Figure 9.—Bole of aspen tree infected with Hypoxylon.

invades trees at dead branch stubs or at fire or

borer scars (Schmitz and Jackson 1927, Christensen et al. 1951). Development ofthe fungus is rapid

in older trees where the decay column may extend

to the tree tops. However, decay most often terminates in the stump and seldom extends into the

roots. Trees in which decay is in the advanced

stages are easily broken by wind; most such trees

show a number of conks or sporophores and are

generally left by loggers even though they contain

usable bolts.

Merchantable volume lost to decay increases

with stand age—one study showed that the loss was

5 percent at 30 years, 8 percent at 45 years, but 20

percent at age 70 for aspen in northern Minnesota

(Schmitz and Jackson 1927). In Ontario and Saskatchewan, cull caused by heartrot is not appreciable in aspen untilthe stands are about 90 years old

(Riley 1952, Kirbyci ai. 1957, Morawskietaí. 1958,

Basham 1960).

18
LAKE STATES

F^16564

Figure 10.—^Trees damaged by Hypoxylon canker are easily broken off by wind.

Shoot Blights

Young aspens may be damaged by shoot blights

such as Venturia tremulae (Hepting 1971). This

fungus develops on the leaves and may grow

through the petioles into the stems. An infection

occurring near the tip of a tree may kill the shoot

which then withers and becomes bent. This

"shepherd's crook" is common, especially in

young stands. Many other stem and leaf diseases

also are found on aspen (Appendix 11), but they

seldom affect extensive areas.

Mammals

Although quaking aspen is used for food by several species ofmammals, they seldom cause appreciable damage except where overpopulations exist.

Of the big game animals feeding on aspen, the

white-tailed deer is the most important for it occurs throughout the aspen type in the Lake States

whereas moose have a much more restricted range.

Most use of aspen by deer occurs during the

first 3 to 5 years after a stand is cut. Deer browsing

causes little lasting damage in most sprout stands

because deer normally eat only the leaves, small

twigs, and sprouts. Where other foods are scarce

and deer populations are high, however, suckers

may be browsed so heavily that serious losses of

reproduction result (Graham 1958; Westell 1954,

1960). Such losses are less common in Minnesota

than in lower Michigan (Westell 1956) and Wisconsin where deer are much more abundant. If the

browsed suckers and twigs are more than Vi inch in

diameter, this indicates that there are too many

deer and their food supply is inadequate in both

quantity and quality (Graham et al. 1963).

Where severe browsing damage occurs, the deer

population may be brought into better balance

with food supply by a combination of one or more

of the following: (1) killing-back overbrowsed

sucker stands by burning, by disking, or by using

herbicides to stimulate vigorous sprout regeneration; (2) making enough clearcuttings in merchantable aspen to provide an abundant supply of

browse; and (3) permitting an increased harvest of

deer (Graham et al. 1963).

Quaking aspen twigs and suckers are a preferred

food ofmoose. In areas where there is a high population of moose, such as Isle Royale and parts of

northeastern Minnesota, considerable damage to

aspen reproduction has occurred (fig. 11) (Aldous

and Krefting 1946, Krefting 1951). In 1971 Minnesota initiated a program of regulated hunting to

control the moose population.

The young bark, twigs, and leaves of aspen are a

favorite food of beavers. Stands within 300 feet

(sometimes 650 feet) of a beaver lodge or dam may

eventually be completely destroyed (Bradt 1947).

Consequently, where beavers have been plentiful,

there is usually little aspen near lakes and streams.

After the larger aspen are consumed, the beavers

move to other areas. Although beavers can cause

considerable local loss of aspen, their impact on

the resource is insignificant compared to that

caused by decay and insect outbreaks.

The snowshoe hare {Lepus americanas Erxleben) and the cottontail rabbit (Sylvilagus

floridanus mearnsii) (J. A. Allen) will girdle and

kill aspen suckers extending above the snowline.

Most root systems resucker; hence the damge involves only the loss of a few years' height growth

(Graham et al. 1963). Mice and voles will girdle

suckers underneath the snow. Damage from small

animals is important only in years of peak populations; this is about every 10 years in the case of

snowshoe hares.

Porcupines (Erethizon dorsatum L.) rarely

cause extensive damage to aspen although Graham

et al. (1963) reported that about 20,000 cords of

merchantable material were destroyed on a 3,000-

acre tract of aspen in lower Michigan. The animals

19
QUAKING ASPEN

tS«!*,»-- •*»'=i ' .:,SA^-Mm¡aí.?mtmi*¿

Figure 11.—Repeated heavy browsing by moose caused

poor form on these aspen. (Photo by L. F. Krefling,

USDI Bureau of Sport Fisheries and Wildlife.)

may consume the smooth outer bark of the upper

trunk and branches during the winter months; if

the exposed inner bark and cambium die, this

sometimes kills a tree above the injured area.

Where more preferred species, such as tamarack

and sugar maple, are readily available, however,

aspen consumption by porcupines is usually limited to twigs and buds during the spring.

Much of the aspen land in the Lake States is

farmer-owned and some of this is grazed. Trampling by livestock compacts the soil, interfering

with moisture absorption and root growth. Grazing, especially by sheep, destroys or damages any

hardwood reproduction that may invade the stand.

Where timber management is a major objective,

grazing should be prevented; if grazing is of higher

priority, the woodlot should be cleared for pasture.

Fire

Although fire is a useful tool in aspen management, it can also have adverse effects. Repeated

burns can destroy all or most of the humus layer,

causing reduced moisture absorption and retention. During the regeneration stage, a series offires

at 2- to 3-year intervals may completely destroy

the suckering ability ofthe root systems (Buckman

and Blankenship 1965). Although this suggests that

controlled burns will reduce aspen suckers enough

to favor reproduction of other species, too much

time and effort are involved to make this technique

practical (Horton and Hopkins 1965).

Saplings are killed to the ground by fires. The

thin bark of large trees provides little protection

for the cambium layer. The only visible damage

after fires may be fire scars at the base ofthe tree,

but these allow entry of borers and heart-rotting

fungi. Both sapwood and heartwood of fire-killed

trees are rapidly invaded by fungi and borers. By

killing trees, fires reduce current stocking and

volume and may affectthe rate ofgrowth in a stand.

In older stands, however, fires seldom cause

enough harm to the root systems to adversely affect

suckering.

Climatic Factors

Quaking aspen stands may be damaged by wind,

hail, ice storms, or unseasonable temperature extremes. High winds may uproot even sound trees

and cause considerable breakage in those that are

badly cankered. Such damage is much less frequent in young timber (Christensen et al. 1951,

Forbes and Davidson 1962). Most heavy

windstorms are local in effect, but some have affected a wide area in the Lake States (Stoeckeler

and Arbogast 1955).

Severe hailstorms kill smaller trees and reduce

the growth and vigor of large ones by breaking off

twigs and small branches and scarring the larger

branches and the trunks (Basham 1953, Riley 1953,

Thomas 1956). Bruises from the hailstones likely

serve as infection courts for Hypoxylon canker

(Christensen et al. 1951). The trees may be so severely damaged that their crowns look one-sided

and thin for many years (Riley 1953). Although they

seldom affect extensive areas, one hailstorm covered an area of about 10 square miles (Basham

1953).

Ice or glaze storms, either alone or accompanied

by sticky, wet snow, can cause heavy breakage of

20
LAKE STATES

aspen crowns. Severe storms may essentially destroy entire stands (Christensen et al. 1951, Davidson and Newell 1956), but aspen is not as vulnerable to ice storms as the conifers (Cayford and Haig

1961).

Although frosts seldom cause serious damage to

young aspen leaves, they will be killed when a

period of unusually warm weather is followed by

temperatures well below freezing. Such a situation

occurred in 1953 over a wide area in Minnesota and

adjoining Ontario and Manitoba—^the death ofthe

foliage was partly responsible for ending an outbreak offorest tent caterpillar (Rose 1958, Hildahl

and Reeks 1960). Leaves killed by early frosts are

replaced within a few weeks, so little actual loss of

volume growth results.

Sunscald often follows heavy thinnings (Bickerstaff 1946), and some clones appear to be more

susceptible to such injury than others (Graham et

al. 1963). Scars from sunscald always occur on the

south side ofthe trunks. Little direct damage usually results but the scars may provide access for

heartrot diseases (Graham et al. 1963).

Severe drought will kill young seedlings and reduce the growth rate and vigor ofsprouts and older

stands, making them more vulnerable to attack by

insects or disease (Christensen et al. 1951). This

combination of factors can cause considerable

mortality in older trees.

YIELD TABLES

The potential volume yields of aspen stands are

limited by site quality because this factor strongly

influences both height and diameter growth rates.

The most recent forest surveys of the three Lake

States show that about 11 percent ofthe aspen type

is on poor sites (S.I. <50), 58 percent on average

sites (Í.I. 50 to 69), and 31 percent on good to

excellent sites (S.I. ^70).

Yield Tables for Unmanaged Stands

Kittredge and Gevorkiantz (1929) developed the

first normal yield tables for aspen stands in Minnesota and western Wisconsin. Their tables showed

that yields increased steadily up to age 80; the

maximum was 80 cords per acre on excellent sites.

Experience showed that these tables overestimated the yields of unmanaged aspen stands so

Gevorkiantz revised them (table 8) to allow for

mortality and the decrease in growth rate with

stand age (Zehngraff 1947). However, he was unable to allow for the increased proportion of cull

trees in stands of advanced age. Most Lake States

aspen stands are pathologically mature by age 60,

after which cull trees may reduce merchantable

volumes 60 percent or more (Zehngraff 1947).

The Gevorkiantz table shows that pure stands of

quaking aspen on good sites will produce a

maximum yield of 47 cords of pulpwood or 9,000

board feet ofsaw logs per acre at 50 years, the usual

rotation age.® Medium sites produce their

maximum yields at a rotation age of 45 to 50 years.

TABLE 8.—Gross yields per acre of aspen in

unmanaged stands by age and site index i

Site index

Age

class 70 60 50 70 60 50

20

25

Standard cords ^

o

Board feet (Scribner)^

19 7

30 29 16 5 1,300 300 —

35 36 24 13 4,000 1,400 —

40 42 30 17 7,000 3,000 1,100

45 46 32 18 8,500 5,000 2,400

50 47 33 16 9,000 6,000 3,000

55 46 30 13 9,100 6,000 2,900

60 43 26 10 9,000 5,800 2,500

65 37 20 6 8,400 5,200 1,800

70 29 14 4 7,400 4,500 1,400

75 21 9 — 6,000 3,200 700

80 12 4 — 4,200 1,500 —

^In lower Michigan, bigtooth aspen produces one-third to

two-thirds more volume than quaking aspen on land ofthe same

quality (Graham et al. 1963).

^ Prepared by S. R. Gevorkiantz, Lake States Forest Experiment Station (Zehngraff 1947).

^ Gross volume of peeled wood in trees 4 inches d.b.h. and

lai^er, to a minimum diameter of 3 inches inside bark.

^Gross volume of trees 7 inches in d.b.h. and larger, to a

minimum of 6 inches inside bark.

Aspen on some relatively poor sites may produce

up to 18 cords of pulpwood per acre (table 8); however, average yields of 11 cords per acre were reported for such sites in lower Michigan (Graham et

al. 1963). Yields on poor sites are low because of

slow growth rate, inadequate stocking, and greater

loss from such diseases as Hypoxylon canker and

various decays (Cox 1914, Zehngraff 1947, Anderson 1953, Basham 1958).

21
QUAKING ASPEN

Yield Tables for Thinned Stands

Thinnings cannot improve the inherent capacity

of a site to produce fiber. However, the volume

utilized from trees thinned early in the rotation to

reduce anticipated mortality will increase the total

yield obtained from a stand. Such thinnings are

usually made from below, so volume growth is concentrated on fewer and larger trees. Stand quality

also is improved where poorly formed trees and

unmerchantable species are removed.

Steneker and Jarvis (1966) predicted that total

volume production of aspen stands in Manitoba

and Saskatchewan might be increased about 25

percent from thinnings made at 5-year intervals if

all-sized material could be utilized. However, they

concluded that (1) returns from early thinning

have little effect on total cordwood production

because most trees removed are too small to be

merchantable, and (2) operable thinnings usually

would not be possible until age 30 to 40, when stand

volume is between 15 and 30 cords per acre.

Because young aspens respond well to increased

growing space, early thinnings enable trees to sustain rapid diameter growth rates, thus more trees

reach veneer or saw log size in the normal rotation.

The effect of early thinnings on diameter growth

rate was confirmed in long-term studies conducted

in Minnesota. Aspen stands growing on a wide

range ofsites were thinned once to assigned stocking levels when the stands were from 10 to 30 years

old. Periodic measurements made over the following quarter century provided data for even-aged

stands ranging from 10 to 57 years in age and growing under a variety of stocking and site quality

conditions.

Schlaegel (1971) used these data to develop equations for predicting stand volume in cubic feet

based on combinations of site index, age, average

diameter, and basal area stocking. With these equations, he prepared tables showing yields in cubic

feet for stands with various average diameters and

specific assumed utilization standards (Appendix

III). He also used the basic data to prepare a table

showing yields in cords per acre by stand age, basal

area, and site index.

The height curves (fig. 12) Schlaegel used in preparing his tables are based on periodic height

measurements of the same trees. As a result, they

provide a more accurate estimate of height growth

than the traditional curves which are based on

single measurements oftree height and age. For the

same site index, the Schlaegel curves show greater

heights of dominant trees at 20 and 30 years than

100

90

UJ

2

O

80

70

60

50

40

90

85

80

75

70 5

i

65 S

20 30 40 50 60

TOTAL AGE (YEARS)

Figure 12.—Site index curves for quaking aspen in

north-central Minnesota.

those shown in the curves prepared by Gevorkiantz

(fig. 7) and Plonski (1956). Thus, Schlaegel's site

index curves should be used with his yield tables,

even though this might result in higher estimates of

site index for young stands than indicated by the

Gevorkiantz curves.

Schlaegel's tables show that predicted yields on

all sites keep increasing through age 60 but at a

decreasing rate. This indicates that some stands

might be grown longer than 60 years, but any further increase in gross volume might be offset by

losses in net volume because ofdecay, even on good

sites.

Although they are based on measured stands that

were located in a limited geographic area and on

medium-textured soils, tests have indicated that

these yield tables are applicable to pure aspen

stands elsewhere in the Lake States (Schlaegel

1971). The cubic foot volumes associated with average tree size, site, and basal area in Schlaegel's

tables generally agree with those reported by others

(Plonski 1956, Kirby et al. 1957, Zehngraff 1947).

Merchantable aspen yields for most natural stands

will be less, of course, because other species are

present and stocking will be less uniform. If these

factors are considered in applying Schlaegel's yield

tables, however, good volume estimates of the

aspen component can be obtained.

22
LAKE STATES

HARVESTING

Aspen management in the Lake States at the present time typically consists of giving stands reasonable protection from fire and then cutting them

when they reach merchantable size. Because aspen

grows in even-aged stands, all sound trees 5 inches

d.b.h. and larger customarily are harvested in one

operation. Where markets permit, 4-inch trees also

are taken. However, loggers seldom cut a tree that

will not yield at least two pulpwood sticks, so most

trees in the 4-inch class are left standing.

Hardwoods and conifers that might be used for

pulp also are often left because no local market is

available.

Where special markets exist, the landowner may

decide to harvest the large logs first and remove the

other aspen in a later cut. Ifthe landowner decides

to use this two-cut approach in mature aspen, the

first cut should remove no more than 40 percent of

the merchantable saw log volume and 15 percent of

the merchantable trees (Zehngraff 1947). Because

cull percent usually increases rapidly after age 45,

the final harvest cut should be made not more than

5 years later. Any further delay in making this final

cut also increases the chance that tolerant conifers

or hardwoods will replace aspen in the new stand

or at least form a mixed type.

The adverse effects of past cutting practices on

the quality of young aspen stands were evident in

an inventory of the forest lands in Carlton, Cook,

Lake, Pine, and St. Louis Counties of Minnesota

(Office of Iron Range Resources and Rehabilitation and Lake States Forest Experiment Station

1964). Of the 240,000 acres of aspen less than 20

years old, only 27 percent had a stocking of 70

percent or more. An additional 12 percent of the

stands were moderately stocked (40 to 70 percent)

but seedbed or competition conditions indicated

that a considerable investment would be required

to make them fully productive.

Partial Cuttings

Overmature aspen stands often contain many defective, low-value trees. A commercial cutting may

remove only the large sound trees for saw logs or

veneer bolts and leave the small or poor-quality

trees. Unless the residual trees are cut or killed,

aspen suckers will be inadequate to form a wellstocked aspen stand. Instead, other species released by the partial cutting tend to take over the

site.

Little is gained by partial cuttings from above,

even when they are made in thrifty mature stands.

An indication of what can happen following such

partial cuttings was furnished by a study in a sawtimber stand on a good site on the Pike Bay Experimental Forest in Minnesota. Trees were removed to fixed diameter limits of 8, 9, and 10

inches at age 45 (fig. 13). During the 5 years following this cutting, the saw log volume added in these

stands was the same or less than that in an adjacent

uncut stand. Aspen regeneration suffered; the partially cut areas were invaded by brush or shadetolerant hardwoods so the aspen suckers could not

F-313759

Figure 13.—Forly-five-year-old stand of aspen left after

cutting from above to a 10-inch diameter limit.

23
QUAKING ASPEN

develop properly because of the partial shade

(Zehngraff 1947).

Mechanized Harvesting

Because well-stocked mature aspen stands contain a relatively high volume per acre in trees having a limited range of diameters, they provide excellent opportunities for mechanized harvesting.

In addition, year-round harvesting is feasible on

most aspen sites.

Mechanization of timber harvesting in the Lake

States began in the early 1960's when rubber-tired

skidders and self-loading trucks and trailers became available. The current trend is toward using

more sophisticated machines such as timber harvesters, tree processors, feller-bunchers, and tree

shears. For example, portable chippers are now

available that can convert tree-length logs or full

trees directly into chips for hauling to the mills in

bulk carriers. Many of these machines are still in

the developmental stage. As they become more efficient and versatile, their use is expected to increase.

Mechanization has increased productivity per

man. A two- or three-man crew using chain saws

and tree-length or full-tree skidding can produce

up to 4,000 cords per year. Full mechanization

could increase this to 7,000 cords per year.^ The

^ Paper presented by Z. A. Zasada, University ofMinnesota, at

the joint meeting ofthe Great Lakes Deer Group and the Ruffed

Grouse Workshop, Hill City, Minnesota, September 22, 1970.

substantial investment in equipment is a strong

incentive for year-round logging operations that

provide stable jobs.

Machines are designed to handle a variety of

jobs, so the woods operation may take several

forms. Trees may be processed into shortwood in

the woods, or they may be felled and limbed at the

stump and hauled to mills in full merchantable

lengths. In other operations, the trees are felled

and forwarded to a nearby landing where they are

limbed and either cut into pulpwood lengths or

converted into chips.

Although the heavy machines used to fell and

process trees cause varying degrees of site disturbance, little adverse effect on soils or watershed

values has been observed (Zasada 1972). The

greatest disturbance has resulted from full-tree

skidding and summer logging. Full-tree skidding

also has destroyed most ofthe brush. Aspen regeneration usually has been abundant except on main

skid trails and at landings.

A major advantage of mechanized harvesting is

that it can create conditions favorable for regenerating well-stocked stands of aspen. Slash can be

concentrated where desired; brush can be uprooted and largely destroyed; and unmerchantable

trees can be felled or broken off at low cost during

the logging jobs. If properly used, mechanized

harvesting systems thus can facilitate aspen management for sustained timber and wildlife production without causing serious damage to watershed

or scenic values.

ESTABLISHING VIGOROUS REPRODUCTION

Clearcutting is the best way to regenerate aspen

stands because completeness of cutting largely determines the success of establishment and subsequent growth rate of new aspen forests. A complete clearcut removes all cull and nonmerchantable trees, some ofwhich also are potential sources

of Hypoxylon and rot infections.

An ideal way to achieve a complete clearcutting

would be by utilizing all of the trees on an area.

Improvements in efficiency of harvesting and

processing equipment may soon make this practical. In 1972, field trials in southern Michigan

showed that it was possible to cut all trees 2 inches

d.b.h. and larger and convert them directly into

chips that were usable by local industries. Although converting the chipped mixture of wood,

bark, twigs, and leaves into fiber products usually

requires modification of traditional techniques,

these problems can be solved. If this harvesting

system becomes economically feasible, it will encourage development of stands dominated by aspen.

As a rule, commercial cuttings in thrifty, wellstocked aspen stands remove or destroy nearly all

the trees and a new aspen stand develops. Where

commercial harvest cuttings are made in overmature stands or stands of mixed composition, however, many unmerchantable trees as well as small

hardwoods and brush are left. This residual stand

restricts the production and growth of aspen suckers (Stoeckeler and Macon 1956) (fig. 14). The results will be either an uneven, partially stocked

stand of aspen and brush, a mixture of aspen and

conifers or hardwoods, or an understocked stand

24
•*SÇ«'-**TI

LAKE STATES

V *'•\

»^ ^j^;.,i|^ i

H^^^B^^^^^^I^^^I^^Bs''H^i ^^H^'F;

î

11

F-522788

Figure 14.—This commercial clearcutting left so many

trees that aspen regeneration will be inadequate,

of thrifty aspen mixed with worthless culls. Although mixtures of aspen and conifers can be desirable, mixtures with other hardwoods may be

considerably less productive. For example, most

hardwoods associated with aspen in northern Minnesota consist of defective sugar maple, low-grade

American elm and green ash, and slow-growing bur

oak.

Eliminating Residual Trees and

Brush

The requirement that residual trees must be cut

or killed sometimes is included in timber sale contracts for National Forest and other public lands.

Zasada and Tappeiner (1969) reported that

mechanized full-tree harvesting can remove nearly

all trees and brush. However, most commercial

logging operations leave enough trees or brush to

hinder successful establishment and growth of

aspen suckers. Various methods can be used to

control such unwanted vegetation.

Mechanical Equipment

Residual trees can be felled with chain saws.

Brush can be controlled with brush choppers, KG

blades, rock rakes, or other special machines capable of removing small- and medium-sized trees

as well as brush. Costs are high but these heavy

machines sometimes are used to regenerate aspen

for wildlife habitat improvement. '

Chemical Herbicides

Herbicides are useful tools in aspen management. They affect aspen and other woody plants in

varying ways and degrees, depending on the chemical ingredients and when and how the herbicide is

applied. Some herbicides kill aspen and other

hardwoods without appreciable damage to conifers; others kill only the above-ground parts of

aspen and result in prolific sucker development. A

few herbicides are nonselective—they will damage

or kill all vegetation.

Costs of chemicals vary considerably; some are

relatively expensive. Where much unwanted vegetation must be controlled, however, this can be

accomplished at lower cost with herbicide applications than with mechanical methods.

Some herbicides are suspected sources of environmental contamination. The potential hazards

associated with such herbicides are being evaluated; some already have been approved for use

under specified conditions. The forest manager

should keep informed about current restrictions

on herbicide use.

In aspen management, a primary use of herbicides has been to control culls, small trees, and

brush that would prevent or restrict aspen sprout

development on cutover areas. The kind and

amount of the vegetation to be controlled usually

determines what treatment is needed.

Where the brush is scattered and offers little

competition, treatment of individual trees may

suffice. Research has shown that most trees can be

killed in any season with a solution of 2,4,5-T

applied to fresh cuts in the bark,^" or with undiluted 2,4r-D amine applied with metering injectors.

However, ifindividual aspen trees are treated during the peak of the growing season (June-August),

the root systems may be killed, which would prevent later sucker production (Arend 1953, Worley

et al. 1954).

Where the presence of many trees and heavy

brush will restrict sucker initiation and development, aerial application of herbicides has been

cheaper than individual tree treatment. To avoid

killing the aspen root systems, too, Perala (1971)

recommended delaying aerial spraying until early

'"A 16 to 20 pound acid equivalent of 2,4,5-T ester formulation per 100 gallons of fuel or diesel oil has been effective.

25
QUAKING ASPEN

August; although the existing aspen suckers would

be killed, new ones would be produced the following year.

The above-ground parts of aspen trees have been

killed by aerial application of2V2 to 3 pounds (acid

equivalent) of a low volatile 2,4-D ester in égalions

of water emulsion per acre. In northern Minnesota, this treatment killed nearly all the 90-

year-old aspen culls and controlled a dense underbrush of mountain maple and hazel so that excellent aspen suckering followed (fig. 15). Such

species as red maple are resistant to 2, 4-D; where

the residual stand contained many such trees, good

control has been achieved by aerial applications of

IV2 pounds each of 2,4-D and 2,4,5-T esters.

F-506116

Figure 15.—^This dense stand of aspen developed where

the overstory and brush were killed with herbicides.

Prescribed Burning

Where the operation can be handled without

hazard to adjacent lands, research indicates that

prescribed burning will set back the brush, kill

unwanted trees, and get rid of some of the slash.

Such burning is possible only when the aspen slash

is dry enough to burn, however, and this may not

be until the second spring or fall after logging. Any

existing aspen suckers killed will resprout. Burning does not give lasting control of the brush, although enough stems may be killed to give the

aspen suckers a chance to develop. Prescribed

burning must be used with great caution and

only by those who are thoroughly familiar with the

behavior of fire. Actual costs may exceed those of

chemical treatment because burning is possible

only when the fire risk is high.

Increasing the Stocking of Sucker

Stands

Because of past logging practices, many young

stands are so poorly stocked with aspen or other

merchantable species that future yields will be

low. If growing aspen is his objective, the landowner may decide to let such stands grow until the

aspen can be harvested and then make a clearcutting. An alternate solution is to eliminate the present stand by using herbicides or fire as previously

described. This will encourage aspen sucker production and increase ultimate aspen yields.

Limited trials indicate that the number of aspen

suckers in understocked stands also can be increased by disking. Where a Wisconsin area was

disked in the fall, for example, 2 years later there

were 5,500 to 7,800 suckers per acre compared with

1,200 stems on an undisked area. In the Upper

Peninsula, Zillgitt (1951) found that disking increased stocking from 2,700 stems to 11,400 stems

per acre within 1 year; on a somewhat poorer site,

stocking was increased from 1,600 to 6,100 stems

per acre by disking. These apparent benefits of

disking are somewhat deceiving, however, because

subsequent growth of the suckers was poor, and

disking costs considerably more than other methods.ofsite preparation to stimulate sucker production.

Logging During the Bark-Peeling

Season

As recently as 1966, about half of the aspen

pulpwood cut in the Lake States was sold after the

26
LAKE STATES

bark had been peeled by hand. The bark-peeling

season lasts from early May to early July. Where

stands are cut after the end of May, however, the

number of vigorous suckers produced may be inadequate to ensure regeneration of a new aspen

stand. It is not always possible to schedule logging

during May when the bark is easily peeled, so

chemical debarking has been tried as a substitute

for hand peeling. Applications of such chemicals

as sodium arsenite and ammate, or the hormone

herbicides 2,4-D and 2,4,5-T have been effective.

but chemical debarking has never been widely

used in the Lake States.

The problem of planning harvesting operations

to coincide with the period of easy peeling is becoming less critical. Many pulpmills find it more

efficient to practice year-round logging to reduce

the area needed for cordwood storage and to prevent the loss in pulp brightness resulting from long

storage of peeled wood (Auchter 1972). Other factors causing this change include the shortage of

skilled loggers and the increasing use of

mechanized harvesting and peeling.

MANAGEMENT ALTERNATIVES

In many respects, aspen is an ideal multipurpose

tree. It can be managed at low cost to produce

salable timber products while providing highly desirable wildlife habitat. Dependable regeneration

from root suckers, intolerance causing early natural thinning and pruning, and fairly rapid volume

growth over a short rotation make it possible to

grow crops of aspen without treatments such as

thinnings. In most instances the only direct investment involved will be provision for establishment and release of the aspen sprouts—treatment

of residual trees and brush when the stands are

harvested.

A higher level of management will increase

timber crop values. For example, thinnings can

increase the average size of trees at maturity, produce more veneer and sawtimber volume, and

shorten the time needed to grow merchantable

trees. Such thinnings may also increase total cubic

volume yields over a rotation, but they also increase management costs.

Where continuous production of aspen is the

management objective, some ofthese costs may be

offset by other benefits of treatment. Increased

yields per acre reduce costs per unit volume of

harvesting and timber sale administration. In succeeding rotations, it will be easier to maintain

aspen as the predominant species. Thus, the degree

to which investments are expected to reduce the

long-term costs of aspen management also should

be considered by the forest manager.

Regardless ofhow aspen stands are managed, site

quality limits potential growth rates and volume

yields. Little can be done to increase the low aspen

yields on poor sites. Medium-quality sites will produce trees of pulpwood size; practical treatment

usually is limited to eliminating unmerchantable

trees when stands are harvested to ensure vigorous

aspen regeneration. Highest yields of both

pulpwood and saw logs can be expected on the

better sites where a much wider range of cultural

treatments can be considered. Wide variations in

site quality may occur within a limited area because of differences in aspect, topographic position, and soil characteristics. Extensive areas of

uniformly good sites can be treated more efficiently than scattered small areas.

The distribution ofthe age or size classes must be

considered by the aspen landowner in management planning. If the aspen land is fairly evenly

divided into mature timber, pulpwood, poles,

seedlings, and saplings stands, an orderly program

of management could be readily installed. Where

there are definite deficiencies in certain size classes, however, the best of management cannot prevent periods of lean returns. Such poor distribution can be corrected to some extent by adjusting

the rotation length in the older age classes—

shortening it in some stands or lengthening it in

others. Of course, mature and overmature stands

usually must be harvested as soon as possible to

prevent further losses from decay.

Treatments to Increase Growth Rate

The abundant suckers produced after aspen

stands are harvested ensure perpetuation of the

type, but most ofthese suckers die long before they

reach merchantable size. While they survive, however, these trees and those of unmerchantable

species occupy growing space, use moisture and

nutrients, and undoubtedly reduce the growth rate

of the trees that live to form the merchantable

crop.

If enough of these "excess" trees could be removed early in the rotation to provide adequate

27
QUAKING ASPEN

growing space for the potential crop trees, these

would reach merchantable size in fewer years.

Some trees would grow fast enough to produce saw

logs, especially on the better sites. Such thinnings

also could eliminate most trees of unmerchantable

species, so the final stand would be dominated by

aspen. Thus there is a good possibility that thinnings could increase net volume and value growth.

In deciding whether it would be profitable to

thin aspen stands, the forest manager needs answers to several questions. What are the results of

thinnings in stands of various ages? How early

should thinnings be made to get maximum growth

response? How many crop trees should be left?

How long should thinnings be continued?

Research has shown that: (1) repeated thinnings

before age 20 can accelerate diameter and volume

growth ofselected trees, reduce losses from natural

mortality, and eliminate unwanted species; (2)

thinning stands during the small pole stage (ages 20

to 30) provides enough growing space for selected

trees so they will maintain maximum diameter

growth rates; and (3) a single thinning should be

considered in pole-sized stands between 30 and 35

years where a premium price is expected for large

products and where the yield from the thinning

itself will either show a profit or offset the costs.

These studies also show that both costs and risks

must be considered in planning thinnings. Time is

required to select the potential crop trees and to

cut or deaden the others. The small trees cut in

early thinnings usually would have little value, and

thinnings in older stands may not yield enough

merchantable volume to offset marketing and harvesting costs. Heavy thinnings increase the risk of

losses to disease, windthrow, and sunscald. The

thin bark of newly released aspen trees is subject to

sunscald iflarge openings are created, so thinnings

must leave enough trees to protect the boles of crop

trees. A higher percentage of trees may become

infected by Hypoxylon in heavily thinned stands

(Anderson and Anderson 1968).

Although opportunities for profitable thinnings

now are limited because of the low value of aspen,

thinnings might become feasible if the market improves. The results ofpast studies provide valuable

guidelines for such thinnings.

Thinnings in aspen sucker and sapling stands

should improve stand quality and composition as

well as give the residual trees more growing space.

The largest trees should be reserved except when

they are obviously diseased, deformed, or have

other undesirable characteristics. Spacing of the

trees left is of less importance than their quality.

No slash disposal is necessary.

Herbicides cannot be used to thin aspen stands

because of their interconnected root systems.

Suckers and small saplings can be cut with

machetes, bolo knives, or Phelps tools (fig. 16).

Axes or small power saws, such as those used in

brush clearing, are needed to cut larger trees.

F-476286

Figure 16.—Tools used to thin sapling stands. (The Phelps

tool is on the right.)

In one study, an average of 11 man-hours per

acre was required, using bolo knives and Phelps

tools to cut aspen up to 3 inches in diameter and

using axes to cut larger trees. An additional 3

man-hours per acre were needed to fell unwanted

ash, oak, and elm, an operation that might be unnecessary where there is a potential market for

such species.

No data are available on the time required to

make thinnings in pole-sized and older stands of

quaking aspen. However, Blair and Ralston (1953)

reported that thinning 12-acre compartments in a

35-year-old stand of bigtooth aspen required 3.6

man-hours per cord for a heavy cutting from above

(12 cords removed per acre), and 4.0 man-hours

per cord for a heavy cutting from below (13 cords

removed per acre). The 12-acre compartment that

was clearcut required 3.0 man-hours per cord and

yielded 22 cords per acre.

Thinnings in Sucker Stands

Because of the intense competition in typical

dense sucker stands, relatively few trees attain

diameters exceeding 2 inches in 8 to 10 years. In

theory, at least, thinning such stands should

sharply increase the growth rate of the remaining

trees.

28
LAKE STATES

Graham et al. (1963) reported that 6,000 to 12,000

well distributed suckers per acre are more likely to

develop into a better stand than 35,000 to 40,000.

Results of a thinning study in a 1-year-old stand of

aspen suckers in Minnesota indicated that even

6,000 stems per acre may be more than enough.

Where stocking had been reduced from 10,000 to

1,000 stems per acre, Sorensen (1968) reported that

basal area increased almost as much in 13 years as

in an unthinned stand. Average tree diameter was 1

inch greater in the thinned stand, but the gain in

average diameter for the 400 largest trees per acre

was only 0.4 inch. After 20 years, the unthinned

stand contained more volume per acre, although

average tree diameters still were less than in the

thinned stand.

Moreover, part ofthe increase in average diameter must be attributed to removal of small trees.

Thus, the benefits were not adequate to justify the

substantial costs. Sorensen (1968) concluded that

areas stocked with from 1,000 to 10,000 1-year-old

aspen stems per acre will produce an adequate

number of potential crop trees, and that lack of

thinning will have little effect on their diameter.

Thinnings in Sapling Stands

If thinning is postponed until the sapling stage,

fewer trees will need to be cut and treatment still

could shorten the time until cash returns can be

obtained. This hypothesis has been under evaluation by the North Central Forest Experiment Station in a study begun 35 years ago in a 13-year-old

stand and in a second study begun 20 years ago in an

11-year-old stand. Both stands are located on good

sites in north-central Minnesota.

In the first study, five degrees of thinning were

tested on 0.6-acre plots having from 3,500 to 4,900

stems per acre (fig. 17). After treatment, there were

from 400 to 1,700 stems per acre on the thinned

plots compared with 3,600 stems per acre on the

check plot. None of the trees left was more than 3

inches in diameter; tree heights ranged from 23 to

27 feet (fig. 18).

After 5 years, volumes ranged from 1 to 5 cords

per acre. In 10 years, this had increased to 11.2

cords on the check plot as compared to 11.1 cords

on the plot thinned to 540 trees (fig. 19) and to 10.4

cords on the plot where 980 trees were left. The

other thinning treatments reduced volume growth

considerably. At this time (stand age 23 years) an

additional thinning was made in all but the check

plot. Actual pulpwood yields from this thinning

ranged from 1.7 to 1.9 cords per acre.

F-392287

Figure 17.—Competition is intense in dense aspen sapling

stands such as this; thinning would remove most ofthe

trees that would die normally and concentrate volume

growth on the residual trees, Chippewa National Forest, Minnesota.

F-326058

Figure 18.—Thirteen-year-old aspen sapling stand just

after thinning to 540 trees per acre, Chippewa National

Forest, Minnesota.

29
QUAKING ASPEN

F-439564

Figure 19.—Pulpwood volume is 11.1 cords per acre in

this stand 10 years afterit was thinned at age 13 to leave

540 trees per acre, Chippewa National Forest, Minnesota.

Subsequent growth continued to be rapid, so

additional cuttings for pulpwood were made from

below on all but the lightest thinned plots at age 28

and on all the thinned plots at age 33.

After 35 years (stand age 48), the unthinned plot

contained the least aspen volume; total volume was

highest but 29 percent of this was in low-value

hardwoods (table 9). Early thinning and control of

these other hardwoods in the other plots resulted

in more total aspen production than in the unthinned plot.

Thinning also increased the number of lai^e

trees containing potential saw logs or veneer bolts.

Although the plot thinned to leave about 400 trees

per acre contained more trees 14 inches d.b.h. and

larger, overall volume and quality production

were better on plots where more trees were left.

Early results of the small-scale study were encouraging, so a 20-acre area was thinned in an 11-

year-old stand to see if leaving about 750 trees per

acre would be a practicable level to use in aspen

saplings. Other tree species were eliminated from

the thinned stand. An untreated portion of the

stand was used as a check.

After 20 years, the thinned and unthinned stands

contained about the same number of trees per

acre, but distinct differences in diameter distribution were evident at stand age 31 years. There were

nearly twice as many aspens 7.6 inches d.b.h. and

larger (95 versus 53 per acre) in the thinned stand,

and many of these can be expected to produce saw

logs or veneer bolts at maturity. The thinned stand

also contained 6 cords more aspen volume per

acre.

However, this thinning had some adverse effects.

In the first 15 years after thinning, 23.6 percent of

the aspens were killed by Hypoxylon in the

thinned stand compared with 14.4 percent in the

unthinned stand (Anderson and Anderson 1968).

This reduced stocking in the thinned stand below

the optimum for maximum volume production. Of

TABLE 9.—Aspen volume production per acre in stands on good sites given

noncommercial thinnings to various densities at age 13 (Pike Bay Experimental Forest, Minnesota)

Trees left per acre in first thinning

Data 3,630

(check) 1,700 1,210 980 540 400

Stand at age 48

Harvested in thinnings

Total production

Stand at age 48

Harvested in thinnings

Total Production

^3,058

3,058

38.7

38.7

3,673

224

3,897

46.5

2.8

49.3

- Cubi feet»

3,162

504

3,666

Cords'

40.0

6.4

46.4

3,612

1,017

4,629

45.7

12.9

58.6

3,385

868

4,253

42.8

11.0

53.8

3,150

551

3,701

39.9

7.0

46.9

'Merchantable cubic volume inside bark to a 3-inch top (d.i.b.) of trees 3.6 inches d.b.h. and larger.

^The check plot also contained other hardwoods; these had a volume of 1,118 cubic feet (14.1 cords).

'Based on 79 cubic feet per rough cord.

30
LAKE STATES

all trees that died in the thinned stand, more than

two-thirds were killed by Hypoxylon, which emphasizes the susceptibility ofhigh-vigor treesto this

canker. To reduce the risks of Hypoxylon infection, the authors suggested that aspen stands should

be maintained at or near full stocking to assure the

greatest fiber yield even though the growth rate of

individual trees will be adversely affected.

In Manitoba, Steneker (1964) evaluated the effects of early noncommercial thinnings in wellstocked aspen stands 14, 19, and 23 years old on

good sites. Each stand was thinned to leave trees

spaced 12 by 12, 10 by 10, and 8 by 8 feet apart.

Thinning to an 8 by 8 spacing resulted in production of more large trees in 10 years than either of

the wider spacings or the control, and more pulp

volume than where fewer trees were left.

Thinnings in Pole^Sized Stands

The effectiveness of crop tree thinningwas tested

in 20-year-old stands on good site (S.I. 70+) on the

Chippewa National Forest, Minnesota. Selected

trees were released by cutting competing trees of

the same crown class; intermediate and suppressed

trees were left. Treatments compared growth in an

uncut stand with that where crop trees were spaced

about 10, 15, and 20 feet apart. The stands were

given no further treatment until they were harvested 30 years later at age 50.

After 30 years, pulpwood volumes of both aspen

crop trees and of all trees were highest in the unthinned stand and where crop trees were spaced

about 10 feet apart (table 10). Inthe thinned stands,

yields of aspen saw logs were from 500 to 800 board

feet per acre more than in the unthinned stand.

Average tree diameter was directly related to thinning intensity, ranging from 7.8 inches in the unthinned stand to 11.6 inches where crop trees were

spaced 20 feet apart. Many of these larger trees

were quite limby, however, and produced only one

clear log. Thus, the net effect ofthese noncommercial thinnings at age 20 in stands growing on good

sites was the production of fewer but larçer trees

containing more saw log but less pulpwood volume.

On excellent sites, however, thinnings in young

stands can greatly increase volume growth rate. For

example, where 460 trees per acre were released in

a 25-year-old stand (S.I. 90), average annual growth

rate per acre during the next 20 years was 1.69 cords

compared with 1.25 cords in an adjacent unthinned stand. ^^ Although a pulpwood thinning at age

39 removed 13.4 cords per acre from the thinned

stand, total aspen volumes at age 45 were about

equal in both stands—from 39 to 40 cords per acre.

At age 45, average tree diameter was 10.0 inches in

the thinned stand compared with 7.6 inches in the

unthinned stand. These results suggest that a noncommercial thinning on excellent sites can speed

up diameter growth enough to make a commercial

thinning feasible.

First Thinning at Age 30 or Later

Only the best sites (S.I. 70+) produce enough

volume at age 30 to 35 years to support a profitable

thinning, so the opportunities are limited. The operation should yield 10 or more cords per acre and

still leave a good stand (60 to 80 square feet basal

area) of thrifty dominant or codominant trees.

^^Unpublished results ofa study by John W.'Hubbard, on file

at Boise-Cascade Corporation, International Falls, Minnesota.

TABLE 10.—Stand basal area and volume per acre 30 years after a crop tree

thinning in aspen stands at age 20, Chippewa National Forest, Minnesota

Treatmentcrop tree

Aspen crop trees All trees 1

Basal

area

Volume

Basal

area

Volume

Pulpwood Saw log Pulpwood Saw log

Not thinned

10 by 10

15 by 15

20 by 20

100

100

74

80

Cords^

37.4

36.8

26.2

19.7

Fhm^

5,530

6,390

6,290

6,370

Ft^

109

106

97

87

Cords^

39.7

39.1

35.0

31.4

Fhm^

5,930

6,470

6,420

6,660

^ All crop trees plus ingrowth of alLspecies during the 30 years.

'Volume in rough cords of trees 3.6 inches d.b.h. and larger to a 3-inch top d.i.b.

®Board-foot volume (International y4-inch rule) of trees 7.6 inches d.b.h. and larger to a 6-inch top d.i .b.

31
QUAKING ASPEN

A study on the Chippewa National Forest compared the growth and yield of 30-year-old stands on

good sites afterthe following treatments: (1) a moderate thinning from below leaving about 275 trees

per acre; (2) a heavy thinning from below leaving

150 trees per acre; and (3) a moderate thinning

from above. The thinnings removed from 7.7 to

17.6 cords per acre (table 11). Volume production

^ in the thinned stands was compared with that in an

adjacent uncut stand.

After 27 years, the uncut stand and the stand that

was thinned moderately from below contained

more cordwood and saw log volumes than either of

the otherthinned stands. However, total cordwood

production was 27 percent higher, and actual

growth during the 27-year period was 24 percent

higher in the stand thinned moderately from below

(fig. 20) than in the uncut stand. Saw log volumes

were considerably less in stands thinned from

above or heavily thinned from below.

In another study made on an excellent site, thinnings in 32-year-old, well-stocked aspen stands

yielded an average of 27.9 cords and left 29.5 cords

per acre (Hubbard 1972). After 17 years (stand age

49), volume had increased to 52.8 cords per acre.

Total volume production was 80.7 cords per acre in

the thinned stands, as compared to 63.6 cords per

acre in an adjacent unthinned stand of the same

age. Mean annual volume production per acre was

1.65 cords in the thinned stands where the average

tree diameter was 11 inches; corresponding values

for the unthinned stand were 1.30 cords and 9.3

inches.

In contrast, Schlaegel and Ringold (1971) reported that a single thinning in a 37-year-old aspen

stand did not increase either total volume production or the number of veneer-sized trees after 10

years. Response to thinnings apparently decreases

-rS

F-328304

Figure 20.—Moderate cuttings from below in quaking

aspen ofmedium age such as this 30-year-old stand on

the Chippewa National Forest, increase the size ofthe

final crop trees as well as total yield.

as Stands near rotation age, but the critical age

probably varies among aspen clones.

Few studies have been made of thinnings in

older stands on medium or poor sites. Pike (1953)

reported a small increase in yield during the 20-

year period following light and medium thinnings

from below in a 35-year-old stand on a medium site

TABLE 11.—Effect on volume growth ofaspen stands ofsingle thinnings at age 30

to different stocking levels, Chippewa National Forest, Minn.

Volume age 30 Volume age 57

Growth in

Total Cut Left To 3 in. top Saw logs production 27 years

Cords 1 Cords 1 Cords' Cords 1 Fbm' Cords^ Cords

Moderate thinning from below 26.6 14.2 12.4 47.2 15,370 61.4 34.8

Heavy thinning from below 24.6 17.6 7.0 29.1 10,750 4é.7 22.1

Moderate thinning from above 21.1 7.7 13.4 43.3 11,960 51.0 29.9

Unthinned 20.4 — 20.4 48.4 14,200 48.4 28.0

'Volume per acre in rough cords of trees 3.6 inches and larger to a 3-inch top d.i.b.

^Board-foot volume per acre (International Vi-inch rule) of trees 7.6 inches and larger to a 6-inch top.

'Sum of original cut plus stand volume at age 57.

32
LAKE STATES

in Manitoba. On the basis ofthe growth made during a 10-year period on plots thinned at 17 and 40

years on medium sites and growth after a thinning

at 22 years on a good site, Bickerstaff (1946) concluded that thinning of aspen is not practical except on the best sites.

Improving Genetic Quality of Aspen

Stands

Quaking aspen clones vary greatly in growth rate

and bole form, so it should be possible to increase

stand productivity by upgrading average genetic

quality. Garrett and Zahner (1964) tested several

treatments designed to favor sucker production of

selected bigtooth aspen clones in Michigan. They

reported wide variation in suckering ability among

clones, and concluded that drastic treatments

would be required to ensure adequate propagation

of some desired clones. A possible solution would

be: (1) cut all trees ofthe less desirable clones and

kill their root systems to prevent suckering; and

(2) cut trees of the selected clones a year later so

their sprout regeneration would dominate the new

stand.

A more reliable way to improve the genetic quality of aspen stands would be to plant hybrids or

selected clones that show superiority in growth rate

and in resistance to insects and diseases, and that

will also produce high-quality wood and fiber. Research has shown that trees having many of these

desirable characteristics can be produced; the

major remaining problem is development ofsatisfactory regeneration techniques. After such improved aspens become available in sufficient

quantities, they could be planted on the best available sites where intensive culture could be used to

maximize volume and value yields.

OTHER MANAGEMENT ALTERNATIVES

Quaking aspen in the Lake States often grows in

stands that include varying proportions of paper

birch, northern hardwoods (sugar maple, yellow

birch, American basswood, and northern red oak),

or conifers (pines, spruces, balsam fir, and northern white-cedar). In some stands, these other

species occur as scattered trees or groups of trees

that are codominant with the aspen. In other

stands, the more tolerant conifers or hardwoods

may form a dense understory. Variations among

species in tolerance and rotation age often make it

difficult to manage mixed stands for maximum

volume and value yields. Available markets may

make it more profitable to discriminate against

aspen on sites where other species can produce

wood of higher value.

Aspen with Complete Understory

Conversion is easily accomplished where the associated species form a more or less complete understory (fig. 21). If the aspen is of merchantable

size, it can be harvested to release the overtopped

trees. Early release is especially beneficial to balsam fir because frequency of decay is highest

among suppressed trees and response to release

seems to be more dependent on absence of decay

than on age. Conversion to other species seldom

will be completed in a single rotation regardless of

the harvesting method used. Harvesting only merchantable trees will be more economical than

complete clearcutting, and the partial shade of residual trees will inhibit aspen suckers. Moreover,

at least some of the aspen trees left may grow lai^e

enough to furnish an additional yield when the

next harvest cut is made (Cooley and Lord 1958).

Mixtures of Aspen and Other Species

In many mixed stands, the species growing with

aspen make up a relatively small proportion of

total stocking. Unless intensive measures are used

to eliminate the present stand and plant or seed

some preferred species, changing stand composition will be a gradual process requiring several

rotations.

The simplest approach is to use measures favoring the more tolerant species—harvest the aspens

as they mature without any attempt to cut cull trees

or control brush and reproduction. This will restrict development ofthe aspen suckers, and other

species will eventually replace the aspen. This harvesting practice has been responsible for most natural conversion in the past, so the results can be

predicted.

Rate of conversion and composition of the new

stands are largely uncontrolled, but periodic yields

of aspen and other species are possiI)le. Harvest

cuttings ofshade-tolerant trees made in the winter

or spring following good seed crops will favor their

regeneration. If conditions warrant it, some type of

seedbed preparation could be made in advance of

seed fall.

33
QUAKING ASPEN

-fc ,. '^^!Ä'^!*.^^

F-460880

Figure 21.—Well-stocked, near mature aspen stand with a

fairly dense understory of thrifty balsam fir. Aspen is

36 years old and on good site, Nicolet National Forest,

Wisconsin,

Where mixed stands are to be converted to easily

wind-damaged species, such as balsam fir and

spruces, excessive windthrow may result if the

stands are opened up too much in one cutting. This

occurred in a Minnesota stand composed of mature aspen mixed with uneven-aged balsam fir and

considerable low-grade sugar maple, ash, and elm.

The objective was to convert the stand to balsam

fir. After all merchantable aspen and high-risk

balsam firs were harvested, the cull aspens and

larçer hardwoods were killed with herbicide and

the smaller hardwoods were cut with a power saw.

This postlogging cleanup was a mistake—it opened

up the stand so much that practically all of the

thrifty balsam fir blew down. The aspens suckered

so abundantly that the new stand consisted almost

entirely of aspen instead of a balsam fir stand containing a few aspen.

Aspen and Balsam Fir as Alternate

Crops

On some sites, aspen and balsam fir are the most

abundant species, and they could be grown as alternate crops. Both species grow rapidly and are

quite short-lived. They can be handled on rotations of about the same length. Balsam fir is tolerant and will become established under aspen,

whereas aspen suckers outgrow balsam fir seedlings and soon become dominant. All that is needed

to begin such alternation is either one ofthe following situations: (1) a near mature stand of aspen with

a good understory of balsam fir, or (2) a mature

stand of fir containing a scattering of aspen trees.

Clearcutting a mature aspen stand will release a

balsam fir understory, which will reach merchantable size in another 30 or 40 years because of its

rapid growth. Most understory balsam stands have

openings that will be invaded by the aspen suckers.

As a result, when the balsam fir stand matures, it

will contain some aspens, as in the second situation

described above. If both aspen and balsam fir are

cut at the same time, a sucker stand will be obtained that rapidly overtops the small balsam fir

seedlings common under most balsam fir stands.

Converting Aspen Lands to Pine or

Spruce

Lands capable of growing aspen usually are suitable for pine or spruce. Land managers may prefer

to grow these species for wood products or to provide a more diversified forest cover, but natural

conversion of aspen or other hardwood types to

conifers other than balsam fir seldom occurs.

Thus, special efforts are necessary to establish

satisfactory stands of pine or spruce.

34
LAKE STATES

Competing vegetation must be controlled by cutting or other mechanical methods, by use of registered herbicides, or with a combination of these

methods. Trees usually must be planted, although

direct seeding may be effective in special cases.

Subsequent release of the established conifers

usually is required to ensure their proper development.

Detailed descriptions of the steps necessary to

establish conifers are available in the various

planting and seeding handbooks. Chances of successful establishment are improved by careful site

selection and preparation, by planting good growing stock ofsuitable species, and by providing adequate subsequent release. The high costs undoubtedly will limit conversions of aspen landsto pine or

spruce.

GUIDELINES FOR ASPEN MANAGEMENT

In the Lake States and adjacent Canada, research and experience have shown that the key to

successful aspen management is harvesting by

clearcutting to ensure vigorous sucker production

and development. Aspen grows faster, reaches

larger size, and produces higher yields on good

than on poor sites. Thus, where premium prices

are expected, a thinning may be justified on good

sites to increase yields ofsaw logs and veneer bolts.

Although intensive culture will further increase

volume yields, actual financial gains are limited by

the relatively low present value of aspen.

In most cases, harvesting only the merchantable

trees will not create the conditions needed for adequate sprout regeneration. Both the number and

vigor of suckers can be increased if residual trees

and brush are controlled by cutting, burning, or

use of registered herbicides. In general, the better

the site, the greater the need for and benefits derived from such treatments. Minimum sucker

stocking needed is 3,000 to 6,000 vigorous stems per

acre ifthese are well distributed and free to grow.

Where successive aspen crops are planned, the

final harvest cutting should be made at or near the

suggested rotation age. If harvest is delayed more

than 10 years, there is risk of appreciable losses in

yield and quality. Harvest cuttings made in the

dormant season result in the most abundant sucker

development, but adequate stocking can be expected regardless of when an aspen stand is clearcut.

The following guidelines are suggested for managing aspen stands on sites of three broad quality

classes.

Good and Excellent Sites (S.I. 70 or

Higher)

On these better sites aspen grows faster, produces larger, higher quality products, and is most

responsive to treatment. Because maintaining pure

stands of aspen on such sites also provides highly

desirable habitat for deer, grouse, and other

wildlife, growing repeated crops of aspen justifies

the special efforts required to prevent natural conversion to other species. The first and most crucial

requirement is that a clearcutting must be made—

all culls and unwanted tree species must be cut or

killed and excess brush must be controlled. This

will encourage vigorous aspen suckering and ensure good stocking. Plan for a rotation of 50 to 60

years.

Maximum production of large, high-value

products will be achieved where the stands are

thinned from below at least once during the rotation. In well-stocked stands, an operable thinning

often can be made at age 30 to 35 to leave 60 to 80

square feet basal area. Earlier thinnings will increase growth rates and ultimate size of the potential crop trees even more. As markets improve for

high-quality aspen logs, thinnings are expected to

become more profitable on good aspen sites.

Average Sites (S.I. 50 to 69)

Because most aspen stands ofthe Lake States are

growing on sites within this broad range, maintaining good production rates on these sites is essential

to ensure adequate supplies of aspen for industry

and to maintain desirable wildlife habitat.

Potential yields are high enough to justify favoring aspen, especially where site index exceeds 60.

The major goal is production of pulpwood on a 40-

to 50-year rotation, but some trees will produce

veneer bolts and saw logs. Mature stands usually

will be commercially clearcut; the loggers should

be encouraged to break off or uproot as many unmerchantable trees as possible.

Aspen regeneration and future yields will be further increased by a complete clearcutting and control of excess brush. This is recommended where

existing or expected markets favor maximum

35
QUAKING ASPEN

aspen production. However, where markets are

poor, the forest manager may decide to leave scattered trees and brush. Noncommercial thinnings

are not recommended, but a single commercial

thinning at age 30 to 35 should be considered where

premium prices are expected for large logs.

Poor Sites (S.I. Less than 50)

Managing aspen primarily for wood production

is impractical on poor sites because of low yields

and quality. When stands mature at 30 to 35 years.

they may be harvested if an operable cut can be

made. No investment can be justified to ensure

aspen regeneration. It may be desirable to convert

some poor aspen sites to jack pine, red pine, or

spruce, but choice of species often is limited.

Inherent low productivity limits the potential

value of poor aspen sites for deer and grouse

habitat. However, where more suitable sites are not

available, a combination of prescribed burning

and aspen harvest cuttings will stimulate production of desirable food and cover for wildlife.

SUMMARY

Aspen forms the largest and most widely distributed forest type in the Lake States where it occupies about one-fourth of the commercial forest

land. There are over 13 million acres of aspen

forest in Minnesota, Wisconsin, and Michigan.

The dominant species, quaking aspen, may grow in

essentially pure stands but varying numbers of

other species usually are present. Common associates in the Lake States include paper birch,

balsam fir, jack pine, spruces, northern red oak,

elms, big tooth aspen, red pine, or white pine.

Over its wide range, aspen occurs on a variety of

soils and sites. Growth rate varies with soil fertility

and moisture. Tree heights at age 50 range from 90

feet on deep fertile loams to 40 feet on dry sands,

rock outcrops, water-logged mineral soils, or peat.

About 11 percent ofthe aspen type occurs on poor

sites (S.I. <50), 58 percent on average sites (S.I. 50

to 69), and 31 percent on goodto excellent sites (S.I.

^70).

Most Lake States aspen stands are young. About

70 percent are less than 40 years old and only 4

percent are distinctly overaged. Over half the

stands are pole-sized; a third are seedlings or saplings. Only 6 percent of the type is owned by industry; the rest is nearly evenly divided between public and small private ownerships.

Aspen is one of the simplest species to manage

because it is easy to regenerate from root suckers,

and its intolerance causes early natural thinning

and pruning. Even without thinnings, aspen stands

on average and better sites produce cordwood

along with some larger products in a short rotation.

The only direct investment usually needed is

treatment ofresidual trees and brush at the time of

harvest to stimulate production and rapid growth

of aspen suckers.

The recommended practice is to make either a

complete clearcut or a commercial harvest followed by cutting or killing the remaining overstory. The brush that is often present on the better

sites may be controlled using prescribed burns, but

application of approved herbicides is more reliable. Mechanical treatments also are effective although costs will be higher. Favorable growing

conditions must be provided for aspen sucker development.

Volume growth rate and yields are related to

both site quality and aspen stocking. Average aspen

yields in unmanaged mixed stands often are only 10

to 15 cords per acre. Pure, well-stocked aspen

stands on excellent sites yield 60 or more cords per

acre, but poor sites may not produce enough volume to be worth harvesting. On the better sites, a

single commercial thinning from below should be

considered at age 30 to 35 years, especially where

large, high-quality trees will bring premium prices

in the final harvest.

Periodic defoliation ofaspen stands by the forest

tent caterpillar or other leaf feeders may reduce

volume growth during infestations. Trees of any

age can be attacked by the aspen borer, but infestation is most frequent in poorly stocked or thinned

stands. Hypoxylon canker is the most serious disease, resulting in death or breakage of many trees;

infection may be reduced by maintaining wellstocked stands. Because losses to decay fungi increase rapidly in overmature stands, aspen harvest

should not be unduly delayed.

To minimize losses to insects and diseases, aspen

should be grown in well-stocked stands and harvested promptly at maturity. Recommended rotations for aspen stands range from about 30 years on

poor sites to 50 or 60 years on good sites.

36
LAKE STATES

Growing continuous crops of aspen also plays a

key role in maintaining other natural resources.

Aspen suckers are a staple food of moose and deer.

The staminate flower buds of aspen trees are a

necessary winter food for grouse and stands of all

ages provide favorable habitat for grouse and other

birds. Aspen bark and twigs are the primary food

of beaver. The easily regenerated aspen provides

soil cover that helps stabilize the water regime,

and aspen forests have considerable esthetic and

recreation value.

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1942. Standardized plant names. Ed. 2: 675 p. Harrisburg,

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Kenety, W. H.

1917. Preliminary study of white spruce in Minnesota.

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Kirby, C. L., W. S. Bailey, and J. G. Gilmour.

1957. The growth and yield of aspen in Saskatchewan. Sask.

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Kittredge, Joseph, Jr.

1938. The interrelations of habitat, growth rate, and associated vegetation in the aspen community of Minnesota

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Kittredge, Joseph, Jr., and S. R. Gevorkiantz.

1929. Forest possibilities of aspen lands in the Lake States.

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Leuschner, William A.

1972. Projecting the aspen resource in the Lake States.

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1953. Check list of native and naturalized trees of the

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1960. Invasion of grasslands by Populus tremuloides in the

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1967. Variation in the vegetative propagation oiPopulus in

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1972. Silvics and ecology in Canada. In Aspen: symposium

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1930. Les variations Laurentiennes du Populus tremuloides

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39
QUAKING ASPEN

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1948. Some aspects ofpoplar borer, Saperda calcarata Say

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1952. Studies in forest pathology. IX. Fomes ignarius decay

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1953. Hail damage in forest stands. For. C hron. 29:139-143,

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1935. Forest soils—^the basis of forest management. USDA

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1958. The effect of defoliation on foliage production and

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40

Sandberg, Dixon, and Arthur E. Schneider.

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1945. Harvesting young aspen in the Cloquet Forest. J. For.

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1971. Growth and yield of quaking aspen in north-central

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1971. Thinning pole-sized aspen has no effect on number of

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Shirley, Hardy L.

1941. Restoring conifers to aspen lands in the Lake States.

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1962. Outbreaks ofthe forest tent caterpillar, Malacosoma

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1938. Site as a factor in silviculture with special reference to

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1968. Size of aspen crop trees little affected by initial sucker

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1972. Wisconsin's 1968 timber resource—a perspective.

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1949. Ninety years change in a northern hardwood forest in

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1964. Ten-year results of thinning 14-, 19-, and 23-year-old

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1960. Soil factors affecting the growth of quaking aspen

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1961. Organic layers in Minnesota aspen stands and their

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Stoeckeler, Joseph H., and Carl Arbogast, Jr.

1955. Forest management lessons from a 1949 windstorm in

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States For. Exp. Stn., St. Paul, Minn.
LAKE STATES

Stoeckeler, Joseph H., and John W. Macon.

1956. Regeneration of aspen cutover areas in northern Wisconsin. J. For. 54: 13-16, illus.

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1966. A third look at Minnesota's timber. USDA For. Serv.

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St. Paul, Minn.

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1961. Wisconsin's forest resources. USDA For. Serv., Lake

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For. Exp. Stn., St. Paul, Minn.

Strothmann, R. O.

1960. Evaluating the growth potential of aspen lands in

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Exp. Stn., Stn. Pap. 86: 20 p., illus. Lake States For. Exp.

Stn., St. Paul, Minn.

Strothmann, R. O., and Miron L. Heinselman.

1957. Five-year results in an aspen sucker density study.

USDA For. Serv., Lake States For. Exp. Stn. Tech. Note

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Tew, Ronald K.

1970. Root carbohydrate reserves in vegetative reproduction of aspen. For. Sei. 16: 318-320.

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1956. Hail damage in Lake Nipigon area. Can. Dep. Agrie,

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1915. Reproduction studies in the Minnesota National Forest. Ames For. 5: 80-86, illus.

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1974. Seeds of woody plants in the United States. U.S. Dep.

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Vaartaja, O.

1960. Ecotypic variation of photoperiodic response in trees

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illus.

Verry, Elon S.

1972. Effect of an aspen clearcutting on water yield and

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1957. The effect of soil characteristics on the growth of

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Weitzman, Sidney, and Roger R. Bay.

1959. Snow behavior in forests of northern Minnesota and

its management implications. USDA For. Serv., Lake States

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Exp. Stn., St. Paul, Minn.

Weitzman, Sidney, and Roger R. Bay.

1963. Forest soil freezing and the influence of management

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1954. Available browse following aspen logging in lower

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1956. Ecological relationships between deer and forests in

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1960. The ecology of deer and aspen in lower Michigan.

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1950. Growth oftrembling aspen in relation to ground water

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347, illus.

Wilde, S. A., and E. L. Zicker.

1948. Influence ofthe ground water table upon the distribution and growth of aspen and jack pine in central Wisconsin. Wis. Conserv. Dep. Tech. Note 30: 12 p., illus.

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1954. Effect of seasonal basal sprays on root suckering of

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Zahner, Robert, and Ned A. Crawford.

1965. The clonal concept in aspen site relations. In Forest

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Univ., Corvallis, Oreg.

Zasada, Zigmond A.

1948. Aspen lumber grades and characteristics. USDA For.

Serv., Lake States Aspen Rep. 6: 9 p. Lake States For. Exp.

Stn., St. Paul, Minn.

Zasada, Zigmond A.

1972. Mechanized logging can aid management. In Aspen:

symposium proceedings. USDA For. Serv. Gen. Tech. Rep.

NC-1: 154 p., illus. North Cent. For. Exp. Stn., St. Paul,

Minn.

Zasada, Zigmond A., and J. C. Tappeiner.

1969. Full-tree harvesting system aids forest management.

Minn. For. Res. Note 205: 4 p.

Zehngraff, Paul J.

1946. Season of cutting affects aspen sprouting. USDA For.

Serv., Lake States For. Exp. Stn. Tech. Note 250: 1 p. Lake

States For. Exp. Stn., St. Paul, Minn.

Zehngraff, Paul J.

1947. Possibilities of managing aspen. USDA For. Serv.,

Lake States Aspen Rep. 21:23 p. Lake States For. Exp. Stn.,

St. Paul, Minn.

Zehngraff, Paul J.

1949. Aspen as a forest crop in the Lake States. J. For. 47:

555-565, illus.

Zillgitt, W. M.

1951. Disking to increase stocking in aspen stands. USDA

For. Serv., Lake States For. Exp. Stn. Tech. Note 357: 1 p.

Lake States For. Exp. Stn., St. Paul, Minn.

41
QUAKING ASPEN

APPENDIX I.-

COMMON AND SCIENTIFIC NAMES OF PLANT SPECIES MENTIONED«

\

>

Trees Shrubs and Herbs

Ash, black

Ash, white

Aspen, bigtooth

Aspen, European

Aspen, quaking

Basswood, American

Beech, American

Birch, paper

Cherry, pin

Cottonwood, eastern

Elm, American

Fir, balsam

Hemlock, eastern

Maple, red

Maple, sugar

Oak, bur

Oak, northern red

Pine, eastern white

Pine,jack

Pine, red (Norway pine)

Poplar, balsam

Poplar, white

Spruce, black

Spruce, white

Tamarack

White-cedar, northern

Yellow-poplar

Fraxinus nigra Marsh.

F. americana L.

Populus grandidentata

Michx.

P. trémula L.

P. tremuloides Michx.

Tilia am^ericana L.

Fagus grandifolia Ehrh.

Betula papyrifera

Marsh.

Prunus pennsylvanica

L.f.

Populus deltoides Bartr.

Ulmus americana L.

Abies halsamea (L.) Mill

Tsuga canadensis (L.)

Carr.

Acer ruhrum L.

A, saccharum Marsh.

Quereus macrocarpa

Michx.

Q. rubra L.

Pinus strobus L.

Pinus banksiana Lamb.

P. resinosa Ait.

Populus balsamifera L.

P. alba L.

Picea mariana (Mill.)

B.S.P.

P. glauca (Moench) Voss

Larix laricina (DuRoi)

K. Koch

Thuja occidentalis L.

Liriodendron tulipifera

L.

^^Common and scientifíc names are based on Little (1953),

Feraald (1950), and Kelsey and Dayton (1942).

Aster, bigleaf

Beadlily, yellow

Beadruby, Canada

(Canada

May-flower)

Bedstraw, sweetscented

Blackberry

Blackberry, dwarf red

Bracken, eastern

Bush-honeysuckle,

dwarf

Chokecherry, common

Dogbane, spreading

Dogwood, bunchberry

Fireweed

Goldenrod

Grape

Hazel, beaked

Ladyfern

Maple, mountain

Meadowrue, early

Raspberry, red

Ricegrass, roughleaf

Sarsaparilla, wild

Sedge

Serviceberry

Strawberry

Sweet-fern

Twistedstalk, rosy

Aster macrophyllus L.

Clintonia borealis (Ait.)

Raf.

Maianthemum

canadense Desf.

Galium triflorum

Michx.

Rubus sp. L.

Rubus pubescens Raf.

Pteridium aquilinum

(L.) Kuhn

Diervilla lonicera Mill.

Prunus virginiana L.

Apocynum

androsaemifolium L.

Cornus canadensis L.

Epilobium

angustifolium L.

Solidago spp. L.

Vitis spp. L.

Corylus cornuta Marsh.

Athyrium Filix-femina

(L.) Roth

Acer spicatum Lam

Thalictrum dioicum L.

Rubus idaeus var.

strigosus (Michx.)

Maxim.

Oryzopsis asperifolia

Michx.

Aralia nudicaulis L.

Carex richardsonii R.

Br.

Amelanchier spp.

Medic.

Fragaria spp. L.

Comptonia peregrina

(L.) Coult.

Streptopus roseus

Michx.

42
/

LAKE STATES

APPENDIX II.—

COMMON INSECTS AND DISEASES DAMAGING QUAKING ASPEN

BY SIZE OF TREE AFFECTED AND SYMPTOMS ^^

Size of aspen

Suckers

Saplings and

small poles

Symptoms

Insects

Leaf curling and dwarfing

Leaf curling and withering

Petiole swellings and galls

Tip bending and dieback

Succulent stems cut off

at ground line

Breakage of suckers

about V2 inch in

diameter

Breakage from borers

weakening stems

Girdling of roots

Diseases

Dieback of young shoots

and leaves

Inkspot on leaves

Anthracnose of leaves

Canker on young suckers

Insects

Borer galleries at base

Winding tunnels underneath

bark of weakened trees

Cause

Aphids including (Pterocomma

populifoliae (Fitch));

speckled poplar aphids

Chaitophorus populicola (Thomas);

Aphis maculatae

Oestlund; and others

Leafhoppers of genera

Idiocerus, Oncom^etopia,

Macropsis, Oncopsis and

Agallia; also the lacebug,

Corythucha elegans Drake

Poplar petiolegall and

twiggall aphids. Pemphigus

spp.

Willow shoot sawfiy, Janus

abbreviatus (Say)

Armyworm, Pseudaletia

unipuncta (Haworth) and

other cutworms

Borers including Saperda sp.

and Oberia

schaumi LeC.

Aegeria tibialis (Harr.) and

Oberia schaumi LeC.

Agrilus horni Kerr

Venturia tremulae Aderh.

Ciborinia bifrons (Whetz.)

Whetz.

Marssonina populi (Lib.)

Magn.

Cytospora chrysosperma

(Pers.) Fries

Saperda imitans

Felt and Joutel

Bronze poplar borer, Agrilus

liragus Barter and Brown

^3 Sources: Boyce 1961, Graham et al 1963, Hepting 1971,

Baker 1972.

43
QUAKING ASPEN

Size of aspen

Saplings and

small poles

\

Symptoms

Winding tunnels in bark

Frass-filled tunnels near

branch stubs

Roughened areas of bark

Cause

Bark miners of the fly

family, Agromyzidae

Flat-headed borers including Dîcerca

tenebrica (Kby.); D. divaricata

(Say); D. callosa Casey, and

Poecilonota cyanipes (Say)

Oystershell scale, (Lepidosaphes

ulmi (L.)); and a wooly

aphid, Prociphilus sp.

Diseases

Rough irregular tumors at

or near ground line on

saplings and on trunk or

branches of larger trees

Agrobacterium tumifaciens

(E. F. Smith & Town.) Conn.

Insects

Small poles and

larger trees

Defoliation

Leaves rolled or tied

with silk

Folded leaf margins

Galleries in sound wood

of living trees

Diseases

Black roughened bands on

aspen trunks and gall-like

knots on the branches

(rough bark disease)

Cankers, usually on trunk

Butt and stem rots

Forest tent caterpillar,

Malacosoma disstria Hübner;

Aspen leaf beetle,

Chrysomela crotchi Brown;

other leaf beetles including

C. scripta F.; C, tremulae

F.; and C. interrupta F.

Large aspen tortrix,

Choristoneura conflictana

(Walker)

Leaf-rolling sawflies,

Pontania spp.

Poplar borer, Saperda

calcarata Say

Diplodia tumefaciens (Shear)

Zalasky

Hypoxylon mammatum (Wahl.)

MilL

Nectria spp., or Ceratocystis

spp.

Armillaria mellea Vahl ex Fr.;

Pholiota spectabilis Fr.;

White heart rot,

Fomes ignarius (L. ex Fr.)

Kickx.;F. applanatus (Pers.

ex S. F. Gray) Gill, Radulum

cascearium (Morg.) Lloyd

44
LAKE STATES

APPENDIX III.—

ASPEN YIELDS BY SITE INDEX, STAND AGE,

AND BASAL AREA (Schlaegel 1971)

TABLE 12.—Total yieldper acre in tens ofcubicfeet, excluding hark (alltrees 0.6

inch d.b.h. and larger)

Site

index

Basal area per acre

Stand age 20 40 60 80 100 120 140 160

65

70

75

80

85

90

Years

20

30

40

50

60

20

30

40

50

60

20

30

40

50

60

20

30

40

50

60

20

30

40

50

60

20

30

40

50

60

35

45

51

54

57

38

48

55

59

62

40

52

58

63

66

43

55

62

67

70

46

59

66

71

75

49

62

70

75

79

70

90

101

109

114

76

97

109

117

123

81

103

117

126

132

86

110

125

134

141

92

117

132

142

150

97

124

140

151

158

105

134

152

163

172

113

145

164

176

185

121

155

175

189

198

130

165

187

201

211

138

176

199

214

224

146

186

210

226

238

14€

179

202

218

229

151

193

218

235

246

162

207

234

251

264

173

221

249

268

282

184

235

265

285

299

194

248

281

302

317

176

224

253

272

286

189

241

273

293

308

202

259

292

314

330

216

276

312

335

352

230

293

331

356

374

243

310

351

377

396

211

269

304

327

343

227

290

327

352

370

243

310

350

377

396

259

331

374

402

422

276

352

397

427

449

292

337

421

452

475

246

314

354

381

401

265

338

382

411

431

283

362

409

440

462

303

386

436

469

493

321

411

463

499

524

340

435

491

528

554

281

359

405

436

458

302

386

436

469

493

324

414

467

503

528

346

441

499

536

563

367

469

530

570

599

389

497

561

603

633

45
QUAKING ASPEN

TABLE 13.—Merchantable yield per acre in tens of cubic feet^ to a 3-inch top

inside bark when average stand diameter is 6 inches (all trees 3.6 inches

d.b.h. and larger)

Site

index Stand age 20 40

Basal area per acre

60 80 100 120 140 160

65

Years

20

30

40

50

60

32

41

47

49

52

64

82

92

99

104

96

122

139

149

157

128

163

184

199

209

161

204

231

248

261

192

245

277

298

313

224

286

323

347

366

256

327

369

398

418

70 20

30

40

50

60

35

44

50

54

57

69

88

99

107

112

103

132

150

161

169

138

176

199

214

224

172

220

249

267

281

207

264

298

321

337

242

308

348

375

393

275

352

398

428

450

75 20

30

40

50

60

36

47

53

57

60

74

94

107

115

120

110

141

160

172

181

148

189

213

229

241

184

236

266

286

301

222

283

319

344

361

258

330

373

4^1

421

295

378

426

459

482

80 20

30

40

50

60

39

50

57

61

64

78

100

114

122

129

119

150

171

183

192

158

202

227

244

257

197

252

285

306

321

236

302

341

367

385

276

352

398

428

450

316

402

455

489

513

85 20

30

40

50

60

42

54

60

65

68

84

107

120

130

137

126

161

181

195

204

168

214

242

260

273

210

267

302

325

341

252

321

362

389

409

293

375

422

455

478

335

428

483

520

546

90 20

30

40

50

60

45

57

64

68

72

113

128

138

144

133

170

192

206

217

177

226

256

275

289

222

283

320

344

361

266

340

384

412

433

310

397

448

482

505

355

453

512

550

577

46
LAKE STATES

TABLE lá.^Herchantable yield per acre in tens ofcubicfeet, excluding bark, to

a 3-inch top inside bark when average stand diameteris 8 inches (alltrees 3.6

inches d.b.h. and larger)

Basal area per acre

Site

index Stand age 20 40 60 80 100 120 140 160

Years

65 20 34 68 102 136 170 204 238 272

30 44 87 130 173 217 260 304 34S

40 49 98 147 196 245 294 343 392

50 52 106 158 211 263 317 369 422

60 55 110 166 222 277 332 388 443

70 20 37 74 109 146 183 220 257 292

30 46 94 140 187 233 281 327 374

40 53 106 159 211 264 317 370 422

50 57 113 170 227 284 341 398 454

60 60 119 179 238 298 358 417 477

75 20 39 78 117 157 196 235 274 314

30 50 100 150 200 251 300 350 401

40 56 113 169 227 283 339 396 452

50 61 122 183 243 304 365 426 487

60 64 128 192 256 319 383 447 511

80 20 42 83 126 167 209 251 293 335

30 53 106 160 214 267 320 374 427

40 60 121 181 241 302 362 422 483

50 65 130 195 259 324 389 454 519

60 68 136 204 273 341 408 477 545

85 20 45 89 134 178 223 267 311 355

30 57 113 170 227 284 341 398 454

40 64 128 193 257 320 384 448 513

50 69 137 207 276 345 413 483 552

60 73 145 217 289 362 435 507 580

90 20 47 94 141 188 235 283 329 377

30 60 120 180 240 300 361 421 481

40 68 136 203 272 340 408 475 543

50 73 146 219 292 365 438 511 584

60 76 153 230 307 383 460 536 613

47
QUAKING ASPEN

TABLE 15.—Merchantable yield in tens of cubic feet, excluding bark, to a

3'inch top inside bark when average stand diameter is 10-\- inches (all

trees 3.6 inches d.b.h. and larger)

Site

index Stand age 20 40

Basal area per acre

60 80 100 120 140 160

65

Years

20

30

40

50

60

34

44

50

53

56

69

88

99

107

112

103

132

149

160

169

137

176

198

214

225

173

220

248

267

281

207

264

299

321

337

242

308

348

374

394

276

353

398

428

450

70 20

30

40

50

60

37

47

54

58

61

75

95

107

115

121

111

142

161

173

182

148

190

214

231

242

186

237

268

288

302

223

285

321

346

363

260

332

375

404

423

297

379

428

461

484

75 20

30

40

50

60

39

51

57

62

65

80

101

115

124

130

119

152

172

186

194

159

203

230

246

259

198

254

287

308

324

239

304

344

370

389

278

355

402

432

454

318

407

459

494

518

80 20

30

40

50

60

42

54

61

66

69

84

108

123

132

138

128

162

184

197

207

170

217

245

263

277

212

271

306

329

34^

254

325

367

395

414

298

379

428

461

484

340

433

490

526

553

85 20

30

40

50

60

45

58

65

70

74

90

115

130

139

147

136

173

195

210

220

181

231

260

280

294

226

288

325

350

367

271

346

390

419

441

315

404

455

490

515

360

461

520

560

588

90 20

30

40

50

60

48

61

69

74

78

95

122

137

148

155

143

183

206

222

234

191

244

276

297

311

239

304

345

370

389

287

366

413

444

466

334

427

482

518

544

382

488

551

592

622

48
LAKE STATES

TABLE 16.—Merchantable yield in tens of cubic feet, excluding bark, to a

5-inch top inside bark when average stand diameter is 6 inches (all trees

5.6 inches d,b.h. and larger)

Site

index Stand age 20 40

Basal area per acre

60 80 100 120 140 160

65

Years

20

30

40

50

60

20

25

28

30

32

39

50

56

61

64

59

75

85

91

96

78

100

113

122

128

98

125

141

152

160

118

150

170

182

191

137

175

198

213

224

157

200

226

243

256

70 20

30

40

50

60

21

27

31

33

35

42

54

41

65

69

63

81

92

98

103

84

108

122

131

137

105

134

152

163

172

127

162

182

196

206

148

189

213

229

240

169

215

243

262

275

75 20

30

40

50

60

22

29

32

35

37

45

57

65

70

74

68

86

98

105

110

90

116

131

140

147

113

145

163

175

184

136

173

195

210

221

158

202

228

246

258

181

231

261

281

295

80 20

30

40

50

60

24

31

35

37

39

48

61

70

75

79

73

92

104

112

118

97

123

139

150

157

121

154

174

187

196

145

185

209

224

235

169

215

243

262

275

193

246

278

299

314

85 20

30

40

50

60

26

33

37

40

42

51

65

74

79

84

77

98

111

119

125

103

131

148

159

167

128

163

185

199

209

154

196

222

238

251

179

229

258

278

292

205

262

296

318

334

90 20

30

40

50

60

27

35

39

42

44

54

70

78

84

88

81

104

117

126

133

108

138

157

169

177

136

173

196

210

221

163

208

235

252

265

190

243

274

295

309

217

277

313

336

353

49
QUAKING ASPEN

TABLE 17. —Merchantable yield in tens of cubic feet, excluding bark, to a

5-inch top inside bark when average stand diameter is 8 inches (all trees

5.6 inches d.b.h. and larger)

Site

index Stand age 20 40

Basal area per acre

60 80 100 120 140 160

65

Years

20

30

40

50

60

30

38

43

46

48

59

76

85

92

96

89

113

128

137

145

118

151

170

184

193

148

189

213

229

241

178

227

256

276

289

207

265

298

321

338

237

303

341

368

386

70 20

30

40

50

60

32

40

46

50

52

64

82

92

99

104

95

122

138

14^

156

127

163

184

198

207

159

203

230

247

260

191

244

276

297

312

223

285

322

346

363

255

325

368

395

416

75 20

30

40

50

60

34

44

49

53

56

68

87

99

106

111

102

131

148

159

167

137

175

197

212

223

170

218

246

265

278

205

261

295

318

334

239

305

345

371

389

273

349

394

424

445

80 20

30

40

50

60

36

46

52

56

59

72

93

105

113

119

110

139

158

169

178

146

186

210

226

238

182

233

263

282

297

218

279

315

339

356

255

325

368

395

416

292

372

421

452

475

85 20

30

40

50

60

39

50

56

60

63

78

99

111

120

126

116

148

168

180

189

155

198

223

240

252

194

247

279

300

315

233

297

335

360

379

271

346

390

421

442

309

395

447

481

505

90 20

30

40

50

60

41

52

59

63

67

82

105

118

127

133

123

157

177

191

201

164

209

237

255

267

205

261

296

318

334

246

314

355

381

400

287

367

414

445

467

328

419

473

508

534

50
LAKE STATES

TABLE 18.—Merchantable yield in tens of cubic feet, excluding bark, to a

5-inch top inside bark when average stand diameter is 10-\- inches (all

trees 5.6 inches d.b.h. and larger)

Site

index Stand age 20 40

Basal area per acre

60 80 100 120 140 160

65

Years

20

30

40

50

60

33

42

48

51

53

66

84

95

102

107

98

125

142

153

161

131

168

189

204

214

165

210

237

255

268

197

252

285

306

321

230

294

331

357

375

263

336

379

408

429

70 20

30

40

50

60

36

45

51

55

58

71

91

102

110

115

106

136

154

165

173

141

181

204

220

230

177

226

256

274

288

212

271

306

329

346

248

316

358

385

403

283

361

408

439

461

75 20

30

40

50

60

37

49

54

59

62

76

96

110

118

124

113

145

164

177

185

152

194

219

235

247

189

242

273

294

309

227

290

328

353

371

265

339

383

412

432

303

388

437

471

494

80 20

30

40

50

60

40

51

58

63

66

80

103

117

125

132

122

154

175

188

197

162

207

233

251

264

202

258

292

314

329

242

310

350

376

395

284

361

408

439

461

324

413

467

502

527

85 20

30

40

50

60

43

55

62

62

70

86

110

124

133

140

129

165

186

200

210

172

220

248

267

280

215

274

310

333

350

258

329

372

400

420

300

385

433

467

490

344

439

496

534

561

90 20

30

40

50

60

46

58

66

70

74

91

116

131

141

148

137

174

197

212

223

182

232

263

283

297

227

290

329

353

371

273

349

394

423

445

318

407

460

494

519

364

465

525

564

592

51
QUAKING ASPEN

TABLE l9.^Average aspen yields in cords per acre to 3-inch and 5-inch top

diameters inside bark

Basal area per acre

Site

index Age Height 40^ 601 801 1001 1201 1401

90 20 58 9.2 0 12.4 0 12.8 0 10.8 0

30 74 14.6 10.0 21.2 12.2 27.0 10.4 31.0 3.9 32.6 0 28.6 0

40 83 17.2 15.4 25.5 21.8 33.8 26.3 41.3 27.5 47.4 24.5 52.2 14.9

50 90 18.7 18.0 28.0 26.3 37.5 34.4 46.3 40.6 54.4 43.5 62.2 42.8

60 94 19.6 19.4 29.5 28.9 39.3 38.1 49.1 46.6 58.9 53.5 68.0 58.9

80 20 52 8.2 0 11.0 0 11.4 0 9.6 0

30 66 12.9 8.9 18.8 10.9 24.1 9.2 27.6 3.5 28.9 0 25.4 0

40 74 15.3 13.8 22.7 19.4 29.9 23.3 36.7 24.5 42.1 21.8 46.4 13.2

50 80 16.6 15.9 24.9 23.4 33.2 30.5 41.1 36.0 48.3 38.7 55.2 38.0

60 84 17.5 17.3 26.2 25.6 35.0 33.9 43.7 41.4 52.3 47.5 60.5 52.4

70 20 46 7.2 0 9.6 0 9.9 0 8.4 0

30 57 11.4 7.8 16.5 9.5 21.0 8.1 24.1 3.0 25.3 0 22.4 0

40 65 13.4 12.0 19.9 17.0 26.2 20.4 32.1 21.4 36.8 19.0 40.6 11.6

50 70 14.5 13.9 21.8 20.5 29.1 26.8 36.0 31.5 42.3 33.9 48.4 33.3

60 73 15.2 15.1 22.9 22.5 30.5 29.6 38.2 36.2 45.9 41.7 52.9 45.8

iLeft column shows merchantable cords to 3-inch top diameter; right column, to 5-inch top diameter.

Ú U.S. GOVERNMENT PRINTING OFFICE: 1976 0—579-943

52